As more and more gas turbines make their way from the drawing board to the plant, attention will begin to shift from ensuring proper installation practices to ensuring proper MRO (maintenance, repair and operations) practices. Smaller crews, increased turbine complexity and the economic imperative of high availability all reinforce the criticality of gas turbine maintenance and repair. The $36 million investment in an F-class turbine will be wasted unless that turbine is effectively maintained, and then repaired when necessary, to guarantee its availability over a long operating life.
Advanced, high-performance turbines are particularly sensitive to maintenance concerns. The existing fleet of 150-plus F-class turbines is expected to at least triple by 2004. “Yet while expected overhaul intervals for F-class turbines are about 24,000 equivalent operating hours (EOH), the initial experience with early F-class machines has been that many hot-section components, particularly first-stage blades, have required replacement at 60 percent of expected EOH,” explains John Sheibel, who manages EPRI’s life management program for advanced turbines. The price of a blade failure is substantial. A new blade row can cost between $2.0 and $2.8 million, compared with about $700,000 for a row of conventional blades.
Turbine owners also must keep an eye on the replacement parts market. According to Sheibel, during the life cycle of the turbine, the cost for replacement parts essentially equals the initial investment in the gas turbine, and the price of replacement parts is going up. So even if the initial investment is recovered in 8-10 years, sustaining the viability of that investment remains a costly prospect.
The secondary market-obtaining OEM-quality parts from non-OEM vendors-is a viable cost-saving opportunity, but the market for advanced-class turbine parts is still developing. Some users are reportedly exploring internal reverse engineering projects to reduce costs or improve performance, but this takes dedicated talent and may void certain OEM guarantees.
Since many of the new turbines-frame-size and aeroderivatives-are being installed to satisfy and capitalize on peak power demand opportunities, it is in the turbine owner’s best interests to effectively maintain their machines. “It’s always our burden,” says Mike Pollard, superintendent of combustion turbine technical support for Carolina Power & Light. “The big costs are in lost generation, particularly for peaking units, which have to be available to run when needed, or we have no use for them.”
To ensure high availability, several plant practices should be in place, according to E.J.I. Westerhof of EPON, a utility and plant developer/operator in the Netherlands, which has extensive experience with advanced turbines from GE, Siemens and ABB Alstom:
- Highly skilled personnel – Extensive training programs should be available to prepare employees for working with advanced technology. A simulator that duplicates the control instruments in the plant is typically requi red.
- Equipment selection – Where applicable and economic, redundant configurations are preferred since even the best equipment can fail. In combined-cycle units, for example, feedwater pumps, circulation pumps and condensate pumps can be doubled up.
- Inspections – Inspections should be carried out on a regular basis to optimize reliability and availability. The latest design video cameras and/or borescopes should be used to gather as much information as possible.
- Spare parts – A formal system for controlling spare parts is essential, enabling the plant to track high-value parts and assist in developing an optimal outage schedule.
- Condition monitoring – An effective condition monitoring program is important to protect the unit against forced outages. This monitoring program should include vibration analysis, pyrometry and dynamic pressure systems.
Evaluating a gas turbine maintenance program against these, and probably other categories, will help in keeping availabilities in the ranges necessary for economic operation.
Recognizing the importance of gas turbine MRO in today’s environment, this special section offers several valuable features and references. Ron Natole of Natole Turbine Enterprises describes the important points to consider when making gas turbine component repair decisions and when selecting a repair shop. This is followed by an alphabetical listing of the majority of U.S. repair shops for frame-size gas turbines on pages 60 through 75; the listings provide short histories, contact information, shop details, and capabilities.