Failure analysis of the oil transport spiral welded pipe

The spiral welded pipe for oil transport failed catastrophically fracturing along the spiral welding line. The failure was in the base metal close to the heat-affected zone. Passive inclusions in the rolled metal are responsible for the pipe failure. Microstructure examination and Charpy-V notch tests reveal that the crack follows the oxide inclusions and is associated with their distribution, since the base metal toughness is insufficient to retard cracking. Improvement of the steel purity is suggested to prevent future pipe failures. Improving the welding technique to reduce the residual stress acting on the base metal also decreases the risk of pipe failure.