Pickling and Oiling Steel Steel Foundations
Pickling is a chemical treatment to remove stains, contaminants, rust, and scale from the surface of hot rolled steel coil.
Surface scale forms naturally during the hot rolling process while the stains, contaminants, and rust typically form during storage. Both carbon steel and stainless steel need to be pickled prior to most subsequent processing steps.
During the pickling process, the coil is unwound and submerged in pickling tanks containing a strong acid solution called pickle liquor, which is a liquid solution containing hydrochloric or sulfuric acid. Several pickle tanks are used with varying concentrations of acid to ensure the steel is fully descaled and cleaned prior to further processing. After going through the acid tanks, the coil is rinsed with water to remove any residual acid. Next, the coil is dried using high pressure and hot air to remove any residual water. The rinsing and drying are to ensure that the acid and water used in the pickling process do not remain on the surface of the steel and damage it. Since pickled steel will oxidize if exposed to humid atmospheric conditions, a thin coating of rust-preventative oil is applied as a protecting barrier.
After pickling, it is easy to observe surface defects on the clean, dry surface of the carbon or stainless-steel strip, so many inspection activities are performed during the pickling process.
The strip pickling process is generally carried out in continuous pickling lines. However, there are many pickle lines that process one coil at a time, which are called Push, Pull Pickle Lines (PPP Lines) because the entry end pushes the front end of the coil through the line until the exit end is able to put the rest of it through.