Q1: What is the difference in production cost between electric resistance welded pipe and seamless pipe?
The production cost of welded pipe is 30-50% lower than that of seamless pipe because: ① Hot rolled coil is used instead of solid billet, material utilization rate is ＞95% (seamless pipe is only 70%); ② Continuous forming welding speed can reach 60m/min (seamless perforation is only 2-3m/min); ③ Low energy consumption (welded pipe is about 300kWh/ton, seamless pipe requires 500kWh). However, the premium of high-end alloy steel seamless pipe can offset the cost disadvantage. The cost advantage of welded pipe is most obvious when Φ≤168mm.
Q2: Under what conditions must seamless pipe be used instead of welded pipe?
① Ultra-high pressure conditions (such as oil well casing P≥110MPa); ② Extreme temperature (boiler tube wall temperature＞600℃); ③ Strong corrosive media (such as HCl environment); ④ High fatigue load (such as aviation hydraulic pipe); ⑤ Nuclear grade pipeline (requires overall homogeneity). In these scenarios, the characteristic of seamless pipe without weld weakness becomes the key. However, modern HFW welded pipes can partially replace seamless pipes with diameters of Φ≤457mm through heat treatment.
Q3: What are the advantages of welded pipes in terms of dimensional accuracy?
The outer diameter tolerance of welded pipes can reach ±0.2% (such as ±0.23mm for Φ114mm pipes), while that of seamless pipes is ±0.75%; the wall thickness uniformity of welded pipes is ±7.5%, while that of seamless pipes is ±12.5%. This is because welded pipes use cold-rolled precision strip steel, and the sizing unit has an accuracy of 0.1mm. The roundness of welded pipes for automobile transmission shafts is ≤0.3mm, far exceeding the level of seamless pipes. Thin-walled pipes (such as δ=1mm) can almost only be produced through welded pipe processes.
Q4: How does seamless processing improve the performance of welded pipes?
Through overall heat treatment (such as 900℃ normalizing), the grains in the weld area are consistent with the parent material, eliminating the banded structure. Online medium-frequency induction heating (800-950℃) combined with tension reduction can achieve the "thermomechanical rolling" effect. The transverse impact energy of the treated welded pipe is increased by 50%, and the anisotropy ratio is reduced to below 1.1. Japan's JFE's "HISTORY" technology can make the performance of HFW welded pipes reach the level of seamless pipes, and has been used in deep-sea pipelines.
Q5: Will welded pipes replace seamless pipes in the future?
In the field of Φ≤508mm, the market share of welded pipes has exceeded 80% (95% for oil and gas pipelines). However, seamless pipes are still irreplaceable in the fields of ultra-thick walls (δ＞50mm) and special alloys (such as nickel-based alloys). The technical development trend shows: ① The strength of welded pipes is improved through the TMCP process; ② The seamless pipe uses oblique rolling perforation + cold rolling to reduce costs. The two will form a complementary rather than completely substitutive relationship. It is expected that the global welded pipe/seamless pipe production ratio will remain at around 7:3 in 2030.
