How to Pickle Metals in HCL

Scale can be removed from iron and steel through pickling.

Pickling metal is an industrial term for the chemical removal of mill scale from metal that has been forged, rolled, or formed. Scale develops on the metals after the manufacturing steps and needs to removal. On iron and steel, the major component of scale is rust. Dipping metal pieces into a tank containing pickling solution removes the scale and in some cases protects the remaining metal finishes from future rusting. The tank contains a mixture of acids, which are often at an elevated temperature to shorten the pickling time. Following the pickling process, a washing step is performed to remove any remaining pickling solution.

Things You'll Need

• Hydrochloric acid
• Water
• Tank or vat
• Pressure washer

Instructions

1. Fill a vat with water to the appropriate level that allows you to add concentrated hydrochloric acid (muriatic acid) to yield a 50 percent hydrochloric acid solution. Throughout the pickling of many pieces of metal, you will need to drain some of the pickling solution due to excessively high metal concentration. After you drain a portion of the pickling solution, you need to replace it with new acid and enough water to keep the concentration of the acid at 50 percent.

2. Set the temperature of the pickling bath. The temperature of the bath determines the treatment time to achieve the results expected. The typical times range from 5 minutes at 118 degrees F to as long as 240 minutes at 68 degrees F using fresh pickling solution. If the acid concentration dilutes due to refilling with water, you can maintain the same processing time for pieces by raising the temperature of the pickling bath.

3. Remove the metal from the vat after sufficient removal of scale and let it hang over the vat to capture as much acid solution runoff as possible.

4. Move to a wash area and pressure wash the metal to remove the last traces of acid from the surface. The wash solution needs neutralization prior to waste disposal treatment.

Tips & Warnings

• Always add acid to water not water to acid.

References

• AvestaPolarit Welding: Pickling Handbook
• Outo Kumpu; LucasMilhaupt; Pickling Solutions Chart