Buried Pipe Corrosion in the Power

Plant Environment

Assessment and Mitigation in Nuclear Power Plants

IAEA Technical Meeting on Buried Pipe

October 15, 2014

Kurt M. Lawson

Mears Group, Inc.

Topics

Background

Buried Pipe Corrosion

Problems in the Plant Environment

Combined Approach to Asset Integrity

2

Formed in 1970 and acquired By Quanta Services in 2000.

Mears Group is comprised of:

Mears Horizontal Directional Drilling (HDD)

Mears Integrity Solutions

> Inline Devices

11 Offices Worldwide: U.S, Canada, Abu Dhabi, Malaysia, Australia and India.

MEARS

Quanta Services • NYSE: PWR

• Member: S&P 500 Index

• Market Cap: $4.5 Billion

• 35 Operating Entities

• 17,000 Employees

• Electric Power

• Pipeline Infrastructure

• Telecommunications

Quanta Operating Entities

Global Reach

Australia

Belize

Brazil

British Virgin Islands

Canada

Costa Rica

Guam

Guatemala

Honduras

India

Indonesia

Iraq

Liberia

Luxembourg

Mexico

Netherlands

Nicaragua

Panama

Peru

Republic of Chad

South Africa

Trinidad

United Arab Emirates

Venezuela

Countries where Quanta has a permanent office or has worked.

Quanta has

successfully completed

projects that are local,

regional, national and

international in scope

Buried Pipe Corrosion

An electrochemical process governed by electrical laws

NACE International

“The deterioration of a metal as a result of a reaction with its environment”

IRON OXIDE BLAST FURNACE BESSEMER

PIPE MILL STEEL PIPE

PIPE CORRODING IRON OXIDE

REFINING PROCESS

CORROSION PROCESS

Energy – The Life Cycle of Steel

Most Energy Required Least Energy Required

Potassium Magnesium Beryllium Aluminum Zinc Chromium Iron Nickel Tin Copper Silver Platinum Gold

Energy Required to Convert

Ore to Metal

ELECTROMOTIVE SERIES

Neutral Soil

Material V, (Cu/CuSO4)

Mg (Galvomag Alloy) -1.75

Mg (H-1 Alloy) -1.55

Zn -1.1

Al (Alclad 3S) -1.0

Cast Iron -0.5

Lead -0.5

Mild Steel (Clean) -0.2 to –0.8

Mild Steel (Rusted) -0.2 to –0.5

Mild Steel (in Concrete) -0.2

Copper -0.2

High Silicon Cast Iron -0.2

Stainless Steel (Type 304) -0.15 to –0.6

Carbon (Graphite, Coke) +0.3

CORROSION CELLS

Requirements

Anode

Cathode

Electrolyte Shared by Anode and Cathode (Soil)

Metallic or Electron Path between Anode and Cathode

CORROSION CELLS

Dry Cell Battery

Zinc Carbon

NH4Cl Solution

Zn+2

H2

+

-

Graphite-Zinc Battery

-

Zinc Case

(Anode)

+

Zn+2

Carbon

Rod

(cathode)

NH4Cl Solution

I

CAUSES OF CORROSION

Differential Soil Aeration

Differential Soil Chemistry

Dissimilar Metals Contact

Stray Current

Microbiological

Challenges in the Plant Environment

In a plant (world) there is really no such thing as a non-corrosive soil

Galvanic effects

Complex piping CONFIGURATIONS

Electrically discontinuous piping

Corrosivity of Soils

Corrosivity of a particular soil is based on the interaction of several parameters: Resistivity

Dissolved salts,

Moisture content,

pH

Presence of Bacteria,

Amount of oxygen, and

Others

Cathodic Protection Challenges in the

Plant Environment

Complex Piping

Current Distribution

Monitoring

Deep Piping

Monitoring

Galvanic Issues

Current Distribution

Monitoring

Geometry

Current Distribution

Complex Piping

Galvanic issues with Reinforcing Steel

Geometry and Grounding

Material V, (Cu/CuSO4)

Mg (Galvomag Alloy) -1.75

Mg (H-1 Alloy) -1.55

Zn -1.1

Al (Alclad 3S) -1.0

Cast Iron -0.5

Lead -0.5

Mild Steel (Clean) -0.2 to –0.8

Mild Steel (Rusted) -0.2 to –0.5

Mild Steel (in Concrete) -0.2

Copper -0.2

High Silicon Cast Iron -0.2

Stainless Steel (Type 304) -0.15 to –0.6

Carbon (Graphite, Coke) +0.3

ELECTROMOTIVE SERIES

Neutral Soil

Role of Electrical Grounding

Three Important Functions

Personnel Safety from Electrical Faults

Lightning Protection

Termination Point for Instrumentation Shields

Accomplished Through

Direct Buried Copper Cables and Vertical Ground Rods

> In Grids

> In Longitudinal Runs

> Around perimeter of Buildings/Pedestals

3

Impact on Corrosion

Grounding Comprised of Copper Material

Plant Piping/Buried Structures

Carbon Steel

Cast/Ductile Iron

Stainless Steel

Copper/Aluminum Bronze

Reinforced Concrete

Pre/Post tensioned Concrete

7

Impact of Grounding on Corrosion

Driving Force For Corrosion = Voltage Difference

Voltage or Potential

An electromotive force, or a difference in potential expressed in volts.

Voltage is the energy that puts charges in motion.

8

Piping Corrosion Rates in Soils

(Uhlig/Romanoff)

Environmental

Factors

General Corrosion Rates, mpy Pitting Corrosion Rates, mpy

Maximum Minimum Average Maximum Minimum Average

Soil Resistivity

Less Than 1,000 2.5 0.7 1.3 12.2 4.3 7.9

1,000 to 5,000 2.3 0.2 0.7 17.7 2.0 5.5

5,000 to 12,000 1.3 0.2 0.7 9.1 2.4 5.5

Greater Than

12,0001.4 0.1 0.6 10.2 1.2 4.3

Drainage

Very Poor 2.3 1.5 1.8 17.7 6.3 11.0

Poor 1.5 0.4 0.9 9.1 2.0 5.5

Fair 2.5 0.7 0.9 12.2 3.1 6.3

10

Impact of Grounding on Corrosion of

Buried Steel Piping

No Copper Couple to Steel

Steel Corrodes at 2- 10 mils/yr (1000ths of inch/year)

Copper/Steel Area Ratio = 1

Steel Corrosion Accelerates by 3x Factor

Copper/Steel Area Ratio = 10

Steel Corrosion Accelerates by 10x Factor

Copper/Steel Area Ratio = 20

Steel Corrosion Accelerates by 30x Factor

11

CP Current Distribution in a Power Plant

Because the interconnection of Low Resistance Grounding Systems

with High Resistance Piping Systems

Majority of CP current goes to bare copper grounding

27

Combined Approach to Asset Integrity

Assess

Analyze

Mitigate

Assessments

Inspection Results

With attention to locations

Cathodic Protection Annual Surveys

Galvanic Corrosion

Soil Corrosivity

Gap Analysis

Where are their deficiencies?

Missing Data or un-assessed locations

> Develop best practice for collecting needed data

Corrosion

> Determine root cause and mitigation approach

Ineffective CP

> Justification of CP level

> CP Adjustments or additions

Excessive CP

Ineffective CP

Insufficient current to adequately

overcome corrosion cells.

Site CP Survey

Adequate

CP ? End

Balance CP

Adequate

CP ?

Yes

No

End

Additional

Monitoring

Adequate

CP ?

Yes

No

End

CP Design

Determining the

Effectiveness of CP

Practical application makes use of structure-to-electrolyte

potentials.

Effective cathodic protection is achieved if NACE Criteria are

satisfied.

Applicable NACE Standards

SP0169 Control of External Corrosion on Underground or Submerged Metallic Piping Systems

SP0285 Corrosion Control of Underground Storage Tank Systems by Cathodic Protection

SP0193 External Cathodic Protection of On-Grade Metallic Storage Tank Bottoms

SP0290 Cathodic Protection of Reinforcing Steel in Atmospherically Exposed Structures

TM0497 Measurement Techniques Related to Criteria for Cathodic Protection on Underground or

Submerged Metallic Piping Systems

Criteria for Underground or

Submerged Iron or Steel Structures

–0.850 VCSE potential--Negative (cathodic) potential of at least 850 mVCSE with

the cathodic protection applied after IR drop is considered

–0.850 VCSE polarized potential--Negative polarized potential of at least 850

mVCSE

100 mV polarization--Minimum of 100 mV of cathodic polarization

• Note: These are specific to carbon steel and lower

temperatures.

Time

Structure-to-Electrolyte Potential

Po

ten

tial (

-mV

)

(+)

( )

ON Potential

OFF Potential

IRIR

Native (Free Corroding, Static) Potential

100 mV

Polarization

100 mV Depolarization

“ON-IR” -850 mVCSE

“OFF” -850 mVCSE

Po

ten

tial (

-mV

)

(+)

( )

ON Potential

OFF Potential

IRIR

Native (Free Corroding, Static) Potential

100 mV

Polarization

100 mV Depolarization

“ON-IR” -850 mVCSE

“OFF” -850 mVCSE

Notes to Criteria

In the presence of bacteria or elevated temperatures, the criteria may not

be sufficient.

In well aerated, well drained soils, corrosion protection may be achieved at

less negative potentials.

Criteria and Grounding

SP0169 6.2.5 Dissimilar Metal Piping:

“A negative voltage between all pipe surfaces and a stable reference electrode

contacting the electrolyte equal to that required for the protection of the most

anodic metal should be maintained.”

Measuring 100mV of polarization based upon mixed potential of a

steel/copper couple may not result in adequate protection of the more

anodic (steel) material.

No true ‘native’ carbon steel potentials exist?

Coupon Test Stations

Coupon Test Stations

Evaluate -850 mV Polarized Potential

Problem Areas

> IR voltage drop error

> Multiple rectifier interruption

> Non-interruptible stray current sources

> Directly connected sacrificial anodes

> Multiple pipeline potential averaging

Typical Installation

40

1. Freely Corroding Coupon

2. Coupon Bonded to Structure/Grounding

3. Energize CP

4-7. Adjustments to CP System

ER Coupons

Corrosion Rate Coupons/Stations

Provides both CP related information and Corrosion Rate Data

Electrical Resistance (ER)

change in resistance of a metal element as it corrodes

Where:

> R = Resistance

> ρ = Resistivity

> L = Length

> A = Cross sectional area

A

LR

ER Coupons - Continued

ER – Continued

Requires many measurements to provide statistical significance

Does not distinguish between general or localized corrosion

ER Coupons - Response time vs. probe life

LPR (Electrochemical) Coupons

Utilizes electrochemical measurements for direct instantaneous

measurement of corrosion rate

Linear Polarization Resistance

LPR theory – Stern-Geary Relationship

corcacor

ca

appapp

pi

B

iidi

dR

3.2

00

Formula uses absolute values of anodic and cathodic

DFn

MimpyCR cor248.1)(

icor – mA/m2 D – density, g/cm3

M – molecular weight, g/mole F=96,490 coulomb/eq

n- number of electrons transferred (valence)

Test Methods:

Polarization – LPR – Sources of Error

Tafel constants unknown

Reasonable estimate 0.100-0.120V for both a and c

Relative comparison (based on Rp) is accurate

Oxidation reactions other than corrosion

If other oxidizing species are present (sulfides, calculated corrosion current will be overestimated

Typically not a concern for soils

Non-steady-state conditions (time issues)

Test Methods:

Polarization – LPR measurements

LPR measures “instantaneous” corrosion rate

Can be used for continuous corrosion monitoring

Can be used for periodic assessment of corrosion state

Used extensively in high resistivity conditions, such as soils, concrete, non-aqueous environments

Cannot determine corrosion rate of cathodically protected surface

Corrosion Rates

Utilize Linear Polarization Resistance (LPR) for Soil Corrosivity studies

Native (un-polarized coupon)

Defensible and Conservative rate

Excessive CP

Unnecessary Consumption of CP Materials

Coating Damage

Cathodic Disbondment

Overprotection of Amphoteric Materials

Lead, Zinc, Aluminum

Titanium Hydriding

Hydrogen Damage to High Strength Materials

Bolts

PCCP

Summary

We have many tools to assist in properly

maintaining buried structures

Utilize all tools in a layered process to

leverage cost savings and ensure integrity

of buried assets

Assess

Analyze

Mitigate

27

Site CP Survey

Adequate

CP ? End

Balance CP

Adequate

CP ?

Yes

No

End

Additional

Monitoring

Adequate

CP ?

Yes

No

End

CP Design