The production process of straight seam steel pipes

Straight seam steel pipes can be categorized into high-frequency straight seam pipes and submerged arc welded (SAW) straight seam pipes based on their production processes.

Continental Steel Co., Ltd is professional welded steel pipes manufacturer, for more details, please contact:sales@cscsteel-manufacturing.com

Among SAW pipes, different forming methods create types like UOE, RBE, and JCOE pipes. Below is an overview of the most commonly used forming processes for high-frequency straight seam pipes and submerged arc welded straight seam pipes.

Submerged Arc Welding (SAW) Straight Seam Pipe Production Process

Plate Inspection
Upon entering the production line, the steel plates intended for manufacturing large-diameter SAW pipes undergo full ultrasonic testing to detect any internal defects.

Edge Milling
Both edges of the steel plate are precisely milled using an edge milling machine to achieve the required plate width, edge parallelism, and bevel shape, ensuring optimal conditions for subsequent welding.

Edge Pre-bending
The edges of the plates are pre-bent with a pre-bending machine to introduce the necessary curvature, improving the forming accuracy.

Forming
Using a JCO forming machine, the pre-bent plate is gradually pressed: first into a "J" shape, then into a "C" shape, and finally into an open "O" shape through multi-step punching. This staged process efficiently shapes the steel into a cylindrical form.

Pre-welding
The open seam of the formed pipe is temporarily joined using gas-shielded welding (MAG) to stabilize the pipe for further processing.

Internal Welding
The internal seam of the pipe is welded using longitudinal multi-wire submerged arc welding, often employing up to four welding wires to ensure robust weld quality.

External Welding
Longitudinal multi-wire submerged arc welding is also performed on the outside of the pipe to complete the weld structure and enhance overall strength.

Ultrasonic Testing (First Round)
100% ultrasonic inspection is conducted on both internal and external welds, as well as the base material on both sides of the weld, to detect any hidden defects.

X-ray Testing (First Round)
Industrial X-ray television inspection is performed on all welds, supported by an image processing system to ensure high detection sensitivity and accuracy.

Diameter Expansion
The entire length of the SAW pipe undergoes diameter expansion to improve dimensional precision and to optimize the internal stress distribution within the pipe body.

Hydrostatic Testing
Each expanded pipe is subjected to hydrostatic testing to verify its ability to withstand the required pressure. Test data is automatically recorded and stored for quality assurance.

End Beveling
After passing the hydrostatic test, the pipe ends are machined to meet the specified bevel dimensions, ensuring ease of installation and welding on-site.

Ultrasonic Testing (Second Round)
A second ultrasonic inspection is carried out on each pipe to ensure no new defects have developed after diameter expansion and hydrostatic testing.

X-ray Testing (Second Round)
Post-expansion and pressure testing, another round of X-ray industrial television inspection and end weld radiographic filming is conducted to ensure the integrity of the welds.

Magnetic Particle Inspection of Pipe Ends
Magnetic particle testing is performed on the pipe ends to identify any surface or near-surface defects that could impact pipe performance.

Anti-corrosion and Coating
Pipes that pass all inspections are coated and treated for corrosion protection according to customer specifications, enhancing their service life and environmental resistance.

High-Frequency Straight Seam Pipe Production Process

Raw Material Preparation
High-quality carbon steel coils are selected as raw materials. The chemical composition, thickness, and width of the steel must comply strictly with production standards to ensure the strength and toughness of the finished pipes.

Uncoiling and Leveling
The steel coil is uncoiled using an uncoiler and then leveled by a precision leveling machine. This process eliminates any stress and unevenness in the strip caused during rolling and storage, providing a stable base for forming.

Forming
The leveled steel strip is gradually formed into a tubular shape through a series of forming stands equipped with specially designed rollers. In center forming, for example, the strip is bent from the center outward, maintaining a constant bending radius to achieve a round profile.

High-Frequency Welding
The edges of the formed steel strip are heated to the welding temperature using high-frequency resistance heat. Under the pressure of squeeze rollers, the edges are fused together to form a continuous longitudinal weld without the addition of filler material.

Deburring
After welding, internal and external burrs are removed using deburring tools. This ensures a smooth pipe surface, which is critical for both structural integrity and performance in applications such as fluid transport.

Sizing
The welded pipe passes through sizing rolls where it is calibrated to the exact specified diameter and roundness. This process ensures dimensional precision and uniform wall thickness across the length of the pipe.

Cutting
The pipes are cut into predetermined lengths using cutting equipment, such as flying saws or rotary cutters, ensuring clean, accurate cuts with minimal deformation.

Non-Destructive Testing (NDT)
The pipes undergo non-destructive testing, including ultrasonic testing and eddy current testing, to detect any internal or surface defects along the weld and body of the pipe. Only pipes passing all inspections proceed to the next stage.

Final Inspection
Dimensional measurements, mechanical property tests, and visual inspections are carried out to ensure compliance with customer specifications and relevant standards. Parameters such as wall thickness, diameter, weld quality, and surface finish are carefully checked.

Anti-corrosion and Coating (Optional)
Based on customer requirements, pipes can be coated with anti-corrosion layers, such as galvanized coatings, epoxy coatings, or polyethylene layers, to enhance durability and service life, particularly for use in harsh environments.