(1) Under-pickling: After pickling, if there are localized areas of oxide scale left on the steel pipe surface, it is called under-pickling defect.
Avoidance: Firstly, reduce the pickling speed. If under-pickling still occurs, appropriately increase the pickling temperature. If under-pickling defects persist, then appropriately increase the acid concentration.
(2) Over-pickling: When the steel pipe stays in the pickling solution for too long, its surface gradually becomes rough and pitted, and the plate surface turns black, which is called over-pickling.
Avoidance: Reasonably control the pickling temperature, pickling speed, pickling solution concentration, and add appropriate corrosion inhibitors to control the reaction time and reaction rate between the iron substrate and the acid. Among these, adding a corrosion inhibitor is a simple and effective method. The main role of the corrosion inhibitor is to adsorb more tightly on the steel pipe surface than hydrogen, thereby effectively organizing the hydrogen reaction and reducing the gain and loss of electrons.
