Stress corrosion cracking of weld joint of pipeline steel X70 in near-neutral solution

The behavior of stress corrosion cracking(SCC) of the weld joint of steel X70 in a near-neutral solution was investigated by means of slow strain rate testing(SSRT),SEM and electrochemical measurement.The results show that stress corrosion cracks initiate in heat affected zone(HAZ) of the specimens.The susceptibility to SCC increases with the decrease of potential in the test solution,but when the potential is too negatively depressed,the susceptibility to SCC decreases.Besides,with the reducing of pH value and increasing corrosion rate,the susceptive potential range becomes more negative.At cathodic potentials,obvious quasi-cleavage fracture is observed on the fracture surface.Transgranular SCC occurs at the edge of the fracture.The mechanism of SCC in HAZ of specimens is analyzed,hydrogen-induced cracking together with anodic dissolution plays an important role in the SCC of pipeline steel X70.The two mechanism combines to cause much more serious SCC of steel X70 at certain potential.