Stress corrosion behavior of X70 pipeline steel in simulated solution of acid soil

Stress corrosion cracking (SCC) of X70 pipeline steel in the simulated solutions of the acid soil environment of Yingtan in China was studied by slow strain rate test (SSRT), SEM observation of fracture surfaces and potentiodynamic polarization curves. Results show that SCC has a transgranular cracking mode at varying potentials. The applied polarization potential played an important role in facilitating SCC. Within anodic potential range X70 pipeline steel was controlled by anode process and unsensitive to SCC, but tended to be attacked by pitting and uniform corrosion. At cathodic potential range, X70 pipeline steel was controlled by a combined electrochemical process of anodic and cathodic processes at a higher potential range, but as the applied cathode potential lowered further, only controlled by the cathodic process. Under the two conditions X70 pipeline steel was sensitive to SCC, under the anodic/cathodic combined electrochemical condition, SCC originated closely together with pits, and under single cathodic condition, cracks originated sparsely and no pits appeared nearby.