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Technical Articles
The Manufacturing Method of the Steel Pipe
Posted: 06/30/2016 13:36:43  Hits: 28
Lineation, Cutting stock and Groove 
1. Steel lineation is base on construction drawings, and considers the factors, such as cutting loss, welding shrinkage and so on. After lining, to label steel section, section number, flow direction, the horizontal and vertical center line, groove angle and cutting line with steel seal and paint. 

2. Steel cutting stock and groove adopt numerical control cutting machine or semi-automatic cutting machine, and the shape, size and cutting quality of steel plate should meet the?norms and requirements. Slag, burr and defects on the surface of groove should be cleared with the angle grinder. After processing groove, it should be sprayed by the nontoxic and anti-rust coating that does not affect the welding performance and quality. 
Rolled Plate 
Rolled steel adopts cold-coiling method. The direction of rolled plate is the same as the direction of steel extension. It is not allowed to bend steel plate port to be shaded or correct curvature by hammering. Rolling steel tube stands up in vertical platform with free state. Steel tube arc were examined with a sample. 

Steel pipe longitudinal joint uses X groove to weld by both sides. The same section of the steel tube longitudinal joint is automatically welded by submerged arc welding. Generally, to weld the inseam is the first step. Then, to inspect the appearance of inseam, if qualified, to use carbon arc air gouging clean the back. Finally, to weld outer seam. Welding procedure is assessed by butt weld specimen, and it should finish before welding. According to the product standard and technical requirement of design, to formulate program for the type, thickness, welding method, welding material mark and groove type of steel plate before assessment. Its process including groove processing, forming a group, cleaning, preheating temperature, interpass temperature, heating temperature and time, welding parameters, welding position, welding layer number and the number, linear energy range, eliminating stress after welding, heat treatment specification and test, test items and procedures. 

Checking circle is carried out with self-designed Mi-shaped pitch circle in platform. After checking circle, add supporter on the steel tube port, to prevent the steel pipe from deforming during welding or dangling. 

Socket Assembly and Welding 
Forming circle is operated on the circle platform, single section of pipe will be modulated according to the number of order, then, to check the steel pipe manufacturing tolerance, and to ensure that its manufacturing tolerance comply with rules. When welding compound steel tube, in order to ensure shrinkage is uniform, each girth should be welded by four welders at the same time, and adopt symmetrical, segmentation, multi-level, multi-channel, regress welding, match with hammering method to eliminate the residual welding stress. Each layer of welding joint stagger 50 mm, weld covering forming at a time. After welding, all welding should pass appearance inspection, after qualified, to conduct internal weld NDT. 

Steel Pipe Anticorrosion Coating
1. After each section of steel pipe production confirmed by the engineer, can start anticorrosion coating according to relevant provisions of the specification requirements and engineers’ requirements, anticorrosion coating is operated in a closed shop. 

2. Anticorrosive process: derusting machine preparation, welding slag and spatter material removal, surface treatment, quality inspection, paint coating, inspection and acceptance. 

3. Anticorrosion coating operations should comply with technical terms and engineers’ requirements.

Matters Needing Attention 
In the process of steel pipe manufacturing, to conduct quality control for steel pipe manufacturing production process from material, process, welding, nondestructive testing, measuring, tooling. Technical personnel is responsible for compiling steel parts processing, material purchasing schedule, welding procedure qualification, tooling design, welding process card, nondestructive testing technology, anticorrosion construction technology, and then engineer authorize it and regard it as the instruction document of steel pipe manufacturing work. 

The difficulty and Control Measures in the Steel Pipe Manufacturing
1. Due to the arc deviation, local distortion of longitudinal seam welding, The radian and ovality deviation of steel pipe will be difficult to ensure the deviation, and it take the following measures to guarantee. 
(1) To design and produce longitudinal seam local arc calibration machine, after welding longitudinal seam, to use machine calibration to ensure its partial arc deviation. 

(2) Set up the reasonable steel pipe support to ensure deformation value and ovality of steel pipe. 

2. In order to ensure the straightness of the deviation when steel pipe assembling, following measures can be taken. 
(1) Improving groove design, adopting asymmetric X groove, leaving no space, cleaning with carbon arc air gouging after the inseam welding, making inside and outside of the weld actual area is almost close to equal, these measures are helpful to reduce the deformation and the residual stress. 

(2) Improving welding technology taking small-area welding, especially the first layer of the welding, increasing welding level, to reduce deformation and decrease steel pipe dimension deviation. 

(3) Straight tube butt: on the seam welding machine, at first, to adjust clearance, wrong tooth and check dimension as a whole, the, if qualified, to weld as a whole. 

(4) Bent pipe assembly: pipe bending is a special socket, the overshoot of dimension error will bring certain difficulties to installment and therefore it requires the whole assembly. 

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