StocExpo 2015StocExpo 2015 17-19 March Ahoy Rotterdam What is the added value Section 5: General...

StocExpo 2015 17-19 March Ahoy Rotterdam

EEMUA 159 4th edition

Published June 2014

The consequences for the users

Author and presenter;

Hans Kuipers

Ex. Principal Engineer conventional & L.P.G. storage facilities , Shell Global Solution.

Ex .Chairman EEMUA storage tanks committee.

Introduction

Objectives of EEMUA 159

What is new in the rev. 4

List of Key changes

What is the added value

Of changes and the revisions

What are the benefits for a storage tank assessor

Assessment methods /tools

The PPM approach

Inspection/ maintenance & criticality assessments

Return of investment

Cost to introduce / implement

Savings on tank maintenance ?

1


Introduction Main objectives of the original EEMUA 159 (1994)

•A practical users guide for tank inspection and maintenance

•Written by the Main Oil companies storage tank specialists

•Initial the O.C.M.A. (Oil Companies Material Association) till 1980.

•For the use of Oil companies and Terminal owners

•Based on over 100 years storage tank experience

•Focus is on prevention

•Rejection values ,criteria, graphs etc. are a guide only,

•Take action within the next 6-9 months when approaching these values

•No code of practice !!

•Guidelines are related to tanks designed in line with (mainly) the BS2654

•Some references made to the API codes

Introduction



List of Key changes





The PPM approach





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What is new in the EEMUA 159 4th Edition

List of Key changes

Main subjects as presented during the launch 12th June 2014

•Scope, tank components, failure modes

•Corrosion rates and inspection techniques

•Tank coating, insulation.

•Appendix B,C,D,E,and F

•Appendix A deleted ? ( grid system )

•Many recommendations to use Finite Element (FE) by assessments

What is the added value ??

Introduction



List of Key changes





The PPM approach





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Section 5: General inspection ( 7 steps ) & Interpretation

•Not clear which inspection lists should be used , ( EEMUA 159 , API 653 , 575 ? )

•The 7 steps does not indicate which / what tools should be used per step

•No indication who should do this ( qualified inspectors - assessors!! )

•Inspection intervals (show the time based inspection table under this section)

Interpretation of inspection data

Only 2 cases mentioned, general and pitting corrosion at shell (section 8 ?)

What is the purpose of the “Fitness for purpose analysis sheet”

Table 4 in this section is not clear.

Focus EEMUA 159 is on “ tanks in service “, designed & built to BS 2654.

For the future, incl. assessment for tanks based on the EN 14015 code.

Minor reference to API 653, why extensive list to old API doc’s .?

Introduction



List of Key changes





The PPM approach





4


Section 6: Tank foundations

A logic set-up for this section would be :

•Typical Tank foundations,

•Settlement of tank foundations

•Impact of foundation settlements on the tank structure

(bottom, shell & roofs)

Section 6 is however a mix of various assessments /evaluations, and design examples without indicating the added value.

For planar tilt, out of verticality or differential edge settlement reference is made to the original EEMUA 159 and/or API 653.

Compare some of the original assessments and the new sections.

Introduction



List of Key changes





The PPM approach





5


Original assessment differential settlement EEMUA 159 1994

Introduction



List of Key changes





The PPM approach





6

Figure 5 Planar Tilt of a tank

Local uneven edge settlement


New edge settlement figures A, B, & C

Note; C is not edge, but bottom settlement

Slope under C is 1:6 !

Max. cone down bottom settlement is f max. ! (page 79)

Introduction



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The PPM approach





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A B C


EEMUA 159 rev.4

does not make reference to an original designed and constructed cone up /down profile, for the assessment of the edge settlement . (See API 653)

Introduction



List of Key changes





The PPM approach





8


New table planar tilt /out of verticality

New

Introduction



List of Key changes





The PPM approach





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The out of verticality of the tank shell (H) is often independent from the tank dia (D). Only small dia tanks on a concrete raft may have a lineair relation with the tank heigth H when subject to planar tilt.

Note: The tank shell out of verticality is not the same as planar tilt !!

Out of verticality of a tank shell Tank bottom horizontal !


Fig . 35 Planar tilt .

Example 1. H = 18.5m and D = 25m The allow. out of verticality is 1.4 % =259 mm ! This is far more then the normal H/100 (185 mm). ( API 653 max. = 127 mm ) Example 2 . H 16.5 m and D 9.05 m, allow. 0.78 % = 129 mm i.s.o. 165 mm.

Added value of any axial or shear stresses in the tank shell under this foundation section. ??? Reference to a factor of safety for the allowable versus actual stress is incorrect. (page 74 & 75)

Quote page 78

Introduction



List of Key changes





The PPM approach





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This formule (API 653) is intended to calculate the permissible out of plane settlement using the best fit (optimal) cosine curve. No reference to rim seals.


Introduction



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Latest update API 653 App. B

S is the permissible +/_ out of plane settlement using the best fit (optimal) cosine curve.


Alternative presentation of survey results for the tank shell

Differential Edged Settlement ( “best fit” Cosine line )

Introduction



List of Key changes





The PPM approach





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Typical presentation of survey results for the tank shell

Verticality and out of roundness condition

Introduction



List of Key changes





The PPM approach





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Settlement tank foundations

Statement on ripple formation by even settlement should refer to section 6.5.4.

Ripple formation refers to the change from a cone up to cone down tank bottom.

Introduction



List of Key changes





The PPM approach





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Section 7 : Tank bottoms / annular plates

Introduction



List of Key changes





The PPM approach





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L minimal corroded is 9.5mm ! ?

What is now the maximal corroded L Minimum acceptable corroded throat thickness is 3 mm ! How to read this in reference with requirements in the EEMUA 180 ?? “Frangible roof joints “


Section 8: Tank shells

Changes to min. corroded Shell thickness calculation When Yield stress unknown, now max. 172 N/mm² i.s.o. 215 N/mm² Why ?

Reference to elevated temperature;

Now reduction factor 0.89 for 100 – 200 C and 0.79 for 200 - 300 C Why ?

(BS 2654 design basis is 150 C .)

Further reduction when t = > 16 mm by 10 N/mm². Why ?

Assessments:

Use BS 2654 design basis for tanks constructed to BS 2654

Venting of tanks (page 126)

Assessment and settings of the vents to be inline with the original design.

Pivoted type emergency vents statement (page 129)

“To provide a safe release of a large volume of product” ???

Introduction



List of Key changes





The PPM approach





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Vent settings in line with the original design codes

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The PPM approach





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Section 8: Tank shells

Introduction



List of Key changes





The PPM approach





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Quote page 110. This form of buckling may also be seen on fixed roof tanks that have experienced failure of the roof due to excessive overpressure or an explosion in the vapour space. A roof failure will commence at the weakest point, generally the roof to shell connection, which gives rise to a non uniform compressive load on the shell.

Tank shell under tensile stress !


Section 9 and 10 : Tank Roofs & Roof support structures Roof plates fixed roof tanks

No back ground on rejection values of 75% (3.75mm) and 80% (4.0mm) Page 120.

T min. 2.25 mm gen. corr. or T min 2 mm at local corr. (500x500mm) Page 121.

Why to use a FE Analysis for simple (5.0mm) roof plates. ?

Roof plate is, at subject area, supported at 3 sides ! (e.g. near tank shell)

No reference to the max. allow. corrosion in the compression zone ( top curb angle )

Max . allowable stress is compressive stress (buckling)

Note BS2654 uses 120 N/mm² and API uses 137,5 N/mm²

Roof support structure (beams,purlins etc.)

Measure the corrosion and check the “reduced” cross sectional area for actual stress, e.g. applicable load(s) . Allowable stress as for tank shell assessment

Column supported roofs (section 10.4)

Section refers to;

tank floor replacement , fatigue cracking , tank jacking and column design ?????

Introduction



List of Key changes





The PPM approach





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Membrane roofs. Item d) Internal pressure (page 121)

Equations used should be part of section 9.3.2.

a) Internal pressure and b) external loading (buckling)

Roof plate t min (corroded) = 80% of t nominal , what is the basis ??

Floating roofs As indicated, current under review no indication when available.

Values on min thickness 50% , 80 % and 91% are quoted without background

No need for FE analysis. Review by simple structural engineering is adequate.

See Storage Tank handbook by Bob Long and Bob Garner for design / assessment or the basic 3 load cases without using F E cal’s

1) Roof to carry 250 mm rain water in product with s.g. 0.7

2) Roof to stay afloat when two adjacent pontoons and centre deck are leaking

3) In landed position to carry u.d.l. of 1.2 kN/m²

For case 1 & 2 Roof drain is considered to be inoperative.

Introduction



List of Key changes





The PPM approach





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Introduction



List of Key changes





The PPM approach





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Rim gap by oval shaped tank

and a rim space of 200 mm.

The typical working range of rim seals by a rim gap of 200 mm

is outward (+) 125 mm and inward (–) 125 mm ( -X /+ X)

Oval shaped tank shell

Perfect round tank shell

Section 11, Rim seals and Appendix D 3



Rim seal working range – X (75mm) & + 3 X. (225mm)

No indication on how to control the 125 mm rim space at point C

Introduction



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The PPM approach





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The floating roof to “jam” already at points A & B ! No reference is made to the roof movement restrictions by the guide/gauge pole position.

B

A

Note that the roof dia is 49.600 plus the rim seal structure / bumperbar of 2x75 mm = 49750 mm The min. “Oval” tank dia is 49850 mm ! ( N-S direction ) Leaving a movement gap of Only 100/2 = 50mm !!

C



Restriction due to the guide/gauge pole position.

Introduction



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This rim seal section and the – X / + 3 X philosophy requires an update to reflect the above restrictions plus the impact when having custody transfer guide poles.


What are the benefits for a storage tank assessor ??

There are no clear benefits indentified for the Tank Integrity Assessor nor the client /owner.

The document is non structured and various subjects with the rejection criteria are repeated in different sections, this makes it hard to read /use.

The numerous references to use a FE calculations is not only costly but needs often to be done by specialists. High cost ! No justification given.

Most assessment / engineering work can be done by structural engineering, without impact on safety, integrity or the functionality of the tank.

Over 100 years experience in tank design, construction and maintenance together with sound structural engineering and common sense tells you often more then the results produced by F E calculations.

Introduction



List of Key changes





The PPM approach





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The EEMUA 159 PPM approach

Inspection / maintenance & criticality assessments.

This typical EEMUA 159 model covers about 80-90 pages on background and example sheets on how to apply this.

At the end, real life time experience and judgment by a team is used to

agree at a next inspection interval. ( factor K )

At most locations there is a shortage of good and experienced staff and ongoing cost saving actions by the companies has an impact on the staff availability and budgets for outsourcing.

There is no reference to the tank maintenance cost savings when applying this method, neither an indication that HSE aspects will improve.

Introduction



List of Key changes





The PPM approach





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Return of investment when applying the PPM method

Cost to introduce / implement ? Savings on tank maintenance ?

There is no reference provided on the cost and time to introduce this method neither the time required by operators / inspectors to get familiar with the system.

Questions raised on these subjects during the launch / presentation in June 2014 could not be addressed in detail.

No reference was available on location(s) where this method is already in use .

Reply on the question regarding the anticipated time of return on the investment was quoted at about 3 years .

Any alternatives ???

Introduction



List of Key changes





The PPM approach





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Use a criticality approach . Details of this method is Available in this revision 4. See the 15 steps under section 17.3 and use the flow chart on the right side. Simple to use in combination with the inspection list(s) , An example is shown on the next slide. Use step 8 only for H rated Components. Review M rated for this step 8 only when safety / structural integrity is involved. Criticality is based on 100 y tank experience and identifies Also the dominant failure modes.

Introduction



List of Key changes





The PPM approach





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The original EEMUA 159 criticality assessment sheets which

Includes the H. M . L. and N qualifications

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Corrosion rates and time based Inspection frequency Table 2 Corrosion rates (page 24)

Table 20 Inspection frequencies (page 237)

Table 20 includes more and new products.

Should be handy to have the same product groups also in the table 2 with an indication of anticipated corrosion rates for the new products.

Noted that bio fuels tanks have a stringent (time based) inspection frequency. Typical bio fuels are:

E 20 Ethanol with gasoline (blending - late )

B 20 Methanol with diesel (quick blending )

Inspection intervals for separate storage of these products are longer???

Reference re coating section C. 5.3.

Table does not show special coating / lining and material requirements for the bio fuels.

Introduction



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The PPM approach





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In conclusion,

•The new document is complex, non structured and not easy to use

•Mixing often various subjects in different and non related sections

•Recommends costly FE calculations without benefits

•Does not show a clear improvement regarding “added values”.

•Not complete for floating roof assessment

•Indicates rejection criteria values without justification / background

•Suggest various advantages when using the PPM but fails to quantify.

Little reference to the original objectives of the EEMUA ;

1) The document is intended as a “Prevention guide” and ……

2) To “use the common sense of the 100 years storage tank experience ”

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Recommended subjects for the next EEMUA 159 revision ;

•More details on secondary containment volumes, distances btw tanks etc.

•Guidance on tank compound volume, drainage facilities incl. requirements under fire fighting / cooling situations

•Overfill protection

•Brittle fracture

•Tank anchorage and rejection criteria when corroded

•Seismic design / verification rules

•Special requirements for the AFS ( Airport Fuel Supply ) tanks and terminals

A reference to the handbook for storage tanks and equipment.

“Guide to Storage tanks by Bob Long and Bob Garner”

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References ;

Papers by ;

•J.B. Denham: Shell to base joint design

•J. de Wit: Allowable foundation settlements

•W. Allen Marr, Ramos and Lambe: Criteria for settlements of tanks

•G.E. Bratchell : Foundation Monitoring Considerations ( Institute of Petroleum)

• J. de Wit: Brittle fracture

•R.O. Long: Roof Designs

•D. Dickie: Floating roof designs

•J. de Wit : Large floating roof design at Europoort .

•H. Kroon: Rotation and stresses at tank shell / bottom connection

•S.C. Palmer: Effects of foundation design & Tank anchorage

•M.O. Engel: Roof frangibility and venting

•Dr. N.J. Adams: Seismic design rules for flat bottom liquid storage tanks

Introduction



List of Key changes





The PPM approach





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StocExpo 2015StocExpo 2015 17-19 March Ahoy Rotterdam What is the added value Section 5: General...

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