All-position Welding Process And Performance Of Pipeline Steel By Laser-induced Arc Hybrid Welding

With the rapid development of economy and the increasing demand for oil,safe and efficient transportation of oil and gas has become increasingly important.Pipeline transportation is an economic way of oil and gas transportation,and has now become the fifth largest transportation industry in my country.In order to improve transportation efficiency,oil transportation pipelines are constantly developing in the direction of larger diameters and thick walls.In the construction of long-distance pipeline engineering,welding efficiency and welding quality are the key links of the project construction,which directly affects the construction efficiency and the safe and reliable operation of the pipeline in the later stage.At present,pipeline construction welding mainly adopts manual arc welding and double-sided automatic welding.The former has problems such as poor quality stability,low efficiency,and high dependence on operator experience,while the latter has high cost and low popularity.Low-energy laser-induced MAG arc welding technology is a new type of arc-based and laser-assisted hybrid welding technology.It uses a pulsed laser with an average power of about500 W to induce an enhanced arc,thereby increasing the arc energy density and reducing heat input.It has the advantages of green energy saving,strong process adaptability,precise and controllable forming ability and so on.With the support of the national key research and development plan,this article introduces the laser-induced hybrid welding technology into the pipeline all-position welding,focusing on the research on the automatic welding process,performance and demonstration application of the pipeline steel all-position single-sided welding and double-sided forming.In this paper,a pulsed laser-induced MAG arc composite heat source is used to perform full-position single-sided welding and double-sided free forming and force analysis on 16 mm thick X65 and 20 mm thick X80 pipeline steels.The test results show that the molten pool is mainly affected by arc pressure,gravity,surface tension,adhesion of the molten pool wall to the molten pool,and laser ablation pressure.Welding heat input is the main reason that affects the occurrence of concave defects in all-position bottom welding.The increase of heat input makes the volume of the molten pool increase,the gravity of the molten pool increases,and the flow tendency increases,resulting in larger concave defects in the bottom welding.The positions of 90° and 180° are more sensitive to heat input,135° is the most sensitive to heat input parameters,and the critical heat input value is the lowest.By adjusting the welding current,welding speed and welding torch angle matching,the force balance of the molten pool can be promoted and the molten pool flow can be reduced.The laser's induction effect on the arc makes the single penetration depth of more than 5mm and good back forming can be obtained.X65 and X80 pipeline steel adopt five-layer five-pass and six-layer six-pass segmented welding technology respectively.Through comprehensive control of welding speed,swing frequency,swing width,and residence time on both sides,all-position welding of pipelines can be welded at all angles for bottoming,filling and covering Well formed.Various mechanical performance tests show that X65 and X80 pipeline steels are fractured in the base material area,the tensile strength is equivalent to the base material,and the impact toughness reaches the standard.Finally,on the basis of laboratory research,the Daqing Petroleum Pipeline Bureau built an all-position welding experiment platform for the first-line pipelines,provided technical support for on-site welding problems,completed on-site equipment installation and commissioning,and successfully implemented on-site applications.