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Introduction to straight seam steel pipe forming process

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This method has the highest productivity and is also the main production method of straight seam steel pipes. The brief production process of this device is to first bend it into a U shape, then press it into an O shape, and then mechanically expand it after welding the inside and outside. The characteristics of this method are that it can obtain very stable steel pipes, has high production capacity, and can produce steel pipes with a length of more than 18m.

Submerged arc welded straight seam steel pipe adopts submerged arc welding technology, filling welding, and particle protective flux submerged arc. The production diameter can reach 1500mm. LSAW is the abbreviation of submerged arc welded straight seam steel pipe. The production process of submerged arc welded straight seam steel pipe includes JCOE forming technology and coiled submerged arc welding technology. When the diameter is large, two steel plates may be used for rolling, resulting in a double weld phenomenon. It can implement the GB/T3091-2008 low-pressure fluid steel pipe production standard, GB/T9711.1-2-1997 oil and gas steel pipe production and use standards, implement the American API 5L pipeline steel pipe implementation standard, and implement the ASTM A53 general steel pipe standard.

The plate rolling method is to bend the steel plate into an open tube after several processes on the plate rolling machine, keeping the edge of the opening straight and not deformed. The opened tube is then fed into the bending machine to continuously bend both edges of the plate. This method has the characteristics of strong adaptability and good economy, but the minimum diameter and maximum wall thickness of the welded pipe produced by this method are limited.

The forming process of the progressive compression molding method is to first send the steel plate into compression molding, and then send it to the bending position by the controller. After passing through a series of dies that match the pipe diameter, an open tube is formed. In operation, there are two controllers. Start by bending one side of the board into a semi-circle, then move the board with the second controller before bending and forming the other side. Since the thickness of the edge of the bending die affects the roundness of the open tube, the thickness of the edge of the bending die must be maintained at a

at the lowest limit. Generally, after the forming is completed, the open tube is sent to the folding machine to continuously roll both sides of the plate into the required shape. This method has the characteristics of strong adaptability and good economy, and can be used to produce small-diameter thick-walled steel pipes.

Steel pipes formed by this method were originally used in the marine industry. Since particularly thick steel pipes are often produced by forming steel pipes in the cold state using controlled rolling plates, and this method has a high forming accuracy and applied pressure, it is used to produce thick-walled steel pipes. Marine industry. This method is characterized by high-strength thick-walled steel pipes. It is suitable for both small and large diameters, so it can be used to make main pipes and marine structural pipes. This system has low equipment cost, strong adaptability and good economy, and can reduce costs even in small batch production. Post-forming manufacturing stage After the above-mentioned forming stage is completed, the subsequent manufacturing stage of large-diameter straight seam steel pipes includes a series of basically similar processes. The main process is:

  1. Welding grooves should be processed on the edge of the plate. Processing methods include milling and planing. On both sides of the board, there may be one or more router heads. Depending on the thickness of the plate, the groove can be processed into an I-shape, a single V-shape or a double V-shape, with a certain blunt edge. For particularly thick steel pipes, the outer weld can be milled into a U-shaped groove. The purpose is to reduce the consumption of welding materials and improve production efficiency, while making the root wider and avoiding welding defects.
  2. Spot welding is usually called pre-welding. Carbon dioxide gas shielded welding is generally used to stabilize steel pipes, and is especially suitable for submerged arc welding to prevent burn-through. After spot welding, perform a visual inspection of the steel pipe to confirm whether the weld is continuous and defect-free.
  3. Internal and external welding of steel pipes, that is, precision welding. After the positioning welding of the steel pipe, the internal and external welding of the steel pipe is mainly carried out, which is an important link in the steel pipe manufacturing process. It is done by submerged arc welding separate from the forming unit. In order to improve production efficiency, multi-wire submerged arc welding is used for internal and external seam welding, and the number of welding wires can reach 5. In order to avoid welding deviation, the welding head is equipped with a special automatic welding seam centering device. Thick-walled steel pipes are welded in multiple layers to reduce heat input and improve the physical properties of the weld.
  4. Welding inspection: In order to find welding defects as soon as possible, ultrasonic flaw detection and X-ray flaw detection should be carried out immediately after the welding operation is completed, and the defects found should be repaired in time.
  5. Cold expansion: The roundness and straightness of the welded steel pipe cannot meet the requirements of relevant standards and technical conditions. Dimensions and straightness are used in the pipe factory and are accomplished by mechanical cold expansion.
  6. Steel pipe hydraulic test: The test pressure can reach more than 90% of the yield strength of the steel pipe material.

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