42. Why is the multi-channel method superior to the single-channel method in acid pickling steel pipes?

The steel pipe undergoes sequential pretreatment in an acid bath with low concentration but high iron salt content. During this stage, the acid solution temperature can be elevated to effectively remove residual oil and impurities on the pipe surface. Secondly, in the high-temperature acid bath, the thick iron oxide scale dissolves more rapidly, facilitating hydrogen diffusion into the pipe substrate to form chlorine gas. As hydrogen escapes, it causes the iron oxide scale to detach. Thirdly, since a significant amount of iron oxide scale and other contaminants remain in the pretreatment bath, this ensures the cleanliness of the acid bath solution in the final acid treatment stage.