Elastoplastic Fracture Mechanics Approach to the Crack Growth Rate Computation of Modified Pipe Steels

A mechanophysical model for crack growth kinetics computation on stress corrosion fracture of modified 06G2BA and 08KhMCHA pipe steels is adequately expressed through the plane stress-strain state d alpha/dt and dJ/dt ratios that are dependent on the strain crack tip rate. The crack growth accelerated by an aggressive environment occurs under static and cyclic loading due to transient dissolution and repassivation processes at the crack tip. Such accelerations are divided into three categories, determined by the strain rate: mechanical cracking (fatigue crack and stationary plastic crack), corrosion-accelerated mechanical cracking (corrosion fatigue and corrosion-accelerated plastic crack), and sulfide stress corrosion fracture. Metallographic studies revealed the change in the crack nucleation and propagation mechanisms, from transcrystalline to intercrystalline, related to the viscoplastic and brittle structure of steel specimens cyclically loaded and simultaneously affected by a corrosive environment.