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Surface treatment of sanitary stainless steel high frequency welded pipe

by:Mayer     2021-08-20
Surface treatment of sanitary stainless steel high-frequency welded pipes. With the continuous development of my country’s economy, the country is vigorously developing the energy industry. Long-distance oil and gas pipelines are an important way to ensure energy. In the process of anti-corrosion construction of oil (gas) pipelines, the surface treatment of steel pipes It is one of the key factors that determine the anti-corrosion service life of pipelines, and it is the prerequisite for whether the anti-corrosion layer and the steel pipe can be firmly combined. It has been verified by research institutes that the life of the anti-corrosion layer depends on factors such as the type of coating, coating quality and construction environment. The surface treatment of the steel pipe has an impact on the life of the anti-corrosion layer about 50%. Therefore, the anti-corrosion layer specifications should be strictly followed. The requirements for the surface of steel pipes have been continuously explored and summarized, and the surface treatment methods of steel pipes have been continuously improved. 1. Cleaning uses solvents and emulsions to clean the surface of steel to remove oil, grease, dust, lubricants and similar organic matter, but it cannot remove rust, oxide scale, welding flux, etc. on the surface of steel, so it is only used in anti-corrosion production. Auxiliary means. 2. Tool rust removal mainly uses steel wire brushes and other tools to polish the surface of the steel, which can remove loose or warped oxide scale, rust, welding slag, etc. The rust removal of hand tools can reach Sa2 level, and the rust removal of power tools can reach Sa3 level. If the steel surface is attached with a firm iron oxide scale, the tool rust removal effect is not ideal, and the anchor pattern depth required for anti-corrosion construction cannot be reached. 3. Pickling is generally done by two methods: chemical and electrolysis. Pipeline anticorrosion only uses chemical pickling, which can remove oxide scale, rust, and old coatings. Sometimes it can be used as a reprocessing 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 easily pollutes the environment. 4. Spray (throwing) rust removal Spray (throwing) rust removal is driven by a high-power motor to drive the spray (throwing) blades to rotate at a high speed, so that the abrasives such as steel grit, steel shot, iron wire section, minerals, etc. are opposed by centrifugal force. Spraying (projecting) the surface of the steel pipe can not only completely remove rust, oxide and dirt, but also the steel pipe can achieve the required uniform roughness under the action of the violent impact and friction of the abrasive. After spraying (throwing) to remove rust, not only can the physical adsorption of the pipe surface be expanded, but also the mechanical adhesion of the anti-corrosion layer and the pipe surface can be enhanced. Therefore, spraying (throwing) rust removal is an ideal way to remove rust from pipelines. Generally speaking, shot blasting (sand) rust removal is mainly used for pipe inner surface treatment, and shot blasting (sand) rust removal is mainly used for pipe outer surface treatment. Several problems should be paid attention to when using spray (throwing) to remove rust. 4.1 Rust removal grade For the construction process of epoxy, ethylene, phenolic and other anticorrosive coatings commonly used in steel pipes, the surface of the steel pipe is generally required to reach a near-white level (Sa2.5). Practice has proved that the use of this rust removal level can remove almost all oxide scale, rust and other dirt, and the depth of the anchor pattern reaches 40-100μm, which fully meets the requirements of the adhesion of the anti-corrosion layer and the steel pipe. The rust process can achieve near-white (Sa2.5) technical conditions with low operating costs and stable and reliable quality. 4.2 Spraying (throwing) abrasives In order to achieve the ideal rust removal effect, the abrasives should be selected according to the hardness of the steel pipe surface, the degree of original rust, the required surface roughness, and the type of coating. For single-layer epoxy, two-layer or three-layer Layers of polyethylene coating, using a mixed abrasive of steel grit and steel shot, it is easier to achieve the ideal rust removal effect. Steel shot has the effect of strengthening the steel surface, while steel grit 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. It can be used on various steel surfaces, even on C-grade and D-grade rusted steel surfaces, except The rust effect is also very good.  4.3 Abrasive particle size and ratio In order to obtain a better uniform cleanliness and roughness distribution, the design of the abrasive particle size and ratio is very important. Too much roughness can easily cause the anticorrosive layer to spike in the anchor pattern 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. Too small roughness will cause the adhesion and impact strength of the anti-corrosion layer to decrease. For serious internal pitting corrosion , Can not only rely on the high-strength impact of large abrasives, but also must rely on small particles to polish away the corrosion products to achieve the cleaning effect. At the same time, the reasonable ratio design can not only reduce the abrasive wear to the pipe and nozzle (vane), but also the utilization rate of the abrasive. It can also be greatly improved. Generally, the grain size of steel shot is 0.8-1.3mm, and the grain size of steel grit is 0.4-1.0mm, of which 0.5-1.0mm is the main component. The sand shot ratio is generally 5-8. It should be noted In actual operation, it is difficult to achieve the ideal ratio of steel grit to steel shot in the abrasive, because the hard and fragile steel grit has a higher crushing rate than steel shot. Therefore, the mixed abrasive should be continuously sampled and tested during operation. According to the particle size distribution, add new abrasive to the rust remover, and the amount of steel grit is the main one. 4.4 Speed u200bu200bof rust removal The speed of rust removal of steel pipe depends on the type of abrasive and the type of abrasive. Displacement, generally should choose the abrasive with low loss rate, which is beneficial to improve the cleaning speed and the life of the blade. 4.5 Cleaning and preheating Before spraying (throwing) treatment, the cleaning method is used to remove the grease and accumulation on the surface of the steel pipe. Use a heating furnace to preheat the pipe body to 40-60℃ to keep the surface of the steel pipe in a dry state. During the spraying (projection) treatment, since the surface of the steel pipe does not contain grease and other dirt, the effect of rust removal can be enhanced. The surface of the steel pipe is also conducive to the separation of steel shot, steel grit, rust and oxide scale, so that the surface of the steel pipe after rust removal is cleaner.   The importance of surface treatment is emphasized in production, and the process parameters during rust removal are strictly controlled. In actual construction Among them, the peel strength value of the steel pipe anti-corrosion layer greatly exceeds the standard requirements, ensuring the quality of the anti-corrosion layer. On the basis of the same equipment, the process level is greatly improved and the production cost is reduced.
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