Micro-electrochemical characterization of the effect of applied stress on local anodic dissolution behavior of pipeline steel under near-neutral pH condition

Local anodic dissolution behavior of smooth and pre-cracked X70 pipeline steel specimens Under applied stress were investigated by micro-electrochemical measurements and numerical simulation. The results demonstrated that the anodic dissolution rate of steel is enhanced by applied tensile stress. Corrosion of the stressed steel is accompanied with the formation of a layer of corrosion product deposit on electrode Surface. However, the deposit layer does not provide effective protection to the underlying steel for corrosion attack due to its loose, Porous Structure. Under small tensile stress, the stress-enhanced dissolution of steel is not significant. With the increase of stress level Lip to 80% of yielding strength of steel, the activity of the steel increases remarkably, resulting in a significant enhancement of the anodic dissolution of steel. A stress concentration is developed at the crack-tip and enhances significantly the local anodic dissolution of steel. The stress effect factor at the crack tip is as high as 3.6 when a tensile force of 3000 N is applied on the pre-cracked specimen, while that for the low-stress area is 1.102 only. The local dissolution rate at the crack-tip is accelerated with the test time, which Would be attributed to the fact that. along with continuous propagation of the crack, the stress concentration at the crack-tip is further increased, which, again, enhances local dissolution. This result reflects exactly the interaction of stress and anodic dissolution at crack-tip during SCC of steel. (C) 2008 Elsevier Ltd. All rights reserved.