Surface Treatment of High-frequency Welded Steel Pipe

long-distance oil/gas pipeline is an important way of energy security, in the oil (gas) pipeline anti-corrosion construction process, the surface treatment of high-frequency welded steel pipe is one of the key factors to determine the useful life of the pipeline. It is the premise that the erosion resistant coating can be firmly bonded to the steel pipe. According to the research institutions, the life of the erosion resistant coating depends on the coating type, coating quality, construction environment and other factors. The surface treatment of steel pipe accounted for about 50% on the life of the erosion resistant coating. therefore, we should be strictly in accordance with the requirements specification of erosion resistant coating to steel pipe surface, continue to explore and summarize, and constantly improve the surface treatment of steel.

1. Cleaning

Using solvents and emulsions to clean the surface of steel to achieve the removal of oil, grease, dust, lubricants and similar things, but it can not remove the rust, oxide, welding, etc. on steel surface, so it only can be an auxiliary means in anti-corrosion production.

2. Toolrust-removal

We mainly use steel wire brush and other tools to polish the steel surface, which can remove loose or tilt oxide, rust, welding slag and so on. Manual tool derusting can reach Sa2 level, power tools derusting can reach Sa3 level. If the steel surface attached to a solid iron oxide skin, the effect of toolrust-removal is not ideal, and can not up to the depth of the anchor required by anti-corrosion construction.

3. Pickling

Generally, we use chemical and electrolytic two methods for pickling treatment. Pipeline corrosion only uses chemical pickling, which can remove the oxide, rust and the old coating. And sometimes it can be used as a re-treatment after derusting by sandblast. Although using chemical to clean the surface can achieve a certain degree of cleanliness and roughness, but the anchor is shallow, and it easy to cause pollution to the environment.

4. Abrasive blasting

Abrasive blasting is through high-power motor rotating to drive jet vane to rotate on high speed to make steel sand, steel balls, wire segments, minerals and other abrasives doing spray treatment on the surface of the steel pipe in the centrifugal force. This method not only can completely remove the rust, oxides and dirt, but the steel pipe under the action of the abrasive impact and friction also can achieve the required uniform roughness.

After the spray treatment, we not only can expand the physical adsorption of the surface of the tube, but also enhance the coating and the pipe surface of the mechanical adhesion. Therefore, the spray (throw) treatment is the ideal way to rust rust pipe repair. In general, shot peening (sand) derusting is mainly used for pipe internal surface treatment, shot blasting (sand) derusting is mainly used for pipe external surface treatment.