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

5

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?