The reason for lifting and lowering bundled steel pipes several times during pickling

During the common practice of pickling bundled steel pipes, it is usually observable that the pipes being pickled in the pickling tank are lifted up and then lowered down several times. This is the simplest method of摆动 acid pickling (swing pickling). By doing so, some of the advantages of swing pickling can be obtained, and even better results may be achieved. When the steel pipes, which have been pickling for a while, are lifted up, the acid pickling solution inside the pipes, which has become diluted due to the reaction, along with unfavorable substances for pickling such as hydrogen, other impurities, and mill scale adhering to the surface, basically flow out. When the pipes are lowered back down, fresh pickling solution enters the inner bore of the steel pipes, simultaneously bringing in a portion of oxygen from the air, both of which are beneficial to the pickling rate. Since the conditions of the inner bore wall are much more severe than those of the outer wall during the pickling of steel pipes, pickling in static pickling solution can lead to a situation where the outer wall has already been adequately pickled while the inner wall is still insufficiently pickled. If pickling is continued, the inner wall may become adequately pickled while the outer wall becomes over-pickled. Therefore, stirring the pickling solution and swinging the steel pipes are methods that can avoid this drawback. The practice of lifting and lowering the bundled steel pipes several times, as mentioned here, is a measure taken for this purpose.