Resistance of the welded joint of X70 steel for main gas pipelines against corrosion-mechanical cracking under cathodic polarization in near-neutral pH solutions

ABSTRACT Resistance of welded joint of X70 steel welded using Sv-08G1NMA and OK 10-74 flux wire against stress-corrosion cracking in near-neutral pH solution NS4 was investigated by slow-strain rate method, voltammetry, optical and scanning electron microscopy, electrolytic permeation of hydrogen. It was established that the stress-corrosion cracking of welded joint occurs through the base metal in the range of potentials more positive than −0.921 V by the anodic dissolution mechanism, more negative than −1.050 V is consistent with a hydrogen embrittlement mechanism, and in the potentials' range from −0.921 V to −1.050 V – both by the anodic dissolution and hydrogen embrittlement mechanism. The susceptibility to stress-corrosion cracking coefficient KS increases with the polarization potential shift −0.750 V → −0.950 V → −1.050 V as follows: for the welded joint – 1.1 → 1.16 → 1.35, for X70 steel as 1.0 → 1.12 → 1.0.