What surface treatments are required before anti-rust paint is applied to ordinary carbon steel pipes?
Sandblasting or wire brushing is required to remove rust to Sa2.5 level (ISO 8501), and the surface roughness is 40-70μm to increase adhesion. Oil stains need to be cleaned with solvents (such as acetone). Phosphating treatment (forming a phosphate film) is required in a humid environment. Primer (such as epoxy zinc-rich) needs to be sprayed within 4 hours after rust removal, and the zinc powder content is ≥80%. When applying multiple layers, each coat of paint needs to be fully cured.
What is the difference between hot-dip galvanizing and electro-galvanized carbon steel pipes?
Hot-dip galvanizing (such as GB/T 3091) has a thick zinc layer (50-150μm), long life but rough surface; electro-galvanizing (such as GB/T 13793) has a thin zinc layer (5-20μm), smooth appearance but poor corrosion resistance. Hot-dip galvanizing requires 430℃ zinc immersion, which may be deformed; electro-galvanizing is suitable for precision small tubes. Hot-dip galvanizing costs 30% more, but its outdoor service life can reach 2-3 times that of electroplating galvanizing.
Why is 3PE anti-corrosion layer commonly used for buried carbon steel pipes?
The structure of 3PE is: epoxy powder (adhesion) + adhesive (transition layer) + polyethylene (mechanical protection), with a total thickness of 2-3mm. The epoxy layer resists cathodic stripping, and PE is resistant to acid, alkali and microorganisms. The service life can reach 50 years, and the cost is 20-30% higher than that of single-layer FBE. The construction requires strict control of the preheating temperature (200±5℃) and cooling rate. It is suitable for long-distance oil and natural gas pipelines.
What are the methods for anti-corrosion of the inner wall of carbon steel pipes?
The methods include: cement mortar lining (suitable for large-diameter water pipes), epoxy resin coating (food grade requirements), and plastic lining (such as HDPE interlacing). Cement lining has low cost (about 50 yuan/m²), but reduces the diameter; epoxy coating requires high-pressure airless spraying, with a thickness of ≥250μm. Drinking water pipes must comply with the GB/T 17219 sanitation standard.
How do stainless steel composite carbon steel pipes balance cost and corrosion resistance?
The outer carbon steel provides strength, and the inner stainless steel (such as 304, 0.5-1.5mm thick) resists corrosion. Explosive composite or hot-rolled composite processes make the bonding strength ≥210MPa. The cost is 40-60% lower than that of all stainless steel pipes, suitable for chemical equipment. It is necessary to protect the inner layer during welding to avoid carbon pollution. Ultrasonic flaw detection and shear test are required for detection.
