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Several surface treatment methods for steel pipes in pipeline anti-corrosion operations are excerpted from "Chinese Anti-corrosion Technology" With the continuous development of our country's economy,* * Vigorously developing the energy industry, long-distance oil and gas pipelines are an important way to ensure energy security. During the anti-corrosion construction process of oil (gas) pipelines, the surface treatment of steel pipes is one of the key factors that determine the anti-corrosion service life of the pipelines. It is the prerequisite for whether the anti-corrosion layer and the steel pipe can be firmly combined. It has been verified by research institutions that in addition to factors such as coating type, coating quality and construction environment, the life of the anti-corrosion layer depends on factors such as the surface treatment of the steel pipe, which accounts for about 50% of the impact on the life of the anti-corrosion layer. Therefore, the requirements for the surface of the steel pipe in the anti-corrosion layer specifications should be strictly followed, and continuous exploration and summary should be carried out to continuously improve the surface treatment methods of the steel pipe. 1. Cleaning uses solvents and emulsions to clean the steel surface to remove oil, grease, dust, lubricants and similar organic matter. However, it cannot remove rust, oxide scale, flux, etc. on the steel surface, so it is only used as an auxiliary means in anti-corrosion production. 2. Tool rust removal mainly uses tools such as wire brushes to polish the steel surface to remove loose or lifted 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 iron oxide scale is firmly attached to the surface of the steel, the rust removal effect of the tool will not be ideal and the anchor pattern depth required for anti-corrosion construction will not be achieved. (China Sandblasting Machine Network www.penshaji.com ) 3. Pickling generally uses chemical and electrolytic methods for pickling treatment. Only chemical pickling is used for pipeline anti-corrosion, which can remove scale, rust, and old coatings. Sometimes it can be used as a reprocessing after sand blasting and rust removal. Although chemical cleaning can achieve a certain degree of cleanliness and roughness on the surface, its anchor lines are shallow and it can easily cause environmental pollution. 4. Spray (throwing) rust removal Spray (throwing) rust removal uses a high-power motor to drive the spray (throwing) blade to rotate at high speed, so that abrasives such as steel sand, steel shots, iron wire segments, and minerals are sprayed (thrown) on the surface of the steel pipe under the action of centrifugal force. Not only can rust, oxides and dirt be completely removed, but the steel pipe can also achieve the required uniform roughness under the action of the violent impact and friction of the abrasives. After spraying (throwing) rust removal, it can not only expand the physical adsorption on the pipe surface, but also enhance the mechanical adhesion between the anti-corrosion layer and the pipe surface. Therefore, spraying (throwing) rust removal is an ideal rust removal method for pipeline anti-corrosion. Generally speaking, shot blasting (sand) rust removal is mainly used for inner surface treatment of pipes, and shot blasting (sand) rust removal is mainly used for outer surface treatment of pipes. Several issues should be paid attention to when using spray (throwing) to remove rust. 4.1 Rust removal level For the construction technology of anti-corrosion coatings such as epoxy, vinyl, phenolic and other commonly used coatings for steel pipes, the surface of the steel pipe is generally required to reach nearly white level (Sa2.5). Practice has proven that using this level of rust removal can remove almost all oxide scale, rust and other dirt. The depth of the anchor pattern can reach 40~100μm, which fully meets the adhesion requirements between the anti-corrosion layer and the steel pipe. The spray (throwing) rust removal process can achieve near white level (Sa2.5) technical conditions with lower 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 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 function of strengthening the steel surface, while steel grit has the function of etching the steel surface. The mixed abrasive of steel sand and steel shot (usually the hardness of steel shot is 40-50 HRC, and the hardness of steel sand is 50-60 HRC) can be used on various steel surfaces. Even when used on C- and D-class rusted steel surfaces, the rust removal effect is also very good. 4.3 The particle size and ratio of abrasives In order to obtain better uniform cleanliness and roughness distribution, the particle size and ratio design of abrasives is very important. Too much roughness can easily cause the anti-corrosion layer to become thinner at the peaks 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, seriously affecting the performance of the anti-corrosion layer. If the roughness is too small, the adhesion and impact strength of the anti-corrosion layer will decrease. For severe internal pitting corrosion, we cannot just rely on high-intensity impact of large-grained abrasives. We must also rely on small particles to grind away the corrosion products to achieve the cleaning effect. At the same time, reasonable ratio design can not only slow down the wear of the abrasives on the pipes and nozzles (blades), but also improve the utilization rate of the abrasives. * * improve. Usually, the particle size of steel shot is 0.8~1.3 mm, and the particle size of steel sand is 0.4~1.0 mm, of which 0.5~1.0 mm is the main component. The sand shot ratio is generally 5 to 8. It should be noted that in actual operation, the ideal ratio of steel grit and steel shot in the abrasive is difficult to achieve because the hard and brittle steel grit has a higher breakage rate than the steel shot. For this reason, the mixed abrasives should be continuously sampled and tested during operation, and new abrasives should be added to the rust remover according to the particle size distribution. Moreover, among the new abrasives added, steel grit should account for the majority. 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 applied to the steel pipe by the abrasive per unit time and the kinetic energy E1 of the single particle abrasive. in the formula: m——Amount of abrasive spray (throw) ； V——abrasive running speed ； m1——The mass of single grain abrasive. m. The size is related to the abrasive crushing rate, and the crushing rate directly affects the cost of surface treatment operations and the cost of rust removal equipment. When the equipment is fixed, m is a constant and y is a constant, so E is also a constant. However, due to the breakage of the abrasive, m1 changes. Therefore, abrasives with lower loss rates should generally be selected, which will help increase the cleaning speed and extend the life of the blades. 4.5 Cleaning and preheating Before spraying (throwing) treatment, use cleaning methods to remove grease and scale on the surface of the steel pipe, and use a heating furnace to preheat the pipe body to 40-60°C to keep the surface of the steel pipe dry. During the spray (throwing) treatment, since the surface of the steel pipe 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 grit, and rust and oxide scale, making the steel pipe surface after rust removal cleaner. 5 Conclusion: Pay attention to the importance of surface treatment in production and strictly control the process parameters during rust removal. In actual construction, the peel strength value of the anti-corrosion layer of the steel pipe * * Exceeding the standard requirements ensures the quality of the anti-corrosion layer. On the basis of the same equipment, * * Improve craftsmanship and reduce production costs.