Stress corrosion cracking of X-70 pipeline steel in near neutral pH solution subjected to constant load and cyclic load testing.

Stress corrosion cracking (SCC) tests were conducted on American Petroleum Institute (API) grade X-70 line pipe steel using smooth specimens in a standard near neutral pH solution, NS4. Both constant loading and cyclic loading conditions were employed. There were some SCC cracks on the surfaces of specimens under constant loading conditions when the applied load and test duration were appropriate. These cracks were related to stress concentration at corrosion pits. Generally, the local strain rate around corrosion pits in constant load tests was not high enough for the transition from pits to cracks to take place, and so long test times were needed for crack initiation. In contrast, cyclic loading tests facilitated near neutral pH SCC by making the local strain rate at the crack tip change under the applied load spectrum and by enhancing the crack tip local strain rate, which appreciably shortened the crack initiation incubation. [ABSTRACT FROM AUTHOR]