Steam Generation – Operational Flexibility and Lifetime Extension ConsiderationsKevin MurraySenior Integrity Engineer
Marsh Power Forum – Istanbul, October 2013
This presentation will incorporate:
• Brief company overview
• Summary of the key integrity issues on steam generating plant, arising from the following:
• Implementation of a flexible operating regime• Life extension of ageing assets
• Overview of the Through Life Asset Management services offered by DB to allow operators to manage component integrity and availability
Objective of Presentation
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Doosan – Heritage
Essentially base loading – around 650 starts in 26 years
Flexible operation – 2250 starts in following 15 years
Illustration – Operational Changes on an Ageing Unit
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AssetEvolution
• Reliability & Availability• Performance & Efficiency• Condition Monitoring• Lifetime Rupture• Integrity Management• Inspection Strategy & Planning• Strategic Spare Parts
• Regulations Compliance • Operational Flexibility• Performance Improvement• Technological Advancements• Modular Upgrade & Retrofit
PlantDegradation
Plant Enhancements
Through Life Asset Life Management – Why?
Asset ageing is not about how old your plant is; it’s about what you know about it’s condition and how that’s changing over time.
− Confidence in initial design and fabrication− Knowledge of through life Plant risk factors− Appreciation and quantification of failure consequences
These are critical to understanding ageing and provision of effective asset life management.
Through Life Asset Life Management – Integrity Risk Factors
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Through Life Asset Life Management – Critical Factors
AssetPerformance
AssetCompliance
& Safety
AssetReliability
AssetAvailability
IntegrityManagement
Two-Shifting of Steam Generating Plant
Two-shifting of steam generating plant increases the risk of damage to components from a number of mechanisms:• Greater and more frequent thermal stress cycles• Increase in frequency of pressure stress cycles• Increased potential for thermal quenching of components
Pertinent Damage Mechanisms
Thermal Fatigue Gradual deterioration and eventual cracking of
material Caused by alternate heating and cooling during
which thermal expansion is constrained Generally associated with stress raisers and
most likely to occur at weld connections or attachments
Corrosion Fatigue Occurs on the waterside surface of tubes The results of a combination of cyclic loading
and offline corrosion Corrosive environment will accentuate the rate
of crack growth
Creep Time/temperature/stress dependant mechanism Not specifically a flexibility-related concern,
although creep / fatigue interaction must be considered
Through Life Asset Life Management Tools Provided by Doosan Babcock
Plant Design & Construction
Operational Data Analysis
Metallurgical & Structural Integrity
Design & Constructability
Review
Risk Assessment & Profiling
Water Chemistry, FAC & Inspection
Plant Upgrade, Retrofit &
Replacement
Engineering Strategy for Life
Extension
Plant Risk Assessment (Technical Review)
OEM & Industry
Knowledge
OEM & Industry
Knowledge
Inspection planInspection plan
Age of PlantAge of Plant
Design reviewDesign review
Client Discussions
& requirements
Client Discussions
& requirements
Operational data
review
Operational data
review
Failure HistoryFailure History
Inspection HistoryInspection History
Repair historyRepair history
Planned Changes
in operation
Planned Changes
in operation
Material
Assessments
Material
Assessments
Engineering
Assessments
Engineering
AssessmentsPlant ModificationsPlant Modifications
Technical Review
Outage Inspections
Inspection techniques including: Boiler condition assessment Metallurgical condition assessment of high temperature
components Conventional and specialist NDT techniques Remote Visual Inspection (RVI) Pipework support survey in both hot & cold condition Interpretation of inspection results and sentencing of defects Capability to manage multi-discipline inspection teams
Expert in specifying and deploying relevant inspection techniques
Living with Defects / Fitness for Service
The discovery of defects does not necessarily mean repair works are necessary
DB have extensive experience in managing the integrity of flawed components, with a programme of ‘Inspection Based Assessment’ defect monitoring in place on steam chests and headers at a major UK coal fired station
Thorough understanding of the component’s design and the nature and behaviour of defects is necessary
Images below shows the application of advanced stress analysis techniques and Fracture Mechanics to justify returning a component to service with known defects
Component Modification / Repair
Bypass / Balance Connections
Star cracking in valve body at penetration
Through thickness cracks inside bypass pipework
Component Modification / Repair
Valve body following removal of bypass
pipework
Bore opened out to remove cracking
Component Modification / Repair
Retrofit – Replacement of End-of-Life Components
DB managed the replacement of this complex component, with the following techniques used in the planning of the works:
– Virtual Survey Engineering / Datum Measurements
– Pipe Stress Analysis / Restraint Design– Specification of machining requirements for
replacement chest– Production of NDT and heat treatment
procedures following installation
Retrofit – Replacement of End-of-Life Components
Loop pipe outlet weld – target root gap achieved following machining. Benchmark NDT / balanced heat treatment carried out following welding.
Replacement chest machined in accordance with DB instructions and shipped to site.
New Build Considerations
• Fatigue cracking at tube stub connections is commonplace, due to differential thermal expansion during start-up
• Exacerbated by weld profile, and mainly observed in tube/weld toe
• Can be remedied by local repair, however poor access particularly within HRSGs – trepanning header often necessary
• Joint configuration on new-build optimised for smooth profile (good option for flexibly operated plant)
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Thank You - Any Questions?
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