Influence of sulphur content and inclusion distribution on the hydrogen induced blister cracking in pressure vessel and pipeline steels

In previous works, extensive desulphurisation, including shape control and low hardness in segregation zones, were pointed out as effective ways for i ncreasing resistance to hydrogen induced cracking (HIC) in steels exposed t o wet H2S environment. In this study, the behaviour of eight plates was eva luated by immersing samples in H2S-saturated NACE solution. HIC susceptibil ity was assessed by an ultrasonic method and correlated with the elongated MnS inclusion distribution. The results allow us to remark that an extremel y low sulphur level is not necessary to reach good HIC resistance, provided that no hard bands are present in the steel. Under this condition, a relat ionship to calculate the minimum average sulphide length which provides low HIC susceptibility was found. (C) 2001 Elsevier Science Ltd. FLU rights re served.