Study on Welding Techniques of 316L Lined Bimetallic Pipe

Abstract

It is well known that welding technique was often a knotty problem for bimetallic lined steel pipes to use widely. A number of failures in secession of weld cracking and weld corrosion had been observed in oil fields in recent years, which seriously disrupted the order of oil and gas production. To solve welding problems of 316L bimetallic lined pipes, works outcome about failure analysis and welding process research were presented in this paper. Failure analysis results confirmed that Welding defects, high hardness regions was the main reasons about failure problems of weld crack while structure design defects of seal weld and bad back-protection effects of flux-cored wire resulted in weld corrosion. Welding defects in the regions of seal weld became the failure source while the high hardness both in the region of seal weld and weld joint formed the crack propagation channel, and therefore both initially contributed to weld cracking. Additionally owing to the structure design of seal weld, liner layer would be heated over and over again during the period of seal weld and then it was not enough to protect CRA layers from being damaged during the period of girth weld. As a result the corrosion resistance in the welding area was reduced to become a weak area. On the basis of failure analysis, further research work was carried out to improve welding performance. Seal weld structure and girth weld process was improved. The difference of welding wires and welding process was analyzed, and their defects were described separately. Results showed that the welding performance welding by ERNiCrMo-3 and supporting technology was more reliable than ATS-F309L and supporting technology, whether seal weld or butt welding. The distribution and value of the hardness could be effectively controlled; Moreover, corrosion resistance performance was also better. Therefore, the seal weld and girth weld conducted by ERNiCrMo-3 and supporting technology was feasible.