How much do you know about JCOE straight seam submerged arc welded steel pipes

The JCOE straight seam submerged arc welded steel pipe forming process is one of the core forming methods for straight seam submerged arc welded (LSAW) steel pipes. Its core characteristics are "step-by-step forming and precise shape control." Through three progressive bending steps—J-forming, C-forming, and O-forming—flat steel is processed into a circular pipe blank. Subsequent submerged arc welding and diameter expansion processes ultimately produce high-strength, high-precision straight seam steel pipes. JCOE straight seam submerged arc welded steel pipes are widely used in high-end engineering fields such as long-distance oil and gas transportation, municipal main pipelines, and heavy structures. Balancing forming accuracy and production costs, it is currently one of the mainstream forming processes for medium and large diameter thick-walled straight seam steel pipes.

First, the core definition and applicable scope of the JCOE straight seam submerged arc welded steel pipe process. 

The full name of the JCOE straight seam submerged arc welded steel pipe forming process is "J-C-O-E forming process," where J, C, and O correspond to the three core forming steps, and E represents the subsequent diameter expansion process. This process uses single-sheet medium-thick steel plates as raw materials, eliminating the need for a plate rolling machine. It involves step-by-step bending using specialized forming molds, and is suitable for forming medium-to-large diameter, thick-walled, straight seam steel pipes with outer diameters of 355mm-1422mm and wall thicknesses of 6.4mm-58.8mm. It is compatible with various steel grades such as Q235B, L245, and X70, and is particularly suitable for the mass production of pipeline steel pipes with high precision and high pressure requirements.

Second, the complete forming process of JCOE straight seam submerged arc welded steel pipe. 

The forming process of JCOE straight seam submerged arc welded steel pipe is continuous, with strict parameter control at each step to ensure the forming accuracy of the pipe blank and the subsequent welding quality. The complete process is divided into six major stages: raw material preparation, three-step forming, seam positioning, welding, diameter expansion, and inspection, as follows: 
1. Raw material preparation for JCOE straight seam submerged arc welded steel pipe. Steel plates conforming to standards such as API 5L and GB/T 9711 are selected. First, the surface is cleaned, and then the edges on both sides of the steel plate are milled and beveled using a high-precision edge milling machine to process bevels that meet welding requirements, ensuring edge flatness and bevel angle error ≤ ±0.5°, laying the foundation for subsequent forming and welding. Simultaneously, the chemical composition and mechanical properties of the steel plate must be re-inspected to avoid raw material defects affecting the forming quality.
2. J-forming of JCOE straight seam submerged arc welded steel pipe. The pre-treated steel plate is fed into a J-forming machine. Using a specialized arc-shaped mold, one edge of the steel plate is progressively bent to form a "J"-shaped arc structure. The key to this step is controlling the bending radius to avoid edge wrinkles and cracks. The bending angle needs precise control to ensure the continuity of subsequent C-forming. Generally, the bending angle is controlled between 45° and 60°. During bending, the deformation of the steel plate must be monitored in real time to prevent excessive bending and material damage.
3. C-forming of JCOE straight seam submerged arc welded steel pipe. The J-formed steel plate is fed into a C-forming machine. Using multiple sets of symmetrical molds, the steel plate is progressively bent from the J-shaped edge to the other side, forming a "C"-shaped semi-tubular structure. This step is crucial for forming. The bending force and speed must be controlled to ensure uniform curvature of the pipe blank, avoiding problems such as localized depressions and uneven wall thickness. Simultaneously, the opening size of the C-shaped pipe blank must be consistent to provide a precise reference for subsequent O-forming seam joining.
4. O-forming of JCOE straight seam submerged arc welded steel pipe. The C-shaped pipe blank is fed into the O-forming machine, and the pipe blank is pressed together by a ring mold, gradually closing the C-shaped opening to form a circular pipe blank (i.e., "O" shape). This step requires strict control of the joint gap (≤2mm) to avoid excessive gap affecting subsequent welding quality. Simultaneously, the roundness of the pipe blank must be monitored to ensure a roundness error ≤±0.5% × outer diameter of the steel pipe. The straightness of the pipe blank must also be controlled simultaneously to prevent defects such as bending and ellipticity.
5. Joint positioning and welding of JCOE straight seam submerged arc welded steel pipe. After O-forming, the joint of the pipe blank is fixed by spot welding to ensure that the pipe blank does not shift during welding. The spot welding spacing is controlled at 100-150mm, and the weld thickness is not less than 1/2 of the pipe wall thickness. Subsequently, a double-sided submerged arc welding process is used to weld the longitudinal seam of the tube blank. During welding, the welding current, voltage, and welding speed must be controlled to ensure that the weld penetration is ≥80% of the wall thickness, free from defects such as cracks, porosity, and slag inclusions. After welding, the weld is preliminarily cleaned.
6. Expansion and Final Inspection of JCOE Straight Seam Submerged Arc Welded Steel Pipes. For steel pipes requiring high precision, cold expansion is necessary. A diameter expander is used to moderately expand the circular tube blank, further correcting its roundness, straightness, and dimensional accuracy. Simultaneously, residual stress within the tube blank is eliminated, improving the mechanical properties of the steel pipe. After expansion, the steel pipe undergoes a comprehensive inspection, including dimensional checks, non-destructive testing, and hydrostatic testing. Only after passing these tests can the pipe be shipped as a finished product.

Third, Key Process Control Points for JCOE Straight Seam Submerged Arc Welded Steel Pipes.
1. Raw Material Control for JCOE Straight Seam Submerged Arc Welded Steel Pipes: The thickness tolerance of the steel plate must be ≤±10%, the surface must be free of obvious scratches and rust, and the sulfur and phosphorus content in the chemical composition must meet the corresponding steel grade standards to avoid cracking during forming due to raw material defects.
2. Die Precision for JCOE Straight Seam Submerged Arc Welded Steel Pipes: The curvature and dimensions of the J, C, and O forming dies must precisely match the steel pipe specifications. The die surface must be smooth and free of wear. The dies must be calibrated regularly to prevent die errors from causing deviations in the pipe blank forming process.
3. Bending Parameters for JCOE Straight Seam Submerged Arc Welded Steel Pipes: The bending force, speed, and angle of the three-step forming process must be strictly implemented according to the process specifications to avoid over-bending or under-bending. Each batch of steel pipes must undergo trial forming first, and mass production can only proceed after the parameters are adjusted and approved. 
4. Joint Gap of JCOE Straight Seam Submerged Arc Welded Steel Pipe: The joint gap during O-forming needs to be controlled between 0.5 and 2mm. An excessively large gap can lead to incomplete weld penetration, while an excessively small gap can cause slag inclusions and cracks. Real-time monitoring and adjustment are necessary during jointing.
5. Residual Stress of JCOE Straight Seam Submerged Arc Welded Steel Pipe: Residual stress is generated during the forming process. This can be eliminated through methods such as diameter expansion and normalizing to prevent deformation and cracking of the steel pipe during subsequent use.

Fourth, Technological Advantages and Limitations of JCOE Straight Seam Submerged Arc Welded Steel Pipe.
1. Technological Advantages: Compared to UOE forming technology, JCOE forming technology requires lower equipment investment, resulting in more advantageous production costs. The step-by-step forming method allows for precise control of billet deformation, resulting in high forming accuracy and superior roundness and straightness compared to spiral welded pipes. It is suitable for forming thick-walled, large-diameter steel pipes. It can flexibly adapt to the production of steel pipes of different specifications and grades, achieving high batch production efficiency and stable weld quality, making it suitable for high-pressure, high-requirement engineering scenarios. 
2. Limitations: The forming process is a step-by-step operation, and the production pace is slightly slower compared to UOE forming; it requires a higher level of technical skill from operators, and improper parameter adjustments can easily lead to defects such as tube blank wrinkles, cracks, and dimensional deviations; it is not suitable for forming small-diameter, thin-walled steel pipes, and is only suitable for medium and large-diameter, thick-walled specifications.

Fifth, Industry Application Scenarios of JCOE Straight Seam Submerged Arc Welded Steel Pipes.
Straight seam steel pipes produced by the JCOE forming process, due to their high precision, high pressure resistance, and high reliability, are mainly used in: long-distance oil and gas trunk lines and gathering pipelines; urban gas, water supply, and heating trunk lines in municipal engineering; bridge columns, high-rise building pile foundations, and pipe piles in heavy structural engineering; and pipelines for transporting corrosive media such as brine and slurry. It is a core pipe forming process in high-end engineering fields.