 View the latest power industries news [June 2007] RWE npower have returned to full service a 500MW steam turbine generator at Fawley Power Station located in the South of England near Southampton.
The unit was taken out of service in 1994. Little preservation work was carried out on the plant, only the Generator had some preservation applied. Twelve years later, after a fifteen month project, the 500MW unit has been successfully returned to full output giving Fawley a generation capacity of 1000MW, helping to maintain a cost effective supply to RWE npower’s 6.8million retail customers.
The bulk of the work to return the unit to service was driven by physical deterioration of the plant, regulatory requirements, replacing spares removed to maintain running plant, obsolescence and known plant limitations. The success of the project is a great achievement for all the staff and contractors involved.
One significant plant item known to need substantial work was the external gas ducting which had been stripped of asbestos some time previously and had been left open to all elements of the weather.
 |
Restored gas ducting |
The critical timescale was the lead time to procure and manufacture forgings to convert two of the three turbine Low Pressure turbines to ‘fat shafted’ rotors.
The turbine High Pressure and the Low Pressure rotors were known to need work if the projected life were to be realised.
Of these, the most significant work content was to the LP rotors. LP’s 1 & 2 had not had the ‘fat shaft’ modification required to address Stress Corrosion Cracking problems associated with rotor discs of original design fitted with semi circular keyways.
|
Part Built LP Rotor on ‘fat shaft’ | The LP rotor disc Fracture Appearance Transition Temperature (FATT) was established through sampling, with further analysis to identify the theoretical crack size beyond which it would be unwise to operate. Through modelling the high risk stress area was shown not to be the shrink fit at the bore as originally expected but the hole for the disc drive button, which was fitted as part of the modification to stop disc slippage in the event of an overspeed due to a full load rejection.
The Intermediate Pressure turbine was not dismantled. There were no life limitation issues associated with the rotor and it was not deemed worth the expense or the extension to the programme. However, an internal inspection was carried out through access points which determined that parts of the rotor which were visible had light surface corrosion but no significant areas of concern.
The most significant piece of plant to be overhauled in-situ was the generator. All hose ‘o’rings and cooling system joints were renewed and all systems electrically tested. Part way through the project, it was agreed to remove the rotor to examine the winding wedges as two recent incidents have occurred at other locations having similar rotors.
|
Generator rotor removal |
One area of work to emerge and become significant was corrosion to various pipe systems, but particularly Auxiliary Cooling Water pipe work. Southampton Water is fully saline and over the years extensive damage had occurred to pipe work in the basement and sub-basement.
The amount of time the boiler had been shut down without preservation raised doubts about the internal condition of the tubes. Of prime concern was the condition of the magnetite layer and whether any of the U bends on the bottom of superheater / reheater elements had suffered corrosion. A significant number of tube samples and cold formed bend inspections showed the boiler to be in remarkably good condition, with oxide thickness as expected for the running hours since the last acid clean and no deterioration.
Obsolescence of electrical and control equipment is a recurring problem. The equipment that has had to be replaced has ranged from motor/pump units to protection relays.
The successful commissioning philosophy planned at the start of the project was to repair all known defects and omissions, carry out staged commissioning of plant in predetermined sub-sections and progressively integrate sub-systems into the whole.
|
Fawley Turbine Hall |
As a result of this project, RWE npower have gained a great deal of knowledge on returning plant to service following long durations of closure which will benefit their future world wide activities.
Back to top
|