scope:

Abstract

There are strong environmental and economic pressures to increase the thermal efficiency of fossil-fired power stations. This has led to a steady increase in steam pressure and temperature in current worldwide plans for ultra supercritical (USC) power plants. To meet the requirements of such plant it is necessary to ensure that suitable steels are available for high temperature thick section components, so that the more demanding conditions do not result in impaired life or reliability. Developments in high strength ferritic steels indicated that such steels had the potential to allow steam temperatures up to about 620°C. However much testing and qualification of fabricated full size components was needed to substantiate this potential.

Thus an international consortium with participants from Japan, UK, USA and Denmark, under EPRI leadership was formed to develop the database needed for commercial acceptance of these steels. The first phase of the project started in 1991 and was completed in 1995. It validated the commercial readiness of two ferritic steels with a long-term creep strength approximately 30% higher than that of existing commercial steels. These steels are now included in the ASME Boiler and Pressure Vessel Code as grades P-92 and P122, respectively. In the second phase of the project, to be reported in this session, forged equivalents of the two steels were qualified and ASME code approved, further micro structural and welding studies were performed, full scale commercial headers were fabricated and installed in an USC plant and an experimental header was tested to failure in an high pressure, high temperature test rig.

Edited by: R. Viswanathan, W.T. Bakker, J.D. Parker