Introduction
Welded pipe is a pipe formed by welding the edges of metal sheets, strips or coils together. It is the most commonly used steel pipe in modern industry, and the global market size is expected to reach US$28.7 billion in 2025. Through this article, you will have a comprehensive understanding of welded pipe.
Two Main Processes For Welding Pipes
Electric resistance welding (ERW) process
Erw uses high-frequency current to instantly heat the edge of the tube to a molten state, and connects them together by extrusion, ERW without the need for welding filler materials.
Submerged Arc Welding (SAW) Process
The submerged arc welding process forms an arc between the continuously fed electrode and the workpiece. The electrode is a conductor that transfers the current to the place where welding is required. The flux is used to produce shielding gas and slag to avoid contamination. The arc moves along the weld at a uniform speed, and the excess flux is also recycled. The heat loss of the submerged arc welding process is also extremely low.
JCOE: J-shape → C-shape → O-shape progressive stamping
UOE: U-shaped → O-shaped two-step pressing
Three Forms
External welding is welding on the surface of the pipe, and the heat generated by the arc is concentrated on the outside of the pipe wall. Internal welding is welding by inserting the welding gun into the inside of the pipe. Double-sided welding requires welding on both the inside and outside. The whole process is first external welding for priming, root cleaning, internal welding for filling, and finally external welding for covering. It should be noted that no matter which welding method is used, there will be seams!
Application
Building and infrastructure: used for building frames, steel structure measuring columns, bridges, tunnel structures, highway guardrails.
Energy and chemical industry: long-distance oil and natural gas transportation. As oil well casing and drilling equipment components in oil field mining. Urban water supply, drainage, gas transportation.
Transportation: automobile chassis, exhaust pipes, body structures, container frames, port crane booms.
Machinery manufacturing and industry: concrete pump truck booms, bearing seats, drive shafts, storage tanks and pressure vessels manufacturing, etc.
Seamless Pipe vs Welded Pipe
From the definition, we can clearly know the essential difference between the two pipes. The welded pipe has welds, while the seamless pipe does not.
Advantages of welded pipe compared to welded pipe
Low cost: The utilization rate of raw materials reaches 98%, and the comprehensive cost is 15%-20% cheaper than other seamless pipes of the same specifications.
High production efficiency: The production efficiency of welded pipes is extremely high, with an average production speed of 60 meters per minute, while seamless pipes are only 3 meters per minute.
Uniform wall thickness: The wall thickness of welded pipes is relatively consistent, with a wall thickness tolerance of approximately ±0.05mm, while that of seamless pipes is ±0.5mm.
Good surface quality: The surface of welded pipes is relatively smooth, so it is less susceptible to corrosion, with a corrosion rate of <0.01mm per year, while that of untreated seamless pipes is 0.15mm per year.
Advantages of seamless pipes over welded pipes
High strength: seamless pipes have no welds, and the overall strength is higher, avoiding weak points due to welding gaps.
Strong pressure bearing capacity: seamless steel pipes can be used in high-pressure environments, while welded pipes can only be used in medium and low-pressure environments due to welds.
Wide range of application: Same as above, the seamless pipe has a wider range of application than the welded pipe because of its strong pressure bearing capacity.
