A new procedure being developed in British Standards for the assessment of creep-rupture data is described and evaluated with trial data sets of gas turbine blading materials. The procedure is applied in phases. An important development by statistical experts is a framework for the main assessment phase that uses maximum-likelihood fitting methods for the treatment of unfailed test points and error variance. The framework selects models from a standard suite (together with any other linear models supplied by the assessor) using statistical criteria, but also incorporates metallurgical judgement. The improved representation of the experimental data compared with previous fitting methods and the associated statistical tests indicate that the new procedure can be used to derive rupture strength values for gas turbine materials with confidence.

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Many large-scale engineering structures, such as steam generation plant and petro-chemical plant, operate under conditions in which the key materials properties diminish with time. Detailed understanding of this degradation is essential for structural integrity assessments, and computerization of the collection and analysis of these materials data can realise significant savings in the cost of structural integrity assessment. The authors give examples of the various methods used to obtain data and to extrapolate rates of material degradation in order to predict failure. It is shown that, from the design stage, certain assumptions, some necessary, some dubious, are incorporated into standard materials property data. Such simplification may be necessary during design but represents a challenge for in-service assessment, when a statistical or stochastic approach is required. In addition, it is noted that hardly any publicly-available computerized materials databases contain the properties of alloys following service exposure. A natural extension of computerized assessment of data is to monitor the consumption of life during service. A continuous monitoring system is described which will take advantage of material degradation models to provide real-time analysis of plant integrity.

CM186 SX is a second generation Rhenium (Re) containing single crystal nickel-base superalloy, which exhibits improved creep and oxidation performance compared with its first generation counterparts. In this paper, the thermomechanical (TMF) response of coated and uncoated <001> single crystal nickel-base superalloy, CM186 SX is presented. In-phase (IP) and Out-of-Phase (OP) cycles were examined using coated and uncoated hollow dumbbell test pieces. Linear heating and cooling with a temperature rate of 6°C/s between 350 and 950°C was applied. The tests were mechanical strain controlled with strain ranges between 0.5 to 1.0%. Detailed examination of the experimental results revealed that variations in wall thickness of the hollow test pieces played a significant role in the set-up of the experiments and interpretation of the results. Finite element analysis was also performed to investigate the influence of the variation in wall thickness and its relevance to the experimental results. Overall, the results showed that the coating reduced the TMF life, particularly for OP cycles. Brittle cracking of the coating, especially at low temperatures, occurred at low strains. For the IP cycle the coating appeared to have less of an influence on life than for OP cycles. The results are compared with those from an earlier program using solid rectangular test pieces.