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Submerged arc steel pipe welding control measures and forming methods

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Submerged arc steel pipe welding control measures:

Submerged arc steel pipe has become the steel pipe for large-scale oil and gas transmission projects at home and abroad because of its large wall thickness, good material, and stable processing technology. In large-diameter submerged arc steel pipe welded joints, welds and heat-affected zones are prone to various defects, while welding undercuts, pores, slag inclusions, incomplete fusion, incomplete penetration, weld bumps, burn-through, and welding cracks It is the main form of welding defects, and it is often the origin of accidents in submerged arc steel pipes. Control measures are as follows:

First, control before welding:

1. The raw materials must be checked first, and only after passing the inspection can they officially enter the construction site, and resolutely use unqualified steel.

2. The second is the management of welding materials. Check whether the welding material is a qualified product, whether the storage and baking system is implemented, whether the surface of the distributed welding material is clean and rust-free, whether the coating of the welding rod is intact, and whether there is mildew.

3. The third is the cleaning management of the welding area. Check the cleanliness of the welding area, and there must be no dirt such as water, oil, rust, and oxide film, which plays an important role in preventing the occurrence of external defects in the weld.

4. To choose a suitable welding method, the principle of trial welding first and welding later should be implemented.

Second, control during welding:

1. Check whether the specifications of welding wire and flux are correct according to the welding process regulations, and prevent welding accidents caused by the wrong use of welding wire and flux.

2. Supervise the welding environment. When the welding environment is not good (the temperature is lower than 0°C and the relative humidity is greater than 90%), corresponding measures should be taken before welding.

3. Before pre-welding, check the groove size, including gaps, blunt edges, angles, gaps, etc., to see if they meet the process requirements.

4. Whether the welding current, welding voltage, welding speed, and other process parameters selected in 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 strike plate at the end of the steel pipe during submerged arc automatic internal and external welding, and strengthen the use efficiency of the arc strike plate during internal and external welding, which helps to improve pipe end welding.

6. Supervise whether the welding personnel has cleaned up the slag first, whether the joints have been processed, and whether there is oil, rust, slag, water, paint, and other dirt on the groove. (Purple Flame)

Submerged arc steel pipe forming method:

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

First, UOE forming method: The forming process of the UOE steel pipe unit is divided into three steps, namely pre-bending, U-shaped press forming, and O-shaped press forming, and finally the cold expansion of the whole pipe to eliminate the pipe-making process stress generated in. The forming unit has huge equipment and high cost, and each set of forming equipment needs to be equipped with multiple casing inner and outer welding machines, so the production efficiency is high. Because it is a copy forming, there are many forming equipment, and a steel pipe with a diameter needs a set of specific forming molds. When changing product specifications, these molds need to be replaced. The internal stress of the formed welded pipe is relatively large, and it is generally equipped with a diameter expanding machine. The UOE unit has mature technology, a high automation level, and reliable products, but the unit equipment investment is huge, which is suitable for the production of large-volume products.

Second, RBE forming method: The stages of RBE forming are rolling, bending and diameter expansion and 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. Because ordinary enterprises cannot bear the huge investment of UOE pipe-making units, RBE pipe-making units developed based on RB have the characteristics of small investment, moderate batch size, and convenient product specification change, so they have developed rapidly. The welded pipe produced by this forming process is close to UOE steel pipe in quality and performance, so it can replace UOE welded pipe in most cases. The RBE pipe-making unit uses three-roll rolling to realize the steel pipe forming. The pipe-making process is that the three-roll forming machine rolls the steel plate into a steel pipe with a caliber, and then bends its edge with a forming roller, or it can be bent after, and then bend its edges with forming rollers, or it can also be bent afterward. Since it is a three-roll continuous roll bending forming, the stress distribution generated during the steel pipe forming process is relatively uniform. However, when changing the bending product specifications, it is necessary to change the core roll and adjust the lower roll appropriately. A set of core rolls of this forming equipment can take care of several specifications of products. The disadvantage is that the production scale is small, and due to the influence of the strength and rigidity of the core roll, 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 an O shape in turn, and E stands for diameter expansion. JCOE forming pipe-making unit is developed based on the UOE forming process. It learns from the working principle of the U-shape and releases and implements the UOE forming process, which greatly reduces the tonnage of the forming machine and saves equipment investment. The steel pipe produced is the same as the UOE welded pipe in terms of quality, but the output is lower than that of the UOE welded pipe unit. This process is easy to realize automatic control in the forming process, and the product is formed better. JCOE forming equipment can be roughly divided into two types, one is bending forming, and the other is compression forming. Bending forming is mainly used in the forming process of thick plate and medium plate, with small steps and low output. The forming process is to roll the two edges of the steel plate into an arc shape according to the curvature radius of the welded pipe on the edge bending machine, and then use the forming machine to press half of the steel plate into a C-shape through multiple step stamping, 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, and the whole steel plate becomes an open O shape from the surface.




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