In the industry, there are only a few methods for producing Q355 straight seam steel pipes from steel plates or strips. The fundamental difference lies in the forming method of the steel pipe. After forming, the subsequent processing of Q355 straight seam steel pipes is basically the same. The forming method depends on the distribution of the weld seams in the Q355 straight seam steel pipe. According to the distribution of weld seams, steel pipes are divided into two basic forms: straight seam steel pipes and spiral seam pipes. Correspondingly, welded pipe production is divided into the production of straight seam steel pipes and the production of spiral seam pipes. The most widely used welding method for straight seam steel pipes and spiral seam pipes is submerged arc welding (SAW), which offers good quality, high productivity, mature technology, and stability.
Currently, straight seam steel pipes are widely used abroad in the following areas:
· Main pipelines for transporting gas, water, and oil on land and at 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.
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.
Firstly, Q355 straight seam steel pipe has high strength, capable of withstanding large pressures and loads, making it 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 pipe has good weldability, enabling good connections with other materials, facilitating construction and maintenance. Furthermore, Q355 straight seam steel pipe also has good corrosion resistance and oxidation resistance, allowing for long-term use in harsh environments without easily suffering corrosion and damage.
In practical applications, Q355 straight seam steel pipe is widely used in pipelines and structural supports in the oil, natural gas, chemical, power, and construction industries. For example, in oil and gas pipelines, Q355 straight seam steel pipes, with their high strength and excellent corrosion resistance, ensure safe and stable 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.
The production of Q355 straight seam steel pipes can be divided into two stages: the forming stage and the post-forming manufacturing stage.
The production of large-diameter straight seam submerged arc welded steel pipes abroad is classified into four types according to the forming method:
·UOE forming (UOE process);
·Rollbending process;
·Progressive forming process;
·Progressive folding process.
Production of Q355 Straight Seam Steel Pipe
A.1 Forming Stages of Q355 Straight Seam Steel Pipe
A.1.1 UOE Forming of Q355 Straight Seam Steel Pipe: 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, it is bent into a U-shape, then pressed into an O-shape, and after internal and external welding, it undergoes mechanical cold expansion. The characteristics of this method are that it can produce steel pipes with extremely stable dimensions, high production capacity, and can manufacture steel pipes with lengths exceeding 18m.
A.1.2 Roll Bending Forming of Q355 Straight Seam Steel Pipe: In this method, after several processes on a roll-bending machine, the steel plate is bent into an open pipe, and the open edge remains straight without deformation. The open pipe is then sent to an edge-bending machine, where the two edges of the plate are continuously rolled and formed. The characteristics of this method are strong adaptability and good economy for medium production volumes, but it limits the minimum diameter and maximum wall thickness of the produced steel pipes.
A.1.3 Gradual die forming of Q355 straight seam steel pipe: This forming method involves first sending the steel plate to a forming press, then a controller moves it to a bending position. After passing through a series of dies matching the pipe diameter, an open pipe is formed. During operation, two controllers are used. One side of the plate is first bent into a semicircle, then the plate is moved by a second controller, and the other side is subsequently bent. 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. Generally, after forming, the open pipe is 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 strong adaptability, good economic efficiency for medium production volumes, and the ability to produce small-diameter and thick-walled steel pipes.
A.1.4 Gradual bending forming of Q355 straight seam steel pipe: 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, 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, applicable to both small and large diameters. Therefore, it can be used to manufacture trunk lines and pipes for marine structures. The system boasts low equipment costs, strong adaptability, and good economic efficiency, reducing costs even for small-batch production.
A.2 Manufacturing Stages of Q355 Straight Seam Steel Pipes After Forming: After the above forming stage, the subsequent manufacturing stages of large-diameter straight seam steel pipes include a series of basically similar processes. The main processes are:
A.2.1 Edge Processing and Welding Beveling of Plates: Processing methods include 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 welding material consumption, increase productivity, and ensure a wider root to avoid welding defects.
A.1.2.2 Tack Welding, also known as pre-welding. Generally, carbon dioxide gas shielded welding is used 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.
A.2.3 Internal and external welding of Q355 straight seam steel pipes, i.e., precision welding. After tack welding of Q355 straight seam steel pipes, the subsequent main process is internal and external welding, a crucial step in the 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 used for internal and external seam welding, with up to 5 welding wires. To prevent weld misalignment, a special automatic weld centering device is installed on the welding head. Multi-layer welding is used for thick-walled steel pipes to reduce heat input and improve the physical properties of the weld.
A.2.4 Weld inspection of Q355 straight seam steel pipes. To quickly identify welding defects, ultrasonic and X-ray inspections are performed immediately after welding. Defects are repaired promptly.
A.2.5 Cold Expansion of Q355 Straight Seam Steel Pipes. After welding, the roundness and straightness of the steel pipe often fail to meet relevant standards and technical requirements. Sizing and straightening are performed at the pipe manufacturing plant using mechanical cold expansion.
A.2.6 Hydrostatic Testing of Q355 Straight Seam Steel Pipes. The test pressure can reach over 90% of the yield strength of the steel material.
A.2.7 Inspection of Q355 Straight Seam Steel Pipes. Finally, the entire Q355 straight seam steel pipe undergoes ultrasonic testing, X-ray testing, and visual inspection.
Post time: Jun-01-2026