Chemical method and electrolytic method are generally adopted for pickling treatment. Only chemical pickling is used for pipeline corrosion prevention, which can remove oxide scale, rust and old coating. Sometimes it can also be used as the reprocessing after sandblasting. Although chemical cleaning can make the surface reach a certain degree of cleanliness and roughness, its anchor pattern is shallow and easy to cause pollution to the surrounding environment. Large diameter square pipes shall be submitted for acceptance in batches, and the batch rules shall comply with the provisions of the corresponding product standards.

The inspection items, sampling quantity, sampling position and test method of large-diameter square pipes shall comply with the provisions of corresponding product standards. With the consent of the demander, hot-rolled large-diameter square tubes can be sampled in batches according to the rolled root groups.

If the test results of large-diameter square tubes do not meet the requirements of product standards, the unqualified ones shall be removed and double samples shall be taken from the same batch of large-diameter square tubes for re inspection. Unqualified items. If the re inspection results (including the indexes required by the engineering test) are unqualified, the batch of large-diameter square pipes will not be delivered. If the following inspection items fail to pass the initial inspection, they shall not be re inspected: a. macroploid tissue has white spots; Bay. Microstructure.