There are only a few methods in the industry for producing straight seam steel pipes from steel plates or strips. The fundamental difference lies in the forming method of the steel pipe; the subsequent processing after forming is basically the same. The forming method depends on the distribution of the weld seam. Based on the weld seam distribution, steel pipes are divided into two basic forms: straight seam steel pipes and spiral steel pipes. Correspondingly, welded pipe production is divided into the production of straight seam steel pipes and spiral steel pipes. The most widely used welding method for both straight seam and spiral steel pipes is submerged arc welding (SAW), which offers good quality, high productivity, mature technology, and stability. Q355 straight seam steel pipe is a type of straight seam steel pipe made from Q355 steel. Q355 is a low-alloy high-strength structural steel with excellent mechanical properties, weldability, and corrosion resistance. Therefore, Q355 straight seam steel pipe inherits these excellent characteristics and has wide applications in various industrial fields.

First, what are the application ranges of straight seam steel pipes?
• Main pipelines for transporting gas, water, and oil on land and sea;
• Stainless steel pipes for transporting chemical raw materials and products in the chemical industry;
• Structural pipes for the marine industry;
• Pipes for boiler manufacturing and structural pipes for special purposes.

Firstly, Q355 straight seam steel pipes have high strength, capable of withstanding large pressures and loads, making them suitable for various applications requiring heavy loads and high pressures, such as pipelines in the oil, natural gas, and chemical industries. Secondly, Q355 straight seam steel pipes have good weldability, enabling good connections with other materials, facilitating construction and maintenance. Furthermore, Q355 straight seam steel pipes also possess excellent corrosion resistance and oxidation resistance, allowing for long-term use in harsh environments without being easily corroded or damaged.

In practical applications, Q355 straight seam steel pipes are widely used in pipelines and structural supports in the oil, natural gas, chemical, power, and construction industries. For example, in oil and natural gas pipelines, Q355 straight seam steel pipes, with their high strength and good corrosion resistance, ensure the safety and stability of transportation. In the construction industry, Q355 straight seam steel pipes are often used as the main supporting and load-bearing components of bridges, high-rise buildings, and other structures, ensuring the stability and safety of the buildings.

In short, Q355 straight seam steel pipes, as a high-quality, high-performance industrial product, have been widely used and recognized in various fields. With continuous technological advancements and market expansion, the application prospects of Q355 straight seam steel pipes will be even broader.

Secondly, what are the stages of straight seam steel pipe production? 

The production of straight seam steel pipes can be divided into two stages: the forming stage and the post-forming manufacturing stage. Foreign manufacturers of large-diameter straight seam submerged arc welded steel pipes classify the production according to four forming methods: UOE forming (UOE process); roll bending forming (Rollbending process); progressive forming process; and progressive folding process.

1. Forming Stages of Straight Seam Steel Pipes
1.1 UOE Forming: This method has the highest productivity and is the most important production method for straight seam steel pipes. The simplified production process of the unit is as follows: first, the steel sheet is bent into a U-shape, then pressed into an O-shape, and after internal and external welding, it undergoes mechanical cold expansion. This method is characterized by its ability to produce steel pipes with extremely stable dimensions, high production capacity, and the ability to manufacture steel pipes exceeding 18 meters in length.
1.2 Roll Bending: In this method, the steel sheet is bent into an open tube after several processes on a roll-bending machine, with the open edges remaining straight and undeformed. The open tube is then sent to an edge-bending machine, where the two edges of the sheet are continuously rolled and formed. This method is characterized by its strong adaptability and good economic efficiency for medium production volumes, but it limits the minimum diameter and maximum wall thickness of the produced steel pipes.
1.3 Gradual Die Forming: In this method, the steel sheet is first sent to a forming press, then controlled by a controller to a bending position. After passing through a series of dies matching the pipe diameter, an open tube is formed. During operation, there are two controllers; one side of the sheet is first bent into a semi-circle, then the sheet is moved by a second controller, and the other side is subsequently bent and formed. Because the thickness of the bending die blade affects the roundness of the open pipe, the thickness of the bending die blade must be kept to a minimum. After forming, the open pipe is generally sent to an edge-bending machine, where the two edges of the plate are continuously rolled into the desired shape. This method is characterized by its high adaptability and good economic efficiency for medium production volumes, and it can produce small-diameter and thick-walled steel pipes.
1.4 Gradual Bending Forming: This method of steel pipe forming was initially used in the marine industry. Because it is often necessary to cold-form controlled-rolled plates to produce particularly thick steel pipes, and this method offers high forming accuracy and pressure application, it is used to produce thick-walled steel pipes for the marine industry. This method is characterized by its suitability for high-strength and thick-walled steel pipes; it is suitable for both small and large diameters, and therefore can be used to manufacture mainline pipelines and pipes for marine structures. The system equipment cost is low, highly adaptable, and economical, and costs can be reduced even for small-batch production.

2. Manufacturing Stages of Straight Seam Steel Pipes After Forming
After the forming stage described above is completed, the subsequent manufacturing stages of straight seam steel pipes include a series of basically similar processes, the main processes being:
2.1 Edge Processing and Welding Beveling of Plates: This involves milling and planing. One or more milling or planing heads can be used on both sides of the plate. Depending on the plate thickness, the beveling can be processed into an I-shape, a single V-shape with a certain blunt edge, or a double V-shape. For particularly thick steel pipes, the outer seam can be milled into a U-shape. The purpose is to reduce the consumption of welding materials and improve productivity, while the root is wider to avoid welding defects.
2.2.2 Tack Welding. Generally, carbon dioxide gas shielded welding is used. The purpose is to stabilize the steel pipe, which is particularly useful for subsequent submerged arc welding, preventing burn-through. After tack welding, the steel pipe should be visually inspected to confirm that the weld is continuous and free of defects.
2.3 Internal and External Welding of the Steel Pipe, i.e., Precision Welding. After the tack welding of the steel pipe, the subsequent main process is the internal and external welding, a crucial step in the steel pipe manufacturing process. This is completed using a submerged arc welding method separate from the forming unit. To improve productivity, multi-wire submerged arc welding is employed for both internal and external seams, with up to five welding wires. To prevent weld misalignment, a special automatic weld centering device is installed on the welding head. For thick-walled steel pipes, multi-layer welding is used to reduce heat input and improve the physical properties of the weld.
2.4 Weld Inspection. To quickly identify welding defects, ultrasonic and X-ray inspections are performed immediately after welding. Defects are repaired promptly.
2.5 Cold Expansion. After welding, the roundness and straightness of the steel pipe often do not meet the relevant standards and technical requirements. Sizing and straightening are performed at the pipe manufacturing plant using mechanical cold expansion.
2.6 Hydrostatic Testing of Steel Pipes. The test pressure can reach over 90% of the yield strength of the steel pipe material.
2.7 Inspection. Finally, the entire steel pipe was subjected to ultrasonic testing, X-ray testing, and visual inspection.