Rosenhain Centenary Conference - 1. Engineering requirements 1.6 Gas turbine requirements Discussion

Abstract

The C.E.G.B. interest in gas turbines has developed steadily during the past decade from auxiliary service functions in large fossil-fuelled power stations to small power stations, entirely of gas turbine plant, whose principal purpose is to meet peak load demands. Here the ability of the gas turbine to be started up very rapidly is an important attribute. The great majority of these gas turbine units have been derived from the use of established aero engines, such as the Avon and Olympus, as gas generators to drive a power turbine. These units are subject to planned maintenance after, at the most, 2000 h of operation when burning distillate fuel. There have been instances of blade corrosion problems due to sulphidation attack and related high sodium levels in the fuel; the solution to this problem has been to control the fuel quality. Two prototype industrial gas turbines, each of ca. 55 MW output, are due to be commissioned at one of the Board’s power stations in the near future. Here the aimed-for operational life before undertaking planned maintenance will be ca. 20000 h. This places greater emphasis on the need to appreciate any time-dependent process affecting engineering performance. From a materials standpoint these are corrosion resistance, thermal and high strain fatigue and creeprupture. Specific problems under study in blade materials are the consequences of corrosion-resistant coatings upon the mechanical properties and the limits of acceptability of defects. The latter involves crack growth monitoring under conditions of creep, high strain and high cycle fatigue. As the future emphasis should be directed towards gaining a better understanding of material behaviour in the projected engineering situations the physical metallurgist has to think beyond the metals themselves and consider, for example, the interactions that occur between metals and coatings.