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The aim of the present study was to evaluate the corrosion resistance of weldments produced by the Indirect Electric Arc technique. The material studied was API grade X-65 steel, which was corroded in NACE solution saturated with H 2 S. Three different temperatures were employed, room temperature (25uC), 37uC and 50uC. The test methods used included potentiodynamic polarisation curves, hydrogen permeation measurements and slow strain rate tests. The anodic corrosion current density and sulphide stress cracking susceptibility of the weldments were found to be unaffected by temperature over the range 25-50uC. However, values of the steady-state hydrogen permeation current, hydrogen permeation rate, effective diffusion coefficient, and the concentration of hydrogen atoms at the entrance side all increased with temperature. The cracking of the X-65 weldments is explained in terms of a hydrogen embrittlement mechanism.

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Stress corrosion cracking (SCC) susceptibility of API X65 steel nonconventionally heat-treated was evaluated through slow strain rate tests (SSRTs) using the synthetic soil solution NS4 at 20, 40 and 60 8C. Polarization curves (PCs) and corrosion potential (E corr ) measurements were also performed. The non-conventional heat treatment (HT) was made by heating plates at 1050 8C for 30 min followed by water quenching. The tensile strength of the heat-treated plates increased to values similar to API X80 steel. The SCC index obtained by ratios of mechanical properties indicated that X65 steel without HT is not susceptible to SCC whereas with HT is slightly susceptible to SCC. The SCC mechanism in the soil solution in the heat-treated plates was influenced by hydrogen diffusion as confirmed by the internal cracks and the brittle fracture observed in the specimens. The electrochemical study suggests that the corrosion process of X65 steel with and without HT occurs via a mix mechanism where the charge transfer resistance is influenced by a mass transfer process. Crevice corrosion features were found in the surface of the steel. It is likely that this type of corrosion could have sensitized the X65 steel and induced cracks when the steel was under tensile stress.

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