API 934 Minutes Stress Eng ATT E

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Coke Drum Technology Update for API

934-G Round TableLife Assessment

Issues, Problems, and SolutionsLow Cycle Fatigue Analysis and Measurement in Delayed Coke Drums

Richard Boswell, P.E.

April 26, 2010

New Orleans


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SESs approach to drum life

assessment issues

SES technical services are usually in partnership

with client/owner using: SES tools and experience

Clients proprietary information and situation

Clients technical experience and engineering

support


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Typical Client Life Assessment

Questions

How long will it last?

When is the economic end of life? How many cycles are left? When will we have a through wall crack? Which repair is best and when to repair? How can we extend the end of life?


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Why are there Questions? Drums were not designed/fabricated for this

cyclic service

Not Just a pressure vessel

Service conditions were not fully understood or they

have changed

Being operated for maximum economic return notmaximum life (in most cases)

The game changes as the vessel changes

Bulges and corrugations Consequences Safety, Environment, and

Financial


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What is the answer?

The answer depends on when the question is

asked During design?

When new drums installed?

First turn-a-round?

Or during the final years of service?

SES approach is structured to fit the situation andcondition of the drum Todays discussions will be focused on a mid-life

situation


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Stress Engineering Services, Inc.Confidential

SES Drum Assessment and

Extension Tools

AET Testing for Active Cracks during operation

Fatigue and Thermal Measurement in Shell and Skirt Process Change Comparisons Bulge Severity Evaluations Probabilistic Crack Growth Calculations Material Evaluation Weld Repair Procedures Weld Overlay Reinforcement

Nozzle Cracking Analysis Skirt Repair Procedures Shell Replacements


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SES Integrated Approach for

Coke Drum Life Extension Practice

1. Search for bulging and evaluate it

2. Search for cracking

3. Repair the cracks

4. Determine actual cyclic stress in shell and skirt

5. Perform structural, mechanical and

metallurgical evaluation of the drum

6. Develop Long Term Operation, Inspection,Repair and Replacement Plans


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Assessing Current Condition AET global or local for active crack detection Long Term monitoring of drum performance

Damage Histograms

Fatigue Damage Calculation

Abnormal stress events

Thermal transients

Process cause and effect on remaining life

Bulge Severity Evaluation Metallurgical Examination


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CD A

Switch out CD A

Switch in CD B

Switch in CD A

Switch out CD B

Data acquisition when TCs A and B (both)

are above 300 FTwo TC controlling data acquisition (TC-A,

TC-B)

Six TCs monitoring skin temperatures for

thermal gradients

State-of-the-art Digital AMSY4 VallenSystem, remotely operated

Remote AET data acquisition:

AET system controlled by TC

readings

Data transfer via Internet or

clients IntranetNear real time data analysis


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High Temperature Strain Gage with

Intrinsically Safe Instrumentation

1100 F Max


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Large Transient Stress During Quench

Coke Drums arenot simple

pressure vessels

During Quenchthe skirt and shell

experience a verylarge transient

stress


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Drum Bulges

Corrugations cause variation in the stress field

Bulge Severity illustrated with Bulge StressConcentration Factor Analysis

Encourages Low Cycle Fatigue from bendingstress amplification

Relationship to seams is critical Bulge severity reduced with designed structural

weld overlay


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1995 Citgo Coker I

F201B

Drumview Scan

F-201 B Nominal insideradius = 126

November 94 survey :8.4% bulge

May 95 survey : 9.5 %bulge

How Bad IS Bad? Replacement drums

designed for actual

conditions

Design was limited byexisting foundation

capacity


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What are the consequences of

Bulging Pressure Vessel?

HOOP SCF = 2 AXIAL SCF = 4


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Tools for Bulge Severity Analysis

Bulge Stress Concentration Factor

A bulge corrugation increases all surface stress due to geometryand Ring Bending Effects

Finite Element solution of exported laser scan using internal

pressure loading provides ratio of bending to membrane stress

Allows extrapolation from one location to another

Bulge Intensity Factor Ranks bulge severity for likelihood of cracking

Geometric Surface solution of exported laser scan

Useful when little information is known from inspection


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Coke Drum Skirt Fatigue

The problem for the skirt is not in the basic

pressure vessel design or in the Steady Stateload condition when it is hot.

It is in the transient as the drum heats quickly,and later cools sometimes even more quickly.

The skirt is pushed outward and then pulledback inward by the vessel.

It is not simply push and release, but it is pulledback from its thermally expanded diameter.

A reversed bending stress happens that createsa large stress range for fatigue damage.


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Fatigue Analysis by Strain Gage Method - Skirt

Temperature

Hoop Stress

Axial Stress


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FATIGUE LIFE CALCULATION FOR A SKIRT FEA

Improved Prediction Using Actual Thermal TransientsDesign (by others) predicted

152 years

SES Transient analysis

performed prior to T/A

Maximum stress intensity

range during transient =

143,430 psi

Using ASME code Section

VIII Division 2 fatigue design

Table 5-110.1, UTS < 80 ksi,

a fatigue life of 1228 cycleswas obtained. After 5 years (~1369 cycles)cracks were discovered in all

4 drum skirts (no slots)

Finite Element Model vs Reality


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Stress Engineering Services, Inc.

Confidential

Examplesof Rapid

Quenching

in Shell


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Stress Engineering Services, Inc.

Confidential

Sources of Large Cyclic Stress

Thermal distributions/gradients and self

constraint Thermal heating and cooling rates Coke bed interactions

Random local flows through coke bed andaround it near wall

Bulges amplify bending stress in hoop and axialdirections


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Drum Weld Repair

Automated temper bead technology

Reduce outage time for repair Full PWHT not required Repair from inside and/or outside Window replacement

Material is too degraded and must be removed

Bulge is too severe for weld overlay

Weld Overlay for Bulge Reinforcement Cone, shell, and head repads (if any)


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Temperbead Welding

HAZ created by 1st weld layer

HAZ is

tempered by

deposition of

successive

layersPictures Courtesy of WSI


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Shell, Cone, and Skirt Repair with

Automated Temper Bead Technology

Pictures Courtesy of WSI


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Structural Weld Overlay to Reinforce Severe Bulges

Z

XY


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New Generation Drum Design

Fabrication Quality, Coke Stiffness and Drum Vassingfrom 1998 CITGO Drum Design Patent


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Thank You

Documents

API 934 Minutes Stress Eng ATT E