Effect of welding technology on the mechanical properties of welded joints in pipes for deep water offshore gas pipelines

Results of investigations into the dependence of mechanical properties of welded joints of pipes for offshore pipelines on welding conditions are presented. In particular, the results show that the mechanical properties of pipes of the strength categories K60 (X70) and K56 (X65) are influenced mainly by the heat input, the fracture toughness of welded joints, and pipes of a high strength category are lower by 30–35% than in the case of the K56 (X65) pipes. The hardness of the weld metal in the upper layers is 15–17% higher for automatic submerged arc welding and in the lower layers for gas-shielded automatic arc welding. In inspecting the mechanical properties of the welded joints, special attention must be given to the longitudinal welded joints in the pipes.