| Abstract |
The successful use of mild and low alloy steels in geothermal steam depends on the formation and properties of corrosion product films which cover and protect the underlying metal. Significant corrosion takes place only in a layer of condensate formed due to heat losses, such as in steam pipes. The corrosion products and the corrosion rates depend on temperature and steam condensate chemistry. Corrosion rates have been obtained and corrosion products dentified for coupons exposed at the Broadlands BR 22 corrosion test rig. Initially, on a corrosion-product film free surface, corrosion rates are unacceptably high but decrease, under certai n condi ti ons, wi t h i ncreasi ng exposure time as corrosion products begin to cover the surface and thicken. The high hydrogen sulphide content of the steam at BR 22, Broadlands, leads to the formation of a series of iron des, macki nawi t e, cubic ron sulphide, t r o i 1 t e, pyrrhotite and pyrite. These compounds have been and characterised using X-ray di tion and optical and electron microscopy. In steam and bore fluid environments there was a trend to sulphur rich iron sulphides with increasing time of exposure. A layer of magnetite adjacent to the metal was observed which was protected from the corrosive solution by the iron sulphides. The uniformity of the corrosion products was greatest in bore fluid compared with separated steam which corresponds with the lower corrosion rates observed in the former environment. |