Stainless Steel - Surface finish & Polishing
The specification of surface finish probably falls into 3 main headings –
- as welded
- satin polished
- bright polished.
The specification of the surface finish can be an aesthetic consideration based on the required final appearance. However, it can have a significant effect on the in-service performance of a stainless steel component or fabrication.
The availability of the type of surface finish varies widely between sheet, plate and sections.
Please Note - polishing terminology, and the meaning of polishing terms varies widely across different industries. Your Sales contact will be happy to discuss your requirements.
Satin polish can vary depending on expectation. We usually think of it as a matt finish.
Dull buffed - a uniform straight grained finish usually achieved by 180-220 grit – Approximate Ra value of 1.25µm.
Satin polish - a clean cut surface, not very reflective. Finished with 240 grit – Approximate Ra value of 0.5µm.
Sheets and plates can be cold formed and folded with the use of a non-marking film to maintain the surface finish. Individual components of a fabrication can be polished prior to fabrication and welding. The completed fabrication can then be polished to blend in the welds and produce a uniform finish.
Bright polishing produces a bright reflective finish. Approximate Ra value of 0.05µm.
Individual components of a fabrication can be bright polished prior to fabrication and welding. The completed fabrication can then be polished to produce a uniform finish.
Surface finish and corrosion protection
The surface finish can make a difference to the corrosion performance of a fabrication in certain environments.
Satin Polish The peak-trough height of a satin finish allows salts and particulate matter to adhere to the surface. The ‘broken’ nature of the surface does not promote the cohesion of the passive film, which when combined with entrapment of salts and particulates can lead to localised corrosion. This can be cleaned with proprietary stainless steel cleaning solutions to restore the stainless surface.
Bright polish The flatness and smoothness of the bright polish surface helps the stainless to be ‘self cleaning’. The nature of the very smooth surface helps prevent the build up of corrosive salts and other particulates. This seems to disrupt the initiation of corrosion. It also allows rain water to keep the surface washed, and in the case of handrails, the regular use keeps the surface clean and the polish bright.
Polishing after welding
Welding produces a coloured oxide layer and a depleted chromium layer. This can be removed by the application of a pickling paste to the affected area. The paste removes the weld colour and helps to reestablish the protective passive film.
The ‘as welded’ profile can then be polished to blend with the fabrication.
Bead blasting is a surface treatment that produces a uniform finish.
In our experience we have found that this surface is easily marked unless carefully handled and protected in service.