understanding the in-service behaviour of materials: why it’s … · 2018-04-27 · corrosion...

Title of Presentation © 1 January 2014 EDF Energy plc. All rights Reserved1

Understanding the In-Service Behaviour of Materials: Why it’s important

11th April 2018A.Morris(Chief Mechanical Engineer, EDF Energy Coal, Gas and Renewables)

Fuel and Energy Research Forum, Environment Interest Group Seminar, University of Sheffield


Agenda

Set the context (EDF Thermal plant, Market, History, Challenges)

Current practice, to determine condition and residual life; some examples from- New plant (High Temperature Manifold)- Old plant (Steam Turbine), life extension

Current EDF R&D: to address shortfalls in understanding of in-service material behaviour in Coal/CCGT plant

Closure: Points to bear in mind and Opportunities

Mechanical Engineer’s view based on working; a)in R&D, b)providing consultancy services, advice to UK Utilities,c)currently for the Operator

How are decisions influenced by our understanding of in-service material behaviour?


Cottam

West Burton A

West Burton B

2000MW Coal, each site•Commissioned late 1960’s, early 1970’S•Closure date…...to be decided……run to 2025?•Coal stocks being run down

Commercial•Station break even, costs ~ £110K per day (£40M/pa)•Rise in renewables sources, improving margins for gas plants, increasing costs for coal plants due to carbon price support•Impact of the capacity market on revenue

1300MW CCGT•3 independent Units (GE steam and gas turbines)•2013 commercial operation•Currently at ~ 23Khr and 900 starts•Expect ongoing high number of annual starts•25 year, 200Khr design life

Commercial•Financial review for plant build taken ~ 2008-2010


Future Operation

1 2 3 4

1. Baseload (Design Intent)2. Flexible (Market Driven)3. Investment (Emissions, Efficiency)4. Capacity Market (Transition Low Carbon)


2018-2021 2025 onwards2021-2025

Coal

CCGT

• Year on year financial review• Safety, old (vintage) plant……..• Reliability is key for revenue opportunities• Avoiding unnecessary inspections, exploit existing

plant monitor and inspection data (Big Data)• No Capex, constrained Opex funds• Increased condition monitoring (Material

behaviour)

Legacy, methods, practice, experience, people…..(Opportunity)

• Adapting to capacity market world; expect through life revenue lower than original plan

• Lean staff numbers• Optimising maintenance/inspection• Exploit legacy from Coal• Flexible plant operation• Increased condition monitoring (Material

behaviour)

Renewables

• Transitioned to Lower Carbon economy

• Optimised inspection, maintenance, operation

• Acceptable revenue• Multi-skilled staff• Legacy embedded• Condition monitoring ‘the

norm!’


The Current Inspection/Assessment ProcessPlants strive to optimise and add value from invasive inspections and to better utilise data routinely captured .

Ref; ‘The role of small specimen creep testing within a life assessment framework for high temperature power plant’, Morris, Cacciapuoti, Sun, International Materials Review, June 2017


Loading(Force)

•Load path through structure,•Installation,•Time and Rate,•Transients, loading envelope•Fault conditions,•History and sequence,•Credible?

Material Behaviour(Resistance)

•Properties,•Time and Rate dependency,•Environmental factors,•Composition,•Manufacturing process,•Ageing in service,•Predictive model, •Failure Mode(s)?

Inspection/Monitoring(Reality)

•Evidence of condition, NDT, metallurgy,•Online monitoring,•Observations from other plant,•Big data, what’s important?•Forewarning of failure, indicators?

• Seek a balanced view,• Maintain safe operation,• Inform your perception of risk,• Identify opportunities,• Implement the right action for the plant at the right time,

Potential Barriers• Rarely do we have the full picture,• We may have to apply some degree of subjective assessment,• Lack of clarity tends to drive over conservative decisions (expensive),

The Challenge: How do we make the right decision?

Prob

abili

ty

Consequence

Risk and Opportunity


Example 1: Pressure Systems, P91 material branch weldsCCGT: HRSG: HP superheater 3 outlet manifold branch welds creep damage.

Implications?Safety and Residual life: Premature creep damage at the branch welds

Statutory inspection: Unit 2: 201616Khr and 724 starts (Problem first detected)at < 10% of design lifeOEM bulletin (2013) and service provider investigations on other similar plants; Prior insight. First inspection of P91 welds usually after ~40Khr

Variable creep damage across the 12 branch welds. Other two Units affected

Initial site assessment based on surface replication, grind to clear, replicate. MPI/UT revealed no macro cracks•Extract boat samples for worst welds, examine, repair weld, return to service,•Define re-inspection interval at 6K EOH,•Site investigation on root cause, measurements, modelling,•Re-design underway, planned replacements from 2020,

Boat sample removed

To HP turbine


HP Superheater Manifold Welds – Creep Damage Assessment

Service Provider

Definition (Creep

cavity count)

Creep cavities

per mm2

Clear 0

Very isolated 1-10

Isolated 10-50

Low orientated 50-250

Orientated (Including

high orientated - HO)

250-500

Grouped 500-1000

Aligned 1000-1500

Crit

ical

ity

VGB Definition

(Creep cavity

count)

Creep cavities

per mm2

1 0

2a (Individual

cavities)

Up to 150

2b (numerous

cavities, random)

Over 150

3a (numerous and

with orientation)

3b (chains of

cavities)

Crit

ical

ityVGB scale for low alloy steels: Ref: VGB-TW 507, Guidelines for the Assessment of Microstructure and Damage Development of Creep Exposed Materials for Pipes and Boiler Components. VGB Technical Association of Large Power Plant Operators, 1992.

[1]. Concari, S., Residual Life Assessment and Microstructure.ECCC Recommendations, 2005. 6(1).

Loading•Perceived to be the problem (design),•Site measurement of displacement (model),Material Behaviour•No adverse findings regarding material - OK•P91 tends to not reveal significant signs of ageing (from traditional metallurgy) until relatively late in life,•A reliable predictive model not readily available, Inspection/Monitoring•Onload operation temperature, pressure data available – within design - OK•Traditional surface replicas, hardness, sampling approach……some trends can be observed but difficult to define a predictive life

ECCC studies equate VGB level 3 as t/tfail 0.69, low alloy steel HAZ [1]

Hence: ‘HO’ level is ~ to VGB 3a


Example 2: Low Pressure Steam TurbineLP Steam Turbine: Pencil shaft failure;

implications for operating fleet

Safety and Residual life: 2012 excessive vibration, turbine stopped, inspected, large crack in pencil shaft. The shaft vibration monitoring worked. Risk to the other turbines in operation of the same design (12 in operation + 12 spares across two Coal sites)

Prior advice: Circa 2008-2010 stations with this type of construction advised to conduct advanced NDT inspections of critical areas such as pencil shaft shoulders (failure location) and of more importance the disc button drive locations and disc bore locations

Suspected corrosion pitting at shaft shoulder fillet leading to eventual crack initiation

Failed rotor disassembled and fracture examined. Inspections of other rotors accelerated across the fleet (2014-2016), no defects identified above NDT threshold. Various integrity assessments undertaken to assess risk of continued run to closure based on; inspection threshold, loading, material behaviour

Note: Circa £1-2M to pull a rotor from berth, workshop inspect and return to berth

• Original turbines, ~ 1970 first operation,~ 270Khr, 3500 starts

• History of past inspections, berths, storage not complete


Centre collar fillet region

Corrosion fatigue, crack tip blunting observed, adjacent to main crack

Multiple initiation points on circumference

Loading•Main components that drive initial low cycle fatigue are well defined (Operational data, models) – OK,•Some uncertainty on transient loads on run through critical speeds (thought to provide a contribution to crack growth),Material Behaviour•Prior research (CEGB), plentiful data on pitting in these materials and fatigue crack growth thresholds - OK. No truly predictive model available – need the history! (corrosion pits to cracks…… crack tip blunting!),Inspection/Monitoring•Current vibration monitoring proven for this type and location of failure -OK,


Current EDF R&D: to address shortfalls in understanding of in-service material

behaviour in Coal/CCGT plant


Abundant opportunities to help the operator via improved material behaviour models and tools………………as long as they;

a) Are pragmatic where necessary and limits are identified,b) Ideally use data already collected and available,c) Are implemented with the operator in mind to guide and inform,

Must always balance information available on loading, materials and inspection (The ability to conduct some degree of sensitivity assessment will always be required). Is your hypothesis credible?

Current drive is to reduce inspection/maintenance cost, increasing need for condition monitoring, avoiding repairs-replacements until absolutely necessary………life extension will present further challenges and opportunities

Need for ‘tools’ that the operator can use to assess condition and importantly predict (Smarter approaches to data mining and processing is part of the solution)

Era of Big Data is here; Stations are currently not in a position to handle it effectively

EDF is moving in this direction

One final slide!

Summary

understanding the in-service behaviour of materials: why it’s … · 2018-04-27 · corrosion...

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