44. Why do you need to lift and lower the steel pipes several times during the acid pickling process?

In the acid pickling process of bundled steel pipes, it is common to observe that the pipes being pickled in the tank are periodically lifted and lowered several times. This is the simplest method of the swing pickling technique. This approach not only retains but enhances the advantages of swing pickling. When the pipes are lifted during pickling, the diluted pickling solution inside, along with surface contaminants such as hydrogen, impurities, and iron oxide scale, are effectively flushed out. During the lowering process, fresh pickling solution enters the pipe's interior while introducing oxygen from the air, both of which accelerate the pickling rate. Since the inner wall conditions during pickling are significantly harsher than the outer wall, static pickling solutions may result in the outer wall being fully treated while the inner wall remains untreated. If continued, this could lead to the inner wall being fully treated while the outer wall has already been over-pickled. The agitation of the pickling solution and the swinging of the pipes effectively prevent this issue. The repeated lifting and lowering of bundled steel pipes serves precisely this purpose.