Research Of Robotic Narrow Gap MAG Vertical Welding Technology On Q690E High Strength Steel Plate

Legs are the main load-bearing structure of offshore platforms, while leg rack plate is the core of the platform lift, so the leg rack plate butt welding is the key to offshore platform construction. The material of Q690 E High Strength Steel used for thick Plate welding has high requirements for performance. However, for the present weld production conditions is backward, the productivity is low, the quality of welding is difficult to guarantee, the welding position is difficult to be adjusted and etc. This paper mainly focus on Q690 E high strength steel robot narrow gap MAG vertical welding technology.Firstly, the forming law robot MAG vertical welding was studied with the application of flat welding and variables control. On this basis, the problem of weld forming and sidewall fusion of robot narrow gap MAG vertical welding was researched, the key parameters for good weld of two types of wire: solid wire and flux cored wire was obtained. Then weld material tests were conducted to determine the stable forming parameters of the robot narrow gap MAG vertical welding and to the elect the best wire which has superior performance and meet the requirements of drilling platform leg rack plate steel welding.Combining the results above, Q690 E high strength steel robot narrow gap MAG vertical welding process was studied and optimized, the mechanical properties of welded joints and microstructure under different heat input and different welding specifications were analyzed. After mechanical properties tests and careful observation of the microstructure analysis, the best process parameters of Q690 E high-strength steel robot narrow gap MAG vertical welding were determined. Finally, by conducting a series of tests and microstructure observation, the impact of different preheat/interpass temperature on the microstructure and properties of welded joints.The final study results show that:(1) by increasing the arc residence time at the side wall and maintain a certain wire-groove side distance, the problem of poor sidewall fusion in narrow gap welding can be effectively solved.(2) The matching tests of three kinds of Q690 grade consumables showed that all of them had stable welding process, smooth weld and good sidewalls fusion, the weld metal microstructure were mainly acicular ferrite, solid wire MG- S88 A has the best microstructure and mechanical properties, the weld joint impact energy ≥90J@-37℃, meeting the requirements of production.(3) By comparing two different welding specifications, it can be found that the microstructure and mechanical properties of welded joints was better under trapezoidal swing mode. The heat input range of Q690 E HSLA steel robot NG-MAG vertical welding was narrow, when the heat input was 2.4KJ/mm, the weld microstructure and mechanical properties of the joint was the best with highest low temperature impact toughness, tensile properties, scoliosis performance and etc. and meet the standards and production requirements.(4) For the Q690 E HSLA steel robot NG-MAG vertical welding process, when the heat input was 2.4KJ/mm, the preheat/interpass temperature was 70℃, the performance and the microstructure of the weld joint was the best. The microstructure of the weld joint, the-37℃ impact toughness and hardness met the requirements of production, the weld zone impact fracture SEM picture showed that this area had dense dimple.