Anticorrosive surface treatment of steel pipe
The surface treatment of the steel pipe is one of the key factors to determine the anti-corrosion service life of the pipeline, and it is the premise of whether the anti-corrosion layer can be firmly combined with the steel pipe. According to the verification of research institutions, the life of anticorrosive layer depends on the type of coating, coating quality and construction environment and other factors. The influence of the surface treatment of the steel pipe on the life of anticorrosive layer is about 50%. Therefore, the surface treatment methods of the steel pipe should be explored and summarized continuously in strict accordance with the requirements of the anticorrosive layer specification on the surface of the steel pipe.
1 Cleaning
The solvent and emulsion are used to clean the steel surface to remove oil, grease, dust, lubricant and similar organic matter, but it cannot remove rust, oxide skin, welding flux and so on on the steel surface, so it is only used as an auxiliary means in anti-corrosion production.
2 Remove rust using tools
Mainly use wire brush and other tools to polish the steel surface, can remove loose or warped oxide skin, rust, welding slag and so on. Hand tools can reach Sa2 level, power tools can reach Sa3 level, if the steel surface is firmly attached to the oxide sheet, the tool rust removal effect is not ideal, can not reach the anticorrosive construction requirements of anchor grain depth.
3 Pickling
Generally, chemical and electrolytic methods are used to do pickling treatment. Pipeline anticorrosion only uses chemical pickling, which can remove oxide skin, rust and old coating. Sometimes, it can be used as reprocessing after sandblasting. Although chemical cleaning can make the surface reach a certain degree of cleanliness and roughness, its anchor line is shallow and easy to pollute the environment.
4. Spray (throw) to remove rust
Spraying (throwing) ejection derusting is driven by a high-power motor to spray (throwing) ejection blade at high speed, so that abrades such as steel sand, steel pellets, iron wire segments and minerals are sprayed (throwing) ejection treatment on the surface of the steel pipe under the action of centrifugal force, which can not only completely remove rust, oxide and dirt, but also the steel pipe under the action of abrasive fierce impact and friction force. It can also achieve the desired uniform roughness. After spraying, not only can expand the physical adsorption of the pipe surface, but also can enhance the mechanical adhesion between the anticorrosive layer and the pipe surface. Therefore, spraying is an ideal way to remove rust in pipeline. Generally speaking, shot peening (sand) rust removal is mainly used for pipe inner surface treatment, shot peening (sand) rust removal is mainly used for pipe outer surface treatment. Several problems should be paid attention to when using spray to remove rust.
4.1 Derusting grade
For the construction process of epoxy, ethylene, phenolic and other anti-corrosion coatings commonly used in steel pipes, the surface of steel pipes is generally required to reach nearly self-grade (Sa2.5). Practice has proved that almost all the oxide skin, rust and other dirt can be removed by this rust removal grade, and the anchor grain depth can reach 40 ~ 100 μm, which fully meets the adhesion requirements of the anticorrosive layer and the steel pipe. The spray (jetting) ejection process can achieve near white grade (Sa2.5) technical conditions with low operating cost and stable and reliable quality.
