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
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
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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
WELD-LIFE – Preventing premature weld failure
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
WELD-LIFE – Preventing premature weld failure
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)
WELD-LIFE – Preventing premature weld failure
• 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
WELD-LIFE – Preventing premature weld failure
• 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
WELD-LIFE – Preventing premature weld failure
• 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
WELD-LIFE – Preventing premature weld failure
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:
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WELDLIFE