L51838 Cyclic Stress Strain Behavior and SCC Susceptibility of Line Pipe Steels

This report presents results of a preliminary evaluation of a mechanical property that has the potential to correlate with susceptibility to Stress-corrosion cracking (SCC). This mechanical property measures the evolution of the microplastic response of line pipe steels, which underlies high pH SCC, and is believed by many to be essential for near-neutral SCC. If such a property can be proven to reflect susceptibility to SCC, operators could better contain maintenance costs and specify steels for new pipelines that are inherently resistant to SCC. Limited experimentation using X60 line-pipe steel indicated that the onset, duration, and intensity of microplasticity correlated with electrochemical indicators of SCC for the high-pH cracking environment. These results show sensitivity sufficient to detect the incidence and magnitude of plastic strain that evolves in load-controlled cycling under conditions typical of pipeline service, as well as in histories where such behavior has been exhausted by prior strain hardening. Thus, these data indicate that the protocol evaluated herein is potentially capable of identifying susceptible steels, and has sensitivity of the order needed to discriminate susceptibility between steels.

Benefit: While the concept and related experimental techniques hold promise as a screening tool for susceptibility, some experimental issues must be resolved before its use can be conclusively established. These and other related aspects are outlined in the discussion section, and the recommendations section of the report.