One of the most widely seen pipes in the industry is the straight-seam welded pipe. Various manufacturing processes are used to fabricate these steel pipes. Due to these, they have different properties, dimensions, and applications. Today, we will discuss two crucial techniques of steel pipe fabrication in depth. We are talking about high-frequency resistance welding, also known as ERW. The other technique, Longitudinal Submerged Arc Welding, is also crucial for several applications.
ERW Steel Pipes
The main raw material for making electric resistance-welded pipes is steel coils. First, it is subjected to edge milling to give it a ‘U’ shape. Then, it is inserted into a roller to shape it cylindrically. Further pressing by dies gives it the appropriate diameter. The pipe manufacturing line contains an electric resistance welding machine. It welds the pipe longitudinally, and a milling tool removes the excess weld material.
Manufacturing ERW pipes does not involve thermal melting or additional welding materials. It ensures that the composition of the final product is the same as the base material. After welding, steel pipes undergo annealing to increase their internal and external stress tolerance. ERW pipes offer diverse mechanical properties.
LSAW Steel Pipes
One of the main differences between LSAW and ERW pipes is the raw material. LSAW(Longitudinally Submerged Arc Welding) pipes use steel plates instead of steel coils. Longitudinal submerged arc welding produces pipes with a large diameter. ERW fabrication cannot achieve similar results. In LSAW fabrication, steel plates are affixed together longitudinally according to the required diameter. Then, they are welded with filler material.
Although LSAW pipe fabrication requires multiple wires for welding, the heat generated is minuscule. Ultimately, heat affects only a minute part of the pipe. The production process of LSAW pipes ensures good internal and external stress tolerance. For this reason, LSAW pipes attain 100% flaw detection by ultrasonic waves. Due to costlier raw materials and production, LSAW pipes are more expensive than ERW pipes. They are preferred for specialized use cases.
How They Differ in Raw Materials and Production Capacity
The primary raw material of ERW steel pipes is hot-rolled steel coils. LSAW pipes require hot-rolled steel plates. These differences lead to different production methods and factory output. Since steel coils are easy to manipulate in an assembly line, ERW steel pipes can be manufactured quickly and efficiently. The average production productivity of ERW pipes is 12 meters per minute. The upper limit for wall thickness is 25mm, while the maximum diameter is 660mm.
Since hot-rolled steel plates are thicker and stronger, they cannot be produced on an assembly line. LSAW pipes are manufactured using high-power presses in a tube blank or forming device. LSAW steel pipes can achieve more dimensional requirements than ERW pipes. The upper limit for LSAW pipe thickness is 40mm, and the maximum pipe diameter is 1422mm. LSAW pipe production has an average speed of about 4 meters per minute. The different metal forming methods in LSAW are UOE, JCOE, and HME.
Difference in Welding Techniques
ERW and LSAW pipes are welded using different techniques. For LSAW, the various forming methods are UOE, JCOE, and HME. In UOE molding, the pipe is subjected to internal and external welding. In the JCOE method, the pipe undergoes pre-welding and cold expansion. HME steel pipes are rolled by the mandrel method in accordance with “C-C-O” and then welded.
Two primary types of welding are used for ERW pipes: DC and AC. AC welding may utilize high, super medium, medium, or low-frequency current. Different frequencies are preferred for distinct thicknesses of pipes. For example, high-frequency DC welding suits pipes with low wall thickness. DC welding is performed for steel pipes with small outside diameters. One of the primary differences in welding techniques between ERW and LSAW pipes is the welding wire. While LSAW steel pipes require one or multiple welding wires, ERW pipes do not.
Appearance Differences
LSAW pipes are thicker and broader than ERW pipes. Their welded seams on the inner and outer walls are taller than those of ERW pipes. It makes them more susceptible to corrosion. However, due to their physical parameters, LSAW pipes are preferred for heavy-duty applications. Long-distance oil & gas pipelines are made from LSAW pipes. According to API regulations, only LSAW pipes are fit for passing through Class 1 and Class 2 zones. Class 1 and Class 2 zones include mountainous areas, beaches, and urban landscapes.
The welding material on the seams of ERW steel pipes is removed during production. This gives its surface a smoother finish and prevents corrosion. Commonly employed in wire casings, ERW steel pipes have a small defect probability and are resistant to scratches. Due to good welding quality, they are suitable for transporting natural gas in some scenarios.
Cost and Procurement Factors
Cost is a critical factor for manufacturers and suppliers alike. Difficulty in material procurement and production can lead to higher prices. While LSAW pipes are an excellent investment for particular applications, they have a high production cost. The rolling of steel plates involves high-tonnage presses and dies. In addition, submerged arc welding is a slow process that longitudinally joins the rolled steel plates. These factors contribute to making LSAW pipes more expensive than ERW pipes. The price difference can range from 10 to 25%.
The manufacturing of ERW pipes benefits from assembly line optimization. It leads to a higher production rate. Raw materials for ERW pipes are also cheaper to procure and manipulate. Steel coils are easier to handle than steel plates. In addition, ERW pipes can often be procured locally, whereas LSAW pipes may need to be imported.
Conclusion
The core differences between ERW and LSAW pipes lie in their material, dimensions, and applications. While ERW pipes are great for general-purpose use, LSAW pipes are indispensable for heavy-duty applications. Are you looking for medium-sized construction, agricultural, or transportation applications? In that case, the ERW pipe is suitable for you. Are you looking for more specialized applications? Perhaps you want to transport crude oil, natural gas, or other hydrocarbons? In large-scale and heavy-duty implementations, LSAW pipes are superior. Contact us with any questions you might have on ERW or LSAW tubing. We are enthusiastic to help you!