The pickling solution used in the pickling process of seamless square tubes is generally a mixture of various acids, mainly sulfuric acid, nitric acid and hydrofluoric acid, etc. These mixed acids are highly corrosive and have strong oxidizing properties. The temperature is also relatively high, which puts forward high requirements on the corrosion resistance of anti-corrosion materials.
There are many anti-corrosion materials suitable for seamless square pipes, and the best ones for seamless square pipes are epoxy resins and their modified resins. The principle of pickling of seamless square tube is to use acidic liquid to remove the oxide skin on the surface of the seamless square tube after pretreatment, remove the metal ions on the surface, and make it have a beautiful finish. The material forms of pickling include belt washing, tube washing, plate washing, line washing, etc. Due to defects such as cracks in the hot-rolled tube blank or after the high-precision cold-drawn tube is made into an oil cylinder, there is almost no fracture during use. Plastic deformation occurs, generally brittle fracture.
Brittle fracture is caused by a variety of reasons. For example, when there are precipitates on the grain boundary, no matter its strength is stronger or weaker than that of the matrix, it is the cause of cracks; the segregation of inclusions on the grain boundary is also the cause of fracture; in addition, even at the intersection far less than the yield limit Under the action of variable load, fatigue fracture will also occur. In the process of low stress brittle fracture in high-strength metal materials, the material structure is not uniform and isotropic.