The surface of Stainless Steel Pipe is actually and extremely thin but stable and passive Chromium rich oxide film, on which Stainless Steel Pipe relies for its excellent corrosion resistance. The surface finish on Stainless Steel Pipe should therefore be developed and maintained to ensure this vital property, and also for the secondary reason of the pleasing aesthetic appearance of Stainless Steel Pipe.
Standard Mill Finished – Stainless Steel Pipe
The Standard Mill Surface Finished are laid down in Specifications BS 1449, Part 4, and the Committee of Stainless Steel Pipe Producers, American Iron & Steel Institute.
The finished are designated by a system of numbers, and these are broadly described hereunder relative to the finishing operations employed. It should be remembered that different grades of Stainless Steel Pipe can result in a variation of visual appearance for the same finishing operation. The thickness can also have an effect, generally the thinner the material the smoother the surface finish.
The thicker gauge sizes of Stainless Steel Pipe are hot rolled. This is done at high temperatures and will always result in a scaled surface. Stainless Steel Pipe Flat Product is supplied in the annealed ie fully softened condition.
This is also a high temperature operation and unless carried out in a very closely controlled inert atmosphere, will result in oxidation (scaling) of the surface.
The scale is usually removed by a pickling process, that is the removal of the scale by use of suitable acids, and the passivated by the use of Nitric Acid.
Much of the 2B Finish sheet imported is not a true 2B Finish. Mills which operate bright annealing facilities will often carry out all the annealing operations of Cold Rolled material in such facilities. This leads to a superior “2B” finish as no oxidation or scaling takes place during the annealing operation, even though the actual rolling may be effected on polished rolls as for normal 2B Finish, but not highly polished as would be needed to produce a BA finish.
The following finishes are all mechanically produced polished finishes. As well as being standard mill finishes, they are also applied to Stainless Steel Pipe articles and components to meet the required aesthetic criteria. It should be appreciated that factors such as hand polishing vs. mechanical polishing; polishing a flat product as against a component of complex shape; thickness and composition of material can affect the visual appearance of the final surface.
Source: Zhejiang Yaang Pipe Industry Co., Limited (www.yaang.com)