Submerged arc steel pipe has become the steel pipe of large-scale oil and gas transportation projects at home and abroad due to its large wall thickness, good material quality and stable processing technology. In large-diameter submerged arc steel pipe welded joints, the weld seam and heat-affected zone are the places that are prone to various defects, while welding undercuts, pores, slag inclusions, inadequate fusion, incomplete penetration, weld bumps, burn-through, and welding cracks It is the main form of welding defect, and it is often the origin of accidents of submerged arc steel pipe. The control measures are as follows:
1. Control before welding:
1) The raw materials must be checked first, and only after passing the inspection can they enter the construction site formally, and resolutely use unqualified steel.
2) The second is the management of welding materials. Check whether the welding materials are qualified products, whether the storage and baking system is implemented, whether the surface of the distributed welding materials is clean and rust-free, whether the coating of the welding rod is intact and whether there is mildew.
3) The third is the clean management of the welding area. Check the cleanliness of the welding area, and there should be no dirt such as water, oil, rust and oxide film, which plays an important role in preventing external defects in the weld.
4) To choose a suitable welding method, the principle of first trial welding and subsequent welding should be implemented.
2. Control during welding:
1) Check whether the specifications of the welding wire and flux are correct according to the welding procedure regulations to prevent the wrong use of welding wire and flux and cause welding accidents.
2) Supervise the welding environment. When the welding environment is not good (the temperature is lower than 0℃, the relative humidity is greater than 90%), corresponding measures should be taken before welding.
3) Before pre-welding, check the groove dimensions, including gaps, blunt edges, angles and misalignments, whether they meet the process requirements.
4) Whether the welding current, welding voltage, welding speed and other process parameters selected in the automatic submerged arc welding process are correct.
5) Supervise the welding personnel to make full use of the length of the pilot arc plate at the end of the steel pipe during automatic submerged arc welding, and strengthen the use efficiency of the pilot arc plate during internal and external welding, which helps to improve pipe end welding.
6) Supervise whether the welding personnel first clean up the slag during repair welding, whether the joints have been processed, whether there is oil, rust, slag, water, paint and other dirt at the groove