In the electrolytic polishing process of stainless steel electrolytic tubes, localized over-corrosion is typically closely related to uneven current density distribution, electrolyte composition fluctuations, temperature control failures, and improper process parameter settings. To avoid these problems, systematic control is needed from multiple dimensions, including current distribution optimization, electrolyte management, temperature control, and process parameter adjustment.
Current density is a core factor affecting the uniformity of electrolytic polishing. During the electrolysis of stainless steel electrolytic tubes, abrupt changes in geometry at the edges or sharp corners of the tube can easily lead to localized current density concentration, resulting in over-corrosion. To address this issue, the electric field distribution can be optimized by adjusting the cathode layout. For example, using irregularly shaped cathodes that match the tube shape, or adding auxiliary cathodes to disperse edge currents; for complex tube structures, insulating shielding tape can be applied to the corners to limit localized current density, thereby balancing the overall dissolution rate.
The stability of the electrolyte composition directly affects the polishing quality. The ratio of phosphoric acid to sulfuric acid needs to be precisely adjusted according to the pipe material: Excessive phosphoric acid concentration will form a viscous film, hindering electrolyte flow and causing localized overheating; excessive sulfuric acid concentration will accelerate metal dissolution, increasing the risk of over-corrosion. Furthermore, the accumulation of metal ions (such as iron ions) in the electrolyte will reduce solution activity, requiring regular filtration or electrolyte replacement. In practice, electrolyte cleanliness can be maintained through a circulating filtration system, and corrosion inhibitors can be added to suppress abnormal dissolution reactions.
Temperature control is crucial to avoiding over-corrosion. During the electrolytic polishing of stainless steel electrolytic tubes, localized temperature increases can accelerate the chemical reaction rate, leading to uncontrolled dissolution. Therefore, a constant-temperature electrolytic tank, coupled with a cooling circulation device, is required to stabilize the electrolyte temperature within the process requirements. For long pipes or mass production, temperature can be controlled in sections to prevent heat accumulation. Simultaneously, it is essential to ensure sufficient electrolyte flow to prevent concentration polarization caused by temperature differences in the liquid layer.
The matching of process parameters is critical to the polishing effect. Parameters such as current density, voltage, and electrolysis time need to be comprehensively set based on the pipe material, wall thickness, and surface condition. For example, thin-walled pipes require lower current densities and shorter electrolysis times to prevent perforation; pipes with high surface roughness require staged polishing, first using a high current density for rapid leveling, then a low current density for fine finishing. Furthermore, the pipes must be thoroughly pre-treated before polishing to remove oil, scale, and other impurities, avoiding abnormal dissolution caused by poor local conductivity.
The fixture design directly affects the uniformity of current conduction. If traditional fixtures have insufficient contact area with the pipe, it can easily lead to increased contact resistance and intensified localized heat generation. Improvements include using elastic fixtures to increase the contact area or using materials with excellent conductivity (such as copper alloys) to make the fixtures. For internal hole polishing, a dedicated cathode tool can be designed to achieve uniform coverage through rotation or reciprocating motion, avoiding localized over-corrosion caused by static contact.
Real-time monitoring during the electrolysis process is an important means of preventing over-corrosion. By observing the distribution of bubbles, the uniformity of the current density can be determined: during normal polishing, the bubbles should be fine and evenly distributed. If some bubbles are too large or too few, the parameters need to be adjusted immediately. Furthermore, regularly monitoring the electrolyte density, pH value, and metal ion concentration can detect signs of compositional imbalance early, preventing quality accidents.
The post-treatment process is crucial for consolidating the polishing effect. Neutralization cleaning must thoroughly remove residual acid to prevent subsequent corrosion caused by acid residue on the pipe surface. Passivation treatment can form a dense oxide film, significantly improving corrosion resistance, especially suitable for environments containing chloride ions. The drying process requires controlled temperature and time to avoid pitting corrosion caused by residual moisture. By fully implementing the post-treatment process, potential over-corrosion hazards during electrolytic polishing can be effectively eliminated, ensuring the long-term stable performance of the stainless steel electrolytic tube.
