How to prevent the surface passivation film of stainless steel pipes from being damaged during polis

To avoid damaging the surface passivation film during the polishing process of stainless steel pipes, the following measures can be taken:

Select appropriate mechanical polishing parameters

Choose suitable abrasive materials: Based on the material of the stainless steel pipe and its initial surface condition, select abrasive materials with appropriate particle size. For stainless steel pipes with higher roughness requirements, a coarser particle size can be used for rough polishing to remove larger processing marks, and then gradually switch to finer abrasive materials for fine polishing, such as transitioning from 80 mesh, 120 mesh, to 800 mesh, 1200 mesh, or even finer, to avoid excessive damage to the passivation film by coarse abrasive materials.

Control polishing pressure and speed: During polishing, avoid applying excessive pressure. The pressure should generally be controlled at 1 - 3 kg/cm². At the same time, adjust the rotational speed of the polishing machine according to the diameter and length of the stainless steel pipe. For smaller stainless steel pipes, the rotational speed can be slightly higher, such as 2000 - 3000 r/min. For larger pipes, the rotational speed should be controlled at 1000 - 2000 r/min to prevent damage to the passivation film due to excessive pressure and speed.

Optimize electrolytic polishing process

Precisely adjust the electrolyte: Follow the process requirements to precisely adjust the composition of the electrolyte. For the commonly used phosphoric acid - sulfuric acid type electrolyte, the proportion of phosphoric acid, sulfuric acid and water is usually controlled between 60% - 70%, 20% - 30%, and 10% - 20%, and some additives such as corrosion inhibitors and brighteners can be added according to the material of the stainless steel pipe and polishing requirements to improve the polishing effect and protect the passivation film.

Strictly control electrolytic parameters: Accurately control the temperature and current density of electrolytic polishing. Generally, the temperature is controlled at 40 - 60℃, and the current density is controlled between 15 - 30 A/dm² according to the material and surface area of the stainless steel pipe. At the same time, set the electrolytic time reasonably, usually 5 - 15 minutes, to avoid excessive dissolution of the stainless steel pipe surface due to improper temperature, current density and time, which may damage the passivation film.

Use gentle polishing methods

Choose chemical polishing: For some stainless steel pipes with not extremely high surface quality and complex shapes, chemical polishing can be used. Chemical polishing can dissolve the microscopic protrusions on the surface of the stainless steel pipe to make it smooth, and it causes relatively less damage to the passivation film. For example, using a chemical polishing solution containing nitric acid, phosphoric acid and acetic acid, polishing can be carried out under appropriate temperature and time conditions to achieve better polishing results and protect the passivation film.

Try magnetic polishing: Magnetic polishing uses the force of the magnetic field to drive magnetic abrasive materials to polish the surface of the stainless steel pipe. This method has uniform polishing force and causes less damage to the surface of the stainless steel pipe, effectively avoiding excessive damage to the passivation film, especially suitable for small-sized and precise stainless steel pipe polishing.

In addition, regardless of which polishing method is used, cleaning and passivation treatment should be carried out promptly after polishing to restore and enhance the passivation film on the surface of the stainless steel pipe, improving its corrosion resistance.