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Introduction to
Corrosion in Cooling Towers |
Causes:
- Demise of chromates
- Piping & heat exchanger
system containing a mix of steel and copper pipes
- Low to moderate levels of
copper corrosion caused by excessive chloride
- Plating out of dissolved
copper on steel surfaces, forming a 'battery'
- Localised, concentrated
galvanic corrosion of steel around discontinuities in the copper
plating
- Growth and proliferation
of bacteria due to microbially influenced corrosion (MIC)
- Poor water treatment
practices
Damage:
- Growth of tubercles -
large, impervious structures - on pipe internal walls around
corrosion sites. Tubercles are formed from corrosion product and
biological matter and obstruct most of the
cross-sectional area of steel pipes
- Synergy between bacteria
and galvanic corrosion processes in tubercles can cause extreme
pitting rates
- Pitting leads to
significantly reduced system life at best, rapid perforation of
steel pipes at worst
- Corrosion product can coat
heat exchangers to reduce
system efficiency, as well as acting as a chemical 'sink',
increasing water treatment costs
Health Risks :
- Tubercles can provide
conditions suitable for growth of Legionella
- Slow leaks can cause
fungal growth and lead to severe
indoor air quality problems
Timeframe:
- Significant tubercle
structures can form within 12 months, under appropriate conditions
- Penetration of 3.6-4.5 mm
thick steel pipe walls is possible after 1-2 years of operation of a
new system
Remediation / Prevention :
- Remediation costs can
range from $50,000 to $500,000 dependent on extent of damage. In
badly damaged systems, replacement of steel pipes can be the only
viable option. Professional supervision is essential for cleaning
procedures and pipe-lining processes, as damage can be exacerbated
if cleaning is incorrectly implemented.
- Prevention is better than
cure - the key approach to ensure appropriate water treatment is not
to allow cost to influence choice of contractor. Evaluate, then
choose a reputable contractor able to guarantee a minimum level of
performance through use of water condition monitoring techniques.
Independent
performance evaluation of contractors and suppliers is highly recommended.
CETEC provide s
independent performance evaluations of contractors and suppliers. We also specialise in identifying
and remediation of corrosion problems. For
more articles about Corrosion and Cooling Tower Systems
click here |
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