What are the main production methods of carbon steel pipes?
The main methods include seamless steel pipe production (hot rolling, cold drawing) and welded steel pipe production (straight seam welding, spiral welding). Seamless pipes are formed by perforation and rolling, and have high pressure bearing capacity; welded pipes are welded after forming with coils, which is efficient but the welds may become weaknesses. Seamless pipes are mostly used in high-end fields (such as oil drilling), while welded pipes are often used in building scaffolding. The process selection depends on cost, size and usage requirements.
What is the production process of hot-rolled seamless steel pipes?
The process includes: round steel billets are heated to 1200℃ → perforators form rough pipes → rolling mills extend → sizing machines adjust the size → cooling → straightening → testing. The key link is perforation, which requires uniform wall thickness; after sizing, the steel pipe needs to be slowly cooled to reduce internal stress. Hot-rolled pipes usually have oxide scales and need to be pickled or sandblasted. This process is suitable for the production of large-diameter (such as Φ426mm or above) thick-walled pipes.
How to ensure the quality of welds in high-frequency welded (ERW) carbon steel pipes?
ERW welded pipes use high-frequency current to melt the edge of the steel plate and weld under pressure. Quality assurance includes: clean edges of raw materials (no rust), current frequency control (usually 100-400kHz), and post-welding heat treatment to eliminate stress. The welds must be inspected by ultrasonic or X-ray to ensure that there is no unfused or pores. The weld strength of high-quality ERW pipes can reach more than 90% of the parent material and is widely used in water pipes and oil pipes.
What effect does the cold drawing process have on the performance of carbon steel pipes?
Cold drawing reduces the diameter and wall thickness of the steel pipe through die drawing, improves dimensional accuracy (tolerance ±0.05mm) and surface finish (Ra≤1.6μm). Work hardening increases strength (such as a 20% increase in tensile strength), but plasticity decreases, and annealing is required to restore toughness. Cold-drawn pipes are suitable for precision hydraulic cylinders or bearing sleeves, but the cost is higher than hot-rolled pipes. Excessive cold drawing may cause microcracks.
How to control residual stress in carbon steel pipe production?
Residual stresses are caused by uneven deformation or cooling and can be eliminated by annealing (heating to 600°C and then slow cooling). Cold-rolled tubes require intermediate annealing; welded tubes require weld annealing. Vibration aging or mechanical stretching can also reduce stress. Unrelieved stress can cause processing deformation (such as bending after cutting) or stress corrosion cracking. Detection methods include X-ray diffraction or drilling.
