This paper presents the results of a research program to study the effects of metallurgical variables, ethanol-gasoline blends, dissolved oxygen, and inhibitors on the stress corrosion cracking (SCC) of carbon steel in ethanol. The study utilized both slow strain rate (SSR) and fatigue precracked compact tension (CT) tests to characterize the effect of metallurgical and environmental variables on SCC. Metallurgical factors, including steel grade within a range of pipeline grades, welds, and heat-affected zone, do not appear to have a significant effect on the degree or rate of SCC. In terms of environmental factors, it is shown that SCC does not occur even in a fully aerated condition if the ethanol-gasoline blends contain less than approximately 15 vol% ethanol; SCC susceptibility and crack growth rate are higher in 50 vol% ethanol gasoline blend (E-50) than in either lower or higher ethanol concentration blends; oxygen scavenging can be an effective method to prevent SCC; water content above 4.5 wt% prevents SCC in ethanol; and fatigue precracked CT tests show similar trends in SCC susceptibility as SSR tests.

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This paper provides an overview of mechanisms for high-pH and near-neutral pH stress corrosion cracking of underground pipelines. Characteristics and historical information on both forms of cracking are discussed. This information is then used to support proposed mechanisms for crack initiation and growth.

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This paper summarizes the results of research, funded by the Canadian Energy Pipeline Association (CEPA), to determine whether the initiation of near-neutral pH stress corrosion cracking (SCC) could be correlated with pipe metallurgical factors. The factors considered included residual stress, surface roughness, chemical composition, cyclic stress-strain behavior, inclusion properties (number, area, and composition), microhardness, and local galvanic behavior. The project focused on pipes installed from the 1950s through 1970s that exhibit near-neutral-pH SCC. Fourteen pipe samples were examined, ranging in diameter from 8 to 42 inches and grades from X52 to X70.