Resistance of the Welded Joint of X70 Steel for Main Gas Pipelines Against Corrosion-Mechanical Cracking Under Cathodic Polarization in Near-Neutral pH Solutions

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 the slow-strain rate method, voltammetry, optical microscopy, scanning electron microscopy, and electrolytic permeation of hydrogen method. It was established that the stress-corrosion cracking of welded joint occurs through the base metal in the range of potentials more positive than −0.92 V by the anodic dissolution mechanism, more negative than −1.05 V is consistent with a hydrogen embrittlement mechanism, and in the potentials’ range from −0.92 V to −1.05 V, both by anodic dissolution and a hydrogen embrittlement mechanism. The susceptibility to stress-corrosion cracking coefficient K_S increases with the polarization potential shift −0.75 V → −0.95 V → −1.05 V as follows: for the welded joint as 1.1 → 1.16 → 1.35, for X70 steel as 1.0 → 1.12 → 1.0.