Assessment of Corrosion Performance of Construction Materials in Geothermal Steam

Abstract

The reliability of geothermal power station performance depends to a large extent on the choi ce of appropriate materi s for the various station components. Geothermal development in respect to materials "know is at a stage where many of the peculiarities of the corrosion processes have been identified. The corrosion rate and the cracking susceptibi1ty of engineeri n g alloys depends on the chemical composition of the geothermal steam, in particular the hydrogen sulphide content. Although it is possible to predict the stable corrosion products which form, there is no quantifiable relationship for corrosion rates or degradation in mechanical properties, as a function of steam chemistry. The approach which will be adopted for the Ngawha geothermal field (NZ) for materials testing and selection is to measure steam chemistry and relative and absol corrosion performance and to compare these with the existing Broadlands database. In a 4 to 8 week test programe surface corrosion monitors - ASTM coupons and electrical resistance probes - will be exposed in test vessels ical designed for geothermal fluids. Cracking susceptibility will be assessed using the Slow Strain Rate technique. By recording steam is t r y at the same time, the corrosion results obtained can be compared with materials performance from other geothermal fields. The programme described is suitable for any prospective steam field in the Pacific region. The results obtained will provide information relevant to the exploitation of the field of interest and also expand the database avai 1 e to 1 users of geothermal steam.