CO₃^2--HCO₃^- stress corrosion test of welded joint for X80 pipeline steel

The susceptibility to stress corrosion cracking (SCC) of the welded joint of X80 pipeline steel in solution of 0.5 mol/L Na₂CO₃ and 1mol/L NaHCO₃ was investigated by means of slow strain rate testing (SSRT) and scanning electron microscope. The results showed that all tensile test specimens cracked in welded joint and heat affected zone (HAZ). The general tendency in the studied potential range was that with positive increasing of potential, reduction in area, fracture time and elongation of specimens increased, and mean crack growth rate of SCC and the susceptibility to SCC decreased. At cathodic potentials, obvious quasi-cleavage fracture was observed in the fracture area of specimens. At open circuit potential and anodic potential, ductile fracture was the common fracture pattern. The mechanism of the stress corrosion could be explained with anodic solution theory and hydrogen induced cracking.