How to Avoid Tea Staining on Stainless Steel Enclosures
Tea staining of stainless steel is a discoloration of the metal surface, which leaves a brown stain along the grain of the material, much like that left by tea in a cup, according to a release from B&R Enclosures.
Although it can be unsightly, tea staining is not a serious form of corrosion and in general will not affect the structural integrity or longevity of equipment. However, in public places where the aesthetics of stainless steel are important, there are procedures that can help.
Tea staining usually occurs along the coastal fringes and whereever there is high salinity water. It is formed when salt water is evaporated in minute crevices in the stainless steel surface. While this is evaporating, it creates a super concentrated chloride solution, which causes the corrosion along the grain of the metal surface.
To minimize tea staining, B&R recommends:
- purchasing enclosures made from stainless steel grade 316, as lower grades such as 304 are significantly less resistant to salt solutions;
- an N4 surface finish with a maximum RA of 0.4 micrometers will minimize crevices, to give a good balance between finish and cost;
- the grain of the enclosure have a vertical orientation to reduce the chance of chloride buildup;
- regular cleaning with fresh or rain water will help remove the salt deposits causing problems;
- installing the enclosure where it will not be subject to salt spray but will be in position to get wet from rain water;
- a coating can be applied, but this can make things worse depending on the product. The company recommends using Nycote, a clear nylonic polymer resin.