The pickling solution used in the pickling process for seamless square tubes is typically a mixture of various acids, mainly including sulfuric acid, nitric acid, and hydrofluoric acid, among others. These mixed acids are highly corrosive and possess strong oxidizing properties, and the temperature of the corrosive medium is also relatively high. These factors place high demands on the corrosion resistance of anti-corrosion materials.

Seamless square tubes can be coated with various anticorrosive materials, with the best being epoxy resins and their modified varieties. The pickling principle for seamless square tubes involves using acidic liquids to remove the oxide skin from the surface of the pre-treated tubes, eliminating surface metal ions, and achieving a smooth finish. The forms of pickling materials include tube pickling, plate pickling, and wire pickling, etc. Due to cracks and other defects in hot-rolled tube billets or the brittleness of cold-drawn tubes after being made into hydraulic cylinders, which generally result in brittle fractures with little plastic deformation during use.

Brittle fracture is caused by various factors. For instance, when precipitates occur at grain boundaries, whether they are stronger or weaker than the matrix, they are both causes of cracking; the segregation of inclusions at grain boundaries is also a cause of fracture; in addition, fatigue fracture can occur even under alternating loads far below the yield limit. In the process of low-stress brittle fracture in high-strength metallic materials, the material structure is far from uniform and isotropic. Proper use of Q345B seamless square tubes ensures long-term service for the pipe fittings, creating more production benefits. Alloy tubes should be processed to a fine surface as much as possible.