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Straight Seam Steel Pipe Forming Process

This method has the highest productivity and is also the main production method for straight seam steel pipe. The brief production process of the device is first bent into a U shape and then pressed into an O shape, followed by mechanical cold expansion after welding inside and outside. The characteristic of this method is that it can obtain very stable steel pipes, high production capacity, and can produce steel pipe with a length of more than 18m.

Submerged arc welding straight seam steel pipe uses submerged arc welding technology, filler welding, particle protection flux submerged arc. The caliber of production can reach 1500mm. LSAW is the abbreviation for 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 caliber is large, it may be rolled with two steel plates, which will form the phenomenon of double welds. Executable GB/T3091-2008 low-pressure fluid steel pipe production standard, GB/T9711.1-2 -1997 oil and gas steel pipe production and use standard, the implementation of the US API 5L pipeline steel pipe execution standard, and the implementation of ASTM A53 general purpose steel pipe standard.

The roll bending method is to bend the steel plate into an open tube after several processes on the roll bending machine, and keep the opening edge straight and not deformed. Then, the opened pipe is sent to the bending machine, and the two edges of the sheet are continuously bent. 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 to compression molding, and then send it to the bending position by the controller. After passing through a series of stampers matching the pipe diameter, an open pipe is formed. In operation, there are two controllers. First bend one side of the board into a semi-circle, then move the board through the second controller, and then bend and form the other side. Because 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 kept to a
minimum. Generally, after the forming is completed, the open tube is sent to an edge bending machine, and both edges of the plate are continuously rolled into a desired shape. This method has the characteristics of strong adaptability and good economy, and can be used to produce small-diameter thick-wall steel pipe.

Steel pipe formed by this method were initially used in the marine industry. Since it is often necessary to form a steel tube in a cold state with a controlled rolled plate to produce a particularly thick steel tube, and this method has high forming accuracy and applied pressure, it is used to produce thick-walled steel tubes for the marine industry. This method is characterized by high-strength thick-walled steel pipe. It is suitable for both small and large diameters, so it can be used to manufacture trunk pipes and marine structural pipes. The 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 the large-diameter straight seam steel pipe includes a series of basically similar processes. The main process is:
1. Welding grooves should be processed at the edge of the board. Processing methods include milling and planing. On both sides of the board, there may be one or more milling and planing heads. According to different board thickness, the groove can be processed into I-shaped, single V-shaped or double V-shaped, and has certain blunt edges. 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 productivity, while the roots are wider to avoid welding defects.
2. Spot welding is usually called pre-welding. Generally, carbon dioxide gas shielded welding is used to stabilize steel pipes, which is especially useful for submerged arc welding to prevent burn-through. After spot welding, the steel pipe shall be visually inspected to verify whether the weld is continuous and free from any defects.
3. Internal and external welding of steel pipes, that is, precision welding. After positioning welding of steel pipes, internal and external welding of steel pipes is mainly performed, which is an important part in the manufacturing process of steel pipes. It is done by submerged arc welding separate from the forming device. In order to improve productivity, multi-wire submerged arc welding is used for inner and outer seam welding, and the number of welding wires can be up to 5. In order to avoid welding seam 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 identify welding defects as soon as possible, ultrasonic flaw detection and X-ray flaw detection should be performed 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 steel pipe after welding cannot meet the requirements of relevant standards and technical conditions. The size and straightness are used in the tube factory and are completed 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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