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PREVENTING COASTAL CORROSION – “Tea Staining”
STAINLESS STEEL IS NOT MAINTENANCE FREE – BUT MAINTENANCE FRIENDLY.
THE CHOICE OF GRADE AND FINISH OF MATERIAL WILL DETERMINE THE LEVEL OF
MAINTENANCE REQUIRED FOR CONTINUED VISUAL APPEAL.

When specified and used properly, stainless steel enjoys a strong and enduring reputation for it’s visual appeal and structural integrity in a wide range of applications and environments. Incorrect specifications, fabrication or subsequent handling in coastal environments may cause stainless steel to stain or discolour, impairing the overall visual appeal. This brown discolouration, or ‘tea staining’ DOES NOT affect the structural integrity or the longevity of the material – only the visual appeal. This phenomenon is avoidable and can be controlled!

WHERE AND WHY DOES “TEA STAINING” OCCUR

Tea staining occurs most commonly within around 5 kilometres from the coastline. It becomes progressively
worse as one moves closer to the marine source. However, winds carrying saline moisture and other
contaminants, swimming pool chemicals, varied forms of industrial pollution and higher temperatures can also create an environment where tea staining might occur as far as 20 kilometres from the sea.

When stainless steel is produced, the chromium within the metal forms an outer oxide layer. As long as this
outer layer remains intact, the stainless steel remains passive and if cleaned regularly will not alter in
appearance. But once the oxide layer begins to break down, as a result of any one of the above factors, the
stainless steel becomes active and it’s corrosion resistance is reduced. It is at this point that ‘tea staining’
occurs.

MINIMISING RISK AND MAINTENANCE THROUGH CORRECT SPECIFICATION

It must be recognised that keeping the pristine appearance of any stainless steel system depends to a large
degree on the choice of grade as well as the correct choice of surface finish. Rough surface (or brushed/satin
finishes) leave surface grooves which promote the collection of chlorides and other contaminants which are the major cause of tea staining.

It is therefore highly recommend that grade 316 (marine grade) stainless steel with a smooth polished finish should be selected within 5 kilometres of the coast (basically the entire Cape Peninsula – considering the oceans on either side), as well as all West and East coast towns and cities. Grade 316 has a higher level of corrosion resistance where typical architectural components are exposed to extreme weather and climatic conditions (as is the case in coastal environments).

Poor design and bad fabrication can also lead to tea staining. Good designs will avoid crevices such as
intermittent welds and areas where water can collect. Competent stainless steel fabricators will work carefully
so as to avoid carbon steel contamination which has a chemical reaction when coming into contact with
stainless steel and promotes tea staining. All new systems should be washed and inspected for imperfections or contaminants (metal filings etc) caused during the manufacture and installation processes. If discovered imperfections should be cleaned off and surface should be re-polished with suitable stainless steel polish.

HOW TO MAINTAIN STAINLESS STEEL

Whether using stainless steel outdoors or indoors you still need to clean periodically, especially in aggressive
coastal environments and areas around swimming pools. Regular rain washing or fresh water rinsing will
reduce the risk of tea staining for a limited period. A good clean at least once every three months is advised,
where the best way to clean stainless steel is to wash it with soap (or mild detergent) and warm water,
followed by a rinsing with cold water. If so required the further polishing of the surface with ‘Marine Shine’ can
commence after first wiping the system dry.