p91-p92 steels: improved welding& heat treatmentto · pdf filep91-p92 steels: improved...

Outline of a new Group Sponsored Project (GSP) launched by ETD

WELDLIFE

P91- P92 Steels: Improved Welding & Heat Treatment to

Prevent Premature Weld Failure & Extend Component Life

Dr David J Allen, IMPACT PowerTech Ltd

Dr Ahmed Shibli, ETD Consulting

Dr David Robertson, ETD Consulting

[email protected]

www.etd-consulting.com

Preamble: This presentation gives the background and outline of a proposed project which is based on thepreliminary findings of the recent UK and European industry R&D. We aim to run a webinar for the interested partieson 15th January 2015 and then hold a meeting of the interested parties sometime after that (in Leatherhead - justsouth of London or in central London) to discuss and agree on the details of this project.

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� The project will be run and managed by ETD

� Technical leadership by Dr David Allen

• Biography – David Allen

• Doctorate in metallurgy

• 37 years experience in the power industry – R&D and technical support

• 1990 – 2014: E.ON (formerly PowerGen) Technology Centre, Ratcliffe-on-Soar, UK

• UK and European collaborative R&D, testing and performance of high temperature power plant materials

• Weld “Type IV” cracking, plant support, “GENSIP” P91 project, advanced “MARBN” materials, Chairman ECCC (European Creep Committee)

• From April 2014 – Independent materials consultant –IMPACT PowerTech Ltd

[email protected]

[email protected]

2

PRESENTATION OVERVIEW

• Introduction

Weld Type IV cracking in high temperature plant – What it is, why it matters,

and how it can cause premature failures, outages and repairs / replacements

• Research Update

Two recent UK R&D projects have shown that we can do something about

Type IV cracking – with good prospects for x2-x3 life improvement

• WELDLIFE

A practical development project to improve welding and heat treatment,

make realistic plant components, and undertake long term and full scale high

temperature testing to validate the new technology for Code acceptance

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BACKGROUND

What can go wrong? – Weld Type IV Cracking

• P91/P92 – A triumph of

intelligent materials design

• Two-stage heat treatment for

optimum creep strength

• Fine lath martensite structure

• Micron-scale precipitates

Then - welder applies uncontrolled HT!

Weld heat-affected zone (HAZ) is weak

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What can go wrong? – Weld Type IV Cracking

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Montage by Steve Brett

Plant Experience – Type IV Cracking - UK

• P91 – Developed in the US during the 1980s

• Initial application 1990s – UK coal plant retrofit headers

• 1996 – West Burton violent endcap failure after 36,000h– Flat endcap – inferior design

– “Stress relieving groove” at weld root – still a stress concentrator

– F91 material high Al content – hence relatively weak

• 2004 and onwards – Flank cracking (weld segments perp. to

hoop stress direction) at header branch, stub and attachment

welds– Occurring after some 60-100Kh operation (NB, design life 150Kh+!)

– Mainly in high Al / high Ni Grade 91

– No violent failures – but several headers replaced

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Plant Experience – Type IV Cracking - UK

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West Burton endcap weld

- High stress at root

Ground-out Type IV cracks

at flanks of stub welds,

UK P91 header

Multiple cracking – Repair

economics unfavourable

Plant Experience – Type IV Cracking - Worldwide

• US – Welded “Wye” piece failed

after 35,000h at 568°C (photo)

- Code compliant

• Japan – Several Type IV failures

in P122 (12CrMoVNb) and P91

NB – P92 – Experience relatively limited

• Unreported failures – US, worldwide

• Belgium – Damage first seen after ≈ 70,000h

• Germany – Better experience – Operation mainly not above

550°C – Creep damage not found until > 100,000h operation

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Type IV cracking in low alloy CrMoV steel

Parent material ferritic –

Parent quite weak in creep.

Crack typically in intercritical HAZ –

Partially reaustenised zone

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Type IV cracking in high alloy steel

Parent material martensitic – Parent is

strong in creep.

Crack typically in fine grained HAZ – Fully

reaustenised zone

Very different from low alloy steel

Typical

high alloy

parent

material

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E911 weld strength factor – plotted against stress

E911 weld strength reduction factors

0.50

0.60

0.70

0.80

0.90

1.00

0 50 100 150 200 250

Parent stress [MPa]

WS

F

550ºC

570ºC

590ºC

610ºC

630ºC

650ºC

most probable

worst case

Allen and Servetto 2001 – ECCC project

Analysis by PowerGen UK (now E.ON) and Italian Welding Institute 11

At realistic plant

stresses, the weld

strength reduction

compared with the

base material is

about 40% or worse

E911 – European version of high alloy martensitic steel similar to P91 and P92

10

100

1000

1000 10000 100000 1000000

Rupture life, h

Str

es

s,

MP

a

530°C540°C550°C560°C570°C580°C590°C600°C

Lines - Bell predicted mean P91 Type IV life as a function of stress

Points - Design stress limit values from BS12952, plotted on the

corresponding Bell line for the applicable temperature

Consequences – Standard design fails at high temp.

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At 530°C – Weld lasts beyond plant design life - But

At 570°C – Weld life may fall to as little as 50,000h

PROJECT BACKGROUND

WELDLIFE – A project to avoid premature weld failure

Recent UK industry initiated R&D shows - We can act to avoid weld Type IV cracking

1. By improving the welding process

2. By improving heat treatment (in the factory)

The WELDLIFE project will

• build on these laboratory-based developments

• develop practical technology solutions

• provide validation for Code acceptance

• improve plant integrity assurance

• reduce in-service inspection costs

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Improving welding technology

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Research of “VALID” project – Dr David Allen, formerly with E.ON “VALID” – a UK R&D collaborative project supported by TSB and led by Dr John Rothwell, TWI

Creep testing, metallography and analysis carried out by E.ON in parallel with Doosan Babcock (UK)

weld

metal

weld

metal

HAZ

Welding process B

Coarse weld HAZ

structure – Better

creep performance

Welding process A

Fine weld HAZ

structure – Poor

creep performance

Macro

Macro

Micro

Micro

LIFE INCREASE

- UP TO x 3

Improving welding technology

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Creep tests on seven welds – all at same stress and temperature

Welds with coarser HAZs consistently demonstrate longer creep lives

Research of “VALID” project – Dr David Allen, formerly with E.ON “VALID” – a UK R&D collaborative project supported by TSB and led by Dr John Rothwell, TWI

Creep testing, metallography and analysis carried out by E.ON in parallel with Doosan Babcock (UK)

Improving heat treatment – In principle

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Research of Prof. Fujio Abe, NIMS, Japan

Novel heat treatment

sequence.

Simulated weld HAZ

almost matches creep

life of parent P92

Normal heat treatment.

Simulated weld HAZ

shows poor creep life

Renormalise the base metal (in workshop): Make weld: Then heat-treat complete

welded vessel component to combine tempering (base metal) and PWHT (of weld)

Improving heat treatment – Real welds

17Research of Dr David Allen, formerly with E.ON (UK)Work funded by and carried out at E.ON - “Avoidance of Type IV Cracking” project

Average P91 weld creep life compared with normal heat treatment:

x 2.5 - Renormalise, weld, PWHT

x 1.6 - Renormalise, half-temper, PWHT

Normal heat treatment

Improved heat treatment

Base material

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Weld (left) and HAZ HAZ and parent (right)

Weld made using novel heat treatment sequence

Weld and base material structure and properties - All normal

HAZ creep strength increased – but very fine-grained, not as strong as base material

WELDLIFE will investigate combining coarser HAZ with novel HT – Optimised?

Improving heat treatment – Real welds

Research of Dr David Allen, formerly with E.ON (UK)Work funded by and carried out at E.ON - “Avoidance of Type IV Cracking” project

WELD-LIFE – Preventing premature weld failure

Recent UK R&D shows - We can act to avoid weld Type IV cracking

• By extending laboratory-based R&D on: a) welding, and, b) heat treatment

• By upscaling to model component manufacture, testing, validation

The aims of the WELDLIFE project are to:

• maximise P91 and P92 weld life improvement, a) by improved welding technology, b) by improved heat treatment sequencing

• quantify and validate life improvement by plant-realistic long term high temperature stress rupture/creep testing out to 30,000 hours

• manufacture a mock-up model header barrel in the fabrication workshop using the improved a) welding and b) heat treatment technology

• carry out instrumented pressure vessel testing to demonstrate life improvement compared with conventional welding and heat treatment

• undertake design assessment and pursue ASME Code Case acceptance of the novel heat treatment technology for workshop manufacture

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PROJECT OUTLINE


Phase 1 - Laboratory development and testing

• to build upon and extend advances already demonstrated in the UK

• to develop and assess improved technologies for both P91 and P92

• to investigate improved weld technology for advanced alloys e.g. MARBN

Phase 2 - Component manufacture and testing

• to take the optimised technologies forward

• pilot-scale model header manufacture – P91 (or P92 if sponsors prefer)

• validation by long term testing and pressurised vessel testing

• potential demonstration in operational power plant – if host available

Upscaling to model vessel manufacture and testing will

• identify and overcome practical constraints

• develop manufacturing expertise

• prove that the concepts work in reality

• demonstrate that novel technology is suitable for Code approval

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WELDLIFE

WELDLIFE – Outline of Project Plan & Timescales

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Month

Work Package / Task 6 12 18 24 30 36 42 48 54 60

WP1 - Improved Heat Treatment

Heat treatment trials

Machining / manufacturing trials

Microstructural investigations

WP2 - Improved Welding Technology

Weld modelling

Welding process investigations

Optimise welding and heat treatment

Welding procedure qualification

WP3 - Improved Weld Performance

Short term creep testing of alternative options

Long term creep testing for validation

Weld characterisation, mechanical testing

WP4 - Pilot Component Manufacture

Model header - development, manufacture

Pressure test vessel manufacturing

WP5 - Pressure Vessel Testing

Pressure vessel test operation

Condition monitoring and NDT

Damage assessment and post-test evaluation

WP6 - Design Development and Code Approval

Design for conventional and improved welds

Design model header

Design pressure test vessel

Pursue Code Case approvals

WP7 - Project Management

Project Manager - ETD

Project Leader - Impact PowerTech

Project control - Steering Ctee - All Partners


Cylindrical P91 pressure vessel, e.g. 320mm OD x 30mm w/t x 1.5m length, pressurised and if possible end-loaded, tested at 625°C / 650°C

OD machined down to ≈20mm w/t in vicinity of each of two circumferential butt welds,

Butt Weld A (novel HT) and Butt Weld B (conventional HT) – so thicker endcap welds will not be at risk of failure

Butt Weld A – Made first in as-renormalized P91 pipe (≈400HV): Then vessel PWHTd, thus base material also tempered.

Butt Weld B – Made later in the P91 pipe after its retempering (to ≈220HV, i.e. normal condition): Weld then PWHTd

Each weld to include 3 segments each extending 120° around circumference:

(1) normal weld, (2) optimised variant X, (3) optimised variant Y

Option to also include dummy stub or small branch welds deposited onto (a) renormalized P91, (b) tempered P91

Option to interrupt test periodically for weld HAZ replication and other NDE etc.

Run until leak occurs – This identifies weakest weld - Repair vessel and continue testing

Aim to generate sequence of failures and show life improvement for novel welding / HT technology

Option to remove some welds un-failed and rank these in terms of extent of damage

Option to commission additional vessel tests subject to budget and timescale constraints

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WELDLIFE – Model header design (indicative only)


• Key deliverable

A comprehensive package of validated and coded

design, welding, and heat treatment technology –

To minimise or eliminate the risk of premature weld creep

and creep-fatigue failure in high temperature steam plant

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WELDLIFE


• Preliminary costings, based on obtaining 5 sponsors, are expected to be in the region of £100,000 per sponsor per year for a 5 year project.

• The figures are subject to review as the project scope is developed. If more sponsors are identified, then the cost per sponsor could fall.

• Sponsors are very welcome to offer part in-kind contributions toward their sponsorship fees, including materials, test specimens, and technical work.

• Project budget will be mainly spent on external contracts – welding, heat treatment, NDT, pressure vessel manufacture and testing, etc – Project management estimated at ≈ 15% of total costs.

• We intend to develop the full proposal and project in consultation with potential sponsors. The plans will evolve to meet sponsors’ needs and budgets.

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INDICATIVE COSTS & TIMESCALES


• Who should join the project as sponsoring partners?

Power plant operators – Coal and gas plant

Plant manufacturing companies

Plant inspection, repair and maintenance companies

• Who will also be involved?

Component manufacturers

Welding companies

Heat treatment specialists

Pressure vessel testing organisations

Specialists in weld modelling

Specialists in microstructural examination, including SEM / TEM

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WHO SHOULD JOIN


Thank you for your time and attention

We will now have a short discussion session –

so please let us have your questions and comments

For all future enquiries, please contact us:

[email protected]

[email protected]

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WELDLIFE

p91-p92 steels: improved welding& heat treatmentto · pdf filep91-p92 steels: improved...

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