Sulfide stress corrosion behavior of X65 line-pipe steels

摘要

Sulfide stress corrosion cracking (SSCC) behaviorof X65 line-pipe steels was studied by a constant elongation ratetest method to understand the sulfide stress corrosion mechanism.The SSCC test was carried out in aqueous acetic acid solutioncontaining chloride ion in the strain rate range of 5×10-5~5×10-7sec-1. The corrosion potential and the corrosion rate in theaqueous solution were -580 mVSHE and 4.2×10-3 Acm-2,respectively. Degradation of the mechanical properties such asyield strength and ultimate tensile strength was observed duringSSCC test. The SSCC resistance expressed by relative fractureenergy ratio decreased from 55% to 13.5% at an open circuitpotential of -580 mVsHE as the strain rate decreased from 5×1O-5to 5×1O-7/ sec. Anodic or cathodic polarization at about t ±100mV resulted in reducing the SSCC resistance, which was explainedby a model related to anodic dissolution and hydrogenembrittlement. The brittle fracture surface with intergranular andtransgranular cracking was observed. The corrosion products onthe failed surface were the mixture of iron oxide and sulfide.