L51552 Surface Effects on Stress Corrosion Susceptibility of Line Pipe Steels

The objectives of this program were to identify factors that affect variability of the SCC data and that control SCC susceptibility, and to identify the cause of the high susceptibility of seasoned surfaces on some line pipe steels. Seasoning refers to the exposure of mill scaled surface to an in ground environment. The experimental approach consisted of a careful reexamination of the tapered tensile test specimens from prior project NG-18 research and experimental studies designed to confirm the trends apparent from the data analysis. In the specimen examination task, mill scalecoverage, corrosion* pit number and depth, surface residual stresses, and decarburization were measured on selected specimens and related to the variability in the SCC susceptibility. Three types of variability were of interest: side-to-side and specimen-to-specimen variability for replicate specimens of a single steel (which produce scatter in the SCC results), and material-to-material variability which indicates actual differences in SCC susceptibility.