Abstract
Abstract The near-neutral pH environmentally assisted cracking (EAC) initiation and propagation behavior of X70 pipeline steel was investigated in NS4 solution deaerated with N2/5% carbon dioxide (CO2) under the low-frequency cyclic load. The test results show that an increase in the applied stress level promotes the crack initiation. Based on the crack initiation sites, the cracks are divided into two types, pit cracks and non-pit cracks. Non-pit crack initiation is found to be the dominative cracking mechanism on the original external pipe surface, but as the tests progress, the contribution of pit cracks becomes significantly pronounced. The pits acted as the crack initiation sites are related to the localized dissolution at/around the nonmetallic inclusions. Therefore, it is expected that the EAC initiation resistance of steel can be improved by reducing the inclusion content in the steel. The crack propagation rate is found to be essentially independent of the applied stress level. By comparing the c...
Published Version
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