ecocool 100R
Page 23
Operating Manual
www.grantinstruments.com
7.0 Technical Tips
7.1
Which water should you use in your equipment?
For the long-term reliability of the equipment it is important to use oxygenated water that
is free from ions and minerals that can cause corrosion of stainless steel. We
recommend the use of distilled water and de-ionised water from modern ion exchange
systems that do not use salt back flushing to regenerate the ion-exchange cartridges.
Stainless steel is protected from corrosion by a layer of chromium oxide. If the chromium
oxide layer is damaged, oxygen present in water can reform the oxide layer. If the water
is distilled or de-oxygenated, and the oxide layer is damaged, ions can corrode the
stainless steel tank. If a water bath has been unused for some time, or the water has
been boiled, we recommend changing to fresh distilled water or the correct type of de-
ionised water as explained below.
Water normally contains calcium or magnesium ions. De-ionised water has most ions
removed as indicated by its conductivity level; the purer the water the lower the
conductivity. It is important to use only de-ionised water from an ion exchange system
with replaceable cartridges. Do not use de-ionised water generated from an ion-
exchange system that incorporates a salt back-flush system to regenerate the ion-
exchange resin as this can leave sodium ions that are very corrosive to stainless steel.
7.2
How to prevent rust in the equipment
Most Grant tanks, and other parts which are immersed in water, are made from type 304
stainless steel. Type 304 stainless steel is an extremely versatile general-purpose grade
of stainless steel. It is the excellent forming characteristic that has made this grade
dominant in the manufacture of laboratory and industrial water baths, as well as domestic
sinks and saucepans. Type 304 stainless steel is highly suitable for applications where
hygiene is important; it exhibits good heat resistance and excellent resistance to
corrosion.
However, despite resistance to general surface corrosion, stainless steel is susceptible to
specific types of corrosion, in particular pitting (small pin hole style corrosion) and stress
corrosion cracking. It can also undergo general corrosion in specific environments, such
as one containing hydrochloric or sulphuric acids.
Stainless steel is protected by its high content of alloying elements, primarily chromium
and nickel. Chromium is the most important with respect to corrosion resistance,
although the nickel assists in allowing the chromium to do its job. The chromium forms an
oxide layer on the surface of the steel, which inhibits further oxidation. This layer adheres
extremely well to the metal substrate, but it is essential that it remains intact, and must be
protected from various forms of damage.
If the surface chromium oxide layer becomes damaged, oxygen present in water can
partially reform the oxide layer, so it is advisable to ensure that water is always fresh and
well oxygenated. Baths that will be out of use for an extended period should be emptied,
and all moisture should be wiped from the bottom of the tank.
In some cases, a brown layer may appear on the surface of a stainless steel tank. In
most cases this is not rust, but it may be a surface deposit of minerals from the local
water supply, it can also be caused by ferrous particles or salts that have fallen into the
tank. These surface deposits can usually be removed by using a household metal polish.
