What are the common methods for cutting carbon steel pipes? How to avoid defects?
The methods include: grinding wheel cutting (high efficiency but many burrs), plasma cutting (high precision, protective gas required), saw cutting (cold processing, no heat affected zone). After cutting, burrs need to be removed (file or grinder), and the verticality deviation of the cut is ≤1°. Thick-walled pipes (＞20mm) are recommended to be preheated to prevent cracks. Stainless steel composite pipes require special cutting discs to avoid carbon pollution.
Main points for processing carbon steel pipe threaded connection (thread)?
A tapered pipe thread (such as R thread of GB/T 7306) is required, with a taper of 1:16. The steel pipe needs to be straightened before processing, and the thread length ≥ the standard engagement length (such as 15mm for DN25 pipe). Use cutting oil for cooling, and the thread surface roughness Ra≤3.2μm. The seal needs to be wrapped with polytetrafluoroethylene tape or coated with sealant. Shoulder joints (such as API threads) are recommended for high-pressure systems.
How to deal with the groove before welding of carbon steel pipe?
V-groove angle 60±5°, blunt edge 1-2mm (thick wall pipe requires U-groove). Clean the groove inside and outside 20mm to metallic luster (no oil, rust). Stainless steel composite pipes need to weld carbon steel layer first, then weld transition layer. Preheating 100-150℃ is required when the ambient temperature is below -5℃. High-strength steel (such as Q345) requires low-hydrogen welding rods (such as E5015), and the interlayer temperature is controlled ≤230℃.
How to calculate the spacing of overhead carbon steel pipe supports?
Formula: L=0.124√(EI/q), where E is elastic modulus (206GPa), I is moment of inertia, and q is pipe weight + medium weight. For example, Φ159×4.5mm water pipe (q=18kg/m), the spacing is about 5m. Considering thermal expansion and contraction, sliding brackets (spacing enlarged by 1.2 times) and fixed brackets are required. Vibrating pipes require shock absorbers, and the spacing is shortened by 30%.
How to compensate for thermal expansion and contraction of carbon steel pipes?
Methods include: natural compensation (L/Z elbow), bellows compensator (axial compensation 100-300mm), sleeve compensator (for steam pipes). Calculate the expansion amount ΔL=α×L×ΔT (α=12×10⁻⁶/℃, ΔT is the temperature difference). The spacing between fixed brackets shall not exceed 70% of the maximum compensation of the compensator. Buried pipes can use Ω-shaped expansion bends with a bending radius ≥4 times the pipe diameter.
