Fatigue Crack Propagation in SAW Seam Welds of API 5L X42 Steel Pipe in the Radial Short Direction

Abstract

Fatigue crack propagation (FCP) rates in submerged arc welding (SAW) seam welds of 1524 steel (API 5L X42) pipe were measured by using an arc-shaped bend specimen with the same radius of curvature of the body of the pipe so the material did not have to be cold worked to get a flat shape nor extensively machined. The test direction was girth radial and the stress intensity factor (K) function was calibrated for this type of nonstandard specimen. The FCP tests were carried out in air at room temperature, testing the three zones: The base metal, the deposited metal, and the heat affected zone (HAZ). A fractographic analysis was done to analyze the role of the microstructure in the FCP in the three zones. It was found that the zone of greater resistance to FCP was the base metal, whereas the deposited metal showed the least resistance to crack propagation. FCP in the deposited metal and the HAZ behaved according to the Paris law, unlike the base metal, which showed a high data dispersion. The behavior in the base metal was attributed to the propagation of the crack in the transverse direction of the preferential alignment of the microstructure, while the deposited metal and the HAZ had a more homogeneous microstructure.