First, submerged arc steel pipe welding control measures:
Submerged arc steel pipe has become the steel pipe for large oil and gas transportation projects at home and abroad due to its large wall thickness, good material, and stable processing technology. In large-diameter submerged arc steel pipe welding joints, welds and heat-affected zones are prone to various defects, and welding undercuts, pores, slag inclusions, incomplete fusion, incomplete penetration, weld bumps, burn-throughs, and welding cracks are the main forms of welding defects, and are often the source of accidents involving submerged arc steel pipes. The control measures are as follows:
1. Control before welding:
(1) First, the raw materials must be checked. Only after they have passed the inspection can they officially enter the construction site. Unqualified steel materials must be used resolutely.
(2) The second is the management of welding materials. Check whether the welding materials are qualified products, whether the storage and baking systems are implemented, whether the surface of the welding materials issued is clean and rust-free, and whether the coating of the welding rod is intact and mildew-free.
(3) The third is the cleaning management of the welding area. Check the cleanliness of the welding area. There should be no water, oil, rust, oxide film, or other contaminants. This is important for preventing external defects of the weld.
(4) Choose the appropriate welding method and implement the principle of trial welding before welding.
2. 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 the wrong use of welding wire and flux.
(2) Monitor the welding environment. When the welding environment is not good (temperature below 0℃, relative humidity greater than 90%), take corresponding measures before welding.
(3) Before pre-welding, check whether the groove size, including gap, blunt edge, angle, and misalignment, meets the process requirements.
(4) Whether the process parameters such as welding current, welding voltage, and welding speed selected during submerged arc automatic internal and external welding are correct.
(5) Supervise the welders to make full use of the length of the arc starter plate at the end of the steel pipe during submerged arc automatic internal and external welding, and enhance the efficiency of the arc starter plate during internal and external welding, which will help improve the welding of the pipe end.
(6) Supervise whether the welders clean the slag first, whether the joints have been processed, and whether there is oil, rust, slag, water, paint, and other dirt on the groove.
Second, the forming method of submerged arc steel pipe: the forming methods of submerged arc steel pipe include continuous torsion forming (HME), row roll forming method (CFE), UingOingExpanding forming method (UOE), roller bending forming method (RBE), JingCingOingExpanding forming method (JCOE), etc., but the three forming methods of UOE, RBE and JCOE are widely used.
1. 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 then the whole pipe is cold expanded to eliminate the stress generated during the pipe making process. The forming unit equipment is large and expensive. Each set of forming equipment needs to be equipped with multiple sets of internal and external welding machines for high production efficiency. Since it is a copy-forming method, there are many forming equipment. A steel pipe of one diameter needs a set of specific forming dies. When changing product specifications, these dies need to be changed. The internal stress of the welded pipe after forming is relatively large, and it is generally equipped with a diameter expander. 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 batches of products.
2. RBE forming method: The RBE forming stages are rolling, bending, and diameter expansion. The production process is mature. In the past, RB was mainly used to manufacture pressure vessels with large outer diameters and short lengths, structural steels, and water supply and drainage pipes. Since general enterprises cannot afford the huge investment of UOE pipe-making units, the RBE pipe-making units developed based on RB have the characteristics of small investment, moderate batch, and convenient product specification change, so they have developed rapidly. The welded pipes produced by this forming process are close to UOE steel pipes in terms of performance, so they can replace UOE welded pipes in most cases. The RBE pipe-making unit uses three-roll rolling to form steel pipes. The pipe-making process is that the three-roll forming machine rolls the steel plate into a steel pipe of a certain diameter, and then bends its edge with the forming roller, or takes a back bend. Since it is a three-roll continuous rolling bending forming, the stress distribution generated during the steel pipe forming process is relatively uniform, but when changing the product specifications, it is necessary to change the core roller and adjust the lower roller appropriately. A set of core rollers of this forming equipment can take into account products of several specifications. The disadvantage is that the production scale is small. Due to the influence of the core roller strength and rigidity, the wall thickness and diameter of the steel pipe are greatly limited.
3. 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 represents the expansion of the diameter. The JCOE forming pipe-making unit is developed based on the UOE forming process. It draws on the working principle of the U shape, releases and implements the UOE forming process, greatly reduces the tonnage of the forming machine, and thus saves the investment in equipment. The steel pipe produced is the same as the UOE welded pipe, but the output is lower than that of the UOE welded pipe unit. This process makes it easy to realize automatic control in the forming process, and the product forming is better. JCOE forming equipment can be roughly divided into two forms, one is bending forming, and the other is die pressing. Bending forming is mainly used for the forming process of thick plates and medium and thick plates, with a small step width and low output. The forming process is to first roll the two edges of the steel plate into an arc shape on the bending machine according to the curvature radius of the welded pipe, and then use the forming machine to press half of the steel plate into a C-shape through multiple step stamping, and then start stamping from the other side of the steel plate. After multiple-step stamping, the other side of the steel plate is also pressed into a C shape, so that the entire steel plate becomes an open O shape.
Post time: Dec-25-2024