MECHANISTIC STUDIES OF INITIATION AND EARLY STAGE CRACK GROWTH FOR NEAR-NEUTRAL pH SCC ON PIPELINES

摘要

Evidence from laboratory experiments and field observations on near-neutral pH SCC of pipeline steel is reviewed. Emphasis is placed on the effects of environmental parameters, such as potential, pH and HCO_3~- / CO_3~(2-) concentration, on the SCC mechanism. The results are interpreted in terms of either a dissolution-based or hydrogen-based mechanism. The weight of evidence supports a hydrogen-based mechanism for near-neutral pH SCC. Dissolution may play a role in SCC initiation. Enhanced rates of hydrogen evolution and permeation appear possible under near-neutral pH SCC conditions, whilst the observed dissolution rates and the absence of an efficient mass-transport mechanism to support rapid crack-tip dissolution seem to rule out dissolution as an important contributor to crack growth.