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ABSTRACTMetallic structures operating at high temperatures can have creep as a life-limiting mechanism. The limit can arise by nucleation and growth of creep cavities that eventually merge becoming the leading damage of the fracture mechanisms. Understanding and modelling for creep cavitation can therefore help in prediction of structural safety and condition of such structures. The present paper will introduce a new model to predict creep cavitation damage so that the associated creep strain is also modelled out of the predictive expression without losing accuracy in the time to critical damage and corresponding residual life. The model was verified for OFHC copper, low-alloy 0.5CMV steel and higher-alloy X20 steel, to cover a wide range of polycrystalline metals and their microstructures. The new model performed as well as or better than the classical approach which requires access to measured strain. The model was applied to predict creep cavitation damage from time, stress and temperature as predictive variables.

Self-heating of coal depends partly on intrinsic, coal-related factors. This article aims to discuss the Smith–Glasser index as a potential indicator of the self-heating propensity of a large set of bituminous coals with similar heating value but different origins. For this purpose, recorded properties and experience were reviewed for 7.5 million tonnes of coal delivered to the same power plant operator. The results suggest that the propensity to self-heat can be conveniently indicated by Smith–Glasser index that only involves routinely measured moisture and volatile contents of coal. The results appear consistent with the observed incidences of self-heating in storage.

Oxide growth and thermal degradation of three ferritic SOFC interconnector alloys have been investigated. The materials included a standard grade (alloy 430) and two alloys (Crofer 22 APU, ZMG 232) specifically designed for interconnector service. All alloys appear to follow parabolic oxidation up to 500 h at 740{degree sign}C in air. During oxidation, a consistent decrease of iron and increase of chromium and manganese were observed in the surface oxide. Some chromium transport was detected on the cathode side surface of the cell after 500 h at 740{degree sign}C. The results emphasise the importance of appropriate coating of the interconnectors, to prevent chromium poisoning on the cathode. A natural coating material would be similar or compatible with the ceramic cathode. Such a coating also has the additional advantage that simpler and cheaper steel grades could be used as the interconnector material.

Supercritical (SC) service at high operating values aims for good plant efficiency, but the waterside oxidation resistance can then become life-limiting. In this paper, selected materials and modeling options are compared for life assessment under waterside SC oxidation, particularly for thermal power plants that increasingly need to accommodate cyclic service, fast ramping, and low minimum loads to an extent to which the conventional design practices and materials solutions only partially accounted. For example, the life reduction by high-temperature oxidation and corrosion via lost load-bearing wall thickness is more easily accommodated than the impact on crack growth or material ductility.

The advantage of using supercritical water (SCW) systems for power generation is based on the increased thermodynamic efficiency when operating at higher temperature and pressure. Steam oxidation has become an important issue for power plants as operating temperatures increase from current to 650°C and even higher. Three alloys, FeCrAlY, NiCrAl, and Sanicro 25, were investigated in an elevated steam oxidation condition. All three materials showed relatively good initial SCW oxidation resistance, but after 100 hr, the oxidation rate of FeCrAlY increased rapidly compared to NiCrAl and Sanicro 25, which both showed a steadier and lower rate of oxide growth and weight gain.

Oxide growth and thermal degradation of three ferritic SOFC interconnector alloys have been investigated. The materials included a standard grade (alloy 430) and two alloys (Crofer 22 APU, ZMG 232) specifically designed for interconnector service. All alloys appear to follow parabolic oxidation up to 500 h at 740{degree sign}C in air. During oxidation, a consistent decrease of iron and increase of chromium and manganese were observed in the surface oxide. Some chromium transport was detected on the cathode side surface of the cell after 500 h at 740{degree sign}C. The results emphasise the importance of appropriate coating of the interconnectors, to prevent chromium poisoning on the cathode. A natural coating material would be similar or compatible with the ceramic cathode. Such a coating also has the additional advantage that simpler and cheaper steel grades could be used as the interconnector material.