Introduction to the production process and inspection standards of thick-walled straight seam steel pipes
Date:2024-12-30
Thick-walled straight seam steel pipes are made by rolling long strips of steel strips of certain specifications into round tubes through high-frequency welding units and welding them into straight seams. The shape of the steel pipe can be round, square, or special-shaped, depending on the sizing rolling after welding. The materials of welded steel pipes are mainly low-carbon steel and low-alloy steel or other steels with σs≤300N/mm2, and σs≤500N/mm2. The production process of thick-walled straight seam steel pipe is as follows:
1. Plate inspection: After the steel plate used to manufacture large-diameter submerged arc welded thick-walled straight seam steel pipe enters the production line, the first full plate wave inspection is carried out;
2. Edge milling: The two edges of the steel plate are double-sided milled by the edge milling machine to achieve the required plate width, plate edge parallelism, and groove shape;
3. Pre-bending edge: The plate edge is pre-bent by the pre-bending machine to make the plate edge have the required curvature;
4. Forming: First, half of the pre-bent steel plate is pressed into a "J" shape through multiple-step punching on the JCO forming machine, and then the other half of the steel plate is bent in the same way and pressed into a "C" shape, and finally an open "O" shape is formed.
5. Pre-welding: make the formed straight seam welded steel pipe joint and use gas-shielded welding (MAG) for continuous welding;
6. Internal welding: use longitudinal multi-wire submerged arc welding (mostly four wires) to weld on the inside of the thick-walled straight seam steel pipe;
7. External welding: use longitudinal multi-wire submerged arc welding to weld on the outside of the straight seam submerged arc welded steel pipe;
8. Wave inspection I: 100% inspection of the internal and external welds of the straight seam welded steel pipe and the parent materials on both sides of the weld;
9. X-ray inspection I: 100% X-ray industrial television inspection of the internal and external welds, using an image processing system to ensure the sensitivity of flaw detection;
10. Diameter expansion: expand the entire length of the submerged arc welded thick-walled straight seam steel pipe to improve the dimensional accuracy of the steel pipe and the distribution of stress in the steel pipe;
11. Water pressure test: The expanded steel pipes are inspected one by one on the water pressure test machine to ensure that the steel pipes meet the test pressure required by the standard. The machine has automatic recording and storage functions;
12. Chamfering: The steel pipes that have passed the inspection are processed at the pipe end to achieve the required pipe end groove size;
13. Wave inspection II: Wave inspection is performed again one by one to check the defects that may occur in the straight seam welded steel pipes after expansion and water pressure;
14. X-ray inspection II: X-ray industrial television inspection and pipe end weld filming are performed on the steel pipes after expansion and water pressure test;
15. Magnetic particle inspection of pipe ends: This inspection is performed to find defects at the pipe ends;
16. Anti-corrosion and coating: The qualified steel pipes are anti-corrosion and coated according to user requirements.
The development focus of seamless steel pipes is energy-saving and emission-reduction technology. Thick-walled straight seam steel pipes are developed with high steel grade (X100) and large wall thickness (≥60mm) products. The use of full pipe expansion is a reasonable solution for spiral submerged arc welded pipes to eliminate residual stress. Straight seam high-frequency welded pipes should play their advantages in weld heat treatment. When formulating relevant policies, it is advisable to focus on macroeconomic regulation rather than involving the approval of specific units; it is necessary to eliminate the contradiction of overcapacity and prevent blind comparison of overcapacity.
At present, the product structure of steel pipes in my country is characterized by an oversupply of low-end products and insufficient products, but this does not mean that all enterprises must develop in the direction of products. Instead, each enterprise should determine its market positioning according to local conditions, or be customized, personalized, or standardized, while preventing homogenization. Therefore, enterprises should grasp the correct direction in the process of adjusting their technical structure and product structure.
Given the small, numerous, and scattered characteristics of steel pipe enterprises, especially private enterprises, enterprises can be integrated into industrial clusters according to production process characteristics, product scale, technical equipment, and other conditions. There are many types of steel pipes, each with different characteristics. Therefore, the advantages of technology and product structure should be complementary, and the strengths should be strengthened and the weaknesses should be avoided. Regarding the structural adjustment of the seamless steel pipe industry, energy-saving and environmental protection technologies should be actively adopted, among which online normalization technology, regenerative heating furnace, and ring furnace waste heat utilization technologies have significant energy-saving effects; attention should also be paid to the treatment and comprehensive utilization of wastewater and waste acid to achieve a circular economy.
Thick-walled straight seam steel pipes and spiral steel pipes are both types of welded steel pipe. They are widely used in national production and construction. Thick-walled straight seam steel pipes and spiral steel pipes have many differences due to different production processes. The following specifically discusses the differences between thick-walled straight seam steel pipes and spiral steel pipes.
The production process of straight seam welded pipes is relatively simple. The main production processes are high-frequency welding thick-walled straight seam steel pipes and submerged arc welding thick-walled straight seam steel pipes. Thick-walled straight seam steel pipes have high production efficiency, low cost and rapid development. The strength of spiral welded pipe is generally higher than that of straight seam welded pipe. The main production process is submerged arc welding. Spiral steel pipe can produce welded pipes of different diameters with the same width of billet, and can also produce welded pipes with larger diameters with narrower billets. However, compared with thick-walled straight seam steel pipes of the same length, the weld length increases by 30~100%, and the production speed is lower. Therefore, most smaller-diameter welded pipes use straight seam welding, while large-diameter welded pipes mostly use spiral welding. When producing larger-diameter thick-walled straight seam steel pipes in the industry, T-welding technology is used, that is, short sections of thick-walled straight seam steel pipes are butt-jointed to a length that meets the needs of the project. The probability of defects in T-welded thick-walled straight seam steel pipes is also greatly increased, and the welding residual stress at the T-weld is large. The weld metal is often in a three-dimensional stress state, which increases the possibility of cracks.