Testing valves for leakage costs little but can save a lot. Energy drops across many valves exceed 1,250 Btu/lb, and leakage rates can be higher than 1,000 lb/hr. In a plant burning fuel priced at £5 to £10 per million Btu, a single valve with a modest leak (Figure 1) can account for £50,000 to £100,000 in lost fuel costs annually. That's at least an order of magnitude greater than the £2,000 to £5,000 cost to replace it.

Fig 1 Look familiar? Over one year, the cost in wasted fuel of ignoring a leaking isolation valve is typically many times the cost of replacing it

Theory into practice

AES Red Oak (Figure 2) is an 832-MW gas-fired 3 x 1 combined-cycle plant in Sayreville, N.J., that entered commercial service in September 2002. An energy trading company buys power from the plant under a 20-year tolling agreement that includes incentives for improving its heat rate.

Fig 2
Quality shutoff valves often weren't installed under its turnkey contract.
An ultrasonic testing and valve
replacement program paid immediate
dividends in the form of lower unit heat rates
Courtesy: AES