Fatigue Crack Growth in SAW Welded Joints of API 5L Steel Pipe in the Short Radial Direction

The fatigue crack growth of longitudinal SAW welds of a API 5L X42 steel pipe was evaluated using curved three point bend test specimens, where the radius of curvature of the specimens was equal to the pipe radius, so that no extensive machining or flattening was required. The fatigue crack growth tests were done in a servohydraulic closed loop machine under load control, in air at room temperature. The da/dN vs ∆K plots and Paris’s equation constants were obtained for the base metal, deposited metal and heat affected zone in the CR orientation, which corresponds to the short transverse direction of the pipe. The greater resistance to fatigue crack growth was the base metal, whereas the deposited metal showed the least resistance to the fatigue crack propagation. The deposited metal and the heat affected zone behaved according to Paris’s law, unlike the base metal, that showed a high dispersion of the fatigue crack growth rates. This behavior was due to the propagation of the crack in the direction transverse to the banded microstructure. Furthermore, the differences in fatigue crack growth rates among each zone were also related to the roughness of the fracture surfaces and fracture toughness.