Don’t panic this is known as “tea staining”, a common cause of the deterioration of stainless steel surfaces. This is the unsightly brown discolouration caused by corrosion. While it is a cosmetic issue only, and does not affect the structural integrity or lifetime of the material, it makes the appearance of initially pristine stainless steel, very unattractive.
Stainless steel is used in applications that require good visual appeal and structural integrity in a wide range of environments. With minimal care, your stainless steel wire or mesh product will continue to look good for many, many years. However, stainless steel is “LOW maintenance”, not “NO maintenance”.
Major Cause of Tea Staining
The presence of sea salt on the surface of stainless steel is the major cause. Sea salt stays “wet” (and corrosive) until a very low relative humidity. Tea staining also occurs in polluted urban environments.
Tea staining generally does not occur indoors because of the clean environment and low humidity.
Stainless Steel selection – Grade 304 or 316?
We offer grade 304 and 316. As a general rule, grade 316 should be selected for applications within 5km of a surf coast, or 1km from sheltered coastal waters, however, tea staining can occur up to 20km from the coast, depending on environmental factors.
Factors that can increase tea staining are
- High temperatures and high relative humidity, as found in tropical areas. The moisture in the air dissolves the salt deposits on the surface and keeps them wet
- Rain sheltered areas, such as the under side of a sloping roof or a building rain shadow
- Poor drainage or designs with corners, grooves, folds and crevices which can trap water. These can lead to more serious corrosion than tea staining
Fabricating with Stainless Steel
When fabricating with stainless steel wire or mesh, be aware that other causes of staining that are not “tea staining”, include carbon steel contamination, uncleaned welds and chemical fumes, such as hydrochloric acid or bleach.
Prevention, Minimising & Maintenance
Tea staining can be prevented or minimised, firstly by selecting a 316 grade product, and then by regular washing of stainless steel surfaces. An ideal wash is a warm soapy water wash, followed by a fresh water rinse and dry, but if this is impractical, conduct a high pressure, fresh water wash.
A guide to specifying and cleaning external stainless steel
|Environment||Grade 304||Grade 316|
|Clean Inland||3 – 6 months||6 -12 months|
|Polluted urban/Industrial||Not suitable||6 -12 months|
|Coastal/Marine (not splashed)||Not suitable||3 – 6 months|
Or keeping it simple when you wash your windows wash your stainless steel!The washing frequency may be reduced for surfaces subject to regular flushing by natural rainfall.
However if your application is for architectural or external use and you want to maintain the stainless steel- silver appearance then it’s time to consider ‘The Lasting Look’.
The Lasting Look
You’ve made ‘the lasting decision’ and now for ‘the lasing look’. Cleaning with soap or a mild detergent or even an industrial cleaner is not a realistic approach with the fine meshes- as you cannot reach between all the weaves and the tea staining will continue to occur. Pickling & passivation and electro polishing- is the solution! Please note as with anything internal or external cleaning and maintenance is still required to keep your mesh clean and preserve its appearance.
Pickling & passivation and electro polishing- is a simple and inexpensive process that will last and stand the test of time.
For further information have a look at our care page