Steel pipe rust removal method:
Tool to rust
The steel surface is mainly polished by a tool such as a wire brush to remove loose or raised scale, rust, welding slag, and the like. The descaling of manual tools can reach Sa2 level, and the rust removal of power tools can reach Sa3 level. If the surface of the steel is adhered with strong iron oxide scale, the rust removal effect of the tool is not ideal, and the anchor pattern deep pickling that does not meet the anti-corrosion construction requirements cannot be achieved.
Pickling and rusting
Generally, chemical cleaning and electrolysis are used for pickling treatment. Pipeline anti-corrosion is only chemical pickling, which can remove scale, rust and old coating, and can sometimes be used as re-treatment after sandblasting and rust removal. Although chemical cleaning can achieve a certain degree of cleanliness and roughness, its anchor pattern is shallow and it is easy to cause environmental pollution.
Spray (throw) to rust
Spraying (polishing) rust removal is a high-speed motor that drives the spray (throwing) to rotate the blade at high speed, so that the abrasive grains such as steel grit, steel shot, wire segment and mineral are sprayed (throwing) on ​​the surface of the steel tube under the action of centrifugal force. Not only can rust, oxides and dirt be completely removed, but the steel tube can also achieve the required uniform roughness under the action of abrasive impact and friction. After spraying (polishing) and removing rust, not only can the physical adsorption of the surface of the tube be enlarged, but also the mechanical adhesion of the coating layer to the surface of the tube can be enhanced. Therefore, spray (throwing) radiation derusting is the ideal way to remove corrosion from pipelines. In general, shot blasting (sand) descaling is mainly used for the inner surface treatment of pipes, and shot blasting (sand) descaling is mainly used for the outer surface treatment of pipes. There are several problems to be aware of when using blasting to remove rust.
Rust removal level
For the construction process of epoxy, vinyl, phenolic and other anticorrosive coatings commonly used in steel pipes, it is generally required that the surface of the steel pipe reaches near white level (Sa2.5). Practice has proved that the use of this descaling level can almost remove all oxide scale, rust and other dirt, anchor depth of 40 ~ 100μm, fully meet the adhesion requirements of anti-corrosion layer and steel pipe, and spray (throwing) The rust process can achieve near-white (Sa2.5) technical conditions with lower operating costs and consistently reliable quality.
Spray (throwing) abrasive
In order to achieve the desired descaling effect, the abrasive should be selected according to the hardness of the surface of the steel pipe, the degree of original corrosion, the required surface roughness, the type of coating, etc. For single-layer epoxy, two-layer or three-layer polyethylene coating, Mixed abrasives of steel sand and steel shots are more likely to achieve the desired descaling effect. Steel shots have the effect of strengthening the steel surface, while steel sand has the effect of etching the steel surface. Mixed abrasives of steel grit and steel shot (usually the hardness of steel shot is 40-50 HRC, the hardness of steel sand is 50-60 HRC can be used on various steel surfaces, even on steel surfaces with grade C and D corrosion The rust removal effect is also very good.
Abrasive particle size and ratio
In order to obtain better uniform cleanliness and roughness distribution, the particle size and proportion design of the abrasive is very important. The roughness is too large, which may cause the anti-corrosion layer to become thinner at the anchor peak; at the same time, because the anchor pattern is too deep, the anti-corrosion layer is easy to form bubbles during the anti-corrosion process, which seriously affects the performance of the anti-corrosion layer.
If the roughness is too small, the adhesion of the coating and the impact strength will be lowered. For severe internal pitting, it is not only possible to rely on large-grain abrasives for high-strength impact, but also to remove the corrosion products by small particles to achieve the cleaning effect. At the same time, reasonable proportioning design can not only reduce the abrasion of the pipes and nozzles (blades). And the utilization rate of abrasives can be greatly improved. Usually, the steel pellet has a particle diameter of 0.8 to 1.3 mm, and the steel grit has a particle diameter of 0.4 to 1.0 mm, of which 0.5 to 1.0 mm is a 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 breaking rate than the steel shot. For this reason, in the operation, the mixed abrasive should be continuously sampled and tested. According to the particle size distribution, the new abrasive is added to the descaling machine, and the amount of the steel sand is dominant in the new abrasive.
Rust removal speed
The descaling 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-grain abrasive.
Where: m - the amount of abrasive spray (throwing);
V - the running speed of the abrasive;
M1 - the quality of a single particle abrasive.
m. The size is related to the abrasive breaking rate, and the breaking rate directly affects the cost of the surface treatment operation and the cost of the descaling equipment. When the equipment is fixed, m is a constant, y is a constant, so E is also a constant, but since the abrasive breaks, m1 changes. Therefore, generally, the abrasive with lower loss rate should be selected, which is beneficial to improve the cleaning speed and long blades. Life expectancy.
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