Abstract
Transgranular stress corrosion cracking (TGSCC) of pipeline steels in near-neutral environments was first reported in the mid-1980s. Metallographic examination of these cracks show an extensive dissolution of the crack walls, where the cracks were generally filled with predominantly iron carbonate containing corrosion product. Although there is general agreement that hydrogen plays an important role in TGSCC of line-pipe steels in near-neutral pH stress corrosion cracking (NNSCC), the mechanism of hydrogen generation, along with the anodic dissolution, is not agreed upon. Colwell and Leis proposed a mechanism that attributes the hydrogen generation, in bicarbonate containing trapped solutions, to the decomposition of bicarbonate and further reaction with metal ions to form carbonates. This mechanism also explains how the pH of trapped solutions could be maintained while the hydrogen is generated. The present study was focused to test this mechanism by a systematic study of the effect of individual trapped water constituents to determine their effect on overall crack initiation and growth. TGSCC of pipeline steel was successfully reproduced in laboratory tests with simple bicarbonate solutions.
