Steam Generation – Operational Flexibility and Lifetime Extension Considerations

1. Steam Generation – Operational Flexibility and Lifetime Extension Considerations KevinMurray SeniorIntegrityEngineer Marsh Power Forum – Istanbul, October 2013

2. Objective of Presentation 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

3. Doosan – Heritage 2

4. Illustration – Operational Changes on an Ageing Unit Flexible operation – 2250 starts in following 15 years Essentially base loading – around 650 starts in 26 years

5. Through Life Asset Life Management – Why? Asset Evolution Plant Enhancements PlantDegradation • 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 4

6. Through Life Asset Life Management – Integrity Risk Factors 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.

7. Through Life Asset Life Management – Critical Factors AssetAvailability AssetPerformance IntegrityManagement AssetCompliance& Safety AssetReliability 6

8. 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

9. 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

10. Plant Design & Construction Risk Assessment & Profiling Plant Upgrade, Retrofit & Replacement Operational Data Analysis Design & Constructability Review Water Chemistry, FAC & Inspection Engineering Strategy for Life Extension Metallurgical & Structural Integrity Through Life Asset Life Management Tools Provided by Doosan Babcock

11. Plant Risk Assessment (Technical Review)

12. Outage Inspections Expert in specifying and deploying relevant inspection techniques 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

13. 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 Living with Defects / Fitness for Service

14. Component Modification / Repair Star cracking in valve body at penetration Through thickness cracks inside bypass pipework Bypass / Balance Connections

15. Component Modification / Repair Bore opened out to remove cracking Valve body following removal of bypass pipework

16. Component Modification / Repair

17. 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

18. Retrofit – Replacement of End-of-Life Components • Replacement chest machined in accordance with DB instructions and shipped to site. • Loop pipe outlet weld – target root gap achieved following machining. Benchmark NDT / balanced heat treatment carried out following welding.

19. 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)

20. Thank You - Any Questions? 19