HIC tests were performed for eight types of X65 linepipes in various environments in which H2S partial pressures were in the range of 1x10−5 to 0.1MPa and pH was in the range of 2 to 5. The conditions governing HIC occurrence were investigated and the following results are obtained: (1) [HFe] was formulated as a function of ppH2S and pH ([HFe] =3.1+0.56logPH2S-0.17pH). (2) CAR of HIC increases with an increase in [HFe]. (3) [Hcrit] was expressed as a function of the length of MnS and the maximum hardness of center-segregation zone for the investigated TMCP steels (log [Hcrit] = (1.2-0.0020Hv)-1/4log(acrit)). HIC initiated in the lower critical hydrogen concentration for CR steel. CR steels are also expected to follow this equation, while first term (1.2-0.0020Hv) of this equation for CR steels is supposed to be lower than that for TMCP steels. (4) If the maximum hardness of center-segregation zone and the size of MnS are given, whether HIC occur or not can be predicted for a given environmental condition.

Subject
Steel surfaces, Materials, Piping, Hydrogen concentration, Microstructure, Sour environments, Linepipe, Partial pressures, Thermomechanically controlled processed steels, Maximum hardness, Steel, Hydrophobic interaction chromatography, Inclusions
Keywords:
HIC, linepipe, X65, TMCP steel, CR steel, sour environment, pH, hydrogen concentration in steel, inclusion, manganese sulfide
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1999
Association for Materials Protection and Performance (AMPP)
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