1.Question: What are the commonly used steel strip materials for producing LSAW Pipe, EFW Pipe, ERW Pipe, and HFW Pipe? What are the core grades?
1.Answer: All four types of welded pipes use carbon structural steel and low-alloy high-strength steel as their core materials. Common grades vary depending on the application: general-purpose carbon steels include Q235B and Q195-L, suitable for ordinary fluid transportation; low-alloy high-strength steels include Q355B (formerly Q345B) and X42-X80 (pipeline steel), suitable for high-pressure and long-distance pipelines; for special applications, LSAW Pipe commonly uses X100-X120 ultra-high-strength pipeline steel, HFW Pipe commonly uses corrosion-resistant materials such as 09CrCuSb, EFW Pipe mostly uses precision carbon steel, and ERW Pipe covers the entire range of materials mentioned above, offering the strongest adaptability.
2.Question: What is the wall thickness range of LSAW Pipe? How does its wall thickness differ from the other three types of welded pipes?
2.Answer: LSAW pipes have a wall thickness range of 6.3mm-60mm, primarily producing thick-walled pipes; some special processes can produce ultra-thick-walled pipes up to 80mm thick. HFW pipes have a wall thickness range of 1.2mm-12.7mm, mainly thin-walled and medium-thin-walled pipes. ERW pipes have a wall thickness range of 1.5mm-25mm, slightly wider than HFW pipes. EFW pipes have the narrowest wall thickness range, from 2.0mm-8.0mm, belonging to thin-walled precision welded pipes, and cannot produce thick-walled products.
3.Question: What is the relationship between the weld strength and the base metal strength of the four types of welded pipes? Which welded pipe has a weld strength closest to that of the base metal?
3.Answer: The core rule is: HFW Pipe > EFW Pipe > ERW Pipe > LSAW Pipe. HFW pipes achieve weld strengths of 95%-105% of the base metal strength. High-frequency rapid heating prevents overheating and softening of the base metal, resulting in the best microstructure consistency and closest strength between the weld and the base metal. EFW pipes achieve weld strengths of 90%-98% of the base metal strength due to precise fusion process control. Traditional ERW pipes achieve weld strengths of 85%-95% of the base metal strength, experiencing slight strength loss due to the influence of welding current frequency. LSAW pipes, due to the high heat input of submerged arc welding and a large heat-affected zone in the base metal, have weld strengths of only 80%-90% of the base metal strength, representing the largest difference between the weld strength and the base metal strength among the four types.
4.Question: What are the characteristics of pressure resistance and corrosion resistance for LSAW pipes, EFW pipes, and ERW/HFW pipes?
4.Answer: Regarding pressure resistance: LSAW Pipe (thick-walled, large-diameter) > HFW Pipe > ERW Pipe > EFW Pipe. LSAW Pipe is suitable for high-pressure pipelines above 10MPa (such as long-distance oil and gas pipelines), HFW Pipe is suitable for medium-high pressure scenarios of 2-8MPa, ERW Pipe is suitable for 1-5MPa, and EFW Pipe is only suitable for low-pressure scenarios of 0.5-3MPa. Regarding corrosion resistance: None of the four types of welded pipes inherently possess corrosion resistance; it depends on the material or coating. HFW Pipe is more easily adapted to galvanizing and anti-corrosion coating processes, with strong coating adhesion. ERW Pipe is second best. LSAW Pipe has a more difficult thick-walled coating application process, and EFW Pipe has a slightly weaker overall corrosion resistance due to the thin-walled coating being easily damaged.
5.Question: What is the width of the heat-affected zone of LSAW Pipe? What are its advantages and disadvantages compared to ERW/HFW Pipe?
5.Answer: The heat-affected zone (HAZ) width of LSAW pipes is 2-5mm due to the large heat input (typically 1.5-3.0kJ/mm) in submerged arc welding, resulting in a wider HAZ. HFW pipes have a HAZ width of only 0.5-1.5mm, with concentrated high-frequency heating, leading to a narrower HAZ. ERW pipes (traditional low-frequency welding) have a HAZ width of 1-3mm, falling between the two. Advantages and disadvantages of HAZ width: A narrower HAZ is better, reducing changes in the base material structure and improving the overall toughness and fatigue resistance of the pipe. Therefore, HFW pipes are far superior to LSAW pipes in HAZ control, with ERW pipes being slightly less effective.
