Submerged arc steel pipe welding control measures and forming methods

Control measures for submerged arc steel pipe welding: Submerged arc steel pipes have become the steel pipes of large-scale oil and gas transportation projects at home and abroad due to their large wall thickness, good material, and stable processing technology. In large-diameter submerged arc steel pipe welded joints, the weld seam and heat-affected zone are places where various defects are prone to occur, such as welding undercuts, pores, slag inclusions, lack of fusion, lack of penetration, welding nodules, burn-through, and welding cracks. It is the main form of welding defects and is often the source of accidents in submerged arc steel pipes. The control measures are as follows:
First, control before welding:
1. The raw materials must be inspected first. Only after passing the inspection can they officially enter the construction site. 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, and whether the coating of the welding rod is intact and whether there is mildew.
3. Next is the cleaning management of the welding area. Check that the welding area is clean and free of water, oil, rust, oxide film, and other contaminants, which plays an important role in preventing the occurrence of external defects in the weld.
4. When choosing the appropriate welding method, the principle of trial welding first and then welding should be followed.
Second, control during welding:
1. Check whether the specifications of welding wire and flux are correct according to the welding process regulations to prevent welding accidents caused by incorrect use of welding wire and flux.
2. Supervise the welding environment. When the welding environment is not good (temperature below 0°C, relative humidity above 90%), corresponding measures should be taken before welding.
3. Before pre-welding, check the groove dimensions, including gaps, blunt edges, angles, and staggered edges, to see if they meet the process requirements.
4. Whether the process parameters such as welding current, welding voltage, and welding speed selected during the submerged arc automatic internal and external welding process are correct.
5. Supervise welding personnel to make full use of the length of the arc ignition plate at the end of the steel pipe during automatic submerged arc internal and external welding, and enhance the efficiency of the arc ignition plate during internal and external welding, which will help improve pipe end welding.
6. Supervise the welding personnel to see whether the slag has been cleaned first, whether the joints have been processed, and whether there are oil, rust, slag, water, paint, and other contaminants at the groove during repair welding.

Submerged arc steel pipe forming methods: Submerged arc steel pipe forming methods include continuous torsion forming (HME), roller forming method (CFE), UingOingExpanding forming method (UOE), roll bending forming method (RBE), JingCingOingExpanding forming method (JCOE), etc., but the three most widely used forming methods are UOE, RBE and JCOE.

First, UOE forming method: The UOE steel pipe unit forming process is completed in three steps, namely pre-bending, U-shaped press forming, and O-shaped press forming, and then cold expansion of the entire pipe to eliminate the pipe-making process stress generated. The forming unit has large equipment and high cost. Each set of forming equipment needs to be equipped with multiple internal and external casing welding machines, resulting in high production efficiency. Because it is profiling and there are many forming equipment, a steel pipe of one diameter requires a specific set of forming molds. When changing product specifications, these molds need to be replaced. The formed welded pipe has large internal stress and is generally equipped with a diameter expander. The UOE unit has mature technology, a high automation level, and reliable products. However, the investment in unit equipment is huge and it is suitable for producing large-volume products.

Second, RBE forming method: The stages of RBE forming are rolling, bending, and diameter expansion. The production process is mature. In the past, RB was mainly used to manufacture pressure vessels, structural steel, and water supply and drainage pipes with larger outer diameters and shorter lengths. Since ordinary enterprises cannot afford the huge investment in UOE pipe-making units, the RBE pipe-making units developed based on RB have the characteristics of small investment, moderate batch size, and easy replacement of product specifications, so they have developed rapidly. The welded pipe produced by this forming process is close to UOE steel pipe in terms of performance and performance, so it can replace UOE welded pipe in most cases. The RBE pipe-making unit uses three-roller rolling to form steel pipes. The pipe-making process is that the three-roller forming machine rolls the steel plate into a diameter steel pipe, and then uses the forming roller to bend its edge. Back bending can also be used. , and then use a forming roller to bend its edge, or back-bend it. Since it is a three-roller continuous roll bending, the stress generated during the steel pipe forming process is relatively evenly distributed. However, when changing the bending product specifications, the core roller needs to be changed and the lower roller needs to be adjusted appropriately. A set of core rollers of this forming equipment can accommodate several specifications of products. The disadvantage is that the production scale is small. Due to the influence of the strength and stiffness of the core roller, the wall thickness and diameter of the steel pipe are greatly restricted.

Third, JCOE forming method: JCOE forming has three stages, that is, the steel plate is first pressed into a J shape, and then pressed into a C shape and O shape in sequence. E represents diameter expansion. The JCOE forming and pipe-making unit is developed based on the UOE forming process. It draws on the working principle of the U-shape and releases and implements the UOE forming process, which greatly reduces the tonnage of the forming machine, thereby saving equipment investment. The produced steel pipe is the same as the UOE welded pipe in appearance, but the output is lower than that of the UOE welded pipe unit. This process makes it easy to realize automatic control during the forming process, and the product is better formed. JCOE forming equipment can be roughly divided into two forms, bending forming and the other is molding. Bending forming is mainly used for the forming process of thick and medium-thick plates, with smaller steps and lower output. The forming process is to first roll the two edges of the steel plate into an arc shape according to the curvature radius of the welded pipe on the bending machine, and then use the forming machine to press half of the steel plate into a C-shape through multiple step-by-step punching, and then start from the other side of the steel plate. Stamping, after multiple steps of stamping, the other side of the steel plate is also pressed into a C shape, making the entire steel plate into an open O shape.