Sulfide Stress Corrosion Cracking of Line Pipe

Abstract

Sulfide stress corrosion cracking (SSC) behavior of line pipe steel was investigated using the SSC test method in NACE(1) Standard TM0177-77, "Testing of Metals for Resistance to Sulfide Stress Cracking at Ambient Temperatures." SSC of base metal can be classified into two types, depending on microstructures. In ferrite-perlite steel, the first crack initiates parallel to the pipe surface and propagates perpendicularly to the axis of stress. In ferrite-bainite steel or low C-bainite steel, the crack initiates at the inter-face between the bainite particle and the ferrite. With decreasing carbon content, the threshold stress of SSC (σth) increases, but in low-carbon steel, the σth value of weld seam is lower than that of base metal. SSC of weld seams occurs at the softening zone in the heat-affected zone (HAZ) about 2 to 4 mm away from the fusion line.