CORROSION IN THE ALASKA MARINE ENVIRONMENT RESEARCH AND RECOMMENDATIONS

by

Dennis Nottingham William Gunderson

Susan Schoettle

Peratrovich, Nottingham & Drage, Inc. 1506 West 36th Avenue, Suite 101

Anchorage, Alaska 99503

January 1983

Prepared for:

STATE OF ALASKA DEPARTMENT OF TRANSPORTATION AND PUBLIC FACILITIES

DIVISION OF PLANNING AND PROGRAMMING RESEARCH SECTION 2301 Peger Road

Fairbanks, Alaska 99701

The contents of this report reflect the views of the authors. The contents do not necessarily reflect the official views or policies of the Alaska Department of Transportation and Public Facilities. This report does not constitute a standard, specification, or regulation.

TABLE OF CONTENTS

Page No.

List of Tables

List of Figures

Section 1 Introduction and Scope of Research

Section 2 Corrosion of Steel in the Marine Environment

2.1

2.2

Corrosion Mechanisms and Corrosion Rates in Seawater

Zones of Corrosion in the Alaska Marine Environment

Section 3 Corrosion Control Methods

Design Practices

Coatings

Galvanizing

Cathodic Protection

Combination Control Methods

iv

v

4

4

9

13

13

14

16

17

18

Section 4 Present Worth Economic Analysis of Corrosion Protection Systems 21

4.1 System Summaries 23

4.2

4.3 4.4

System Cost Estimates

Present Worth Analysis

Approximate Coating Costs by Product

Section 5 Field Inspections

5.1 Inspection Summaries

Ketchikan

Sitka

,Juneau

Hoonah

Haines

Cordova

-ii-

26

28

38

39

45

45

52

56

57

58

62

TABLE OF CONTENTS (continued)

Anchorage

Seward

Seldovia

Kodiak

Cold Bay

Section 6 Conclusions and Recommendations

6. 1 Protection Methods

6.2 Economic Analysis

6.3 Field Inspections

6.4 Inspection Program

6.5 Future Research

Appendix A: Glossary of Key Terms

Appendix B: Standard Specifications for Hot-Dip Galvanizing of Steel

Appendix C: Present Worth Formulas

Footnotes

Bibliography

-iii-

Page No.

64

65

68

70

75

76

76

77 78

79 80

82

84

85

86

87

LIST OF TABLES

Table No. Page No.

2.1 Environmental Influence on Piles in Marine Structures 5

3.1 Comparison of Corrosion Protection Systems 20

4.1 Present Worth Summary 29

4.2 Estimated Coating Costs by Product 38

5. 1 Summary of Corrosion Protection Systems Observed in Alaska 42

-iv-

LIST OF FIGURES

Figure No.

1 • 1 Corrosion Penetration of a Steel H-Pile

2. 1 Uniform Corrosion

2.2 Pitting Corrosion of a Weld

2.3 Schematic Diagram of Corrosion Zones

2.4 Approximate Metal Loss Rates on a Pipe Pile in the Alaska

Marine Environment

4.1 Diagram of Dock Used in Present Worth Analysis

4.2 System A - Present Worth Analysis

4.3 System B - Present Worth Analysis

4.4 System C - Present Worth Analysis

4.5 System D - Present Worth Analysis

4.6 System E - Present Worth Analysis

4.7 System F - Present Worth Analysis

4.8 System G - Present Worth Analysis

4.9 System H - Present Worth Analysis

-v-

Page No.

2

6

7

11

12

22

30

31

32

33

34

35

36

37

LIST OF FIGURES (continued)

Figure No. Page No.

5.1 Location of Field Inspections 40

5.2 Pit Gauge Used to Measure Pit Depth 41

5.3 Inspection Procedure 41

5.4 Coal Tar Epoxy Coated Pile, Ketchikan 46

5.5 Dolphin with Corroding Piling, Ketchikan 48

5.6 Dolphin with Corroding Piling, Ketchikan 48

5.7 Corroded Piling, Ketchikan 49

5.8 Piling with No Corrosion, Ketchikan 50

5.9 Bridge Caisson, Sitka 54

5.10 Coating Disbondment, Sitka 55

5.11 H-Pile Flange, Haines 60

5.12 Sheet Pile Penetration, Haines 61

5.13 Weld Damage from Corrosion, Seward 66

5.14 Repaired Weld, Seward 66

5.15 Corrosion of an Isolated Piling, Seward 67

5.16 Corrosion of Pipe Piling, Seldovia 69

-vi-

LIST OF FIGURES (continued)

Figure No. Page No.

5.17 Corrosion of Pipe Pile Seam, Seldovia 69

5.18 Steel Monotube Piling, Kodiak 71

5.19 Steel Pipe Pile with Coal Tal' Epoxy Coating, Kodiak 72

-vii-

1.0 INTRODUCTION AND SCOPE OF RESEARCH

In the design of marine structures, some of the elements which must be

considered are: physical site conditions and . constraints, maintenance

requirements, cost of materials and labor, environmental conditions, intended

use, and desired service life. These various factors effect design to insure

both structural and economic viability during the service life of a marine

structure.

Material selection is an important design decision. Common materials used for

piling in marine environments are concrete, timber, and steel. Steel

possesses a number of characteristics that make it desirable for structural

use. In general, steel can be easily transported and handled, withstand heavy

loads, adapt to various uses, be easily spliced in the field, and be driven

into place with minimal problems. Pile shapes commonly used are H-section,

pipe, and sheet. Deterioration of any type of structural material is an

important factor. When exposed to the marine environment, unprotected steel

will experience considerable damage from corrosion. Figure 1.1 illustrates

corrosion damage to a steel H-pile in the Alaska marine environment.

The effective service life of a structure, along with various related elements

such as maintenance costs, can be significantly altered by the destructive

effects of steel corrosion. Knowledge of the various means of corrosion

protection, including relative costs and effectiveness, is particularly

valuable in Alaska given the strong dependence upon marine transportation and

the aggressiveness of marine environments. Lack of corrosion protection or

ineffective protection is beginning to cause limitations on the allowable

loads and remaining useful life of numerous marine facilities in Alaska.

Effective methods of corrosion protection need to be applied to both existing

and future structures. This report is the first effort to compile information

regarding the steel condition in various marine structures in Alaska and

compare the corrosion protection systems employed.

Several different methods of comparison have been included. A summary of some

various means of corrosion protection outlines the principle available

systems. Advantages and disadvantages of each system are included in brief

-1-

Figure 1.1 One exanple of roIplete piling penetratioo fron rorr'OSioo after ;!;20 years. A nu:nber of other piles in too structure are in similar oon:iitioo. Alaska Railroad Pier, \\hlttier. Ptx>to rourtesy of Norton Corrosioo Limited, Inc.

-2-

descriptions of the corrosion protection methods. Another comparison is

accomplished through a series of present worth analyses of protection systems

which might be installed on a typical Alaskan dock. The present worth

analysis method allows initial costs and future costs of different situations

to be compared on the basis of units of equivalent present worth. A final

comparison is based upon field inspections of various marine structures in

Alaska. Information such as date of construction, available data on salinity

levels, type of protection, and type of materials is included in the facility

condition reports.

Each of the areas outlined above is explained in greater detail in particular

sections of the report. Due to numerous variables beyond the control and

scope of this study, all the comparisons are relative and general in nature.

The information presented in this report is not intended to be used as a

handbook of corrosion protection, but rather as the beginning of a data base

on Alaskan marine structures and of the identification of areas for additional

research and experimentation.

-3-

2.0 CORROSION OF STEEL IN THE MARINE ENVIRONMENT

Corrosion of steel exposed to the environment occurs naturally as the material

oxidizes to return to its original state. This destructive action is

generated by "physical and/or chemical differences present in metals or the

environment." 1 Steel material used in marine structures is exposed to a

particularly aggressive and corrosive environment (see Table 2.1).

The general rate of corrosion is influenced by many factors such as: water

temperature, oxygen concentration, pH values, salinity, water velocity, marine

organisms, pollution, wind, rain, humidity, sun, salt spray and other

particulates, stray electrical currents, mill scale, and dissimilar metals.

Measurement of these various factors and quantification of their effects on

corrosion is a complex and specialized field.

chemical processes of corrosion is available

Detailed information on the

from other sources. This

discussion focuses upon basic corrosion protection methods for marine

structures and observations of their effectiveness in the field. A brief

examination of the characteristics of corrosion in seawater is included to aid

in evaluation of the various protection systems.

2.1 CORROSION MECHANISMS AND CORROSION RATES IN SEAWATER2

Marine environments are particularly corrosive to steel in part because of

high moisture levels, high chloride levels, and the availability of dissolved

oxygen. Corrosion, with a resulting flow of electrons, occurs when seawater

functions as an electrolyte for the metallically coupled anodic surface areas

and cathodic surface areas of a steel pile. When the anodic and cathodic

areas migrate about the structures, uniform corrosion results causing general

surface roughening and metal loss (Figure 2.1). Localized attack, when the

active areas remain in one position, creates pitting corrosion. Pit depths

will be greater when the anode area is small relative to the cathode area,

such as the situation of weld corrosion (Figure 2.2) and small areas of steel

exposed by coating disbQndment. In the case of a stationary marine structure,

corrosion cells caused by oxygen differentials and by different metal

characteristics resulting from heat treatment at the metal surface are a

common cause of corrosion damage.

-4-

Agent

Tide

Wind

Current

Wave action

Ice

Ship impact

Brackish and seawater

TABLE 2.1

ENVIRONMENTAL INFLUENCE ON PILES

IN MARINE STRUCTURES3

PHYSICAL

CHEMICAL

Mechanism

Thermal cycles

Fatigue and overstressing

Erosion by sand

Fatigue and overstressing

Overstressing (freeze-thaw cycles)

Overstressing

Corrosion (submerged, tidal and splash zones)

Polluted water

Fire

Fresh water (submerged, tidal and splash zones)

Corrosion and direct attack

Burning

Corrosion

BIOLOGICAL

Fouling organisms

Aerobic bacteria

Anaerobic bacteria

Marine borers*

* Wood piles only

-5-

Chemical by-products/Differential Oxygen Cell

Chemical by-products

Chemical by-products

Ingestion

Figure 2.1 Unifonn rorrosim of H-pile ~b with reavy pitting m outside and inside of flanges. Corrosim pro<iocts ferric hydroxide, too brick red to b~ scales, and urxierlying ferrous !'vdroxide, a black film, are sin.n. Lutak Dock, Haines, Alaska.

-6-

Figure 2.2 Exarrple of l\eld cBrrage reused by pitting oorrosim of differential rretals.

-7-

The chemical differences of heat treated steel areas around welds to the large

area of untreated steel set up a situation for accelerated corrosion. Because

severe pitting may form areas where structural stresses can concentrate,

pitting can be a more important concern than uniform corrosion.

Initial corrosion rates tend to be relatively high and then decrease somewhat

as a coating of corrosion products forms. A black film under the rust layer

is indicative of active, ongoing corrosion. This film is magnetite (Fe3 04)

and is the direct product of corrosion. The more obvious and familiar brown

to reddish colored scale is the product of a secondary reaction which occurs

outside the metal to form hydrated ferric oxide (Fe2 03)' Some types of heavy

marine growth on the pile also seem to reduce corrosion. Reduction of

corrosion by marine growth and corrosion products is accomplished by reduction

of the oxygen availability at the steel surface. Removal of these coatings

either mechanically, by wave action or scour, or chemically, by elements

present in seawater, exposes bare steel and allows corrosion to continue at a

high rate.

Average corrosion rates are normally calculated by total weight loss of metal

or by metal thickness losses. In most cases, however, corrosion is not

uniform over the surface of the structure and the actual penetration at local

areas can exceed that predicted by average loss rates. Caution should be used

when applying these average rates to a specific structure. Pitting corrosion

rates are generally greater than uniform rates, particularly for the first ten

years after installation. Unfortunately, the ocurrance and rate of pitting is

very difficult to predict, so calculated average uniform corrosion rates are

generally utilized for design purposes. AVerage rates are those referred to

by the terms metal loss rate or corrosion rate. In this report, metal loss

rates are expressed in mils per year (1 mil = 0.001 inches).

Average uniform metal loss rates of 6 mils to 7 mils per year have been

observed for bare steel in Alaskan waters. This is an average rate which can

be helpful for predicting the overall metal loss of a structure. Depending

upon the specific site conditions, actual metal loss rates may easily vary

from 0 mils to 25 mils per year. An extreme loss rate of 25 mils per year has

been estimated on offshore structures in Cook Inlet near Anchorage, Alaska.

-8-

Winter ice conditions in this area cause removal of all corrosion products and

effectively expose totally bare. steel every spring. In addition to the ice

forces, sediments carried in the ice act as an abrasive and essentially polish

the steel surface. The loss rate of 25 mils per year in this case refers to

pitting and not to uniform or average corrosion loss. An estimate of the rate

of corrosion or metal loss on a particular structure is formed by establishing

a certain original steel and/or coating thickness (aided by measurements and

construction records), measuring the remaining steel or coating thickness, and

dividing the mils lost by the age of the structure. Many different

instruments, from simple pit measurement and magnetic coating thickness gauges

to sophisticated electronic devices, may be used in the measuring process.

This method is generally a quick and easy way to generate approximate

corrosion or metal loss rates.

2.2 ZONES OF CORROSION IN THE ALASKA MARINE ENVIRONMENT

The unique conditions of the marine environment create a series of

environmental zones which effect corrosion rates. These zones are apparent

when examining a corroded marine pile and result from different conditions of

moisture, oxygen content, and other factors. Figure 2.3 is a graphic

representation of the five zones. Not only do conditions vary from zone to

zone, but methods of protection and maintenance also vary. The five zones are

described as they are generally found in Alaska. Approximate metal loss rates

per year at various elevations on a pipe pile in the Alaska marine environment

are shown graphically on Figure 2.4.

Atmospheric Zone - This is the area of the pile above the splash zone

which is continuously exposed to the atmosphere. This area is

accessible for maintenance and generally experiences low corrosion

rates.

Splash Zone - This zone includes the area from the bottom of the atmos­

pheric zone down to the level of mean high water (MHW). The pile

surface exposed to the atmosphere is covered by a continuous film of

water and moisture droplets. Maintenance is possible during low tide

with some inconvenience.

-9-

Tidal Zone - The tidal zone is the pile area between the mean high

water level (MHW) and the mean lower low water level (MLLW). It is

subject to periodic wetting by tidal action. Maintenance is difficult,

and corrosion rates are generally uniform throughout the zone.

Submerged Zone - This area is continuously submerged and lies between

mean lower low water (MLLW) and the mud line. Any maintenance requires

special underwater techniques or cofferdaming. Significant metal loss

usually occurs in the area just below the mean lower low water (MLLW)

elevation. Steel scour may be experienced near the mud line from

movement of bottom materials by current action or throughout the zone

when heavy silt is present in moving water.

Soil Zone - This area is totally buried in soil or mud. Piles driven

into undisturbed so.il generally experience very little corrosion. No

maintenance is usually required.

With the various zone conditions and corrosion rates, maintenance and

protection requirements vary. As mentioned above, the area of greatest actual

metal loss observed in Alaska tends to be located just below mean lower low

water level. Conditions at this elevation and in the other zones are very

different. These characteristics must be considered when evaluating corrosion

protection methods.

-10-

ATMOSPHERIC ZONE

TIDAL ZONE

MHW

MLLW

SUBMERGED ZONE

SOli. ZONE

jH-PLE /

! ';

FLANGES

CORRODED SUBSTRATE

UNIFORM CORROSION

RUST TUBERCULE

PITTING CORROSION

FiG. 2.3 SCHEMA7DC CaAGHAM OF C:C~r.qOSION . 4

ZONES aN THE, ALASKA MA~DNE ENVDL=;ONMENT

-11-

EL 20

EL 15

EL 10

EL 5

EL 0

EL -5

EL -10

EL -15

EL -20

- I- EHW-

- I--Mbb'"

-~ELW -

~ MUDl,;INE~ 1

o I 1

I'

, \ , \ \ \ ,~ ,

.", .4I'A

A'

I I 2 3

,I " 't

" , \.

~,."",..-~

~ .,."",..

I 4

I 5

I 6

METAL LOSS RATE PER YEAR IN MILS (0.001 INCHES)

I 7

FDG. 2.4 APPa=iOXDMATE METAL LOSS I!=; A TES ON A PIPE F'ILE IN THE ALASKA

MA~INE ENVDRONMENT

I 8

(BASED UPON MEASUREMENTS .TAKEN AT CORDOVA, ALASKA - 1982)

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3.0 CORROSION CONTROL METHODS

The following basic methods of corrosion control are presented as an

introduction to the combination systems presented in the next section of the

report. Each method entails different procedures and has different areas of

maximum effectiveness. The basic methods have been grouped as: (1) Design

Practices, (2) Coatings, (3) Galvanizing, and (4) Cathodic Protection.

3.1 DESIGN PRACTICES

By considering the nature of corrosion during the design phase, many

potentially corrosive situations may be avoided or greatly minimized. Design

and fabrication procedures should avoid the creation of any localized areas

which would be susceptible to corrosion, such as crevices or pockets of

standing water and couples of dissimilar metals. Welds and fasteners should

be of a material that is slightly cathodic to the main steel bulk to avoid

critical structural harm from accelerated pitting corrosion.

The amount of steel surface area exposed to the environment is determined

during design. Various steel structural shapes differ greatly in their

surface areas. Much less surface is presented by a pipe pile compared to an

H-section pile. Unless structural or site constraints dictate otherwise, pipe

piles will generally be more economical to protect from corrosion and usually

offer the best structural shape for long unsupported lengths such as piles.

Corrosion occurring on the interior of an open-end pipe pile due to

percolation of water up into the pile void is normally slight. Lack of oxygen

and the corrosion products themselves will be severe limits on this type of

corrosion. A penetration of the pile in any zone above the mudline is a

different situation and is discussed later.

Selection of structural steel material and size is also a design

consideration. The corrosion resistance of a particular steel depends upon

its specific chemical' components and upon the specific environmental

condi tions. Extensi ve study has been conducted on this subject, and the

reader is referred to other sources for detailed information. Size of the

steel members does not affect the rate of corrosion; however, size selection

-13-

can include allowances for metal loss. This approach involves increasing the

steel thicknesses to allow for metal loss due to corrosion while still

maintaining structural viability until the end of a desired structure service

life. Besides the potential problems of localized attack such as weld

corrosion and pitting which could shorten the actual service life, this method

is not necessarily more economic than other corrosion protection mechanisms

over a long time period. A comparison based upon a present worth analysis is

included in Section 4.

The type of protection system planned may also effect design and

construction. For long-term protection of submerged steel, cathodic systems

are often utilized and require that all elements of the structure be

electrically continuous. This is most easily and economically accomplished

during construction even if a cathodic system will not be installed

immediately.

3.2 COATINGS

Coatings prevent corrosion by isolating the steel from the corrosive

environment. The mechanism of a barrier may be performed by a wide variety of

materials such as concrete, metal sheathings, paints, mastics, epoxies,

inorganic zincs, and polyurethanes. A common problem of all coatings, except

inorganic zincs and galvanizing, is that corrosion is concentrated at any

voids or faults in the barrier. It is extremely difficult to install or

maintain a voidless coating, and although some are easily repaired above the

water level, the cost of repairing damaged coating area below water severely

damages the economic viability of the system for long-term protection of the

submerged zone.

Some of the more promising coatings presently in use on marine structures in

Alaska are:

Epoxies - Epoxie~ are available in many different chemical formulations

including high percentage solids, sprayable liquids, and fusion bonded

types. They are generally inexpensive but material costs vary widely

according to the specific product. With proper application, epoxies

-14-

have approximately 10 to 20 years of effectiveness in the submerged

zone. Correct application is critical to create good bonding with the

steel. A lengthy and highly controlled cure time is necessary for an

effective coating. Repairs in the field are difficult because of long

cure times and because the original coating must be removed 01" abraided

to assure good bonding. Occasionally, specifications call for an

inorganic zinc rich primer to be used in combination with an epoxy

overcoat to help protect areas where the coating is discontinuous.

Coal-tal" epoxies have been used on many structures in Alaska and have

the appearance of a glossy black enamel. A dull finish is indicative

of application in the field. Many coal tal" epoxies suffer rapid

deterioration and disbondment when exposed to ultraviolet light. A

dull brownish color and powdery disbondment characterize

deteriorization of the coal tal" epoxy, and its effectiveness is greatly

reduced when this occurs.

Polyurethane - The two primary types of polyurethane coatings are

sol ventless, 01" 100 percent solids, and sol vent based formulas. Cure

times are generally much shorter and less restrictive than that

required for epoxies. Solventless systems permit greater first coat

application thickness than the solvent based coatings. However, they

tend to be less flexible and prone to shatter and disbond upon impact

at cold temperatures. The solvent based polyurethanes are more

flexible but seem to have a lower bonding strength and to teal" more

easily. Repairs above water level are fairly simple using a

2-component material system with little 01" no cure time required.

Inorganic Zinc - This type of coating was developed to combine the

benefits of the cathodic action of zinc and the ease of application of

a coating. Zinc will corrode preferentially to steel. This

characteristic is one of the major benefits of galvanizing and

inorganic zinc paints. Galvanizing is difficult 01" impossible for very

large or complicated steel elements. For these elements, a coating

type application is the only feasible choice for protection. Original

formulation of this coating required stoving (application of heat over

a certain time period) which severly impaired the practicality of

-15-

application in many situations. The development of an inorganic zinc

which could be applied through typical painting methods without stoving

made this type of coating viable for corrosion protection. Inorganic

zinc coatings are effective for non-immersed steel but not as durable

as galvanizing. Coating repairs can be minimized, as with galvanizing,

due to the preferential corrosion of zinc over steel. Inorganic zinc

primers are sometimes used under other compatible coatings. The

usefulness of inorganic zincs in the marine environment is limited by

the possible coating thickness. Inorganic zincs may have a maximum

coating thickness of 6 mils to 9 mils, which may not be adequate for

marine use without additional protection from another system.

3.3 GALVANIZING

This process involves coating the steel with a hard, abrasion resistant layer

of zinc. Hot-dip galvanizing involves immersing specially prepared steel in a

vat of molten zinc which chemically bonds to the steel. The zinc coating will

corrode preferentially to the steel even when the coating is discontinuous.

Thus, the galvanizing continues to protect the entire pile until most of the

coa ting is consumed. This sacrificial characteristic is one of the major

advantages of galvanizing. Galvanizing is also highly resistant to mechanical

disbondment and abrasion. Repairs to the coating above the water level can be

made, if necessary, by using a short-life metallic based paint or a long-term

metallic coating applied with heat. Generally, repairs of galvanizing are not

needed in the atmospheric zone due to the preferential loss of the surrounding

zinc galvanizing. The process of hot-dip galvanizing creates a coating on all

surfaces, including the interior surface of a pipe pile. If a pit penetrates

the pile allowing water access and corrosion to occur at the inner face of the

steel, protection of that surface is provided by the galvanizing.

The standard specifications for hot-dip galvanized steel as published by the

American Association of State Highway and Transportation Officials and by the

American Society for Testing and Materials require an average coating weight

of not less than 2.3 oz./ft2 for steel material 1/4 inch and heavier (see

Appendix B). This is approximately equal to a thickness of 3.9 mils. In

actual field measurements, thicknessess of 25 mils and greater have been found

-16-

to be more adequate. To insure this amount of coating, construction

specifications should state the desired thickness. Simple specification of,

for example ASTM A 123 or AASHTO Ml11, may result' in an insufficient coating

for marine use. Observations of structures with original coatings of ±25 mils

have shown the galvanizing to have an approximate effective life of 10 to 20

years below mean tide level. Little or no galvanizing loss is observed above

the mean tide elevation, and protection of this area should exist for the life

of the structure.

3.4 CATHODIC PROTECTION

In contrast to the corrosion protection methods already described, cathodic

protection is electrochemical rather than physical. This method basically

involves harnessing the random actions of corrosion and concentrating them on

external, introduced anode material. Thus, the entire structure being

protected is converted into a cathode. Cathodic protection can effectively

eliminate corrosion of bare and/or coated submerged steel material. For this

type of system to perform, the steel elements of the structure must be

electrically continuous. Any elements of the structure which are electrically

isolated can become possible anodes for the structure and suffer concentrated

corrosion. Cathodic systems give full protection to the submerged and soil

zones but protect the tidal zone only incrementally according to duration of

immersion. Protection by a coating is normal for non-submerged areas. The

two types of cathodic protection systems use either sacrificial galvanic

anodes or impressed current.

Galvanic Anode System This system utilizes sacrificial anode

material. The anode must be immersed in the electrolyte (seawater) and

electrically connected to the structure. Anodes may be suspended from

or attached directly to the structure, placed on sleds, or buried in

the mud bottom and connected by cable to the steel. The amount of

anode material required varies depending upon the area of exposed steel

to be protecte,d, type of anode material, and the particular

environment. Galvanic anode systems require no external power sources

and little maintenance once installed. The structure should be

electrically continuous for maximum protection efficiency. Selection

-17-

of anode material and amounts can extend replacement life to 15 or 20

years. If galvanic protection is used in conjunction with a coating

system, anode consumption rates will be lower than with bare steel.

Common anode materials are zinc, aluminum, and magnesium. Magnesium is

effective and economical in fresh water. Aluminum and zinc alloys are

commonly used in sea water due to efficient consumption rates. Zinc is

commonly used as ship hull anode material in both fresh and salt

water. Galvanic systems have higher initial costs than most coatings,

but costs for protection of submerged areas are lower than with

underwater coating repair. Uncertainty regarding actual anode

consumption rates in cold waters and the lack of monitoring devices or

control over the current output of the system are the disadvantages of

galvanic anodes compared to an impressed current system.

Impressed Current - This system employs an external dc power source

which drives current through the structure to a rare metal anode. This

anode material is then slowly consumed. It is critical that the entire

structure be electrically connected to avoid accelerated corrosion of

any isolated elements. Current requirements should be carefully

monitored to prevent underprotection with resulting corrosion or

oVerprotection with increased energy costs and possible disbondment of

coatings. A typical impressed current system includes: anodes and dc

wiring, dc power supply with current regulation capacity, reference

electrode and means for measuring structure potential, and a negative

return circuit from the protected structure to the dc power supply.

Anode material amounts are greatly reduced compared to a galvanic

system because of considerably lower consumption rates. Initial

installation costs and ongoing power costs make impressed current

systems rela ti vely expensive; however, impressed current is the most

controllable protection method and is generally very effective for

submerged steel.

-18-

3.5 COMBINATION CONTROL METHODS

Used singly, all of these systems have drawbacks. What is effective and

economic for one zone may be unsuitable for another zone. Ideally, the

structure will be neither under- nor overprotected, and combinations of

systems are the only way to approach achievement of this optimal goal.

Cathodic systems provide protection for submerged steel but not steel exposed

to the atmosphere. Many coatings are economical and effective in the

atmospheric zone but are less attractive for the submerged zone due to very

high repair costs. These two systems provide an excellent example of the

possible protection enhancement and economic benefit produced by concurrent

use of different systems. However, not all systems are compatible. Some

coatings, for example, may suffer disbondment when used simultaneously with an

impressed current system. Some coatings do not bond well to certain steel

types. The combined economic and protection benefits are negated or greatly

reduced in situations of incompatibility. In any case where combinations do

work well, further economic benefits may be obtained by introducing the second

system when the effectiveness of an original system has decreased in a

particular zone. The possible permutations and variations are limited by

economic practicalities and the compatibility of different systems. Some

feasible combinations are examined in Section 4 through the process of present

worth analysis.

-19-

TABLE 3.1

COMPARISON OF CORROSION PROTECTION SYSTEMS

EroXY mATING (10-15 yffil" useful life in sutmerge:l zone, unlimited life in atmospheric zone with rep3.irs)

PCLYUREI'HANE mATING (10-15 Yffil" useful life in sutxnerge:l zcne, unlimited life in atmospheric zcne with repairs)

OORGANIC ZINC mATING (unlimited life in atmospheric zcne)

GALVANIZING (15-20 year useful life in sutmerged zcne, unlimited life in atmospheric zcne)

GALVANIC SYSI'EM (15 year anode design life)

IMPRESSED aJRRENl' SYSl'EM (30 year anode design life)

o relatively inexpensive o am be repaired in

atmospheric zone with diffirulty

o stnrter rure time th3n coal tar epoxy

o ffiSy to apply o ffiSy to repair in

atmospheric zcne

o protects steel in areas of voids or coating breaks

o ffiSy to apply o llIi.nirral !1Bintenance costs

in atmospheric zcne

o very durable in all zones o protects steel in areas

of voids or coating breaks o llIi.nirral rraintenance costs

o very effective protection of sul:merge:1 zone

o P3f'tial protectirn of tidal zone

o llIi.nirral rraintenance

o very effective protectioo of su\:merge:1 zone

. 0 P3f'tial protectioo of tidal zone

o anode replacerrmt costs generally l&er than with galvanic systan

o systan am be mcnitored and controlle:1

-20-

o lCt1g am controlle:1 aJre

time recessary o difficult and expensive

to repair un:Ierwater o voids and breaks in coating

create areas of concentrated attack

o !1Bintenance costs

o my disbcnd or tear at cold tanperatures

o diffirul t and eJ<PE!1Si ve to repair underwater

o voids and breaks in coating create areas of concentrated attack

o !1Bintenance coots

o reduce:1 effectiveness in slll"Ioorged areas due to limited applicatirn thickness

o mt as durable as galvanizing

o eventually totally sacrifice:1 fron mean tide level to rru:il1re

o size of steel elements limited by afiplicatirn techniques

o cbes mt protect the atmospheric or splash zones

o an· electrically isolated element my be subject to accelerated attack

o amde replacement costs

o cbes mt protect atmospheric or splash zone

o an electrically isolated element my be subject to accelerated attack

o nrnitoring am rraintenance costs

o continual p&er costs

4.0 PRESENT WORTH ECONOMIC ANALYSIS OF CORROSION PROTECTION SYSTEMS

If time to delivery or initial construction costs are not overriding factors

in the design of a marine structure, a present worth analysis can provide a

basis of comparison for choosing a corrosion system which will provide optimum

protection of a structure. All costs, initial and future, can be converted to

units of equivalent worth through this analysis process.

The total present worth cost of a marine structure is composed of its initial

construction cost and predicted future costs. Future costs include

replacement of structural or other items which might be expected to wear out

before the end of the useful life of the structure. Recurring maintenance and

operational costs, such as inspections, painting, and fixed equipment rentals,

also contribute to future costs. The present worth value of these future

costs is affected by the value of money, or the prevailing interest rate.

Lower first or construction costs do not guarantee a low present worth value

as high periodic costs and/or low interest rates tend to contribuEe to higher

present worth values.

For the purposes of our comparison of corrosion systems, we have eliminated

costs common to all systems such as the initial dock construction cost,

replacement of structural items not related to the corrosion system, and

yearly maintenance and operational costs (except where they are unique as with

the use of an impressed current system). This is not to say these costs are

not real. For instance, if the necessary periodic inspections are avoided,

higher reinstallation costs will have to be considered as rates for metal loss

must be conservatively predicted. Therefore, periodic inspection is valuable

for establishing a history of the structure and avoiding or reducing future

costs.

Each corrosion system was assumed applied to a dock located in Cordova, which

represents an average subarctic marine environment in Alaska. This

hypothetical dock is illustrated in Figure 4.1- Its 105, 16-inch diameter

1/2-inch thick pipe piles are laid out in 21 bents along 5 rows. The dock is

placed in 30 feet of water at MLLW, and its deck is at elevation +20

feet MLLW. Extreme high water is at +16 feet MLLW. Total pile length is

-21-

'; ·;:~:··r·;·::"~/~~J·~';i.'~"~ . '.:. -

II

II 1/ u I' II

II II II II II If II /I II U i.I

EL. +20 EL. +16

"lHHt--lHt- MLL W

EL. -30 Ii I,

II MUDLINE II II II :1 II If fl If

II ,I " II ,f I' IJ \.l ~ LJ 4 EL. -50

FBG. 4.1 CBAG~AM OF COCK USElO IN PIHeSENT WO~TH ANAL VSIS

-22-

80 feet with an assumed embedment of 30 feet. This leaves 50 feet of exposed

steel above the mudline. . This dock represents the minimum structural

condition existing after 60 years in each protection system examined. It is

also the original construction used in Systems A, B, C, and F. Systems D, E,

G, and H deal with modifications of the steel thickness, but the dock layout

is unchanged.

The interest rate chosen for present worth comparision is 10% and does not

iqclude an inflation rate, which would lower the effective interest rate. A

sixty year design life was selected to allow completion of the different

protection system life cycles. Each system proposed is assumed to result in a

structure with 1/2-inch thick steel piles at the end of sixty years.

4.1 SYSTEM SUMMARIES

These system summaries detail the combinations of corrosion protection methods

proposed for a hypothetical dock in Cordova, Alaska. Each combination is an

effort to fully utilize the various protection methods, optimize the life of

the piling in each zone, and produce a structure with 1/2-inch thick steel

piles at year sixty of the comparison life. The order of presentation

reflects increasing present worth cost. The present worth analyses and a cost

summary are contained in Section 4.3, Figures 4.2-4.9 and Table 4.1

respectively.

System A

This system utilizes an epoxy coating applied over the length of the

pilings at the time of construction. At year 15, a galvanic cathodic

protection system would be installed to protect the submerged and tidal

zones. Anodes would be replaced at years 30 and 45. Protection in the

tidal, splash, and atmospheric zones would be provided by the epoxy

with coating repairs every five years. The system overlap in the

splash zone is, justified by the difficulties of protection and

maintenance in those areas.

-23-

System B

The initial

galvanizing

investment for

over the length

this

of

system consists of the cost for

the piling prior to installation.

Galvanic cathodic protection would be installed at year 15, with anode

replacement occurring at years 30 and 45. No maintenance and operation

costs are included because repair of the galvanizing is generally

unnecess·ary. Preferential corrosion of the galvanizing will protect

uncoated areas of the steel. The galvanic protection system will

extend the life of any remaining galvanizing in the tidal and submerged

zones and will protect all submerged steel.

System C

An initial polyurethane coating over the length of the piling combined

with galvanic cathodic protection after 15 years forms this system.

Replacement of the anode material would be required at 15 year

intervals, or at years 30 and 45. Coating repair costs are included at

5 year intervals. These repairs are necessary to insure adequate

protection of non-submerged areas of the pilings.

System D

This system combines galvanizing with a materials allowance for metal

loss. By using 3/4-inch thick galvanized steel above the mudline and

1/2-inch thick galvanized steel below the mudline, the structure could

be allowed to corrode and theoretically have 1/2-inch thickness of

steel remaining at the end of 60 years. In order to determine the

lengths of 1/2-inch thick steel needed for the soil zone, detailed

foundation exploration or test pile driving would be necessary. An

embedment length of 30 feet was used in this report. Initial costs

include the additional steel required for 50 feet of 3/4-inch steel

compared to 1/2-inch thick piles throughout and a detailed foundation

study. No costs for replacement or maintenance of the protection

system would occur. However, a regular inspection program would be

particularly important in this case for monitoring structural

-24-

integrity. The possible occurrance of accelerated corrosion at

vulnerable areas such as welds would effect the service life of the

structure and demonstrates the importance of regular inspections.

Costs of such an inspection program are not included in the analysis

because they are considered common to all systems.

System E

The initial cost of this system consists of the expense of the

additional steel for BO-foot, 1-inch thick steel pilings compared to

1/2-inch thick piles. No galvanizing or coating would be utilized.

The extra metal thickness is an allowance for metal loss from

corrosion. No additional costs are included in the analysis; although,

a regular inspection program would be important for monitoring the

structural condition.

System F

An impressed current system and a field applied epoxy coating above

+5 ft. MLLW .comprise this corrosion protection combination. Initial

costs include installation of the impressed current system and in-field

application of the epoxy. Various future costs would be incurred.

Annual expenditures include power use and monitoring of the system.

These annual costs are include8 in the present worth calculations but

are not shown annually on the cost graph. Underwater anode maintenance

and coating repair costs are anticipated at 5 year intervals. These

annual and 5 year costs are considered as maintenance and operation

costs, while anode replacement at years 20 and 40 is shown as a

replacement cost on the present worth analysis summary.

System G

By combining galvanizing with a metal thickness allowance, this

approach eliminates replacement and maintenance costs and reduces the

-25-

amount of additional steel required as compared to some other systems

examined. Steel piles 3/4-inch thick and 80 feet long with galvanizing

over the entire length would result in 1/2-inch thick steel remaining

at the end of 60 years. As with all the protection systems, regular

inspections are important for monitoring the corrosion processes at the

specific structure.

System H

This analysis examines the present worth value of employing no

corrosion protection 01" metal allowance for the dock. Original

installation would use 3/4-inch thick uncoated steel piles. Corrosion

damage would require replacement of the structure at year 30 to insure

structural integrity through the 60-year design life being used for

comparison. The initial cost for this analysis includes the cost for

the additional steel required. The future cost is the estimated cost

of replacing the dock using 3/4-inch thick uncoated pipe piles.

4.2 SYSTEM COST ESTIMATES

Background data for estimating the various system costs include the unit

material costs, anode consumption rates, total pile surface area, and total

weight of the steel. This information is presented in the following lists and

explanations.

Unit Costs

Steel

Galvanizing

Epoxy Coating (ave. cost)

Polyurethane Coating (ave. cost)

Anode Material

$ 0.50/lb.

0.12/lb. of

2.00/sq.ft.

3.00/sq.ft.

1.25/lb. of

steel

of pile surface

of pile surface

aluminum

The hypothetical dock with 105, 16-inch diameter 1/2-inch thick steel pipe

piles has an estimated total pile surface area of 35,200 square feet. This

amount is used to calculate the epoxy and polyurethane coating costs of

-26-

$70,400.00 and $105,600 respectively. If, as in System E, the coating area is

decreased, a corresponding initial cost decrease occurs; however, because of

the increased cost involved in field application, $6.00 per square foot of

pile surface was used in this case. The unit prices used here are averages of

some of the various actual product costs presented in Section 4.4. Repair

costs scheduled every five years consist mainly of mobilization expenses, and

material costs are relatively minor. When a coating is combined with a

cathodic system, these coating repair costs are absorbed in the anode

replacement costs in the replacement years. Galvanizing costs are based upon

the total weight of the steel. Generally, 16-inch diameter piles weigh 82.76

Ibs./lin.ft. in a 1/2-inch thickness and 122.21 Ibs./lin.ft. in a 3/4-inch

thickness. Depending upon the particular system used (notably Systems B, E,

and G), the total steel weight may vary and cause the galvanizing costs to

vary.

Estimates of the cathodic protection systems involve a few more factors than

these coating costs. Design of cathodic systems must consider many particular

site conditions and characteristics of the specific structure. More detailed

information on this design process may be obtained from published literature

or experts in the field. The following explanation briefly describes the

approach used for this report.

Conditions in Cordova indicate that a cathodic system must have the capability

of providing 12 ma./sq.ft. in the submerged zone and 2 ma./sq.ft. in the mud

zone to maintain complete protection. As a matter of interest, "current

densities as high as 100 milliamperes per square foot have been required,,5 for

offshore structures located in Cook Inlet, Alaska. With a submerged pile area

of 20,340 square feet and a buried area of 13,200 square feet, a cathodic

system for the example dock would have a total requirement of 270,000 rna. or

270 amperes. Anode material amounts and electrical requirements are

calculated upon this amperage requirement. The general rate of consumption

used for design purposes for aluminum anodes in seawater is 6.82 lbs./amp

year. Anode material amounts for a galvanic system are calculated using the

consumption rate, design life, and an 85 percent efficiency factor for anode

material usage. An impressed current system will require less anode material

due to lower consumption rates. However, additional costs are incurred with

-27-

the need for rectifier units, a continuous current supply, and system

monitoring. Power costs for the impressed current system are based upon an

average rate of $0.16 per kilowatt hour. Initial costs for the galvanic or

impressed current systems include engineering/design, installation, materials,

freight, and monitoring expenses. Anode replacement costs include materials,

freight, and installation. Each of these various costs are shown in the

following present worth analyses (Figures 4.2 through 4.9).

4.3 PRESENT WORTH ANALYSIS

An outline of the costs involved with the proposed systems and their total

present worth are presented in Figures 4.2 through 4.9 in order of increasing

cost. Table 4.1 is a comparison summary of the present worth values of each

system. Formulas used in the present worth analyses are included in

Appendix C.

-28-

TABLE 4.1

PRESENT WORTH SUMMARY

Interest = 10%

SYSTEM

A. Epoxy coating with galvanic cathodic

protection installed after 15 years

B. Galvanizing with galvanic cathodic

protection installed after 15 years

C. Polyurethane coating with

galvanic cathodic protection

installed after 15 years

D. 1-inch thick steel piles,

no galvanizing or coating

E. 3/4-inch thick galvanized steel piles

from mudline to top with 1/2-inch thick

galvanized piles below mudline, detailed

foundation exploration required

F. Impressed current cathodic

protection with an

epoxy coating above

elevation +5 feet MLLW

G. 3/4-inch thick steel piles with

galvanizing over entire length

H. 3/4-inch thick uncoated pipe piles

with dock replacement at year 30

-29-

PRESENT WORTH

$ 103,400

$ 109,800

$ 138,600

$ 203,500

$ 262,000

$ 270,200

$ 289,200

$ 446,770

FIGURE 4.2

SYSTEM A

Epoxy Coating With Galvanic Cathodic Protection Installed After 15 Years

Year

Cost

Initial Costs $ 70,400 Epoxy coating applied over total length of piles

Replacement Costs $ 85,000 Install galvanic C.P. after 15 years with replacement of

anodes at 35 and 45 years

Maintenance & 0Eeration Costs $ 5,000 Repairs to coating in atmospheric zone every 5 years

0 5 10 15 dl 25 3J J5 ljQ 45 50 55 ro

5,000 5,000 5,000 5,000 5,000 5,000 5,000 5,000

85,000 85,000 85,000

70,400

Presmt Worth = $ 103,400

-30-

FIGURE 4.3

SYSTEM B

Galvanizing With Galvanic Cathodic Protection Installed After 15 Years

Initial Costs $ 83,400 Galvanizing over total length of 1/2-inch thick piling

Replacement Costs $ 85,000 Install galvanic C.P. after

anodes at 35 and 45 years 15 years with replacement of

Maintenance & Operation Costs None

Yenr 0 5 10 15

Cost

85,000

83,400

Presffit Worth = $ 109,800

35 40 50 55 60

85,000 85,000

-31-

FIGURE 4.4

SYSTEM C

Polyurethane Coating with Galvanic Cathodic Protection Installed After 15 Years

Initial Costs $ 105,600 Polyurethane coating applied over total length of piles

Replacement Costs $ 85,000 Install galvanic C.P. after

anodes at 35 and 45 years 15 years with replacement of

Maintenance & Operation Costs $ 5,000 Repairs to coating in atmospheric zone every 5 years

YEm' 0 5 10 15 35 50 55 60

Cost

5,000 5,000 5,000 5,000 5,000 5,000 5,000 5,000

85,000 85,000 85,000

105,600

Present Worth = $ 138,600

-32-

Year 0

Cost

FIGURE 4.5

SYSTEM D

1-Inch Thick Steel Piles, No Galvanizing Or Coating

Initial Costs $203,500 Extra steel

Replacement Costs None

Maintenance & Operation Costs None

203,500

Presalt Worth = $ 203,500

-33-

FIGURE 4.6

SYSTEM E

3/4-Inch Thick Galvanized Steel Piles From Mudline To Top With 1/2-Inch Thick Galvanized Piles Below Mudline,

Detailed Foundation Exploration Required

Initial Costs $ 104,000 Extra steel

108,000 Galvanizing 50,000 Detailed foundation exploration

$ 262,000

Replacement Costs None

Maintenance & Operation Costs None

Year 0

Cost

262,000

Prese:lt Worth = $ 262,000

-34-

Year

Cost

FIGURE 4.7

SYSTEM F

Impressed Current Cathodic Protection With Epoxy Coating Above Elevation +5 Feet MLLW

Initial Costs $ 140,000 Impressed current system

40,00a Epoxy installed in the field $ 180,000

Replacement Costs $ 50,000 Anode replacement at 20 and 40 years

Maintenance & Operation Costs $ 10,000 Underwater anode maintenance at 5 year intervals

5,000 Coating repair at 5 year intervals $ 15,000 Cost every 5 years

$ 5,000 Power per year 1,000 Monitoring per year

$ 6,000 Annual costs (not shown annually on graph)

0 5 10 15 20 25 30 35 40 45 50

15,000 15,000 15,000 15,000 15,000 15,000 15,000 15,000

50,000 50,000

180,000

Amnl Cost of $6,000

Present Worth = $ 270,200

-35-

55 60

15,000

FIGURE 4.8

SYSTEM G

3/4-Inch Thick Galvanized Steel Piles

Ini tial Costs $ 166,000 Extra steel

123,000 Galvanizing $ 289,200

Replacement Costs None

Maintenance & Operation Costs None

Year 0

Cost

249,400

Present Worth = $ 289,200

-36-

60

FIGURE 4.9

SYSTEM H

3/4-Inch Thick Uncoated Piles With Dock Replacement At Year 30

Initial Costs $ 166,000 Additional steel for original installation

Replacement Costs $4,900,000 Dock replacement at year 30

Maintenance & Operation Costs None

Year 0

Cost

4,900,000

166,000

Presa1t Worth = $ 446,770

-37-

WA'l'OO

4.4 APPROXIMATE COATING COSTS BY PRODUCT

Some coating costs listed by brand-name are presented in Table 4.2. These

costs are divided into the categories of surface preparation, application, and

material cost. All costs are expressed as dollars per square foot. These

costs represent estimated real costs incurred by application of each coating,

including allowance for contingencies for application error. Current bid

prices (December, 1982) may differ from these estimates due to various market

conditions. Average unit costs were used for the present worth analysis due

to the wide variations in cost from product to product. Specifications for

these and other corrosion protection products may be obtained from the

manufacturer.

TABl.E 4.2

ESTIMA'lED WA'l'OO msrs BY PROOOCT

TYPE PROOOCT MANUFACTURER msrs ($/sq.ft.) THICKNESS

(MIlS DFr) SURFACE MATERIAL

PREPARATICN APPLICATICN msr

3 Inorganic Zinc Dimetcote 3 Ameron .40 .15 .52

20 Epoxy Coal Tar Epoxy IlLIJlel'\:)US .40 .25 .50 !lI3l1ufacturers

30 PolyuretiBne PR-475 Products Research .50 .80 1.10 and

Che:nical Corp.

30 Epoxy Inerta 160 Intematiooal .50 1.05 1.38 Paint Co.

30 PolyuretiBne Torbron Zebra .50 1.00 1.70

30 Polyurethane Zebron Ameron .50 2.00 1.25

-38-

'lUrA!.. msr

1.07

1.15

2.40

2.93

3.20

3.75

5.0 FIELD INSPECTIONS

An important part of evaluating the effectiveness of a corrosion protection

system is verifying actual performance in the field. To this end, a number of

marine facilities in the State of Alaska were inspected. Figure 5.1 shows the

general locations. The structures vary greatly in type, size, age, protection

method, specific environment, and physical condition. In addition, variables

such as the quality of application and installation of a protection system and

the general construction methods employed can alter the efficacy of any

corrosion protection method. Comparisons based upon field observations are

invaluable; however, the many variables affecting the structure must be

considered when evaluating the corrosion protection. The inspection summaries

contained in this section are presented for use both as a basis for comparison

of different corrosion protection systems and as an initial data base for a

condition inventory of marine facilities in the state.

Most inspections involved a general visual reconnaissance of the structure and

random detailed spot checks of the steel. Optimally, this type of inspection

is performed during a minus tide because the area of greatest metal loss

observed in Alaska tends to occur in the zone just below mean lower low

water. This critical area is exposed to the atmosphere and accessible for

above water inspection only during a minus tide. Spot checks included removal

of marine growth and corrosion residue by scraping and by the use of a wire

brush to expose a sound coating or bare steel. Pit depth and coating

thickness measurements were made with a Thorpe Pipe Pit Gauge and a magnetic

coating thickness gauge.

was followed at numerous

This procedure, illustrated in Figures 5.2 and 5.3,

locations on the structure at the approximate

elevations -2' MLLW, 0' MLLW, +2' MLLW, and +5' MLLW. Some inspections

included detailed underwater surveys, notably the structures located in

Kodiak, Seldovia, and Cordova. An underwater diving operation is necessary to

obtain a complete survey of the structure. Water samples were collected at

some locations to enabl,e a relative comparison of general salinity levels.

Available data gathered for various structures in Alaska is summarized in

Table 5.1. Inspection summaries with illustrations and more detailed

information on some specific structures are included in Section 5.1.

-39-

I .ro. o I

ANCHORAGE

COLD BAY

FIG. 5.1 LOCATION OF FIELD INSPECTIONS

KETCHIKAN

Figure 5.2 A Th:Jrpe pit gpuge 1.l'3e:I to IIIEBSUI"e pit depth. Insps::tioo, Kcxli.ak, Alaska.

Figure 5.3 Insps::tioo prooedure includ~ reroving any existing marine gr'(Mth and wire brushing the surface to a round 003.ting or tare steel finish before visLB1. eJG3IIlimticn. Bridge CaissCI'1, Sitka, Alaska.

-4 1-

TABLE 5.1

SUMMARY OF CORROSION PROTECTION SYSTEMS OBSERVED IN ALASKA*

Structure

GSA Parking Structure Ketchikan

City Dock Ketchikan

Klawock Timber Dock Klawock

City Dock Sandpoint

Sandpoint Boat Haulout Sandpoint

Hoonah Floating Transfer Bridge

Division of Aviation Fuel Dock

Cold Bay

City Harbor Dock Homer

Pier No. 2 Kodiak

Pier No. 3 Kodiak

Bridge Caissons Sitka Harbor Bridge

Specification

EPOXY COATING

Coal Tar

Coal Tar 16 mils DFT

28 mils DFT on Addition to Dock

3 mils DFT Inorganic Zinc Rich Primer, 20 mils

Min. DFT Coal Tar

Fusion Bonded Epoxy

Fusion Bonded Epoxy

Fusion Bonded Epoxy Per AVailable

Information

Fusion Bonded Epoxy Per Available

Information

20-25 mils DFT Inerta 160

Coal Tar Per Available Information, Appears to

be a Type of Paint

Coal Tar Per Available Information

Coal Tar with Aluminum Anodes for Galvanic Protection

Construction Date

1976

1977

1981

1982

1982

1978

1982

1965, 1972

1971

1971

*Note: Some of these structures are not included in the inspection summaries but are included here as part of the data base on existing corrosion protection systems in the State.

-42-

Structure

Fender System Cordova City Dock

City Dock Dillingham

Float Anchor Piles Harbor Expansion

Cordova

Alaska State Marine Ferry Terminal

Sitka

Alaska State Marine Ferry Terminal

Juneau

City Shuttle Ferry Terminals Ketchikan

City Dock Unalaska

Alaska State Marine Ferry Terminal

Ketchikan

Fender System Dillingham City Dock

Alaska State Marine Ferry Terminal

Cordova

TABLE 5.1 (continued)

Specification

POLYURETHANE COATING

30 mils DFT Products Research Corp.

475 RIS with Primer

30 mils DFT Torbron 1864

60 mils DFT Torbron 1864

GALVANIZING

ASTM 123

ASTM 123

M111

ASTM 123

ASTM 123

ASTM 123

M111

-43-

Construction Date

1982

1982

1983

1982

1981

1973

1982

1972, 1975, 1978

1982

1969

Structure

Alaska State Marine Ferry Terminal

Seward

Lutak Dock Haines

City Dock Seldovia

City Dock Cordova

Port of Anchorage Anchorage

Alaska Railroad Pier

Seward

TABLE 5.1 (continued)

Specification

BARE STEEL

Impressed Current System Installed-1983

Impressed Current System Installed-1979 (Terminal 3),

1980 (Remaining Structure)

Impressed Current System System Installed in 1980

-44-

Construction Date

1955

1950's

1966

1969

1961, Various Addi tions From 1975 to Present

1965

5.1 INSPECTION SUMMARIES

KETCHIKAN

GSA Parking Structure

Located near the mouth of Ketchikan Creek, this structure provides parking

space for Government Services Administration personnel. It is comprised of a

cast-in-place concrete deck and pile bents supported by 14-inch outside

diameter steel pipe piles. The piles were coated with a coal tar epoxy which

has an existing thickness of greater than 25 mils. Coating disbondment has

occurred where it appears that barnacles and mussels have been removed by

mechanical action. Minimal pitting is present on the exposed steel at

elevation MLLW. The larger pits observed were measured by a Thorpe Pipe Pit

Gauge and found to be less than 1/16-inch deep. Since a general prediction of

metal loss rates for bare steel at elevation MLLW is 6 mils per year, it is

probable that these deeper pitted areas were exposed approximately ten years

ago. Several factors could effect the actual rate of corrosion on this

structure. Proximity to the freshwater outfall of Ketchikan Creek could

result in reduced water salinity and corrosion activity. A general salinity

reading of six parts per thousand tends to substantiate this assumption, at

least relative to salinity levels measured at the City Dock and the Shuttle

Ferry. In contrast, a small boat mooring facility and a timber processing

mill located near the structure could release stray electrical current into

the water and could cause an increased rate of corrosion. All of these

factors would need quantification and additional research to determine the

effects on corrosion rates.

City Dock

Originally constructed in 1977, this facility consists of prestressed concrete

panel decking grouted in place to steel bents. The bents were fabricated from

steel channel iron welded to the top of 16-inch outside diameter steel pipe

pile caps. This superstructure is supported by 16-inch outside diameter steel

pipe bearing piles. The original dock structure received one coating of coal

tar epoxy at 16 mils minimum dry film thickness (DFT), while an extension

-45-

F~ 5.4 Ccal tar epoxy mated pile in gcod ooOOitioo with m:in:i..nBl disl:x:ndrtalt and corrosioo. City Dock, KetdUkan, Alaska.

- 46-

Ketchikan (continued)

of the dock completed in 1978, was to receive a primer and one or two coats of

coal tar epoxy (14 mils DFT minimum per coat). A water sample taken at this

structure had a salinity level of approximately 20.75 parts per thousand.

The coating is generally in good condition and measures greater than 20 mils

in thickness. Small localized areas of disbondment and mechanical damage are

present. Corrosion in the zone from elev. -1.5 ft. MLLW to elev. +4 ft. MLLW

in the form of small pits is found in areas of coating loss.

continue from undercutting of the coating by corrosion.

structure is in good condition overall.

Shuttle Ferry Terminals

Disbondment will

The city dock

The two Ketchikan City Shuttle Ferry Terminals were constructed to facilitate

transfer of people and materials by shuttle ferry between the Ketchikan

International Airport and the City itself. Each terminal consists of a number

of dolphins. Two concrete capped pile structures form the counterweight

towers for the loading ramp, and four to five additional breasting dolphins

with fenders are utilized at each terminal. The piles used in these

structures were galvanized to AASHTO M111 (see appendix) specifications. A

general salinity level of 22.25 parts per thousand was present in a water

sample collected at the structure near the airport.

Inspection revealed measurable loss of galvanizing in the zone from elev. +7

ft. MLLW down to elev. -2 ft. MLLW. Remaining galvanizing thickness in this

tidal zone varies from 0 mils to 25 mils. Above elev. +7 ft. MLLW, no

measurable galvanizing loss has occurred. Most pilings which have lost all

galvanizing in the tidal zone exhibit little or no corrosion. This uniformity

may be due to passive cathodic protection from the galvanizing on other

piles. For such prot~ction to occur, the piles in the dolphin must be

electrically connected. In contrast, two piles in the terminal near the

airport were corroding at a rate comparable to bare steel. These piles may be

electrically isolated from the rest of the structure. If this happens, the

-47-

Figures 5.5 'I'w:J cblJhlrn ~ corrosim of me pile in 81m group. 'Ih!se piles my be arxl 5.6 electrically irolate:1 fran the others in 81m dolphin. Shuttle Ferry Tennimls ,

Ketd1ikan, Alaska.

-48-

Figure 5.7 Elrotrically isolated pile {XlSSibly acting as an anode to other piles in the dolpnn. Shuttle Ferry Tennina.l, Ketchi.kan, Alaska.

-49-

Figure 5.8 Pile whim slnls ro rorrosim. This pile is in the same dolrhln as the rorroding pile in Figure 5.6. Shuttle Ferry Terminal, Ketchikan, Alaska.

-50-

Ketchikan (continued)

pile would be isolated from the "protection" and could possibly become an

anode. Loss of galvanizing and rapid corrosion would result.

Alaska State Marine Highway Terminal

This structure was constructed over a number of years and consists of

individual dolphins with steel pipe piles and steel caps. Repairs to some

dolphins were required during the construction period. The steel pipe piles

were galvanized with an approximate thickness of ±25 mils at installation.

Each dolphin has a fender system of galvanized H-section support piles with

galvanized H-section walers for attaching timber rub strips. By design, the

steel fender components are electrically isolated from the dolphin bearing

piles and react to corrosive influences as a separate unit. General salinity

levels of 22.75 parts per thousand were present.

As with the city shuttle ferry terminals, the greatest observed loss of

galvanizing occurred in the zone from elev. +7 ft. MLLW down to elev. -2 ft.

MLLW. The oldest existing dolphin was constructed in 1972 and consists of

steel pipe piles with a concrete cap. One piling in this dolphin appeared to

be acting as an anode and corroding at a higher rate than the other pilings.

This could be due to electrical isolation from the rest of the structure. All

other dolphins consist of steel pipe piles with steel caps and are in good

condition. The fender system components have been well protected by

galvanizing. This is in contrast to the general tendency of H-section walers

constructed with vertically oriented flanges to remain wet and become

localized corrosion cells. When this happens, any galvanizing is rapidly

sacrificed and corrosion can occur at a high rate. The walers in these fender

systems are heavy sections and have experienced minimal damage or corrosion.

An approximate average galvanizing loss rate for this structure is estimated

to be between ±1.5 to 2.5 mils per year.

-51-

SITKA

Sitka Harbor Bridge

Inspection of this structure, built in 1971, focused upon the caissons of the

two center support piers. These support piers are constructed of concrete

filled cellular sheet pile caissons which rise to elev. :!:25 ft. MLLW. The

MP-112, 3/8-inch thick Mariner steel sheet piles were coated with a coal tar

epoxy and electrically connected to aluminum anodes at the time of

construction. As part of the galvanic cathodic protection system, these

anodes were placed on the harbor bottom adjacent to the structures. A water

sample contained a general salinity level of 17 parts per thousand.

Coating conditions vary a good deal at different elevations, and some unusual

conditions were found. From elev. +7 ft. down to MLLW, the coating has

disbonded in many locations and forms irregular and spotty coverage. The

coating becomes less spotty above elev. +7 ft. MLLW and is continuous above

elev. +11 ft. MLLW. Above elev. +7 ft., the coating can be easily removed as

a fine powder. The coating remaining from elev. -1 ft. MLLW to elev. +7 ft.

MLLW varies in condition from well bonded to disbonding in sheets. Corrosion

above elev. +7 ft. MLLW was typical of atmospheric corrosion. At elev. +11

MLLW, a coating thickness of :!:25 mils was present, including a primer

thickness of ±3 mils.

The greatest amount of corrosion activity has occurred at stress points along

the sheet pile interlocks. Corrosion products in the forms of hydrated ferric

oxide, brick red to brown scales, and underlying magnetite, a black film, were

present. Minor pitting was found beneath these layers. The exposed steel

from MLLW to elev. +7 ft. is not pitted and appeared to be well protected by

the anodes. Generally, the steel of the caissons is in good condition.

The coating conditions found on this structure are very unusual when compared

to the other structures inspected. Possible reasons for these conditions

reveal areas for additional research. Anyone or combination of the following

could possibly be responsible:

-52-

1. Coating was not applied properly.

2. Coating does not bond well to the mariner steel type.

3. Coating deterioration due to ultraviolet light exposure.

4. Coating does not remain bonded with concurrent use of the galvanic

cathodic protection.

Further investigation on simultaneous use of a coal tar epoxy with cathodic

protection will be very useful. Many structures in Alaska are coated with a

coal tar epoxy and may require the addition of a cathodic protection system to

assure an extended useful working life.

-53-

Atnx:spheric Zcne

Splash ~

Tidal Zooe

KLW

Figure 5.9 Bridge ~, Sitka, Alaska.

-54-

Figure 5. 10 UnusLBl <XBting disbcndrralt exhibitai (]') Bridge Caissoo at Sitka, Alaska.

-55-

JUNEAU

Highway Bridges

In the Juneau area, three highway bridges with coated pipe pile supports were

inspected. The bridge pilings are subject to periodic salt water intrusion

during high tides, but are predominately in a fresh water environment. The

type and condition of each coating varied from bridge to bridge.

Sheep Creek Bridge pile supports are covered with a ductile epoxy coating of

greater than 25 mils thickness. The epoxy coating is in good condition with

no damage, and no corrosion is present.

Gold Creek Bridge piles have a heavy, hand applied epoxy coating. This epoxy

is soft with a brittle surface and has experienced a fair amount of blistering

and disbondment. Remaining coating thicknesses are greater than 25 mils. No

corrosion is apparent, even in areas of coating disbondment.

The epoxy coating used on Lemon Creek Bridge support piles has been

mechanically abraided and most of the coating on the upstream pile surfaces

has been removed. This abrasion was probably caused by sediments transported

in the water and by some ice movement. Other than mechanical damage, the

coating is in good condition with a thickness greater than 25 mils. No

corrosion was noted.

-56-

HOONAH

Floating Transfer Ramp

This floating marine transfer ramp, installed in 1972, is supported on the

seaward end by FlexiFloats. The approximate salinity level at this facility

was 21.1 parts per thousand. According to the manufacturer, the floats were

coated with a fusion bonded epoxy prior to installation. The FlexiFloats are

approximately 7 ft. in height, 3 ft. of which is submerged. The coating is

intact and in good condition. The minimal corrosion activity noted was

limited to areas above the water line where the coating had been removed by

mechanical damage. Part of the galvanized ramp bearing assembly is

submerged. Minor pitting was found at the water line. The overall condition

of this facility is good, and the steel floats should continue to be protected

by the coating.

On a similar structure in another location which had been removed from the

water, significant corrosion was found on the bottom of the float while the

top and sides were in good condition. The undersides of the floats at Hoonah

were not accessible for inspection, and a similar situation could possibly be

occurring. In the interest of completeness, underwater inspection of this and

other similar structures should ·be performed.

-57-

HAINES

Lutak Dock

The Lutak Dock, constructed in the early 1950' s, is a cellular sheet pile

structure located several miles northwest of Haines. Originally, the uncoated

sheet piles used in construction were 1/2-inch and 3/8-inch in thickness and

were to be connected to a cathodic protection system. This cathodic system is

no longer in use, and it is not known how long the system was in operation. A

water sample collected at this structure had a general salinity level of 6.25

parts pel' thousand.

The sheet pile wall generally exhibits substantial amounts of marine growth

and heavy corrosion residue. A mixture of uniform corrosion and heavy pitting

was found at elevation -1 ft. MLLW. A general survey along the length of the

sheet pile wall located three areas with complete penetration of the steel

sheet piles due to corrosion. These random, complete penetrations occurred

below the elevation +5 ft. MLLW. Because of weep holes present in the sheet

piles, salt water access to both sides of the steel has allowed corrosion and

metal loss to occur simul taneously on both sides. This contributes to

accelerated damage to the structure. Additional penetrations would probably

be found after removing the existing marine growth. Considerable metal loss

was found on the H-pile supports for the concrete deck. Uniform and pitting

corrosion were responsible. In addition, many of the H-piles were poorly

connected to the concrete deck which is spalling badly at these connections.

A number of H-piles moved easily upon direct pressure and seemed to not be

anchored at the bottom. Overall, a fairly advanced stage of corrosion and

corrosion damage was found at this structure.

An interesting aspect of this dock is that an earlier inspection was conducted

and forms a basis for comparison to the present dock condition. This earlier

condition survey, performed in 1976 by R & M Consultants, Inc., included sheet

pile thickness measurements and an underwater inspection. At that time, the

condition report included the following observations: connector sheet piles

had been reduced to less than 2/3 of the original thickness in some places in

the splash zone, exposed areas of the main cell sheet piles in general had

thicknesses greater than 3/8 inch, interlocks and welds were in good

-58-

condition,

condition,

H-pile supports for the

the remaining structural

concr'ete deck wer'e

life of the main

in good str'uctural

cell structur'e was

estimated at 20 years, and significant maintenance r'equir'ements wer'e pr'edicted

in 8 to 10 year's for' the sheet pile connector arcs.

A comparison of the dock condition in 1976 and in 1982 reveals possible

cOr'rosion r'ates gr'eater than pr'edicted. The cOr'rosion penetr'ations of the

sheet piles and condition of the H-pile supports ar'e the major' changes

observed. The possible maintenance requir'ements foreseen in the 1976 r'epor't

may be necessar'Y in the near' future. The corrosion damage to this struture

deser'ves serious consideration and r'emedial action.

-59-

Figure 5.11 Profile of H-pile flange sh::wing metal 1= ch.ie to pitting oorrosim. Lutak Dock, Haines, Alaska.

-60-

Figure 5.12 Steel sl'Eet pile sh:7.illJg randan oomplete penetratiCt1S due to pitting rorrosion. The weep role sro.m. is approximately 3 inches in diameter. Lutak D:Jck, Haines, Alaska.

-61-

CORDOVA

City Dock

This structure, built in 1968, consists of precast concrete panels with grout

seals on poured-in-place concrete caps supported by steel pipe piles.

Seamless 16-inch diameter and 24-inch diameter straight welded seam pipe piles

were used. No evidence of a coating was found. Heavy marine growth was

present in the submerged zone on all piles. Inspection of this structure

included extensive underwater surveys and metal thickness readings. Costs for

the present worth analyses in Section 4 are based upon data gathered for this

facility.

In order to obtain a representative picture of corrosion damage, a 4- to

6-inch wide strip was cleaned for the entire submerged length of a number of

piles. All welds found were exposed around the circumference of the pile.

Active corrosion was observed in the tidal zone beneath approximately 3/16 to

1/4-inch of scale. Pit depth readings made at various elevations ranged from

a minimum of 17 mils to a maximum of 98 mils or from 4% to 24% of the original

wall thickness. The heaviest corrosion on all piles examined was found in the

area just below low water. One weld observed was in good condition with minor

pitting while another had experienced substantial pitting and deterioration

around 75 to 80% of the circumference. Considering the age of this structure,

there was a normal amount of corrosion in the splash zone and no evidence of

spalling at the pile caps. An impressed current cathodic protection system

will be installed at this facility during 1983.

Alaska State Marine Ferry Terminal

The Ferry Terminal towers and dolphins are supported by 16-inch diameter piles

installed in 1969. At that time, the piles were galvanized to approximately

35 ft. below the cap. An underwater inspection with ultrasonic thickness

measurements was performed at this structure. As at the Cordova City Dock, a

4- to 6-inch wide strip was cleaned along the entire submerged length of a

number of piles. All welds encountered were exposed around the circumference

of the pile.

-62-

Galvanizing in the splash zone is intact and has provided good protection.

The splash zone of the piling is in excellent condition. The amount of

galvanizing on the lower portions of the pile quickly tapers off down the pile

until there is no evidence of any zinc beyond five or six feet below the high

water mark. Visual inspection revealed active corrosion below a 1/8 to

3/16-inch thick layer of corrosion product. Pit depths ranged from 13 to 35

mils, or 3 to 8.6% of the original wall thickness on piling sections that were

galvanized. Readings of 30 to 73 mils, or 7 to 18% of original wall

thickness, were observed for pits on bare sections of the piles. All welds

examined were in good condition. In all cases, maximum pit depth was observed

approximately 4 feet off the bottom of the ferry terminal piles. This is

probably due to partial cathodic protection from the galvanizing which was

received by the bare steel. This action also provided protection to adjacent

welds while galvanizing was intact. The upper submerged portion of the piles

and adjacent welds probably received this protection for the first five or six

years.

Metal loss rates for submerged piling averaged 6 mils per year for areas of

bare steel while galvanized sections averaged 3 mils per year. If no damage

is assumed during the five to six years of protection afforded by the

galvanizing, the galvanized pile sections have experienced a metal loss rate

of 5 mils per year since the zinc has been consumed. The corrosion processes

at this structure are unusual in that maximum metal loss was observed at a

greater water depth than in most cases. This occurance

potential cathodic protection provided by galvanizing on

sections.

-63-

is due to the

the upper pile

ANCHORAGE

Port of Anchorage

The Port or Anchorage in Cook Inlet is one or the largest cargo transshipment

racilities in Alaska. Constructed over a period or approximately 15 years,

the entire racility is now protected rrom corrosion by an impressed current

system. Each terminal was constructed with uncoated piling. Terminal No.1,

built in 1961, was designed ror a 20-year lire with extra metal thickness to

allow ror corrosion. Terminal No.3, built in 1975, received the initial

trial impressed current system in 1979. This proved to be very errective, and

the system was expanded during the 1980 construction season to protect the

entire racility. The severe winter icing experienced at this structure makes

it a unique application for corrosion protection.

A visual inspection or Terminal 3 round the piles to be in good condition and

basically free from corrosion even in the unprotected atmospheric zone.

Considerable silt is deposited on the piles with each receding tide. As a

byproduct or the impressed current system, a calcareous coating has formed on

the piles. This coating provides additional corrosion protection and creates

lower current requirements than when the system was first installed.

-64-

SEWARD

Alaska Railroad Pier6

This government owned pier serves as an Alaska Railroad terminus on the Gulf

of Alaska. Built in 1965, the pier is 744-feet long and 200-feet wide with a

precast concrete panel deck grouted in place on concrete pile caps. Lateral

stiffness to the H-section bearing piles is provided by pipe batter piles.

There are approximately 2,400 support piles. A negative bonding system was

installed during construction; however, a cathodic protection system was not

installed.

Several inspections of the structure revealed a normal amount of corrosion

damage in the submerged zone but numerous welds had been severely damaged.

Approximately "133 pilings were found with weld damage in which 50 percent or

more of the weld was gone. In fact, in seven cases there was no weld material

left at all and the piling was completely severed." 7 Most of the damaged

welds were located in the submerged zone on piles directly beneath the

operation area of lar~e traveling cranes. It is possible that vibrations from

the moving equipment caused removal of corrosion products and constant

exposure of bare weld material. Design and installation of an impressed

current system in 1980 involved protection of an unusually large amount of

surface area and consideration of the large tidal variations present in

Seward. Potential readings taken on various piles of the structure indicate

that all submerged areas are protected by the cathodic system. Pile tidal

sections are partially protected according to the duration of time

submerged.

-65-

Figure 5.13 Weld rorrosim d3nEge after :!:12 yrs. of exposure to the llBrine 6win:Jl'Ila1t at the Alaska Railroad Pier at Seward. Photo <XllIrtesy of Norton Corrosioo Limited, Inc.

Figure 5.14 Re¢red Ioeld .rom i'Rs been d3nEge by rorrosim. Alaska Railroad Pier, Seward. Photo <XllIrtesy Norton Corrosioo Limited, Inc.

-66-

Figure 5.15 Corrosim of an isolatOO H-pile (orange-red pile rear center of picture) after instailatim of an impresse1 current systan at the Alaska Railrce.d Pier in Sew3.rcI. 'l'ffi pile \£S subseqLEntly tie1 into the rest of the stl"lK!ture and receives protectioo. Photo courtesy of Nortoo Corrosioo LimitOO, Inc.

-67-

SELDOVIA

Seldovia City Dock

Constructed in 1966, the Seldovia City Dock is utilized for cargo

transshipment, as a work dock for commercial fishermen, and as an Alaskan

Marine Ferry Service Terminal. The concrete panel deck, grouted to a

cast-in-place steel reinforced concrete cap, is supported by 14-inch diameter,

3/8-inch thick and 16-inch diameter, 7116-inch thick steel pipe piles. No

corrosion protection system has been employed for these uncoated seamed pipe

piles.

Evidence of active corrosion, in the form of small diameter pits and large

moon-shaped pockmarks, was found below the splash zone on all piles. Pit

depths varied from 1/32-inch to 3/32-inch. Deterioration was found at all

butt welds with pits in the weld crack ranging from 1/32-inch to 1/16-inch in

depth. Pile seams were easily visible in the submerged zone, due possibly to

corrosion activity within the seam. At some locations, seam separation of

1/16-inch and pitting within the seam were noted. Above approximate elev. +3

ft. MLLW, the pile seams tighten considerably and are barely visible.

Metal loss from this structure due to corrosion varies from a rate of 0 mils

to 9 mils per year. An approximate average metal loss rate for the pile tidal

zone (around elev. MLLW) is 6 mils per year. The remaining metal thickness at

the deepest recorded pit was 0.227 inches, which equals approximately 60

percent of the original steel. Penetration of pile seams has occurred as

evidenced by water weepage from some seams observed during ebb tides. Because

penetration allows water access and corrosion activity to occur on the pipe

pile interior as well as the exposed exterior surface, such piles may be

experiencing metal loss rates greater than the 0 mils to 9 mils per year

observed.

-68-

Figures 5.16 Corrosim of steel pipe piles in Seldovia, Alaska. The pipe seam ms been am 5.17 penetrata:i in sore locations. Heavy pitting is also present.

-69-

KODIAK

Pier No. 2

The City of Kodiak utilizes Pier No. 2 as the city cargo dock. Built in 1965,

this 362-ft. by 64-ft. dock consists of a timber superstructure supported by

148 steel monotube piles. The piles were filled with concrete at the time of

construction. Available information indicates that a coal tar epoxy was

applied to the piles at that time; however, the reddish.coating appears to be

a type of paint. Both above water and underwater inspections were performed

on this dock.

Existing coating condition varies in the different pile zones. In the splash

zone, a majority of the coating is in a blistered state with only 5 to 10

percent of the coating remaining well bonded. Coating loss in this area has

resulted from corrosion undercutting and aggressive wave action. A loss of 40

to 60 percent of the epoxy coating in the submerged zone is attributed to

marine growth, mechanical damage, and corrosion undercutting. Corrosion

products have formed a 3/16-inch to 5/16-inch layer on the pile surface.

Cracks in this layer occur at the peaks of the monotube fluting. The steel is

still protected in areas where the coating is well bonded.

General metal loss rates vary from 5 mils to 15 mils per year. The monotube

fluting peaks in the splash zone have experienced a 30 percent metal loss,

while coated areas of the pile in this zone have suffered no loss. In the

submerged zone, heavy pitting will soon penetrate to the underlying

concrete. This may have already occurred in some locations. Uniform

corrosion has caused a loss of 20 to 30 percent of the original metal in

submerged areas exposed through coating _ disbondment. Actual metal loss per

unit area appeared to be greater in the splash zone than in the submerged

zone.

Pier No.3

Leased to Sealand, this dock is the main cargo transshipment facility for

Kodiak. The 365-ft. by 62-ft. deck of reinforced concrete panels with cap

-70-

Figure 5.18 Steel nrnotube piling;3. Pier No.2, KOOiak, Alaska.

-71-

Figure 5.19 Steel pipe pile mated with a ooal tar epoxy sOOwi.ng lIBr'lre gra./th and atnnspheric corrosioo. Pier No.3, Kcx:liak, Alaska.

-72-

Kodiak (continued)

beams is supported by 144, WF 14 x 87 batter piles and 27, 24-inch diameter

pipe piles. A concrete panel retaining wall abutting the back of the dock is

held in place by WF 16 x 88 soldier piles connected by tie rods to a dead man

anchor wall. The piles, both pipe and H-section, were coated with a coal tar

epoxy. The inspection of Pier No. 3 included above and below water

examination of the structure.

Coating condition and level of corrosion activity varies according to the pile

location and to the elevation. In the splash zone, the coating on support

piles is in very good condition. Coating on the backwall soldier piles,

bearing piles, and whalers has essentially been removed. This is primarily due

to aggressive wave action. No indication of concrete spalling due to

corrosion of the steel reinforcement was found. Any exposed steel reinforcing

noted was clearly caused by mechanical damage. Otherwise, the concrete panels

and beams are in good condition. In the submerged zone, the majority 6f piles

are well protected by the original coal tar epoxy. Higher levels of coating

deterioration, commonly a 60 percent coating loss, were observed on the row of

pilings directly in front of the backwall. This occurrance is probably the

result of wave action reflecting off the backwall.

In areas below elevation +5 ft. MLLW where the coating has disbonded, pitting

of 1/16-inch to 3/32-inch depth was found. Corrosion activity will increase

in area as undercutting accelerates coating disbondment. Wave action will

continue to cause coating loss on the row of piles nearest the backwall. For

the same reason, a higher metal loss rate might occur at those piles and the

backwall soldier piles. General metal loss rates for the seaward piles would

be approximately 5 mils to 10 mils per year.

The concrete panel retaining wall described previously is experiencing failure

in several locations. When exposed to wetting by seawater, this type of

backwall retains a moist conductive medium (seawater) even during low tide.

This soil zone becomes anodic to the seaward side of the backwall and is an

extremely aggressive corrosion environment. Steel tie rods transversing these

zones will experience severe corrosion unless specifically protected. At this

-73-

Kodiak (continued)

structure, tie rod breakage has occurred in several places. The breakage

point seems to have been located in the soil zone approximately 6 inches

behind the backwall. Tie rod pieces, with the nut still attached, were found

which exhibited substantial corrosion over the entire piece. Due to the

inherent corrosion problems, this type of backwall design should be avoided in

marine structures.

Inner Harbor Dock

The structure inspected is an extension of an existing timber dock located in

the Kodiak small boat harbor. Built in 1980, it consists of precast

reinforced concrete deck panels on galvanized H-section

supported by 3/4-inch diameter galvanized steel pipe piles.

steel cap beams

This dock is in

very good condition with no evidence of corrosion of the steel or spalling of

the concrete at this time. The galvanized steel above the tidal zone should

be protected from corrosion indefinitely. Steel in the tidal and submerged

zones should continue to be protected by the galvanizing for approximately ten

years.

-74-

COLD BAY

Division of Aviation Fuel Dock

The Division of Aviation Fuel Dock at Cold Bay was constructed in 1978. The

piles were coated with a fusion bonded epoxy prior to installation. A passive

cathodic protection system consisting of magnesium anodes was installed at the

time of construction.

Visual inspection of the pile coating was facilitated by the minimal amount of

marine growth present. No disbondment of the coating was readily apparent,

and the coating appeared to be in excellent condition from the cap beam down

to elev. MLLW. The dock structure seems to be well protected from corrosion

by the systems employed.

-75-

6.0 CONCLUSIONS AND RECOMMENDATIONS

This report initiates documentation of steel corrosion in Alaska's aggressive

marine environment and examination of both potential protection systems and

those currently in use. Unprotected steel in the marine environment will

experience corrosion damage and possible structural impairment over a period

of time. Widespread use of steel in marine structures has necessitated

development of methods to reduce or eliminate corrosion and the high costs of

corrosion damage. This section of the report includes a brief summary of

corrosion characteristics as observed in Alaskan waters, recommended design

practices, conclusions of the present worth analysis, a listing of facilities

examined where active corrosion indicates a pressing need for protection

measures, recommendations for periodic inspection of marine facilities, and

suggestions for future research.

During the performance of facility inspections throughout Alaska, many

instances of corrosion have been examined. Alaska, with extreme tidal ranges

and temperatures, differs from many other marine environments. As can be

expected, corrosion processes in Alaska also differ. The characteristics

noted comprise much of the body of this report and are summarized as

follows. Measurable corrosion in Alaska generally occurs from mean tide level

down to the mudline. The area of greatest metal loss is usually located just

below the mean lower low water elevation; little corrosion is typically found

in the atmospheric zone. This is in contrast to the corrosion rates observed

in warmer climates. Just above mean high water and just below mean low water

are the locations of highest corrosion rates in warmer climates, and average

corrosion usually occurs in the atmospheric zone. Average maximum corrosion

rates observed for the Alaska marine environment are 6 mils to 7 mils metal

loss per year. Freshwater environments in Alaska generally experience little

or no corrosion in any zone.

6.1 PROTECTION METHODS

Vulnerability to corrosion can be reduced through certain design practices.

The cost of corrosion protection can also be reduced. Construction practices

such as using weld material which is slightly cathodic to the main steel bulk

-76-

and avoidance of designs that create areas which catch and hold water will

help reduce concentrated corrosion attack. Constructing a facility so that

all elements have good electrical continuity will reduce future installation

costs of cathodic protection. Since cathodic protection tends to be the most

efficient system for long-term protection of submerged steel, provision for a

cathodic system is advisable and is most easily accomplished during

construction. Pipe pile shapes present less surface area than H-section piles

and consequently cost less to protect regardless of the protection system

used. Pipe piles are also generally better for use in long, unsupported

lengths such as piling in docks.

The economy of many coatings makes them an attractive choice for initial and

long-term protection of the atmospheric zone. With appropriate coating

thickness and application procedures, a coating may provide protection in the

submerged zone for 10 to 15 years. Protection above the splash zone can be

extended indefinitely with repairs. From field observations, it appears that

a minimum DFT of 30 mils is appropriate for marine use even in the atmospheric

zone. Standard specifications used by the State DOT/PF have resulted in

coatings of lesser thicknesses which are likely to have decreased effective

protection life as evidenced by corrosion on numerous coastal bridges. A 30

mil thickness will help ·to ensure that there is adequate coating even in thin

spots and to discourage penetration by marine growth resulting in coating

disbondment. The coating costs used for analysis in this report were based

upon minimum coating thicknesses of 30 mils DFT. Standard ASTM 01" AASHTO

specifications for galvanizing do not require an adequate thickness for marine

use. To assure an acceptable minimum galvanizing thickness, the engineer

should specify a thickness of approximately 25 mils for steel to be used in

the marine environment.

6.2 ECONOMIC ANALYSIS

As illustrated by the present worth economic analysis in Section 4, the most

economic systems are an epoxy coating, galvanizing, and a polyurethane

coating, in order of increasing cost. Each of these would have a galvanic

system installed after fifteen years to protect the submerged zone. Both the

epoxy and the polyurethane coating require future repairs and can experience

-77-

concentrated corrosion attack at coating voids. Galvanizing, on the other

hand, will protect areas of bare steel through preferential corrosion of the

zinc and should protect the atmospheric zone for an unlimited time without

repairs. The remaining more expensive systems involve either a metal

thickness allowance (designed to allow corrosion to occur), a detailed

foundation study (to allow use of thinner steel below the mudline), an

impressed current system, or total dock replacement. The use of an impressed

current system would probably become more attractive as the amount of area to

be protected increases. Anode material amounts and costs in a galvanic system

could increase to a point where the controlled and greatly reduced anode

consumption rates and material amounts of an impressed current system would be

desired. The cost amounts and present worth of any of the systems will change

if the area to be protected or any costs change. The analysis system

presented should be interpreted as a framework for relative comparison.

Specific numbers will change with any variation of the cost elements; however,

the ranking order from system to system should stay relatively the same.

6.3 FIELD INSPECTIONS

A number of marine structures in Alaska are experiencing active corrosion

which threatens to reduce the usefulness of each facility. Some of these were

constructed in the 1960's, and the effective life of any coating is nearing an

end. There are also some structures which were constructed with bare steel

that are critically in need of attention. Generally, the following structures

need to receive immediate protection: Lutak Dock, Haines; State Ferry

Terminal and adjacent sheet pile structures, Seward; City Dock, Seldovia; and

Pier No.2, Kodiak. Structures including the City Shuttle Ferry Terminals in

Ketchikan and other marine highway facilities need to be closely observed and

provision for protection should be made in the near future. Additional

facilities will need attention as the installed protection system loses its

effectiveness in the submerged zone and possibly requires repairs in the

atmospheric zone. The effective life of a coating or galvanizing will vary

from structure to structure and cannot be predicted without an inspection

history. Each structure should be examined and evaluated individually.

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6.4 INSPECTIONS PROGRAM

In ol"'del'" to fully evaluate and monitol'" cOl"'l"'osion of a stl"'uctul"'e, pel"'iodic

inspections al"'e necessal"'y. Regulal'" inspections with wl"'itten condition I"'epol"'ts

will establish a data base fol'" the facility and allow bettel'" cOl"'l"'osion I"'ate

pl"'edictions, decl"'ease the incidence of undetected concentl"'ated attack such as

weld cOl"'l"'osion, allow needed I"'epail"'s to be made before incl"'eased damage

OCCUI"'S, and facilitate budgeting fol'" maintenance and I"'epail"'. The benefits

accl"'ued thl"'ough a pel"'iodic inspection pl"'ogl"'am would gl"'eatly outweigh the costs

incul"'l"'ed. This type of pl"'ogl"'am would be pal"'ticulal"'ly beneficial to the State

of Alaska fol'" monitol"'ing State-owned facilities and scheduling I"'epail"'s and

capital impl"'ovements thl"'oughout the State. A joint progl"'am sponsol"'ed by the

State involving individual cities and othel"'s with utilization of a few skilled

inspectol"'s might be apPl"'opl"'iate.

A typical inspection pl"'ogl"'am would include at least one visual inspection

evel"'Y two years. Annual inspection is pl"'efel"'l"'ed, pal"'ticulal"'ly if heavy

equipment is opel"'ated on the dock. This inspection would involve examining

the stl"'uctul"'e dUl"'ing a minus tide fl"'om a skiff 01'" othel'" small boat which

allows access undel"'neath the stl"'uctul"'e. Small al"'eas of mal"'ine gl"'owth should

be I"'emoved at val"'ious elevations and the condition and thickness of the

coating 01'" galvanizing noted and measul"'ed. A simple and inexpensive magnetic

pull-away gauge can be used to obtain an appl"'oximate coating thickness

I"'eading. Random piling should be selected fol'" these spot checks but the

entil"'e structul"'e should be visually examined to locate any damage 01'"

detel"'ioration. A I"'ecol"'d should be kept noting the time and date, the piling

inspected, amount of mal"'ine gl"'owth, degl"'ee of cOl"'l"'osion and cOl"'l"'osion pl"'oducts

if any, I"'emaining coating thickness, and genel"'al condition of the stl"'uctul"'e.

These annual 01'" bi-annual inspections al"'e vel"'y low-cost, pal"'ticulal"'ly if a

tl"'ained local employee such as the hal"'bol"'mastel'" 01'" city engineel'" is

utilized.

Evel"'Y ten yeal"'s, a detailed undel"'watel'" inspection should be pel"'formed. This

could include undel"'watel'" photogl"'aphy with eithel'" a still 01'" video camera and

electl"'onic steel thickness measul"'ements. Any welds 01'" seams should be closely

examined. The amount of coating or galvanizing remaining in the submerged

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zone will indicate whether installation of a cathodic protection system should

be considered. Pit depth and electronic metal thickness measurements will

allow calculations of metal loss rates. A detailed record of the underwater

inspection will be invaluable for documenting the structural condition and for

comparison to the findings of other inspections. Since divers and special

equipment are required, underwater inspections are not inexpensive but are

necessary to obtain a complete ptcture of the structure.

If the State developed an inspection/maintenance program for State-owned

facilities such as the Marine Ferry System Terminals, a great deal of

information could be generated with minimum expense. As mentioned previously,

a local employee such as the harbormaster could be trained to perform the

simple annual inspections. An administrative agency in the State could

compile the data from various locations and provide continuity to the

program. In addition to allowing the State to better foresee and budget for

maintenance and repair needs, valuable information on corrosion in Alaska

would be collected.

6.5 FUTURE RESEARCH

The information presented in the field inspections of this report is

beneficial as an initial data base of the steel condition in those

facilities. Except for a few instances where previous inspections had

occurred, these field inspections are static, and it is difficult to make

predictions based solely on this information. It will be important to perform

future inspections and data comparisions to gain a more complete understanding

of corrosion processes over time.

Future inspections will also be necessary for evaluation of the protection

methods currently being installed and of the resul ts of the present worth

analysis presented in this papaer. Use of polyurethane coating material is

fairly recent and should be evaluated in approximately five years. The

Dillingham City Dock and the Cordova City Dock Fender System, both installed

in 1982, will be good facilities to begin evaluating polyurethane coatings.

Other systems which should receive additional future evaluation are

simultaneous use of impressed current with various coating types and the

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benefits of installing galvanic protection and a coating at the time of

construction instead of delaying the galvanic installation.

As research continues, new products and application methods will be

developed. As the age of installed steel structures cause greater need for

corrosion protection, improved methods and products will be generated and will

deserve attention. Anode assembly configurations will become easier to

install and replace. Evaluation of actual performance on Alaskan structures

through periodic inspections is the best insurance for Alaska's numerous

marine facilities. These structures represent a major investment by the

people of Alaska and are indicative of the dependence upon marine

transportation in this State. Maximum utilization of these facilities will

depend upon their protection from the destructive effects of oorrosion.

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APPENDIX A

GLOSSARY OF KEY TERMS8

Note - The major reference used in compiling this glossary was the Handbook of

Corrosion Protection for Steel Pile Structures in Marine Environments

Thomas D. Dismuke, et al. (editors).

ANODE: The electrode of a galvanic or voltaic cell where the positive

electrical current flows from the electrode to the solution; in corrosion

reactions the electrode which has the greater tendency to go into

solution.

BIMETALLIC CORROSION: Corrosion of two metals in electrical contact in an

electrolytic solution in which one metal (cathode) stimulates attack on

the other (anode) and may itself corrode more slowly (be protected) than

when it is not in such contact.

CATHODE: The electrode of a galvanic or voltaic cell where the positive

electrical current flows from the electrolytic solution to the electrode;

in corrosion reactions the electrode which is usually unattacked.

CATHODIC PROTECTION: Reduction or control of the corrosion rate by making the

potential of the metal to be protected more negative or cathodic by means

of sacrificial anodes or impressed current.

CORROSION: For the purposes of this document - the transformation of a metal

used as a material of construction from the elementary to the solution

state.

CORROSION RATE: An average estimate of corrosion activity over time often

expressed as inches penetration per year (ipy), milligrams weight loss

per square decimeter per day (mdd), or metal thickness loss per year

(mils!yr). Expressed as mil loss per year in this paper. See METAL LOSS

RATE.

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ELECTROLYTE: A substance which in solution gives ~ise to ions - elect~ically

cha~ged pa~ticles which mig~ate in an elect~ical field. Seawate~ is a

natural electrolyte.

ELECTROLYTIC SOLUTION: A solution in which the conduction of electric

currents occur by the passage of dissolved ions.

GALVANIC CELL: An electrochemical cell in which chemical change is the source

of elect~ical energy. Consists of an anode and a cathode in contact with

an electroytic solution in which the electrodes are commonly of

dissimilar metals in contact with each other or similar metals in contact

with each other and dissimilar electrolytic solutions.

GALVANIC CORROSION: Corrosion associated with the galvanic cell. The driving

force is obtained by the electrodes being of different metals, inhomo­

geneities in a single metal or differences in the contacting solution,

such as temperature, concentration, etc.

HOT DIP GALVANIZING: Method of galvanizing whe~e metal is dipped into a vat

of molten zinc. An abrasion resistant, chemically bonded coating of zinc

is formed.

METAL LOSS RATE: Expressed as mils per year in this paper. It is an

approximate quantification of the amount of metal thickness lost due to

corrosion.

PITTING CORROSION: Localized corrosion which occurs when an anode area

remains in one position and which results in the formation of pits.

UNIFORM CORROSION: Corrosion in which no distinguishable area of the metal

surface is solely anodic or cathodic, i.e., anode and cathode move about

freely resulting in a general roughening of the metal surface

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1. SCOPE

APPENDIX B

Standard Specification for

Zinc (Hot-Galvanized) Coatings on

Products Fabricated from Rolled, Pressed, and

Forged Steel Shapes, Plates, Bars and Strip9

AASHTO Designation: M 111-78

(ASTM Designation: A 123-73)

1.1 This specification covers the protective zinc coatings, applied on

products fabricated from rolled, pressed, and forged steel shapes, plates,

bars, and strip 1/8 in. (3.2 mm) thick and heavier (Explanatory Note 1) by

dipping the articles in a molten bath of zinc (Explanatory Note 2).

5. WEIGHT OF COATING

5.1 The weight of the zinc coating per square foot of actual surface,

for 1/8 (3.2 mm) and 3116 in. (4.8 rom) steels, shall average not less than

2.0 oz/ft2 (shall average not less than 610 g/m2 and no individual specimen

shall show less than 550 g/m2). For 1/4 in. (6.4 rom) and heavier material,

the coating weights shall average not less than 2.3 oz/ft2 and no individual ? specimen shall show less than 2.0 oz/ft-.

NOTES:

Except for the deletion of a requirement of maximum aluminum content and

corresponding testing preocedure, this specification agrees with ASTM A

123-73.

2 One ounce of zinc. p~r square foot of surface, based upon mathematical

calculation, corresponds to a coating thickness of 0.0017 in.

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APPENDIX C

PRESENT WORTH FORHOLAS10

i = interest rate per interest period (10% per year used in this report)

n = number of interest periods

P = a present sum of money

F = a future sum of money

A = an end-of-period cash receipt or disbursement in a uniform series

continuing for n periods, the entire series equivalent to P or F at

interest rate of i

PRESENT WORTH

F

P

To find P given F, (P/F, i %, n):

P = F (1 + i)-n

SERIES PRESENT WORTH

A A A A A

P

To find P given A, (PIA, i%, n):

(1+i)n_1 P = A

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FOOTNOTES

1Thomas D. Dismuke et al. (eds.), Handbook of Corrosion Protection for Steel Pile Structures in Marine Environments, American Iron and Steel Institute, Washington, 1981,p. 5.

2Ibid ., pp. 3-22.

3Ibid , p. iii.

4Ibid , pp. 4-5.

5J .R. Morgan and J .A. Lehmann, "Cathodic Protection of Jetties and Offshore Structures: American and European Practices," Corrosion/74, Paper No. 112, The International Corrosion Forum, National Association of Corrosion Engineers, 1974, p. 3.

6phillip D. Simon, P.E., "The Design, Installation and Checkout of a 5,500 Ampere Impressed Current Cathodic Protection System for a Steel Pile Pier in Alaska," Corrosion/82, Paper No. 167, The International Corrosion Forum, National Association of Corrosion Engineers, 1982, pp. 1-6

7Simon, p.2.

8Dismuke et al., pp. 181-184.

9Standard Specifications for Sampling and Testing, Part 1, Association of State Highway and pp. 147-148.

Transportation Materials and Methods of Specifications, 12th ed., The American

Transportation Officials, Washington, 1978,

10Donald G. Newnan, Engineering Economic Analysis, Engineering Press, Inc., San Jose, California, 1980, front coverleaf.

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BIBLIOGRAPHY

Annual Book of ASTM Standards - Part .1., American Society for Testing and Materials, Philadelphia, 1981.

Brady, George S. and Henry R. Clauser, Materials Handbook, 11th ed., McGraw­Hill Book Company, New York, 1979.

Dillan, C. P. (ed.), Forms of Corrosion - Recognition and Prevention, Handbook No.1, National Association of Corrosion Engineers, Houston, 1982.

Dismuke, Thomas D., Seymour K. Coburn, and Carl M. Hirsch (eds.), Handbook of Corrosion Protection for Steel Pile Structures in Marine Environments, American Iron and Steel Institute, Washington, 1981.

Escalante, E., et aI, Corrosion and Protection of Steel Piles in a Natural Seawater Environment, National Bureau or-Standards, U.S:-Department of Commerce, Washington, 1977.

Morgan, J .H. and J .A. Lehmann, "Cathodic Protection of Jetties and Offshore Structures: American and European Practices," Corrosion/74, Paper No. 112, The International Corrosion Forum, National Association of Corrosion Engineers, 1974.

Newnan, Donald G., Engineering Economic Analysis, Engineering Press, Inc., San Jose, California, 1980.

Simon, Phillip D., "The Design, Installation and Checkout of a 5,500 Ampere Impressed Current Cathodic Protection System for a Steel Pile Pier in Alaska," Corrosion/82, Paper 156, The International Corrosion Forum, National Association of Corrosion Engineers, 1982.

Standard Specifications for Transportation Materials and Methods of Sampling and Testing, Part 1, SpeCifications, 12th ed., The American Association of State Highway and Transportation Officials, Washington, 1978.

"Steel corrosion cost U.S. industry nearly $2.6 billion last year," Daily Journal of Commerce, Seattle, Washington, August 6, 1981.

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