Experimental study on preheating multi-wire submerged arc welding of straight seam welded pipe

Welded pipes for oil and gas transportation are mostly produced using multi-wire submerged arc welding technology. For welded pipe manufacturing companies, first of all, it is necessary to ensure that the various mechanical properties of the welded pipe meet the requirements. On the other hand, it is also necessary to consider the problem of improving welding production efficiency and reducing welding production costs. To increase the welding speed of thick-walled welded pipes and improve the microstructure and properties of welds and heat-affected zones, this paper adopts a preheating multi-wire submerged arc welding process with faster welding speed and lower welding line energy to conduct a trial production test of X60 steel grade ∅559mmX32mm thick-walled welded pipes.

Through the comparative test of the conventional and preheating wire four-wire submerged arc welding process of the outer weld of the X65 steel grade ∅559mmX32mm welded pipe, it was found that the use of the preheating wire four-wire submerged arc welding process can increase the welding speed by 20%, reduce the welding line energy by about 10%, and the weld inspection has no defects. The weld appearance is uniform and beautiful, the transition of the weld toe area is smooth, the weld fusion width is 27~30mm, and the excess height is 1.8~2.1mm. From the comparative test data of weld flaw detection, macroscopic metallography, tensile test, series temperature shock test, hardness test, bending test, etc. under the two welding processes, it can be seen that the mechanical properties of the welds obtained by the preheating wire multi-wire submerged arc welding process are equal to or better than those of the conventional multi-wire submerged arc welding process. During the entire process of external welding of the preheating wire four-wire submerged arc welding process, the preheating wire submerged arc welding process has reliable arc start, stable welding current and voltage, and the preheating wire welding gun operates stably and reliably without any failure. The preheating wire welding gun is designed with a high-temperature resistant, wear-resistant, and conductive elastic conductive nozzle. The service life of the conductive nozzle is 6 to 10 times longer than that of the ordinary submerged arc welding conductive nozzle. In addition, a high-temperature resistant, wear-resistant, and insulated ceramic tube is designed at the bottom of the welding gun, so there will be no problem of eccentric wear of the welding wire hole, which eliminates the eccentric wear of the conductive nozzle inner hole after long-term, high-current continuous welding of the ordinary conductive nozzle. Therefore, the problem of internal and external weld deviation can be eliminated.