Quality Assurance in Fabrication New Build Power Plants

Copyright © TWI Ltd 2013

Quality Assurance in FabricationNew Build Power Plants

Marcello Consonni

Welding Engineer

TWI


A Brief Introduction to TWI


TWI - Dedicated Resource

• Membership based organisation

• £70M ($115M) of R&D in Materials

Joining, Structural Integrity and

NDT undertaken each year

• Over 780 employees

• Eighteen global offices

• More than 700 Members in 3500

locations in 80 countries


Support for Power Generation

• Specialist repair procedure development • Fabrication/Fabricator audits • Fitness for service audit/review • Fracture Integrity Management/Life assessment • Risk based Asset Management • Materials properties • Structural and process modelling • Advanced NDT and Conventional NDT • Training in welding and inspection • Manufacturing and repair Codes and Standards


Webinar Agenda

1. The ‘need’ for this webinar

2. Potential site problems

3. Case study: fabrication audit of CCGT power plant

4. Case study: assessment of power plant contractors

5. Q&A 20-25 min


Why this webinar?

“…welds were not heat-treated…”

“…caused a …-month delay…”

“…considering sacking key contractors…”

“…welds were not qualified…”


Potential site problems

• Control of consumables (storage, distribution)

• Welding coordination• Welder skills (specific training)• Control of thermal operations (eg PWHT):

– Specification– Monitoring– Records– Checking


Competence is key

• The performance of high-Cr grades such as ’91’ and ’92’ is linked to one specific microstructural condition

• Constant surveillance (you get what you inspect…)

• Application of codes and standards is not necessarily adequate!


P 91 HP Pipework

CCGT Plant

Design Code ASME B31.1

HP steam pipe 450mm x 32mm thick

Hardness in HAZ 449Hv in weld 426Hv

Longitudinal seams in alignment

Is this code compliant?

YES!!


P 91 HP Pipework

CCGT Plant

Design Code ASME B31.1

HP steam pipe - 90° elbow450mm x 36mm thick

Hardness:182 Hv in HAZ

150Hv in parent

Is this code compliant?

YES!!


Fabrication Audit – CCGT Plant


Fabrication Audit – CCGT Plant• Owner’s engineer concerns

wrt workmanship – Four heat recovery steam

generators (HRSGs) with supplementary firing• ASME Section I

– High pressure steam pipes and main superheater outlet headers • P91 steel (9Cr 1Mo modified)

– Header stubs • P22 steel (2¼Cr 1Mo)

– Low pressure components – C-Mn steel


TWI Scope (Phase 1)

• TWI requested to carry out visual examination at site

• Phase 1- 1 week– Inspect accessible pipe and

header welds – Review level of

workmanship and weld quality

– Comment on acceptability of welds to ASME Section I requirements


Phase 1 - Results of review

Significant defects observed:

• P91 welds in HRSGs did not comply with ASME Section I quality requirements

• Welding documentation incomplete

• LOW HARDNESS P91 (parent material, welds and HAZs)– Improper PWHT or chemical

composition ?


Phase 1 - Results of review (2)


Phase 1 - Recommendations

• Full visual and NDE inspection of all four HRSG’s

• Establish the effects of multiple PWHT (time at temperature) on P91 weldments

• Ensure qualified weld repair procedures• Consider removal of defects by

machining/grinding – to eliminate the need for PWHT

• Investigate low hardness values found on the P91 pipework


Phase 2 - 6 weeks• TWI expert on site • Witness full inspection and NDE

– Hardness, PMI, UT/PA, RT, Boroscope inspection

• Identify defects and review implications

• Advise on/Review repair qualification

• Advise on HT/PWHT• Recommend remedial work and

supervise implementation• Advise additional testing

– Creep testing for high Mn+Ni (>3.0%) welds

• Liaise with operator, designer, manufacturer and Third Party Inspection agency


Benefits

Owner assured of integrity of plant

– Delay to plant start up schedule avoided– Confidence gained in operability of the plant

• Additional testing during life of plant to generate data on creep life

– Avoided costly outage and repair once in service• Recommended RBI

– Increase inspection frequency especially for higher risk components with fabrication issues

– Increased safety of plant in operation


Assessment of contractors

Owner of a large power plant hired TWI to assess potential welding contractors:

1. Preparation of a questionnaire to shortlist contractors:• Welding engineer CVs• Sample WPSs• Technical questions on low-alloyed grades

2. Review of quality system and quality procedures

3. Emphasis on welding coordination: interview of nominated welding engineers


Ensuring Competence

• Covers all Cr-Mo grades, with emphasis on P91 and other CSEFs

• Attended by: welding engineers, plant inspectors, design engineers, consumable manufacturers

• Can be customised for individual companies


Any (easy) questions?

Contacts:

[email protected]

(welding, auditing, training)

[email protected]

(membership)

mailto:[email protected]

mailto:[email protected]

Quality Assurance in Fabrication New Build Power Plants

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