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Modern working practices in power generation create new corrosion challenges

The need

The greater contribution of renewable energy to grid electricity has created new challenges for the gas-fired power stations that continue to form the backbone of our electricity supply. To balance fluctuating demand, power stations are moving to 'two-shifting' operation with regular start-up and shut-down; during these periods, steam turbines experience stress and environment transients that can provoke modes of corrosion failure unseen under steady operation.

Failure of turbine systems is very rare, but since it can be catastrophic, with costs as high as £150m, maintaining integrity of steam turbine components and predicting their lifetime and maintenance requirements is critical to sustaining flexible operational capability in a diversified energy supply network.

The impact

We have established ourselves as the world-leading centre for research on environmentally-assisted cracking of steam turbine blades and rotors. We combine state-of-the-art crack measurement techniques, computational modelling and advanced material characterisation to quantify damage development and improve engineering life prediction. Our unique testing capability allows sustained tight control of environmental exposure over tests up to years in duration.

Crack growth rate data for steam turbine materials, produced by NPL, are already being used by major operators to choose inspection intervals and to assess the impact of instances of out-of-specification water chemistry on the risk of damage or failure. Our work has also aided assessments of the viability of novel, next-generation alloys and alternative turbine designs.

The measurement methodology used by NPL to quantify the very slow growth rate of small cracks is currently being developed into the ISO/FDIS 21153 international standard on measurement of environmentally-assisted small crack growth rates. The Electric Power Research Institute funded a collaboration involving NPL to create guidelines for the electricity generation industry, enabling informed assessment of the likelihood of cracking from corrosion pits in rotor steels.

Our research was included in guidelines prepared by Liberty Specialty Markets and Liberty Mutual Insurance to inform insurance underwriters about the impact of new working practices on corrosion risks.

Related:

Corrosion services

Chemical, mechanical and surface characterisation

Electrochemical consultancy and modelling