Influence of welding processes and weld configurationon fatigue failure of natural gas branch pipe

Fatigue test was executed to evaluate the fatigue performance on the fillet and butt weld joint of the natural gas branch pipe. Diameter of the branch pipe, throat thickness, geometrical shape of the fillet weld and welding processes were adopted to assess the fatigue strength of the branch pipe. SMAW and GTAW process were used to compare the welding process and the mechanical performance of the fillet weld joint. API 5 L Gr. B pipe and fitting of ASTM A105 were used for the fillet weld joint. There was no difference in tensile strength with variation of the welding process of the fillet weld joint. All tensile specimens were failed at the base metal of the pipes not weld joint. Fatigue life of the fillet weld joints was improved with larger pipe diameter, the leg length of the branch pipe direction, throat thickness and area of the weld metal. Failure of the fatigue specimens were occurred at the toe or root of the fillet weld joint.