Steel tube Surface Treatment is one of the key factors determining the service life of pipeline anticorrosion, and it is the precondition of the combination of anticorrosion layer and steel pipe.
Verified by the Research Institute, in addition to the life of anti-corrosion layer depends on the coating type, coating quality and construction environment, and other factors, the surface treatment of steel pipe on the life of the anti-corrosion layer of about 50%, therefore, should be in strict accordance with the requirements of anti-corrosion layer of steel pipe surface, and constantly explore and summarize, and constantly improve the surface
The use of solvents, emulsions to clean the surface of steel to achieve the removal of oil, grease, dust, lubricants and similar organic matter, but it can not remove the steel surface rust, oxidation skin, welding drugs, etc., so in the anti-corrosion production only as an auxiliary means.
2, Tool derusting The main use of steel wire brushes and other tools to polish the surface of steel, you can remove loose or warped oxidation of the skin, rust, welding slag and so on.
The manual tool derusting can reach the Sa2 level, the power tool derusting can reach the Sa3 level, if the steel surface attaches the solid iron oxide skin, the tool derusting effect is not ideal, cannot reach the anchorage depth which the anti-corrosion construction request.
3, pickling In general, the chemical and electrolytic methods to do acid pickling, pipeline anti-corrosion only chemical pickling, can be removed from the oxidation of the skin, rust, the old coating, sometimes used as a sandblasting rust after reprocessing.
Although chemical cleaning can make the surface to achieve a certain degree of cleanliness and roughness, but its anchor texture is shallow, and easy to environmental pollution.
4, spray (throw) the removal of rust Spray (throw) The removal of rust is through high-power motor driven spray (cast) The blade high-speed rotation, so that steel sand, steel pill, wire section, minerals and other abrasives in the centrifugal force on the surface of steel pipe spray (cast), not only can thoroughly remove rust, oxides and dirt, and steel pipe in the abrasive impact and friction force,
can also achieve the required uniform roughness. After spraying, the removal of rust can not only enlarge the physical adsorption on the surface of the tube, but also enhance the mechanical adhesion between the anti-corrosion layer and the surface of the tube. Therefore, spraying (throwing) the removal of rust is the ideal way to rust pipeline anti-corrosion. In general, shot peening (sand) derusting is mainly used in the internal surface treatment of pipes, blasting (sand) derusting mainly used for outside the pipe surface treatment.
Several problems should be paid attention to in the application of spraying (throwing) the derusting.
Derusting Grade For steel pipe commonly used in epoxy, ethylene, phenolic, such as anti-corrosion coating construction technology, the general requirements of the surface of the steel tube to achieve near-white (Sa2.5).
Practice has proved that the use of this descaling grade can almost eliminate all the oxide skin, rust and other dirt, the depth of the anchor reaches 40~100μm, fully meet the adhesion requirements of anti-corrosion layer and steel pipe, while the spray (cast) derusting process can be lower operating costs and stable and reliable quality of near-white (Sa2.5) technical conditions.
Spray (cast) abrasive In order to achieve the ideal derusting effect, according to the hardness of the steel tube surface, the original degree of rust, the required surface roughness, coating type, etc. to select the abrasive, for Single-layer epoxy, two or three-layer polyethylene coating, steel sand and steel balls of the mixed abrasive more easily achieve the ideal derusting effect. The steel pill has the function of strengthening the steel surface, while the steel sand has the function of etching the steel surface.
Steel sand and steel balls of mixed abrasive (usually steel pill hardness is 40~50HRC, steel grit hardness is 50~60HRC can be used in various steel surface, even if used in C-class and D-grade rust steel surface, derusting effect is also very good.
Particle size and proportion of abrasive In order to obtain a better uniformity of cleanliness and roughness distribution, the particle size and proportion design of abrasive is very important.
The roughness is too large to cause the anticorrosion layer to thin at the peak of the anchor line, and because the anchor is too deep, the anticorrosion layer in the anti-corrosion process is easy to form bubbles, which seriously affects the performance of the anticorrosion layer. The roughness is too small to cause the adhesion and impact strength of the anti-corrosion layer to decrease. For serious internal pitting, can not rely solely on the large particles of abrasive strength impact, but also rely on small particles polished off corrosion products to achieve clean-up effect, and reasonable ratio design can not only reduce the abrasive on the pipe and nozzle (blade) wear, and abrasive utilization can also be greatly improved. Usually, the particle diameter of the steel pill is 0.8~1.3mm, the grain diameter of steel sand is 0.4~1.0mm, and 0.5~1.0mm is the main component.
Sand pill is generally 5~8. It should be noted that in the actual operation, the abrasive steel sand and the ideal ratio of steel shot is difficult to achieve, because the hard and brittle steel sand than the crushing rate of steel balls.
Therefore, in the operation should be constantly sampling the mixed abrasive, according to the distribution of particle size, to rust machine into the new abrasive, and the new abrasive, the number of steel sand to occupy the main.
Rust Removal speed
The rust-removing speed of steel pipe depends on the type of abrasive and the displacement of abrasive, so the abrasive with low loss rate should be chosen, which is helpful to improve the cleaning speed and the life of long blades.
Cleaning and preheating Before spraying (throwing), the cleaning method is used to remove the grease and fouling on the surface of the steel tube, and the heating furnace is used to preheat the tube body to 40,160 ℃, so that the surface of the steel tube remains dry.
In the spray (cast) treatment, because the surface of the steel pipe does not contain grease and other dirt, can enhance the effect of rust, dry steel tube surface is also conducive to steel pill, steel sand and rust and oxidation of the separation, so that rust after the surface of the steel pipe cleaner. In the production of the importance of the surface treatment, strictly control the rust process parameters, in the actual construction, the steel tube anti-corrosion layer of the peel strength significantly exceed the requirements of the standard, to ensure the quality of anti-corrosion layer, on the same equipment on the basis of greatly improve the process level, reduce production costs.