(1) Under-pickling: After pickling, there may be locally unremoved iron oxide scale remaining on the surface of the steel pipe, which is referred to as under-pickling.
Avoidance: Firstly, reduce the pickling speed. If under-pickling still occurs, appropriately increase the pickling temperature. If the defect persists, 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, with the plate surface darkening, which is referred to as 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 methods, adding corrosion inhibitors is a simple and effective approach. The main role of corrosion inhibitors is to adsorb more tightly onto the surface of the steel pipe than hydrogen, thereby effectively organizing the hydrogen reaction and reducing the gain and loss of electrons.
