Adaptability of X80 Steel and its SAW Welding Wire to the Welding Procedure

Taking into account cost and safety for pipelines transporting oil and natural gas, the strength of the steel used is getting higher and the plate wall thicker. After a good use of X70 steel in China’s East-to-West Gas Transmission Project, X80 steel is drawing more and more attention in the future pipelines, resulting in its successful production in Wuhan Iron and Steel (Group) Company, and also bringing some concerns about welding. With increasing the wall thickness of the pipeline, the welding heat input is expected to increase for an increased deposited rate and a quality weld configuration. However, it is likely for the thermo-mechanically controlled rolled fine-grained steel that the properties of the heat affected zone will get deteriorated after it is subjected to large weld heat inputs, so the influence of the weld linear energy on the weld configuration and the properties of the welded joint have been studied. It is evident that an increased weld heat input can significantly reduce the number of the welding runs, thereby increasing the production proficiency and favoring the welding quality control as well. Furthermore, for Ti, Nb micro alloyed X80 steel, almost no property deterioration was found in this experiment, indicating that X80 steel is adaptable to various welding heat inputs, which gives much possibility of selecting a desirable large heat input. X80 steel is characteristic of low carbon and low sulphur contents with the addition of Mn, Mo alloying elements, and correspondingly, its weld metal should have the similar features that need to be obtained with the welding materials. However, the welding wires for X80 steel aren’t currently and commercially available in domestic market, so developing new welding wires is an urgent task for the mass application of X80 steel. Two submerged arc welding wires, one used for X70 steel and the other one branded as WGX2 with a higher strength were used in this welding experiment on X80 steel. The former produced excellent average impact energy up to 172J at −20°C close to that of the base metal but practically under-matched strengths and unqualified bend properties. The welded joint produced with WGX2 wire practically has a little over-matched strengths, qualified bend properties and satisfactory impact energy as well.