TYPES OF SYSTEMS
Chilled water systems
Heating, low, medium or high temperature
Closed loops in general
Air handling units
If it creates an aerosol you have to consider the
Temp, nutrients, environment, spray, people
Bacterial/fungal growth can be an issue with
Fungal slime growth can block and reduce cooling. Similar
to what scale and iron deposits can do. Bacteria can
corrode metals too. Even stainless steel.
Any system that is supplied with hard water
and cools process systems can deposit
scale at the hotter areas – heat exchangers.
The heat exchangers themselves can be
made of brass, aluminium, copper, iron.
– Different metals in a system can also add to the
corrosion potential by adding to the electrolytic
Fume scrubbers, AHU’s, Vehicle washers spray
water that is typically dirty. They can thus lead to
Metal cutting machinery if often a source of bacterial
infection, including legionella.
Closed systems have slime, scale and corrosion
Heating systems can be either low, medium or high
pressure systems, the higher the pressure the
higher the temperature
Chilled water systems cool water that is pumped
around jacketed vessels or heat exchangers and
frequently involve a holding tank(s).
DOSING AND CONTROL
Dosing pots provide a means to add chemical and
also allow for sampling the water.
Inhibitor considerations need to take into account
what could be the bigger issues. Could be lack of
cooling from scale or corrosion may be a greater
Bacterial control is invariably by non-oxidising
Dosing can be manual, water meter pulsed, or
timer controlled pumps.
Nitrite is the most common inhibitor for closed
systems, coats metals protecting against
corrosion, nitrite is an anodic inhibitor.
Has the potential to foam if overdosed.
Typically dosed to systems with little water losses
like chilled and heating systems.
Has to be dosed at >1200 ppm if Chlorides >100.
Makes pH of system water high at roughly 10-11 –
aluminium corrosion pH level
If not enough is dosed it adds to the problem by
localising the corrosion attack to the remaining
areas not protected.
Most cathodic or resistant to corrosion
18-8 Mo stainless steel (passive)
18-8 stainless steel (passive)
Chromium steel >11 % Cr (passive)
18-8 Mo stainless steel (active)
18-8 stainless steel (active)
Chromium steel >11 % Cr (active)
Steel or iron
Commercially pure aluminium
Magnesium and its alloys
Most anodic or easy to corrode
Gallionella bacterium corrode stainless steel
There are organisms that accumulate iron or manganese. The
accumulation of manganese in biofilms is blamed for several cases of
corrosion of stainless steels and other ferrous alloys in water systems
treated with chlorine or chlorine/bromine compounds.
Certain fungi are also capable of producing organic acids and have
been blamed for corrosion of steel and aluminium. i.e. Aircraft fuel
tanks, sulphate reducing bacteria will produce sulphuric acid and nitrite
reducers will product nitric acid.
Aerobic slime formers can inadvertently produce enzymes that are
capable of intercepting and breaking down toxic substances (such as
biocides) and converting them to nutrients for the cells
Various anaerobic bacteria such as Clostridium are capable of
producing organic acids. Could be a problem in closed water systems
that become anaerobic. In addition anaerobic bacteria produce foul
COPPER AND BRASS
Brass is an alloy of copper with zinc present (10-15%). The zinc component is
susceptible to corrosion resulting in a weakened metal that can fracture under
Pitting corrosion occurred only in low dissolved inorganic carbon (DIC) (5 and
10 mg C/L) and high-pH (9) water in the presence of chloride (20 mg/L) and
was not observed at pH 7 or 8. Sulphate was not necessary to develop pitting
corrosion; however, it did affect the composition of the corrosion by-products
associated with pitting corrosion. Increasing the DIC from 10 to 50 mg C/L or
adding 3 mg PO4/L prevented pitting corrosion at pH 9. A conceptual model
was established that attributed pit initiation to the deposition of copper chloride
or sulphate compounds on the pipe at the anode.
In other words if the pH is less than 7 raise it to between 7 & 9, ensure enough
phosphate is present and the conductivity is high enough. Keep an eye on
chloride levels as they seem to pit just about anything when high enough.
(>200 stainless steel etc)
If the water is soft, the corrosion potential is much greater. TTA is a good
copper inhibitor, but protecting the zinc present in brass is difficult – filming
amine is an option.
Aluminium readily forms a protective layer of aluminium
oxide assuming oxygen is present.
Aluminium readily corrodes usually as a result of the
breakdown in the oxide layer from mechanically being
removed. Also corrosion occurs greatly when iron/copper
deposits on the metal. (electrolytic/battery effect)
At a high pH aluminium is corroded
Protection is via pH control, blended hardness levels and
chemical protection should be at high levels to ensure
sufficient coating / removal of any electrolytic effects.
In soft/softened water systems molybdate treatment, is
the only option at high concentrations, at least 800ppm
VEHICLE WASH SYSTEMS
Produce substantial aerosol.
Can be contaminated with all manner of road
Can be contaminated with surface run off.
Can be contaminated with drift from cooling towers
Have lots of organic matter for food sources.
Should be treated with biocides if a recirculating
Have been implicated in legionellosis outbreaks.
Biocide treatment is usually with Oxycare
METAL CUTTING SYSTEMS
Often have central
solution storage tanks.
Sometimes applied by
spray, ie aerosol.
Prone to biological
– Including legionella
Have been implicated
Treat with nonoxidising biocide
Legionnaires’ bug hit 115 people at spa
club Jul 13 2007
by Graeme Whitfield
The Journal. ONE hundred and fifteen people are believed to have
been affected by the Legionnaires’ disease bug in an outbreak at
a Sunderland leisure club, a report said yesterday.
The Health Protection Agency traced the outbreak last year to
faults in the water treatment system at the Springs health club,
which led to the legionella pneumophila bug colonising the spa
It is now known that the 115 people became ill after visiting the
leisure club from August 11 to 25 last year. Of these, two have
been confirmed as having Legionnaires’ disease and five of
having Pontiac Fever, a milder version caused by the same
legionella organism. Three people needed hospital treatment after
the outbreak, which led Springs to shut the health club earlier this
Dosing and control
Normally two stages
Control system will
maintain control over
Control system will
maintain control over
Complex pipe work
Makes full draining
Potential dead legs
Areas for bacteria to
should be avoided.
Legionella species can give rise to both Legionnaires
Disease and/or Pontiac Fever.
Pseudomonas aeruginosa can give rise to folliculitis
which is an infection of the hair follicles, children and young
adults are most at risk.
Mycobacterium avium has been associated with
Amoeba such as Naegleria fowleri is a rare cause of fatal
meningitis which has been associated with natural spas.
Acanthamoeba species are common in water systems and
can cause eye infections especially in wearers of contact
lenses. This amoeba can also cause encephalitis of the
FOR FURTHER INFORMATION
Contact AKVO Ltd
Tel 0844 244 8726
Or visit www.akvo.co.uk