Straight seam steel pipes are commonly used in the construction of water supply industries, petrochemical plants, and other fields. They are steel pipes where the weld seam is parallel to the longitudinal direction of the pipe. They are generally classified into metric welded steel pipes, welded thin-walled pipes, transformer cooling oil pipes, etc. The production process of straight seam steel pipes is simple, with high production efficiency and low cost, leading to rapid development. Compared with spiral welded steel pipes, they have the advantage of faster production speed.

First, what is a straight seam steel pipe? 
Straight seam steel pipes are generally welded pipes used to transport low-pressure fluids. They are manufactured using Q195, Q215A, Q235A steel, and Q235B ordinary carbon steel. They can also be manufactured using easily weldable 0317 standard model 6012 and 755 mild steel. The steel pipes undergo water pressure, bending, and flattening tests, and have certain requirements for surface quality. The usual delivery length is 4-10m, and fixed-length (or multiple-length) delivery is often required. Welded pipe specifications are expressed in nominal diameter (millimeters or inches). The nominal diameter differs from the actual diameter. Welded pipes are available in two types based on wall thickness: ordinary steel pipes and thickened steel pipes. They are also classified by end type: threaded and unthreaded. Submerged arc welded straight seam steel pipes utilize submerged arc welding technology, employing filler material welding and granular flux for arc protection. The produced diameter can reach 1500mm. LSAW is the abbreviation for submerged arc welded straight seam steel pipe. Production processes for submerged arc welded straight seam steel pipes include JCOE forming technology and roll forming submerged arc-welding technology. For larger diameters, two steel plates may be rolled together, resulting in a double weld seam. Compliant standards include GB/T3091-2008 Low-Pressure Fluid Steel Pipe Production Standard, GB/T9711.1-2-1997 Oil and Gas Steel Pipe Production and Use Standard, and the American API 5L pipeline steel pipe standard.

Secondly, what are the manufacturing processes for straight seam steel pipes? 
Straight seam steel pipes can be classified into high-frequency straight seam steel pipes and submerged arc welded straight seam steel pipes according to their manufacturing processes. Submerged arc welded straight seam steel pipes are further classified into UOE, RBE, JCOE steel pipes, etc., according to their different forming methods.
What are the processes involved in submerged arc welding?
1. Plate inspection: After the steel plates used to manufacture large-diameter submerged arc welded straight seam steel pipes enter the production line, they undergo full-plate ultrasonic testing.
2. Edge milling: The two edges of the steel plate are milled on both sides using an edge milling machine to achieve the required plate width, edge parallelism, and bevel shape.
3. Pre-bending: The plate edges are pre-bent using a pre-bending machine to achieve the required curvature.
4. Forming: On a JCO forming machine, one half of the pre-bent steel plate is first pressed into a "J" shape through multiple step-by-step stamping processes. Then, the other half of the steel plate is similarly bent and pressed into a "C" shape, finally forming an open "O" shape.
5. Pre-welding: The formed straight seam steel pipe is joined together and continuously welded using gas shielded welding (MAG).
6. Internal welding: Welding is performed on the inside of the straight seam steel pipe using longitudinal multi-wire submerged arc welding (up to four wires).
7. External Welding: Longitudinal multi-wire submerged arc welding is used to weld on the outside of the straight seam submerged arc welded steel pipe.
8. Ultrasonic Inspection I: 100% inspection of the inner and outer welds and the base material on both sides of the weld of the straight seam steel pipe;
9. X-ray Inspection I: 100% X-ray industrial television inspection of the inner and outer welds, using an image processing system to ensure the sensitivity of the flaw detection;
10. Diameter Expansion: The entire length of the submerged arc welded straight seam steel pipe is expanded to improve the dimensional accuracy of the steel pipe and improve the distribution of internal stress.
11. Hydrostatic Testing: Each expanded straight seam steel pipe is inspected on a hydrostatic testing machine to ensure that the steel pipe meets the standard test pressure requirements. This machine has automatic recording and storage functions.
12. Beveling: The pipe ends of the inspected and qualified straight seam steel pipes are processed to achieve the required pipe end beveling dimensions;
13. Ultrasonic Inspection II: Each straight seam steel pipe undergoes ultrasonic testing again to check for potential defects after diameter expansion and hydrostatic testing.
14. X-ray Inspection II: X-ray industrial television inspection and end weld radiography are performed on the steel pipes after diameter expansion and hydrostatic testing.
15. Pipe End Magnetic Particle Inspection: This inspection is performed to detect pipe end defects.
16. Corrosion Protection and Coating: Qualified steel pipes are coated with anti-corrosion materials according to user requirements.

Third, Applications of Straight Seam Steel Pipes.
Straight seam steel pipes are mainly used in water supply projects, the petrochemical industry, the chemical industry, the power industry, agricultural irrigation, and urban construction. For liquid transportation: water supply and drainage. For gas transportation: coal gas, steam, and liquefied petroleum gas. For structural applications: piling pipes, bridge construction, docks, roads, building structures, etc.