Fatigue Life Evaluation of ERW Joint in the Pipe Using Monte-Carlo Simulation

The optimum welding condition for the input power was experimentally determined using the ERW simulator. The optimum condition derived from the nondestructive defect inspection and impact energy was the heat input power of 250kW with normalizing treatment at 900oC. In order to evaluate the fatigue life of ERW pipes, fatigue crack growth test for base metal and weld joint with the optimum condition were performed. As stress intensity factor range ( DKS) increased, the fatigue crack propagation rate (da/dN) of the weld joint became slower than that of the base metal. The fatigue life of ERW pipe was statistically estimated using Monte-Carlo simulation with the standard deviation of material constants (C and m) of the Paris law in the specimen. The fatigue life at failure probability PF = 50% is 2.3×105 cycle. Since the fatigue test of pipe in field has a lot of difficulties due to cost, equipment and time, the life derived from the simulation was identified using the common durability simulation software.