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The initiation and propagation of stress corrosion cracking (SCC) of high alloys in sour gas environments ware investigated mainly from the viewpoint of cathodic reactions. The most probable cathodic reaction to support the metal dissolution in the pitting and/ or cracking process was identified by means of electrochemical measurements. Among various environmental constituents, the influence of elemental sulfur on the dynamics and kinetics of the cathodic reaction was clarified. The role of elemental sulfur in the growth of pits and SCC was examined in detail. A suitable prediction technique to determine the SCC limits of high alloys was also discussed in relation to pitting corrosion as a precursor of SCC.

The corrosion behavior of corrosion-resistant alloys (CRA) in sour environments was investigated using a duplex stainless steel as a representative CRA. Changes in corrosion morphologies resulting from changes in environmental aggressiveness were elucidated. The application limits of CRA were shown to be determined by whether pitting corrosion occurred. A theory was proposed for predicting the corrosion morphologies and, thus, determining the application limits of the CRA. The validity of prediction by this new theory was confirmed by good agreement with results from long-term immersion tests and a field test for actual-size test pipes. Since this theory was based on the corrosion mechanism, it showed many advantages: The prediction was accurate, the results for one environment could be extended to other environments, and the prediction was conducted very quickly.

No abstract

Thecorrosion behavior, in particular passivation, of corrosion resistant alloys (CRAs)