Reliability centered maintenance minimizes costs and maximizes plant availability

Irish utility will utilize RCM at its new Poolberg CCGT plant

By Kevin Dodman

European Editor

As gas turbines have become more widely used for baseload power generation, utilities are adopting a variety of approaches to minimize maintenance costs and maximize availability.

The new 750 MW South Humber Bank power station at Stallingborough, eastern England, is currently being commissioned. The station is equipped with three ABB GT13E2 gas turbines, three heat recovery steam generators (HRSG) and an ABB steam turbine. When the plant enters commercial service its operation and maintenance will be the responsibility of IVO Generation Service (UK), part of Finland`s IVO Group. Paul Evans, general manager of the project company, Humber Power Ltd., comments that the seven-year operation and maintenance (O&M) contract makes IVO one of the largest independent power project operators in the UK. He says, “Whilst IVO`s broad experience is not unique, their operating experience in IPP projects is very useful. They are the only multiple plant operator in the UK and one of the few O&M contractors in the country.” The 360 MW Peterborough plant comprises two 120 MW gas turbines supplied by European Gas Turbines and a 120 MW GEC Alsthom steam turbine. Brigg is a 240 MW plant equipped with two 120 MW Vega 206 combined-cycle modules, each comprising two EGT Frame 6 gas turbines, two Stein Industrie HRSGs and a steam turbine.

According to IVO, expertise from Finland will be combined with local labor, with an envisaged ratio of 5 percent Finnish and 95 percent British. Power station manager Matti Saila comments, “The British workers will be trained the IVO way. Some will even be trained in Finland.”

Finnish O&M expertise has been widely promoted overseas by IVO in recent years, mainly based on the high levels of plant availability and the relatively low electricity prices charged to Finnish consumers.

IVO continues to build its reputation for high availability through the operating results at its own plants and through growing numbers of O&M contracts with industrial power plant operators. According to the company, the most usual bonus criteria included in these contracts is availability which provides a strong incentive to achieve the agreed targets. The same criteria is often applied to staff bonus payments, so that employees have a vested interest in ensuring that availability is as high as possible.

Table 1 shows the availability figures for IVO`s own thermal power plants in recent years. The figures shown represent energy-based availability during operation, which is calculated by dividing the maximum available energy by the theoretical maximum for each plant. The company`s target is a five-year average of 95 percent.

The Irish answer

While the trend towards independent power production brings opportunities for O&M contractors, many utilities, even the smaller ones, will continue to handle O&M themselves. An example is the Electricity Supply Board of Ireland (ESB).

ESB has an installed capacity of around 4,000 MW, and demand in the country has been growing at an annual rate in excess of 4 percent. A new combined-cycle gas turbine power plant was identified as the most cost-effective option to meet this growth. The site chosen is at Poolbeg, near Dublin, alongside an existing 510 MW steam power plant.

The project was to be implemented in three phases. First and second phases are gas turbines in simple cycle, and the third phase is the addition of two HRSGs and a steam turbine.

It was decided from the beginning that reliability centered maintenance (RCM) would be applied to the new plant. The reason for choosing RCM was its successful application on several pilot projects. These included:

– the cooling water system of a gas fired 270 MW steam unit,

– the fuel gas compressors for two 110 MW gas turbines and

– the cavern dewatering system for a 4 x 75 MW hydro-pumped storage station.

RCM is a structured approach which is used to determine the maintenance requirements of equipment and was developed by the aviation industry. The process is based on an analysis of the operating context of the plant, identifying its functions, types of functional failures and likely failure modes. These, together with details of the effects of each type of failure, are recorded on an “Information Worksheet.” This information is then used to produce a “Decision Worksheet” which details the tasks to be carried out, by whom and how often.

According to Gilroy, O`Connor and Hamann [1], “The methodology used by ESB is team-based and employs the knowledge and experience of the people whose job it is to operate and maintain the plant. The RCM process is kept on track at the analysis meetings by the facilitator who chairs the meetings and who is a specialist in RCM.”

After ESB decided to apply RCM to the gas turbine to be installed during Phase 1 of the project, a detailed RCM specification was prepared and discussed with the companies that were bidding to supply the machine. The input required from the potential supplier is shown in Table 2.

The bidding process resulted in the award of a contract to Siemens of Germany for the supply of a 150 MW V94.2 gas turbine. Once the contract was signed, meetings were then scheduled between Siemens and ESB personnel to familiarize Siemens management with the RCM concept and the level of involvement required.

Implementing the RCM process involved 17 individual studies covering all the areas of the plant listed in Table 3. A team of eight people was assigned to each study.

Gilroy, O`Connor and Hamann comment, “A schedule of meetings was agreed and issued to all those taking part. Meetings were 3.5 hours long with a half-hour break. There were two meetings each day for five days each week. This meant that Siemens staff who were involved in more than one plant area had seven hours of meetings each day or 35 hours each week.”

Following completion of the meetings, each facilitator spent two to three days reviewing the “Information” and “Decision Worksheets” before presenting them in a form that would be more easily understood by the auditors.

On average, each of the studies resulted in 22 technical questions which were referred to Siemens. However, one study resulted in 100 questions. When all the questions had been answered and the final RCM results had been audited and agreed, a coherent set of mostly time-based maintenance tasks was compiled. These were then fed into the station`s computerized maintenance management system.

A number of ongoing monitoring tasks were also identified and integrated into hourly, daily or weekly operational checklists as appropriate.

Following this rigorous RCM development program, ESB felt that a level of plant understanding had been achieved which would have been difficult to reach through normal training courses. In addition, although the RCM exercise did not alter the existing maintenance regime or the scheduled maintenance costs for any of the hot gas path components, ESB is predicting a large decrease in unscheduled maintenance costs when compared to similar machines located elsewhere.

The plant`s revenue stream will carry heavy penalties for unscheduled unavailability and unscheduled grid disconnections, so minimizing these was a major objective of the program.

According to Gilroy, O`Connor and Hamann, the RCM program is a comprehensive operation and maintenance procedure that is accurate and is easily understood and implemented. The training for the RCM program was also more comprehensive than standard training courses. Because the logic underlying the operation and maintenance procedures is extensive and has been documented, it can be used as a diagnostic tool, for training of new staff and also as a basis for any future plant modifications.

ESB is expecting RCM to result in appropriate operation and maintenance tasks being carried out at cost-effective time intervals. It also anticipates that there will be a long-term improvement in plant performance.

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1 “Reliability Centered Maintenance Applied to a 150 MW Gas Turbine,” Brian Gilroy and Frank O`Connor, ESB, and Bernd Hamann, Siemens KWU, POWER-GEN Europe `96 Conference, Budapest, Hungary, June 26-28, 1996.