With the continuous development of my country's economy, the country has vigorously developed the energy industry. Long-distance oil and gas pipelines are an important way to ensure energy security. In the process of oil (gas) pipeline anti-corrosion construction, steel pipe surface treatment is one of the key factors that determine the service life of pipeline anti-corrosion. It is the premise for the firm combination of an anti-corrosion layer and steel pipe. According to research institutions, the life of the anti-corrosion layer depends on factors such as coating type, coating quality, and construction environment. The influence of steel pipe surface treatment on the life of the anti-corrosion layer accounts for about 50%. Therefore, the requirements of the anti-corrosion layer specification for the steel pipe surface should be strictly followed, and continuous exploration and summary should be made to continuously improve the steel pipe surface treatment method.

1. Cleaning
Use solvents and emulsions to clean the steel surface to remove oil, grease, dust, lubricants, and similar organic matter, but it cannot remove rust, scale, welding flux, etc. on the steel surface, so it is only used as an auxiliary means in anti-corrosion production.

2. Tool rust removal
Mainly use tools such as wire brushes to polish the steel surface, which can remove loose or raised oxide scales, rust, welding slag, etc. Manual tool rust removal can reach the Sa2 level, and power tool rust removal can reach the Sa3 level. If the steel surface is firmly attached to the oxide scale, the tool rust removal effect is not ideal, and the anchor pattern depth required by the anti-corrosion construction cannot be achieved.

3. Pickling
Generally, chemical and electrolytic methods are used for pickling treatment. Pipeline anti-corrosion only uses chemical pickling, which can remove oxide scale, rust, and old coating. Sometimes it can be used as a re-treatment after sandblasting and rust removal. Although chemical cleaning can make the surface reach a certain degree of cleanliness and roughness, its anchor pattern is shallow and it is easy to pollute the environment.

4. Blasting (blasting) rust removal
Blasting (blasting) rust removal uses a high-power motor to drive the blasting (blasting) blade to rotate at high speed so that abrasives such as steel sand, steel shot, wire segments, minerals, etc. are blasted (blasted) on the surface of the steel pipe under the action of centrifugal force. It can not only completely remove rust, oxides, and dirt, but also achieve the required uniform roughness under the violent impact and friction of the abrasive. After blasting (blasting) rust removal, can not only expand the physical adsorption effect on the surface of the pipe but also enhance the mechanical adhesion between the anti-corrosion layer and the surface of the pipe. Therefore, blasting (blasting) rust removal is an ideal rust removal method for pipeline corrosion protection. Generally speaking, shot blasting (sand) rust removal is mainly used for the inner surface treatment of the pipe, and shot blasting (sand) rust removal is mainly used for the outer surface treatment of the pipe. Several issues should be paid attention to when using blasting (blasting) rust removal.

4.1 Rust removal level
For the construction process of epoxy, ethylene, phenolic, and other anti-corrosion coatings commonly used on steel pipes, the surface of the steel pipe is generally required to reach the near-white level (Sa2.5). The practice has proved that this rust removal level can almost remove all scales, rust, and other dirt, and the anchor pattern depth reaches 40~100μm, which fully meets the adhesion requirements of the anti-corrosion layer and the steel pipe, and the spray (blasting) rust removal process can achieve the near-white level (Sa2.5) technical conditions with lower operating costs and stable and reliable quality.

4.2 Spray (blasting) abrasive
To achieve the ideal rust removal effect, the abrasive should be selected according to the hardness of the steel pipe surface, the original rust degree, the required surface roughness, the coating type, etc. For single-layer epoxy, two-layer, or three-layer polyethylene coatings, the mixed abrasive of steel sand and steel shot is easier to achieve the ideal rust removal effect. Steel shot has the effect of strengthening the steel surface, while steel sand has the effect of etching the steel surface. The mixed abrasive of steel grit and steel shot (usually the hardness of steel shot is 40-50 HRC, and the hardness of steel grit is 50-60 HRC) can be used for various steel surfaces, and even on C and D grade rusted steel surfaces, the rust removal effect is also very good.

4.3 Particle size and ratio of abrasive
To obtain better uniform cleanliness and roughness distribution, the particle size and ratio design of abrasive is very important. Too much roughness can easily cause the anti-corrosion layer to become thinner at the peak of the anchor pattern; at the same time, because the anchor pattern is too deep, bubbles are easily formed in the anti-corrosion layer during the anti-corrosion process, which seriously affects the performance of the anti-corrosion layer. Too little roughness will cause the adhesion and impact resistance of the anti-corrosion layer to decrease. For severe internal pitting, it is not only necessary to rely on large-particle abrasive high-intensity impact but also to rely on small particles to grind off the corrosion products to achieve the cleaning effect. At the same time, a reasonable ratio design can not only slow down the wear of the abrasive on the pipe and nozzle (blade) but also greatly improve the utilization rate of the abrasive. Usually, the particle size of steel shot is 0.8-1.3 mm, and steel sand particle size is 0.4 ~ 1.0 mm, of which 0.5 ~ 1.0 mm is the main component. The sand-shot ratio is generally 5 ~ 8. It should be noted that in actual operation, the ideal ratio of steel sand and steel shot in the abrasive is difficult to achieve because the hard and brittle steel sand has a higher crushing rate than steel shot. For this reason, the mixed abrasive should be sampled and tested continuously during operation, and new abrasive should be added to the rust remover according to the particle size distribution, and the amount of steel and should account for the majority of the new abrasive added.

4.4 Rust removal speed
The rust removal speed of the steel pipe depends on the type of abrasive and the displacement of the abrasive, that is, the total kinetic energy E of the abrasive applied to the steel pipe per unit time and the kinetic energy E1 of the single particle abrasive.
Where: m ——abrasive spray (throw) amount; V ——Abrasive running speed; m1——The mass of a single abrasive particle. The size of m is related to the abrasive crushing rate, which directly affects the cost of surface treatment operations and the cost of rust removal equipment. When the equipment is fixed, m is a constant, y is a constant, so E is also a constant, but due to the crushing of the abrasive, m1 changes. Therefore, generally, an abrasive with a lower loss rate should be selected, which is conducive to improving the cleaning speed and extending the life of the blade.

4.5 Cleaning and preheating
Before the spray (blasting) treatment, the grease and dirt on the surface of the steel pipe are removed by cleaning, and the pipe body is preheated to 40-60℃ in a heating furnace to keep the surface of the steel pipe dry. During the spray (blasting) treatment, since the steel pipe surface does not contain grease and other dirt, the rust removal effect can be enhanced. The dry steel pipe surface is also conducive to the separation of steel shot, steel sand, rust, and oxide scale, making the surface of the steel pipe after rust removal cleaner.