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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Stress Engineering Services, Inc.Confidential
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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Stress Engineering Services, Inc.Confidential
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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Stress Engineering Services, Inc.Confidential
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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Stress Engineering Services, Inc.Confidential
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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Stress Engineering Services, Inc.Confidential
What are the consequences of
Bulging Pressure Vessel?
HOOP SCF = 2 AXIAL SCF = 4
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Stress Engineering Services, Inc.Confidential
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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Stress Engineering Services, Inc.Confidential
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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Stress Engineering Services, Inc.Confidential
Fatigue Analysis by Strain Gage Method - Skirt
Temperature
Hoop Stress
Axial Stress
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Stress Engineering Services, Inc.Confidential
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
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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
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