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In order to develop databases of creep information for design purposes for steels and other alloys, large-scale test programmes were undertaken involving several casts , product forms, etc. Little attempt was made to separate materials variables from those due to testing, and, even for simple measures of performance like life to rupture, considerable variability occurred and scatter-bands were large. Design information was obtained using statistical methods and curve fitting to predict long-term performance. The simple design rules incorporated safety factors which, along with the relatively inaccurate materials data , resulted in very conservative designs for power plant and pressure vessels.

This paper presents a review of the information available on the properties and performance of the strong highly corrosion resistant alloy IN939 which is being used increasingly for vanes and blades in land-based gas turbines. Particular emphasis has been placed on the large amount of new data now available from the European Collaborative Project COST50 and it will be seen that the behaviour of the alloy has been well characterised although there is insufficient information on the low cycle fatigue performance. It is shown that the alloy compares favourably with IN738LC and in service has superior corrosion resistance.

The rapid development of metallic materials for high temperature applications that occurred during the 1960fs and early ’70s has given way in the last decade or so to a consolidation phase with the emphasis on optimisation and detailed improvement in alloys. Innovative developments in materials processing technology (melting, casting, fabrication) has enabled the upward trend in temperature capability and loadcarrying capacity to be maintained and considerable scope for further developments in this area remains through the use of computer-aided techniques. Also there has been an increase in the effort directed towards a better understanding of the behaviour of alloys in service as a basis for more effective usage and more efficient design and this activity will undoubtedly develop and intensify in the decade ahead.