Cleaning and treatment of seamless carbon steel pipe

Posted by zora li on December 16th, 2022

1. Tool derusting

Mainly use steel brushes and other tools to polish the steel surface, which can remove loose or warped scale, rust, welding slag, etc. Hand tools can reach Sa2 level, and electric tools can reach Sa3 level. If the iron sheet is firmly attached to the surface of the steel, the rust removal effect of the tool is not ideal, and it cannot meet the anti-corrosion construction requirements of the depth of the anchor pattern.

2. Clean
Use solvents and emulsions to clean the steel surface to remove oil, grease, dust, lubricants and similar organic matter, but cannot remove rust, oxides, and solder on the steel surface, so it is only used as an auxiliary means of rust prevention. -Corrosion occurs.

3. Pickling

Pickling treatment generally adopts two methods: chemical method and electrolytic method. Pipeline anticorrosion only uses chemical pickling, which can remove scale, rust and old coatings, and sometimes it can also be used as a retreatment after sandblasting and rust removal. Although chemical cleaning can achieve a certain degree of cleanliness and roughness on the surface, its anchor pattern is relatively shallow, which is easy to cause pollution to the environment.

4. Spray (throw) rust removal

Spraying (throwing) shot derusting spray is driven by a high-power motor (throwing) to shoot high-speed rotating blades, so that abrasive wires such as steel grit, steel shot, steel shot, steel sheet, minerals, etc. are sprayed out under the centrifugal force of the steel pipe surface ( Cast) processing can not only completely remove rust, oxides and dirt, but also achieve the required uniform roughness under the action of severe impact and friction of abrasives.
Spraying (throwing) coating can not only expand the physical adsorption on the surface of the pipeline, but also enhance the mechanical adhesion between the anti-corrosion layer and the surface of the pipeline. Therefore, spraying (throwing) rust removal is an ideal method for pipe rust removal. Generally speaking, shot blasting (sand) derusting is mainly used for internal surface treatment of pipelines, and shot blasting (sand) derusting is mainly used for external surface treatment of pipelines. Several issues that should be paid attention to when spraying (throwing) rust removal.

4.1 Rust removal level

The commonly used epoxy, vinyl, phenolic and other anti-corrosion coating construction techniques for seamless carbon steel pipe generally require the surface of the steel pipe to reach near-white level (Sa2.5). Practice has proved that the use of this type of derusting grade can remove almost all scale, rust and other dirt, and the depth of the anchor pattern can reach 40~100μm, which fully meets the adhesion requirements of the anti-corrosion layer and steel pipes. The spraying (throwing) derusting process can reach near-white (Sa2.5) process 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 abrasive should be selected according to the hardness of the steel pipe surface, the original degree of rust, the required surface roughness, and the type of coating. Single-layer epoxy, two-layer or three-layer polyethylene coating, it is easier to achieve the desired rust removal effect by using a mixture of abrasive sand and steel shot. Steel shot has the effect of strengthening the surface of steel, while steel grit has the effect of corroding the surface of steel. Abrasive mixture of steel grit and steel shot (the hardness of steel shot is usually 40~50HRC, and the hardness of steel grit is 50~60HRC, which can be used on a variety of steel surfaces, even C, D grade rust prevention, and the rust removal effect is very good.

4.3 Abrasive particle size and proportion

In order to obtain better uniform cleanliness and roughness distribution, abrasive particle size and ratio design are very important. If the roughness is too large, the anti-corrosion layer will become thinner at the peak of 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.
If the roughness is too small, the adhesion and impact strength of the anti-corrosion layer will decrease. For severe internal pitting, not only the high-strength impact of large abrasive particles, but also the corrosion products of small particles are required to achieve the cleaning effect. At the same time, a reasonable ratio design can not only slow down the wear of abrasives on pipelines and nozzles (blades), but also greatly improve the utilization rate of abrasives. Usually, the particle size of steel shot is 0.8-1.3mm, and the particle 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.