Q1: Common corrosion types and protective measures for Q345B steel pipe?
Atmospheric corrosion can be protected by hot-dip galvanizing (zinc layer ≥85μm) or spraying zinc-rich primer. Electrochemical corrosion needs to avoid direct contact with metals with large potential differences such as copper and stainless steel. Annealing should be performed to eliminate residual stress in stress corrosion cracking (SCC) environment. For acidic media (such as H2S), it is recommended to use plastic lining or epoxy coal tar coating. The marine environment requires a "heavy anti-corrosion coating + cathodic protection" combined solution.
Q2: What are the key points of the coating process of Q345B steel pipe?
The surface treatment needs to reach Sa2.5 level (sandblasting and rust removal), with a roughness of 40~70μm. Epoxy zinc-rich primer is recommended (dry film thickness ≥60μm), and micaceous iron epoxy (80~100μm) is used for the intermediate paint. The topcoat can be selected from polyurethane or fluorocarbon paint (50~70μm), with a total film thickness of ≥200μm. The painting environment temperature is 5~40℃, and the relative humidity is ≤85%. Step-type grinding is required for repair, and the overlap width of the new and old coatings is ≥50mm.
Q3: What are the technical parameters of hot-dip galvanizing of Q345B steel pipes?
The zinc liquid temperature is controlled at 445~465℃, and the zinc immersion time is calculated as 1.5min/mm. Pickling (HCl 10%~15%) and auxiliary plating (ZnCl2+NH4Cl) are required before plating. The coating thickness should comply with GB/T 13912 standard (≥85μm for >5mm plate thickness). After plating, water cooling and passivation treatment (chromate) are required. Testing includes adhesion (hammer test) and uniformity (copper sulfate immersion).
Q4: How to choose the anti-corrosion solution for buried Q345B steel pipes?
Three-layer PE anti-corrosion (bottom layer epoxy powder + middle layer adhesive + outer layer polyethylene) is used in ordinary soil environment. Cathodic protection (sacrificial anode or impressed current) is required for high salinity and alkali land. The crossing section adopts enhanced anti-corrosion (thickness ≥ 2.5mm). Heat shrink tape or liquid epoxy + glass cloth is used for the patching part. Regularly test the protection potential (-0.85~-1.2V vs CSE) to evaluate the anti-corrosion effect.
Q5: How to extend the service life of Q345B steel pipe?
Reserve 2mm corrosion margin in the design stage (for a 20-year life cycle). Regularly (once a year) perform coating condition inspection and repair. Avoid long-term contact with corrosive media such as Cl-, SO42-, etc. Raise the ground when storing to prevent water accumulation from accelerating bottom corrosion. Important structures can be installed with corrosion monitoring probes (such as ER probes) for real-time warning.
