Maintenance – Stainless Steel / Copper

M A I N T E N A N C E
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WHY IS IT IMPORTANT TO CLEAN STAINLESS STEEL?

Contrary to popular belief stainless steel MUST be maintained.

There is no such thing as a maintenance free metal product although stainless steel requires much less than normal steel products.

It should be noted that chloride must be avoided as this promotes corrosion of stainless steel.

CORROSION RESISTANCE

316 stainless steel is excellent in a range of atmospheric environments and many corrosive media – generally more resistant than 304.

316 is usually regarded as the standard “marine grade stainless steel”, but it is not resistant to warm sea water.

In many marine environments 316 does exhibit surface corrosion, usually visible as brown staining (commonly named “Tea Staining”).

This is particularly associated with crevices and rough surface finish.

WHERE DOES ‘TEA STAINING’ OF STAINLESS STEEL OCCUR?

Tea staining mainly occurs within approximately 5kms of the surf.

The closer the stainless steel product is to salt water the more likely the product will be affected.

In environments where there is wind exposure, industrial pollution and high temperatures, tea staining may even occur within 20kms from the sea.

The corrosion rate of non-stainless steel metals are even more affected by these factors.

Salt water chlorinated pools are also big contributors to salt contamination due to spray and fine misting during windy weather.

Swimming pools are sterilised with chlorine/bromine or by adding sodium chloride (salt) for salt-water chlorinators.

Chloramine and chlorine are emitted to the air in small amounts by the pool and a significant amount of water is lost through evaporation, surface turbulence, wind
borne spray and splashing.

This moisture rich, chloride (salt) affected air infiltrates under roofs and leads to corrosion of metal fittings, including light fittings and stainless steel fans.

The use of fittings under roofed decks and pergolas next to swimming pools and in coastal areas will require increased maintenance due to the presence of chlorides
(either as common salt or from other compounds in pool chemicals).

The temperatures attained in the peak of a pitched deck or veranda roof can easily exceed 60 – 70°C and especially when coupled with chlorides this will increase
maintenance requirements.

Even indoors in coastal areas, the influx of warm sea air can accelerate the surface corrosion of 316 stainless steel.

This can still happen a great many kilometres from the sea.

When humidity is high and temperature drops, moisture condenses on metal surfaces (such as light fittings).

The layer of moisture can be almost microscopic but it will affect the surface by depositing a tiny layer of salts and thus eventually lead to corrosion if the product is not
properly and regularly cleaned.

Condensation occurs when the temperature of a surface falls below the dew point temperature of the surrounding moisture laden air – it has nothing directly to do with
wet or cold weather, so condensation can occur anywhere when the humidity is high enough and dew point depression (DPD) small enough.

DPD is the difference between “dry bulb” and “wet bulb” temperatures.

This number is then used to determine relative humidity (RH).

The smaller the DPD, the higher the RH and a small decrease in air temperature will lead to condensation forming.

It’s important to clean stainless steel because stainless steels have a colourless chromium rich layer on the surface of the steel.

This protective layer is not impervious and if this protective layer is damaged the steel surface will be attacked and corrosion will take place until the layer re-establishes
itself.

Corrosion levels will be more severe if the layer is not given time to repair itself.

Under normal conditions the layer will repair itself in the presence of oxygen, however, repetitive exposure to aggressive environments (such as salt contamination) will
make it harder for this protective layer to reform itself.

An ordinary, well rinsed, damp cloth should be used to wipe all surfaces to remove contamination left by condensates.

Those surfaces should then be dried using a clean cloth.

Any materials used to clean stainless steel should not have been used on other metal products as tiny specks of these other metals will contaminate the stainless steel
surfaces.

• “Washing removes contaminants (such as salts) that can cause corrosion and is necessary to avoid tea staining.”

• “One of the main causes of tea staining is salt deposited on the surface.
Tea staining is most likely to occur up to five kilometres from a surf beach or a few hundred metres from still marine waters.
There is no hard and fast rule: wind and weather conditions play a big part and the severity of the conditions increases sharply as you approach the surf.”

• “Stainless steel may discolour if left in contact with salts or acids for extended periods.”

• “In coastal environments even smooth stainless steel finishes may tea stain if not washed regularly to remove salt.
As a rule of thumb, it should be washed as regularly as the windows.”

TWO COMMON STAINLESS STEEL MYTHS :

1. “Stainless steel doesn’t rust.”

In normal conditions stainless steel does not usually rust however, as the name states “stain less” will, under aggressively corrosive environments, be attacked.

As explained above, there is a thin colourless layer which forms spontaneously on top of stainless steel and this layer protects the steel from mild corrosion.

However, when this layer is attacked by extreme weather conditions such as high levels of salt in the air, this protective layer may not be able to reform itself quick enough
to stop rust from forming on the stainless steel.

Even though rust might start forming on the stainless steel, the stainless steel will still rust much slower than normal carbon steel.

2. “All stainless steel have the same corrosion resistance.”

The level of corrosion resistance of stainless steel depends on the properties that make up the grade of stainless steel.

The proportion of alloying elements (such as chromium and molybdenum), in the grade of stainless steel, as well as the surface finish and fabrication practice, will affect
the corrosion resistance of the metal.

There can be a significant difference in 316 Stainless Steel quality depending on the country of origin.