37. What quality defects are likely to occur during pickling, and how can they be prevented?

(1) Under-acidizing: After acid pickling of steel pipes, residual iron oxide scale on the surface is referred to as under-acidizing defect.
To prevent this, first reduce the pickling rate. If insufficient pickling persists, appropriately increase the pickling temperature. If the deficiency still exists, then further increase the acid concentration.
(2) Over-etching: When steel pipes are left in the etching solution for too long, their surfaces gradually develop a rough, pitted appearance with blackened plates, a phenomenon known as over-etching.
To optimize the process, it is essential to properly control the pickling temperature, pickling rate, and pickling solution concentration, while adding appropriate corrosion inhibitors to regulate the reaction time and rate between the iron substrate and acid. The use of corrosion inhibitors serves as a simple yet effective method. These inhibitors primarily function by adsorbing onto the steel pipe surface more tightly than hydrogen, thereby effectively controlling the hydrogen reaction and minimizing electron transfer.