Introduction
In addition to the brand, material and production process, the most important factor that affects the price of stainless steel tubes is the surface treatment method of the steel tubes.
In order to further improve the characteristics of pipeline materials, there are generally four methods for treating the inner and outer surfaces of pipelines: Acid Pickling (AP),Mechanical polishing (MP),Bright Annealing (BA) and Electro Polishing (EP) processing. Test data and practice prove that after surface treatment, the roughness of the tube material is reduced and the surface adsorption is weakened. So what is the difference between AP, MP, BP and EP grade stainless steel tubes?
AP(Acid Pickling)
The corrosion resistance of stainless steel mainly comes from the chromium element contained in it reacts with oxygen to form a dense protective layer on its surface. The function of pickling is to make this reaction occur in advance to improve the corrosion resistance of stainless steel tubes. During the pickling process, the oil stains attached to the surface of the tube and other substances contaminated during production will be removed. The inner and outer surfaces of the pipeline are rough and prone to suspension impurities.
BA(Bright Annealing)
During the manufacturing process of steel tubes, the grease grains used for lubrication will also be deformed due to processing. In order to prevent grease from remaining in the steel tubes, argon gas is used as the atmosphere in the furnace during annealing. By combining argon with carbon-oxygen on the surface of the steel tube, the surface of the steel tube is further cleaned to produce a glossy surface effect. This method of using pure argon gas to anneal, heat and rapidly cool the surface to brighten the surface is called glow annealing. Although using this method to brighten the surface can ensure that the steel tube is fully clean without any external contamination. However, compared with other polishing methods, the brightness of this surface will have a feeling of fog if it is mechanical, chemical and electrolytic. Of course, its effect is also related to the content of argon and the number of times it is heated.
EP(Electro Polishing)
Electrolytic polishing is the method of anode treatment. With the principle of electrochemistry, the voltage, current, acid liquid composition and polishing time are appropriately adjusted, which can not only make the surface bright, smooth and clean, but also improve the corrosion resistance of the surface. Therefore, it is the best way to brighten the surface. Of course, its cost and technology have also increased accordingly.
However, because electrolytic polishing will highlight the original state of the surface of the steel tube, if there are serious scratches, holes, or slag, precipitation, etc. on the surface of the steel tube, May all cause electrolytic failure. The difference from chemical polishing is that although it is also carried out in an acidic environment, not only will there be no grain boundary corrosion on the surface of the steel tube, but can by controlling the thickness of the chromium oxide film on the surface to achieve the best corrosion resistance of the steel tube.
MP (Mechanical polishing)
The polishing wheel or polishing belt uses the abrasives in the polishing agent to polish the surface of the stainless steel tube to achieve a smooth polishing effect. Its brightness and effect depend on the type of processing method. In addition, although mechanical polishing is more beautiful, it will also reduce the corrosion resistance, so it needs to be passivatized when used in a corrosive environment, and there is often a residue of polishing material on the surface of the steel tube.
Conclusion
The surface treatment methods of 316L stainless steel tubes include Bright Annealing (BA) , Acid Pickling (AP), Electro Polishing (EP), Mechanical polishing (MP).
Bright annealing (BA) is processed by grinding and polishing to make the tube surface flat and smooth, but attention must be paid to its corrosion resistance. Pickling treatment (AP) can improve the corrosion resistance of stainless steel and remove surface oil stains and impurities. Electrolytic polishing (EP) adjusts voltage, current, acid composition and polishing time through electrochemical principles to achieve the effect of bright, smooth and clean results, while enhancing surface corrosion resistance. Each of these treatment methods has its own characteristics, and the selection needs to be considered according to specific needs and the environment. Mechanical polishing (MP) uses polishing agent to grind to form a bright surface effect, but the surface brightness is related to the type of processing technology and the argon content.
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