Spiral pipe manufacturer: What are the methods for removing rust from spiral pipes?

　　 Spiral pipe manufacturer Sharing with everyone a method for removing rust from spiral pipes?

　　1. Pickling

　　Spiral pipe manufacturers state that chemical and electrolytic methods are used for pickling. Chemical pickling is employed solely for pipeline corrosion protection, effectively removing scale, rust, and old coatings. It is sometimes also used as a post‑treatment step following sandblasting to remove rust. Although chemical cleaning can produce a clean, slightly rough surface, the resulting anchor profile is relatively shallow, making it prone to environmental contamination.

　　2. Blast (or shot) cleaning for rust removal

　　Blast (or shot) cleaning involves a high‑power motor driving a blast wheel at high speed, which propels abrasive materials—such as steel grit, steel shot, wire segments, and mineral abrasives—onto the pipe surface under centrifugal force. This process not only thoroughly removes rust, oxides, and contaminants but also imparts the required uniform surface roughness through the intense impact and friction of the abrasive media. Following blast (or shot) cleaning, the pipe’s surface exhibits enhanced physical adsorption, while the mechanical adhesion between the anti‑corrosion coating and the pipe surface is significantly improved. Consequently, blast (or shot) cleaning is an ideal method for pipeline corrosion protection. In general, shot blasting is primarily used for internal surface treatment, whereas sandblasting is mainly employed for external surface treatment. Several key considerations should be kept in mind during blast (or shot) cleaning.

　　3. Rust Removal Grade

　　Spiral pipe manufacturers state that the application processes for commonly used epoxy, ethylene, and phenolic anti-corrosion coatings on steel pipes generally require the pipe surface to reach a near‑white cleanliness grade (Sa2.5). Practical experience has shown that this level of surface preparation can effectively remove virtually all scale, rust, and other contaminants, with an anchor profile depth of 40–100 µm, fully meeting the adhesion requirements between the coating and the steel pipe. Meanwhile, blast‑ or spin‑blasting derusting can also achieve the Sa2.5 cleanliness standard, offering low operating costs and consistently reliable quality.

　　4. Abrasive blasting (or shot blasting)

　　To achieve optimal rust removal, the abrasive material should be selected based on factors such as the steel pipe’s surface hardness, its initial degree of corrosion, the required surface roughness, and the type of coating. For single‑layer epoxy or two‑ or three‑layer polyethylene coatings, a mixed abrasive consisting of steel grit and steel shot is more effective in attaining the desired rust‑removal results. Steel shot strengthens the steel surface, while steel grit etches it. A blended abrasive of steel grit and steel shot—typically with steel shot having a hardness of 40–50 HRC and steel grit at 50–60 HRC—can be used on various steel surfaces, even those exhibiting Class C or Class D corrosion, delivering excellent rust‑removal performance.

　　To achieve a more uniform cleanliness and surface roughness profile, the selection of abrasive grit size and gradation is critical. If the surface roughness is excessive, the anti-corrosion coating at the top of the anchor chain will become thinner. Moreover, when the anchor lines are too deep, air bubbles are likely to form within the coating during the anti-corrosion process, severely compromising its performance.

　　If the surface roughness is too low, both the adhesion and impact resistance of the anti-corrosion coating will deteriorate. For severe internal pitting corrosion, cleaning can be achieved not only through the high‑intensity impact of coarse abrasive particles but also by using fine particles to polish away corrosion products. Meanwhile, a well‑designed particle‑size distribution can both reduce abrasive wear on pipelines and nozzles (blades) and significantly improve abrasive utilization. Typically, steel shot has a particle size of 0.8–1.3 mm, while steel grit ranges from 0.4 to 1.0 mm, with 0.5–1.0 mm constituting the predominant fraction. The typical grit‑to‑shot ratio is 5:1 to 8:1.

　　Spiral pipe manufacturers note that, in practice, achieving the ideal ratio of steel grit to steel shot in abrasive mixtures is difficult, as hard and brittle steel grit exhibits a higher attrition rate than steel shot. Therefore, during operation, continuous sampling and testing of the mixed abrasive are essential, and new abrasive should be added to the derusting agent based on the particle-size distribution, with steel grit constituting the predominant component.