Rust removal method and inspection steps for straight seam steel pipes
Date:2025-01-07
Straight seam steel pipes are steel pipes with welds parallel to the longitudinal direction of the steel pipe. They are usually divided into metric electric welded steel pipes, electric welded thin-walled pipes, transformer cooling oil pipes, etc. The production process of straight seam welded pipes is simple, with high production efficiency, low cost and rapid development. The strength of spiral welded pipes is generally higher than that of straight seam welded pipes. Narrower billets can be used to produce welded pipes with larger diameters, and billets of the same width can also be used to produce welded pipes with different diameters. However, compared with straight seam pipes of the same length, the weld length increases by 30~100%, and the production speed is lower.
Inspection steps for straight seam steel pipes:
1. Straight seam steel pipes should be submitted for acceptance in batches, and the batch rules should comply with the provisions of the corresponding product standards.
2. The inspection items, sampling quantity, sampling location, and test methods of straight seam steel pipes shall be by the provisions of the corresponding product standards. With the consent of the purchaser, hot-rolled seamless straight seam steel pipes can be sampled in batches according to the rolling root group.
3. If a certain item of the straight seam steel pipe test result does not meet the requirements of the product standard, the unqualified ones should be selected, and double the number of samples should be randomly selected from the same batch of straight seam steel pipes for re-inspection of the unqualified items. If the re-inspection result (including any index required by the test of the item) is unqualified, the batch of straight seam steel pipes shall not be delivered. The following inspection items are not allowed to be re-inspected when the initial inspection fails:
1) White spots in the macrostructure;
2) Microstructure.
4. For straight seam steel pipes with unqualified re-inspection results (including items where the microstructure of the initial inspection results is unqualified and re-inspection is not allowed), the supplier can submit them for acceptance one by one; or re-heat treat them (the number of re-heat treatments shall not exceed two times) and submit them for acceptance as a new batch.
5. If there is no special provision in the product standard, the chemical composition of the straight seam steel pipe shall be inspected and accepted according to the smelting composition
Rust removal method for straight seam steel pipe:
1. Cleaning: Solvents and emulsions are used to clean the surface of the steel to remove oil, grease, dust, lubricants, and similar organic matter, but they cannot remove rust, scale, welding flux, etc. on the surface of the steel, so it is only used as an auxiliary means in fire prevention operations.
2. Pickling: Use chemical and electrolytic methods for pickling. Pipeline anti-corrosion only uses chemical pickling, which can remove scale, rust, and old coatings. Sometimes it can be used as a re-treatment after sandblasting. Although chemical cleaning can achieve the best cleanliness and roughness of the surface, its anchor pattern is shallow and it is easy to pollute the surrounding environment.
3. Tool rust removal: Use tools such as wire brushes to polish the surface of the steel to remove loose scale, rust, welding slag, etc. Manual tools can achieve Sa2-level rust removal, and power tools can achieve Sa3-level rust removal. If the steel surface is firmly attached to the iron oxide scale, the tool rust removal effect is not ideal, and the anchor pattern depth required for anti-corrosion construction cannot be achieved.
4. Spray rust removal: Rust removal is by driving the spray blade to rotate at high speed through a high-power motor so that abrasives such as steel shot, steel sand, wire segments, and minerals are sprayed on the surface of the straight seam steel pipe under the strong centrifugal force of the motor. Not only can oxides, rust, and dirt be removed, but also the straight seam steel pipe can achieve the required uniform roughness under the violent impact and friction of the abrasive.
After spray rust removal, not only can the physical adsorption effect on the surface of the pipe be expanded, but also the mechanical adhesion between the anti-corrosion layer and the surface of the pipe can be enhanced. Therefore, spray rust removal is an ideal rust removal method for pipeline anti-corrosion. Generally speaking, shot peening rust removal is mainly used for the inner surface treatment of the pipe, and shot blasting rust removal is mainly used for the outer surface treatment of the straight seam steel pipe.