What is the impact of the content of ferric chloride (and ferrous chloride) in hydrochloric acid pickling solution on the pickling process?

It is known that when hydrochloric acid solution is used for pickling steel pipes, industrial hydrochloric acid is directly used for this purpose, which allows for a faster pickling rate. During the pickling process, the iron matrix of the steel pipe reacts with hydrochloric acid to produce ferric chloride and ferrous chloride. Ferric chloride acts as a corrosive agent, accelerating the pickling process. Therefore, to achieve a higher pickling rate, a certain amount of used hydrochloric acid can be added to fresh hydrochloric acid solution.