Failure Analysis of L245/316L Double Metal Composite Pipe

In order to find out the cause of the failure of L245/316L bimetallic composite pipe in a gas field in west China, a series tests for physical and chemical properties combined with the actual working conditions in the field were carried out to comprehensively study and analysize the failure. The results show that the elements of Cr and Ni were diluted near the weld toe during welding process. Corrosion grooves were formed obliquely upward with the effect of Cl^-. Micro cracks obliquely downward at the seal weld were found, and the transition welding area had high hardness with martensitic structure. Once the crack extension happened, the welding would not have the ability to stop cracking. The junction between root welding and transition welding contained pore and inclusion, around which stress concentration was easy to appear. Under the joint action of the above three factors, a leaky point was formed, corrosive medium could directly contact with the basic pipe through the leaky point, and the basic pipe wall was reduced because of corrosion until it could not withstand the internal pressure, and then the pipe ruptured.