Observation and Modeling of Stress Corrosion Cracking in High Pressure Gas Pipe Steel

Abstract

Stress corrosion cracking (SCC) is commonly observed to form a colony of closely spaced multiple cracks. Four stages of SCC colony evolution are discussed. The first is the colony initiation stage (CIS), which is associated with formation of corrosion pits randomly distributed over a certain domain of the surface exposed to an aggressive environment. Electrochemical processes play a leading role in CIS. The individual crack growth (ICG) driven by a combination of mechanical stresses and electrochemical processes constitutes the second stage. At the end of the second stage, the individual cracks reach certain proximity of one another resulting in much crack interaction. This becomes a transition to the third, strong crack interaction and clusters formation, stage. Cluster growth and individual crack or a cluster instability leading to the ultimate failure constitute the final, fourth stage of the SCC evolution process. In this article, we present observations and a general approach to modeling the first two stages of SCC, i.e., CIS and ICG, that together constitute the major part of the total lifetime of an engineering structure serving under SCC conditions. A computer simulation of individual SC crack growth is developed and compared with a large set of SCC observation data.