Relation between environmental factors and general corrosion rate of martensitic stainless steel for OCTG (API-13Cr and super 13Cr steels) under CO_2/H_2S environment

摘要

The effect of five factors, CO_2 partial pressure, H_2S partial pressure, temperature, chloride content and bicarbonate content, on corrosion rate of API-13Cr and super 13Cr steels under sweet and light sour environments was systematically investigated and comprehensively analized. Since an essential reaction determining corrosion rate in CO_2 environment is the direct reduction of carbonic acid, the carbonic acid activity becomes a key parameter to synthesize the effects of environmental factors, instead of pH. The CO_2 corrosion rate is equated principally as a function of carbonic acid activity and temperature. The effect of slight amount of H_2S and effect of alloying element content are also described quantitatively.