Abstract
Two types of cracking, namely sulphide stress cracking (SSC) and hydrogen-induced cracking (HIC), were evaluated in linepipe steels using NACE standard solution to establish the metallurgical parameters that control HIC and SSC. Quantitative experiments indicate a threshold hydrogen concentration for HIC below which no cracking will initiate. Propagation of cracks occurs by hydrogen assisted fracture of the matrix surrounding the site where initiation occurs. The HIC susceptibility of steels containing Cr, Ni, and Mo under stress and hydrogen diffusion was been investigated by electrochemical methods. As the content of alloying elements increased, the apparent hydrogen diffusion coefficient (D) and threshold hydrogen permeation rate (Jth) for hydrogen embrittlement decreased. Hydrogen content (Co) in the steel in NACE TM-0177 solutions increased due to decreasing D with increased Cr content, although hydrogen permeability (J × L) decreased, and the susceptibility to sulfide stress cracking (SSC) increased as a result. Moreover, Mo exhibited clear effect of decreasing J × L, and consequently the resistance to SSC improved with increasing Cr content.
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