An approach to power station boiler and turbine life management

The de-regulated electricity market which has existed in the UK for around 15 years has led to energy companies operating their power plant flexibly to maintain profitability in a very competitive commercial environment. To do this, the company maintains a very strong engineering capability in the area of structural integrity of boiler components and high temperature rotating plant.

The key issues for the older 500 MW boiler plant, which is daily two-shifted and operates at temperatures well into the creep range for low-alloy steels, are fatigue and creep damage, the latter being influenced greatly by the operating hours seen by the older coal-fired units which have exceeded their design lives. Major components of the boiler which are subject to rigorous and thorough examination are headers, drums and high-energy steam pipework. Methodologies include on-line plant damage analysis for controlling degradation and optimising start-up procedures, plant modifications, innovative repair and retro-fitting with improved materials.

Steam and gas turbine rotors operate at high speeds at elevated temperatures. Maintaining rotors in a good commercial and safe operational condition in compliance with any regulatory requirements can also bring increased efficiency and reduced costs, for example by incorporating proactive measures into planned overhauls.

Procedures have been developed for both prevention of creep cavitation cracking and assessment of bore high strain fatigue life (for hollow rotors). These use material data, temperature and stress information along with the results of NDE inspections to determine any operational constraints (starts, temperatures, and running hours) which may be necessary. Vibration, which can be an indication of cracking in an operating rotor is monitored remotely and on-line.