What types of carbon steel welded pipes are commonly used in the construction industry?
ERW straight seam welded pipes (such as scaffolding pipes, steel structure pillars), square pipes (decorative frames), galvanized pipes (fire water pipes) and spiral welded pipes (large diameter pipes for pile foundations) are commonly used in construction. Scaffolding pipes are mostly made of Q235 material, with a diameter of 48mm and a wall thickness of 3.5mm; square pipes are used for curtain wall support, and the surface can be sprayed for beautification; galvanized pipes are corrosion-resistant and have a service life of more than 20 years. The core tube structure of high-rise buildings may use thick-walled LSAW welded pipes as load-bearing columns.
Why choose carbon steel welded pipes for oil and gas pipelines?
The cost of carbon steel welded pipes (such as API 5L X70) is only 1/3 of that of stainless steel pipes, and the strength meets the requirements of long-distance pipelines (usually with a pressure of more than 10MPa). Submerged arc welded pipes (LSAW/SSAW) can produce pipelines with a diameter of up to 1420mm, which is suitable for large-scale oil and gas transportation. By adding trace elements such as Cr and Ni and combining with anti-corrosion coating (3PE), its service life can reach 30 years. Compared with seamless pipes, welded pipes are significantly more economical in large-diameter fields, and modern flaw detection technology can ensure zero defects in welds.
What are the use scenarios of welded pipes in mechanical manufacturing?
Precision welded pipes are commonly used in the machinery industry as hydraulic cylinders (20# steel, inner wall honing), drive shaft sleeves (45# steel quenching and tempering treatment) and conveyor rollers (wear-resistant coating). ERW welded pipes for automobile chassis must pass the expansion test to ensure that they do not crack during collision; agricultural machinery uses galvanized pipes to prevent rust; high-strength welded pipes (Q690D) for engineering machinery booms need to withstand alternating loads. Compared with castings, welded pipes can reduce weight by more than 20%.
How is galvanized welded pipe used in water supply systems?
Galvanized welded pipes (GB/T 3091) are traditional water supply pipes with a hot-dip galvanizing layer thickness of ≥65μm, which can effectively prevent rust from polluting water quality. Its advantages are low cost and simple installation (threaded connection), but the zinc layer may fall off after long-term use, resulting in the "red water" phenomenon. Modern water supply systems are gradually replaced by PPR pipes, but fire sprinkler systems are still forced to use galvanized steel pipes (GB 5135 standard) because of their better fire resistance and pressure bearing capacity (≥1.6MPa).
Does the automotive industry use carbon steel welded pipes?
Welded pipes are used for automobile exhaust pipes (mainly 409L stainless steel welded pipes), drive shafts (20CrMo alloy steel welded pipes) and chassis structural parts (Q345B square pipes). The battery pack shell of new energy vehicles uses high-strength galvanized welded pipes (HC420/780DP), which is 30% cheaper than aluminum parts. Welded pipes can be used to manufacture complex cross-section parts, such as A-pillar reinforcement pipes, through hydraulic forming technology, and their bending strength is 15% higher than that of solid parts. Under the trend of lightweighting, the application of high-strength steel welded pipes with a thickness of less than 1.2mm has increased significantly.
