Why is the multi-tank pickling method considered to have more benefits than the single-tank method for pickling steel pipes?

The multi-tank pickling method offers several advantages over the single-tank method when pickling steel pipes. Firstly, the steel pipes are pre-pickled in a tank with a lower acid concentration but a higher iron salt content. During this stage, the temperature of the acid solution can be increased relatively high, which effectively removes minor oil contamination and other impurities remaining on the surface of the steel pipes. Secondly, in the high-temperature acid pickling solution, the dissolution rate of thick iron oxide scales accelerates, facilitating the diffusion of hydrogen atoms into the steel substrate and the subsequent formation of hydrogen gas. As the hydrogen gas escapes, it causes the iron oxide scales to peel off. Thirdly, since a large amount of iron oxide scales and other contaminants are retained in the pre-pickling tank, the cleanliness of the pickling solution in the final pickling tank is ensured.