Welded Pipe Knowledge And How To Prevent Corrosion

The welded steel pipe is a steel pipe which is formed by welding a steel plate or a strip steel after being crimped. Common welded pipes are electric resistance welded pipes, spiral welded pipes, straight welded pipes, etc. The welded steel pipe has simple production process, high production efficiency, many varieties and specifications, and less equipment, but the general strength is lower than that of seamless steel pipe.

Since the 1930s, with the rapid development of high-quality strip continuous rolling production and the advancement of welding and inspection technology, the quality of welded joints has been continuously improved, the variety specifications of welded steel pipes have been increasing, and more and more fields have replaced Seam steel pipe. Welded steel pipes are divided into straight welded pipes and spiral welded pipes in the form of welds.

Straight seam welded pipe has simple production process, high production efficiency, low cost and rapid development. The strength of the spiral welded pipe is generally higher than that of the straight welded pipe. It is possible to produce a welded pipe with a large diameter by using a narrow blank, and it is also possible to produce a welded pipe having a different pipe diameter by using a blank of the same width. However, compared with the straight pipe of the same length, the weld length is increased by 30 to 100%, and the production speed is low. Therefore, the smaller diameter welded pipes are mostly straight seam welded, and the large diameter welded pipes are mostly spiral welded.

1. CleaningSolvents and emulsions are used to clean the surface of steel to remove oil, grease, dust, lubricants and similar organic matter, but it can not remove rust, scale, flux, etc. on the surface of steel, so it is only used as an auxiliary means in anti-corrosion production.
2. Tool rust removalThe 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 rust removal of the hand tool can reach the Sa2 level, and the rust removal of the power tool can reach the Sa3 level. If the surface of the steel is adhered to the iron oxide scale, the rust removal effect of the tool is not ideal, and the anchor depth required for the anti-corrosion construction cannot be achieved.
3. PicklingGenerally, 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.
4. Spray (throwing) shot rust removalSpraying (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.

4.1 Rust removal levelFor 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 ~ 100?m, 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.

4.2 Spray (throwing) abrasiveIn 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 abrasive of steel sand and steel shot (usually the hardness of steel shot is 40 ~ 50HRC, the hardness of steel sand is 50 ~ 60HRC can be used on various steel surfaces, even on the surface of steel grade C and D rust, except The rust effect is also very good.

A worker from a steel pipe company, which is located in China.