After welding stainless steel water pipes, internal scale forms due to the chemical reaction between the metal and oxygen during the high-temperature welding process. This scale not only affects the pipe's inner surface finish but can also reduce its corrosion resistance. Therefore, effective internal scale removal is critical to ensuring weld quality.
Mechanical cleaning is the primary method for removing scale from stainless steel water pipes. For larger diameter stainless steel water pipes, manual grinding with a long-handled wire brush or internal grinding wheel can be used, using a rotating or reciprocating motion to remove the scale. Control the force during this operation to avoid excessive abrasion of the base metal. For smaller diameter pipes, flexible abrasive wire brushes or spring-loaded cleaning tools can be used, leveraging their flexibility to adapt to the pipe's curvature and ensure thorough removal of the scale. Mechanical cleaning offers the advantages of simplicity and cost-effectiveness, but is relatively inefficient and may leave minor scratches.
Chemical pickling is a common method for removing scale from stainless steel water pipes. An acidic solution is injected into the pipe, dissolving the scale through chemical corrosion. Commonly used pickling solutions include a mixture of nitric acid and hydrofluoric acid. The ratio needs to be adjusted according to the thickness of the scale and the stainless steel material. During pickling, the solution concentration, temperature, and immersion time must be strictly controlled to avoid excessive corrosion of the base metal. After pickling, the pipe interior should be rinsed with abundant water and neutralized to remove any residual acid. Chemical pickling offers the advantages of high efficiency and thorough removal, but attention must be paid to wastewater disposal and operational safety.
Electrolytic polishing is an advanced internal scale removal technology. The stainless steel water pipe acts as the anode and is immersed in a specific electrolyte. When powered, an electrochemical reaction removes the scale. Electrolytic polishing not only removes the scale but also forms a smooth, dense oxide film on the pipe interior, enhancing its corrosion resistance. This method requires specialized electrolytic equipment and requires high technical skills, but the treatment results are remarkable and is particularly suitable for stainless steel water pipes with high surface quality requirements.
For thin or light scale, an acidic cleaning solution made from a 1:2 ratio of white vinegar to water can be used. Inject the solution into the pipe, let it sit for a while, and then rinse with clean water. This method is suitable for home use or small projects, as it is low-cost and easy to use, but its removal effectiveness is relatively limited. For stubborn scale, a special pickling paste can be used. Apply it and let it react for a while before cleaning, but the reaction time must be strictly controlled to avoid excessive corrosion.
Ultrasonic cleaning uses the impact force of tiny bubbles generated by high-frequency sound waves in the cleaning fluid to remove scale from the inside of stainless steel water pipes. This method is suitable for complex shapes or small pipes, and can evenly clean the inner wall without damaging the base. During cleaning, the pipe is immersed in the cleaning fluid or circulated through the pipe through a circulation system. Ultrasonic cleaning has the advantages of good cleaning results and no blind spots, but it requires specialized equipment and is relatively expensive.
High-temperature annealing softens and removes oxides on the metal surface by heating, making it suitable for treating thicker scales. The annealing process must be carried out in a controlled atmosphere to avoid re-oxidation. A pickling step is usually required after annealing to remove residual oxides and address surface discoloration caused by the annealing process. This method is suitable for applications requiring high mechanical properties, but it is complex and energy-intensive.
In practice, a single or combined cleaning method can be selected based on the stainless steel water pipe diameter, scale thickness, operating environment, and cost budget. For example, chemical pickling or electrolytic polishing are preferred for large-scale projects; for home repairs, white vinegar cleaning or mechanical polishing are more practical. Regardless of the method used, a passivation treatment is required after cleaning to restore the stainless steel's corrosion resistance and ensure long-term, stable operation of the pipeline.
