Surface treatment method of high frequency welded steel pipe

With the continuous development of our country's economy and the vigorous development of the national energy industry, long-distance oil and gas pipelines are an important way to achieve energy security. In the anti-corrosion construction process of oil (natural gas) pipelines, the surface treatment of steel pipes is one of the key factors that determine the anti-corrosion life of the pipeline. First of all, whether the anti-corrosion layer and the steel pipe can be firmly combined is a prerequisite. The study confirmed that the life of the anti-corrosion layer depends on the type of coating, the quality of the coating and the construction environment. The surface treatment of steel pipes has about 50% impact on the life of the anti-corrosion layer. Therefore, anti-corrosion coating specifications should be strictly adhered to. Continuously explore and summarize the surface requirements of steel pipes, and continuously improve the surface treatment methods of steel pipes.

1. Cleaning
Solvents and emulsions are used to clean the steel surface to remove oil, grease, dust, lubricants and similar organic matter, but they cannot remove rust, scale, flux, etc. on the steel surface, so they are only used as an auxiliary means for anti-corrosion production.
2. Tool rust removal
Mainly use tools such as wire brushes to polish the steel surface to remove loose or warped oxide scale, rust, welding slag, etc. The rust removal ability of hand tools reaches Sa2 level, and the rust removal ability of electric tools reaches Sa3 level. If the steel surface adheres to strong scale, the tool will not remove rust as effectively and will not be able to achieve the depth of anchor lines required for corrosion-resistant structures.
3. Pickling
Usually, two methods, chemical and electrolytic, are used for pickling, and only chemical pickling is used for pipeline anti-corrosion. It can remove scale, rust and old coatings, and sometimes it can be used as a post-treatment after sandblasting and rust removal. Although chemical cleaning can achieve a certain degree of cleanliness and roughness on the surface, its fixing lines are shallow and it is easy to pollute the environment.

4. Spray (throw) rust removal
Spray (throw) rust removal uses a high-power motor to drive the spray (throw) rust removal blade to rotate at high speed to spray (throw) rust removal of steel sand, steel shot, iron wire segments, minerals and other abrasives onto the surface of the steel pipe. Under the action of centrifugal force, not only can rust, oxides and dirt be completely removed, but the steel pipe can also achieve the required uniform roughness under the severe impact and friction of abrasives.
After spraying (throwing) rust removal, it can not only expand the physical adsorption of the pipe surface, but also enhance the mechanical adhesion of the anti-corrosion layer to the pipe surface. Therefore, spraying (throwing) rust removal is an ideal method for removing rust from pipelines. method. Generally speaking, spray (blast) rust removal is mainly used for inner surface treatment of pipelines, while spray (throw) rust removal is mainly used for outer surface treatment of pipelines. Several issues should be paid attention to when using spray (throw) to remove rust.
4.1 Rust removal level
For the construction process of epoxy, ethylene, phenolic and other anti-corrosion coatings commonly used in steel pipes, the surface of the steel pipe is usually required to reach a level close to white (Sa2.5). Practice has proven that using this level of rust removal can remove almost all oxide scale, rust and other dirt, and the depth of the anchoring pattern can reach 40-100m, fully meeting the adhesion requirements between the anti-corrosion layer and steel.
4.2 Spray (polish) grinding
In order to achieve the ideal rust removal effect, the abrasive should be selected according to the hardness of the steel pipe surface, the degree of original rust, the required surface roughness, the type of coating, etc. For a single layer of epoxy, it is easier to achieve the desired rust removal using a mixed abrasive of steel grit and steel shot.