The near-neutral pH SCC initiation and propagation behavior of X70 pipeline steel was investigated using dog-bone specimens with two different surface conditions, the original external pipe surface and a ground surface. The tests were conducted in NS4 solution de-aerated with N2/5%CO2, under low frequency cyclic load (v = 0.1Hz, R = σmin/σmax = 0.5). The fractography shows that the transgranular crack morphology of near-neutral pH SCC is reproduced under the current test condition. In line with the crack initiation mechanisms, the cracks observed are divided into two types, pit cracks and non-pit cracks. Non-pit crack initiation is found to be the dominative mechanism for the original external pipe surface but the contribution of pit cracks depends on the test duration. The test results indicate that the crack initiation rate increases and the crack initiation life decreases with increasing applied stress level. The crack propagation rate is essentially independent of the applied stress level. Finally, the effects of surface condition and non-metallic inclusions on the SCC mechanism of pipeline steels are discussed.
- Pipeline Division
Near-Neutral pH SCC Initiation and Early Propagation of X70 Pipeline Steel
Lu, B, Luo, J, & McCrady, B. "Near-Neutral pH SCC Initiation and Early Propagation of X70 Pipeline Steel." Proceedings of the 2002 4th International Pipeline Conference. 4th International Pipeline Conference, Parts A and B. Calgary, Alberta, Canada. September 29–October 3, 2002. pp. 1821-1828. ASME. https://doi.org/10.1115/IPC2002-27234
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