Stainless Steel Enclosures Tea Staining - What It Is and How to Avoid it

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Tea staining of stainless steel enclosures is a discoloration of the metal surface, which leaves a brown stain along the grain of the material. Although unsightly, tea staining is not a serious form of corrosion however in public places where the aesthetics of stainless steel are important, there are procedures that can help to avoid it.

Tea staining before and after cleaning

Tea staining is brown stain along the grain of the material, much like that left by tea in a cup

Tea staining of stainless steel enclosures, and stainless steel in general, 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.

Although it can be unsightly, tea staining is not a serious form of corrosion and in general will not effect 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 where ever 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 minimise tea staining of stainless enclosures, we would recommend the following: -

  • Enclosures should be stainless steel grade 316, as lower grades such as 304 are significantly less resistant to salt solutions.
  • Smooth surface finishes help minimise the crevices that are part of the problem. B&R Enclosures recommends an N4 surface finish with a maximum RA of 0.4 micrometres, to give a good balance between finish and cost.
  • Ideally the grain of the enclosure should be up and down the enclosure body, rather than across. This helps reduce the chance of chlorides building up in the crevices of the material.
  • Regular cleaning with fresh or rain water will help remove the salt deposits causing problems.
  • Installing the enclosure in positions where it will not be subject to salt spray, and can be rained on can also help. This means that under an overhand of a building it often a less than ideal installation position.
  • If all else fails, a coating can be applied to the stainless. This needs to be done cautiously as coating can make things worse rather than better. A great coating to use is Nycote, a clear nylonic polymer resin. For more details on this please see the article on Tea Staining.

For more information about tea staining prevention and the range of B&R’s stainless steel enclosures designed specifically to help reduce this problem, please see B&R’s website at http://www.brenclosures.com.au and download a more detailed version of this article.

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Ben Bridges
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