New techniques of reliability and their application to offshore wind farms
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New Techniques of Reliability and their Application to Offshore Wind Farms. European Offshore Wind 2009, Stockholm Technology and Innovation Offshore Wind Turbine Reliability 16 th September 2009. Introduction - Michael Starling. Background

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New Techniques of Reliability and their Application to Offshore Wind Farms

European Offshore Wind 2009, Stockholm

Technology and Innovation

Offshore Wind Turbine Reliability

16th September 2009

Introduction - Michael Starling


  • Chartered Mechanical Engineer, started work in 1979, worked for BMT since 1990

  • worked in Renewable Energy since 2004

  • specialise in engineering and risk

  • applied to transport, energy and the built environment

    Current/recent projects

  • construction, transportation and installation system for concrete offshore wind turbine foundations (with Gifford)

  • reliability, maintainability and survivability guide for the European Marine Energy Centre in Orkney

  • navigation impact assessment of a tidal fence across the Severn

Introduction - BMT

British Ship Research Association


British Maritime Technology Ltd

established 1985 (now BMT Group Ltd)

Reliability – Some major projects

  • Air to Air Refuelling Tanker Aircraft

Reliability – Some major projects

  • Channel Tunnel Trains

Reliability – Some major projects

  • Ro Ro Ferries

Reliability – Some major projects

  • Offshore and Subsea Oil & Gas

Reliability – Personal contact with my work

  • Aircraft Fuel Pumps – Airport Baggage Handling – Airport Trains – Metros - Escalators

Reliability – A current project

  • Pulse Tidal Generator

Who achieves high reliability?

Aircraft achieve high reliability

  • An A330 will typically achieve greater than 98.5% operational availability

  • and they guaranteed it from day 1

How do they achieve high reliability?

Fundamental economic driver

  • A complete common purpose between safety, reliability, performance and profitability

International standards driven

  • Everything is specification, certification and approvals led

Technical drivers

  • Complete hierarchy of specification and certification from the smallest component to the whole aircraft and from an individual maintainer to the operator

  • Approvals are technical, organisational and individual

  • There is international commonality and transferability

Functional drivers

  • Aircraft design based on equipment functionality and integrity

    • and on appropriate redundancy

Appropriate redundancy

  • Redundancy “enhances high integrity”

  • It does not “compensate for low integrity”

What process do they follow?

Formal processes of assurance

  • Defining what the equipment, operation or service has to do

  • Designing, operating and maintaining it to do it

  • Finding some assurance that it will “work and keep on working”


  • Aircraft Achieve High Reliability By

  • Reliable Design

  • demonstrated by

  • Reliability Assurance

  • based on

  • Integrity, Functionality, Appropriate Redundancy and Comprehensive Testing

  • mandated by

  • Specification, Certification and Approval

  • and controlled through life by

  • Monitoring and Modification

Three topics for rest of this paper

  • Design for reliability

  • Maintain for reliability

  • Success-based reliability

Design for Reliability

How reliable does a device have to be?

  • Common measure of reliability is Mean Time Between Failure (MTBF)

    • Common belief that a 10 year MTBF means that the equipment will last about 10 years

    • That is a 10 year life not a 10 year MTBF

    • After 10 years running approximately 63% of “10 year” MTBF equipment will have failed

    • For 1% failed the MTBF needs to be approximately 1,000 years

    • Some MTBFs

      • Offshore Wind Turbine, 1 month

      • Domestic Boiler, 5 years – Double Glazing, 10 years

Does redundancy help?

  • Typical solution to poor reliability is redundancy

    • Works well for repairable systems

    • Works badly for non repairable systems

    • It works better for non-repairable systems when the equipment is reliable

    • It is often better to spend money on increasing integrity rather than fitting redundancy

Design for reliability - conclusion

  • Design for high integrity

  • Backup with redundancy only if easy to repair

Maintain for Reliability

What type of maintenance can I do?

  • Preventive Maintenance

    • The routine activities to prevent failure, i.e. the servicing

    • Typically done to a planned schedule based on time or usage

    • Ideal is to do when no wind resource available

      Corrective Maintenance

    • The activities required to respond to failure, i.e. the repairs

    • Typically done to a reactive schedule

    • Ideal is to avoid

  • Predictive Maintenance

    • The activities required to respond to an indicator of future failure, i.e. maintenance triggered by some measurement of condition

    • Ideal is to be able to defer predictive maintenance to times when preventive maintenance takes place

  • Classical “Bathtub”

  • Wear-out

  • Degradation

  • Initial Success

  • Steady

  • Early Life Failure

What type of maintenance should I do?

  • Depends on the nature of the failure

  • Classical “Bathtub”

  • Bit worse

  • Made better

  • Wear-out

  • Bit better

  • Degradation

  • Initial Success

  • Bit better

  • No difference

  • Steady

  • Made worse

  • Early Life Failure

Effect of time scheduled maintenance

  • Classical “Bathtub”

  • Bit worse


  • Made better


  • Wear-out


  • Bit better

  • Degradation


  • Initial Success

  • Bit better

  • No difference


  • Steady


  • Made worse

  • Early Life Failure

Example using of aircraft data

Maintain for reliability - conclusion

  • Define maintenance based on understanding the types of failure

Success-based reliability

A bit of history

  • These success-based techniques grew out of failure

    • failure of reliability techniques to lead to change

    • failure of techniques to improve reliability

    • failure of techniques to be value for money

      Led to questioning the fundamental reliability techniques

    • techniques are focussed on failure

    • should they be focussed on success?

Focus on success

  • For many years those of us in reliability have concentrated on understanding and eliminating failure.

    • why things fails, when they fail, where they fail and how to stop them failing are questions that are examined in great detail.

  • However in doing so we may have overlooked the equal importance of understanding and creating success.

    • why things work, when they work, where they work and how to make them work are equally, or perhaps more important, questions.

How to achieve success? – via assurance

  • to define what the equipment, operation or service has to do

  • to design it and operate it to do it

  • find some evidence that it will work and keep on working.

  • identify and eliminate threats to success.

Assurance via developing a reliability case

  • Part Technical Process

    • that aims to provide the “Evidence of Success” and

    • identify and eliminate the “Risk of Failure”

    • and produce a “Reasoned Argument” supporting expected performance

  • Part Management Process

    • that aims to provide “Scrutiny” that the evidence and argument is valid

  • Assessing the quality of the evidence

    • Proof?



    Producing a reasoned argument

    • The reasoned argument leads to

      • a claim of expected reliability performance

      • an assessment of the level of risk associated with the claim

    There is an obligation to use all evidence, the supporting and the opposing

    Typical Management Process – providing scrutiny

    This philosophy is not new

    • Rene Descartes

    • 1596 - 1650

    • Knowledge should be based on

    • “Proof and evidence rather than just faith”

    • and

    • “Nothing should be accepted unless subject to scrutiny”

    And finally

    • Some advice on how to achieve high reliability

      • Specify the reliability you want

        • and specify it in terms meaningful to your business

      • Design to achieve it

        • but beware the false promise of redundancy

      • Build up a Reliability Case

        • and expose it to scrutiny (and don’t always believe your experts!)

      • Maintain for reliability

        • base your maintenance on understanding failure


    Michael Starling

    BMT Fleet Technology

    +44(0)780 3925110

    Typical Technical Process – building up evidence

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