Steel pipe products are widely used in tap water projects, the petrochemical industry, the chemical industry, the power industry, agricultural irrigation, and urban construction. They are one of the 20 key products developed in my country. For liquid transportation: water supply and drainage. For gas transportation: gas, steam, liquefied petroleum gas. For structural use: as piling pipes, bridges; docks, roads, building structure pipes, etc. However, after long-term use, steel pipes will rust. After rust occurs, tools such as wire brushes are mainly used to polish the surface of the steel to 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 pickling required for anti-corrosion construction cannot be achieved. Generally, chemical and electrolytic methods are used for pickling. For pipeline anti-corrosion, only chemical pickling is used, which can remove scale, rust, and old coatings. Sometimes it can be used as a post-treatment after sandblasting. Although chemical cleaning can make the surface reach the corresponding cleanliness and roughness, its anchor pattern is shallow and it is easy to pollute the environment.

(1) Blasting (blasting) rust removal uses a high-power motor to drive the blasting (blasting) blade to rotate at high speed, so that steel sand, steel shot, wire segments, minerals, and other abrasives are blasted (blasted) on the surface of the steel pipe under the action of centrifugal force. Not only can all rust, oxides, and dirt be cleaned, but the steel pipe can also achieve the required uniform roughness under the violent impact and friction of the abrasive.

(2) Too little roughness will cause the adhesion and impact resistance of the anti-corrosion layer to decrease. For severe internal pitting, it is not enough to rely solely on the high-intensity impact of large-particle abrasives. It is also necessary 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 abrasives on pipes and nozzles (blades) but also greatly improve the utilization rate of abrasives. Usually, the particle size of steel shot is 0.8~1.3mm, and the particle size of steel sand is 0.4~1.0mm, of which 0.5~1.0mm is the main component. The sand-shot ratio is generally 5~8.

(3) After rust removal, it can not only expand the physical adsorption effect on the surface of the steel pipe but also enhance the mechanical adhesion between the anti-corrosion layer and the steel pipe surface. Therefore, rust removal by shot (blasting) is an ideal rust removal method for pipeline corrosion protection. Generally speaking, shot (sand) rust removal is mainly used for the inner surface treatment of steel pipes, and shot (sand) rust removal is mainly used for the outer surface treatment of steel pipes.

(4) To obtain better uniform cleanliness and roughness distribution, the particle size and ratio design of the 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.

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 fragile steel sand has a higher crushing rate than the 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. 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 applied to the straight seam steel pipe per unit time and the kinetic energy E1 of the single particle abrasive. 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, so generally, abrasives with a lower loss rate should be selected, which is conducive to improving the cleaning speed and extending the life of the blades.

For the construction process of epoxy, ethylene, phenolic, and other anti-corrosion coatings commonly used for steel pipes, the surface of the steel pipe is generally required to reach a near-white grade (Sa2.5). The practice has proved that this rust removal grade 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, while the spray (blasting) rust removal process can achieve near-white grade (Sa2.5) technical conditions with low operating costs and stable and reliable. 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, it is easier to achieve the ideal rust removal effect by using a mixed abrasive of steel sand and steel shot. 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 40~50HRC, and the hardness of steel grit is 50~60HRC) can be used on various steel surfaces, and the rust removal effect is very good even on C and D grade rusted steel surfaces.