H2S Corrosion of Carbon Steel in Geothermal Fluids

Abstract

Corrosion of carbon and low alloy steels in H2S containing geothermal two phase fluids, separated steam and superheated steam has long been known to be controlled by the formation of adherent and continuous iron sulphide and iron oxide corrosion products that provide a barrier to the geothermal fluids. This corrosion control mechanism is effective within a narrow range of several factors including: H2S concentration, pH range, CO2 to H2S ratio and chloride concentration. H2S corrosion control can be lost for example by formation of acid condensate, precipitation of excess metal sulphides, deposition of heavy metals from two-phase or brine solutions and aeration. This paper will summarise the beneficial effects of H2S in many geothermal fluids and contrast these with instances where H2S corrosion control of carbon and low alloy steels is lost.