In addition to the factors affecting the price of stainless steel pipes material and production technological process, the most important is the surface treatment of steel pipe. In order to further improve the material properties of pipes, there are four ways to treat the internal and external surfaces of pipes: acid pickling passivation (AP), mechanical polishing (MP), bright annealing (BA) and electro-polishing (EP). So what's the AP, MP, BP and EP?

AP（Acid Pickling）

The corrosion resistance of stainless steel mainly comes from the formation of dense oxide film on its surface after the chemical reaction of chromium element with oxygen. The role of pickling process is to allow this reaction to occur in advance, in order to improve the corrosion resistance of stainless steel tubes. In the pickling process, the oil stains and other contaminants on the surface of the stainless steel tube will be removed.

MP (Mechanical polishing)

Polishing wheel and polishing belt with abrasive in polishing agent polishes the surface of stainless steel pipe, so as to promote the surface of stainless steel tube to achieve smooth polishing effect. Its brightness depends on the type of processing. In addition, mechanical polishing will reduce corrosion resistance although it is more beautiful, so when used in corrosive environment, it needs passivation treatment, and stainless steel pipe surface often has polishing material residues.

BA（Bright Annealing）

In the production process of stainless steel pipe and fittings, the grease grain used for lubrication may be deformed due to production and processing. In order to avoid the grease remaining in the stainless steel pipes, argon acts as atmosphere in furnace at high temperature in the annealing process. By combining argon with carbon oxygen combustion on the pipe surface, the surface can be cleaned to form bright surface effect. This kind of way uses pure argon annealing to heat and rapid cooling, in order to brighten the bright side. This way is called bright annealing. Although this way can keep the stainless steel pipe clean without any foreign contaminants. However, the brightness of this surface will be foggy if compared with other polishing methods. Of course, the effect also depends on the amount of argon and the number of heating times.

EP（Electro-polishing）

Electro-polishing uses the anodic treatment, according to the principle of electrochemistry and appropriately adjusts the voltage, current, acid composition, and polishing time. Not only it can make the surface to achieve bright, smooth, clean effect, but also can enhance the corrosion resistance of the surface, so it is a good way to brighten the surface. However its cost and technology will be more and higher.