How to Improve Rust Removal Effect of Steel Pipes Using Steel Shot and Grit?

　　Steel shot alloy is an ideal abrasive product, playing a crucial role in the sand removal of many castings with excellent results. Steel shot alloy is also widely used for rust removal and derusting of steel workpieces before painting.

　　Steel shot alloys have various classifications. They differ in hardness. Steel shot alloys can be divided into steel pellets, cast iron pellets, glass pellets, etc. Different hardness steel shot alloys have different applications.

　　Steel pellets generally have a hardness of HRC 40~50. For processing some relatively hard metals, the hardness can be increased to HRC 57~62. They have good toughness and a service life several times longer than cast iron pellets, making them widely used.

　　Cast iron pellets have a hardness of HRC 58~65. This alloy steel shot has high hardness, is very brittle upon cooling, is very easy to break, and has a short service life, thus not widely used. It is mainly used in applications requiring high shot peening intensity.

　　Glass beads, with a lower hardness than the previous two, are mainly used in applications where iron contamination is unacceptable, such as with stainless steel, titanium, aluminum, and magnesium. They can also be used as a secondary treatment after shot peening to remove iron contamination and reduce the roughness of parts.

　　During the application of commonly used epoxy, ethylene, and phenolic anti-corrosion coatings on steel pipes, the surface of the steel pipe is generally required to reach a near-white grade (Sa2.5). Practice has proven that this rust removal grade can remove almost all oxide scale, rust, and other contaminants, with an anchoring depth of 40-100m, fully meeting the adhesion requirements between the anti-corrosion layer and the steel pipe. Shot blasting with steel grit can achieve a near-white grade (Sa2.5) with lower operating costs and stable, reliable quality.

　　To achieve the ideal rust removal effect, the abrasive should be selected based on the surface hardness of the steel pipe, the degree of initial corrosion, the required surface roughness, and the coating type. For single-layer epoxy, two-layer, or three-layer polyethylene coatings, using a mixture of steel grit and steel shot more easily achieves ideal rust removal results. Steel shot strengthens the steel surface, while steel grit erodes it. The mixture typically has a hardness of 40-50 HRC for steel shot and 50-60 HRC for steel grit, making it suitable for various steel surfaces, even corroded C and D grade steel surfaces, with excellent rust removal performance.