Download ALWC - BAC Corrosion Control Ltd

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Accelerated Low Water Corrosion (ALWC) is a particularly aggressive form of
microbiologically-induced localised corrosion affecting steel piling and other brackish
or sea water immersed structures, which is most commonly found close to the level
of the Lowest Astronomical Tide (LAT).
To mitigate this, Cathodic Protection (CP) and/or
coatings are currently used in combination with
surface sterilisation. It is, however, expensive and
difficult to apply conventional coatings to existing
corroded structures under water to prevent further
In some cases, a calcareous film, a deposit of
Calcium Carbonate (CaCO3) and Magnesium
Hydroxide (Mg(OH)2) produced on steel structures
has been proved to be an effective and an
inexpensive substitute for a conventional corrosion
control coating.
When deposition conditions are appropriately
controlled, it provides corrosion protection for steel
in seawater.
BAC Corrosion Control Ltd (BAC) and partners Mott MacDonald and The
University of Manchester have developed a patented treatment, LATreat™, to
counter the problem of ALWC by applying a calcareous deposit in a controlled
process. The process can be used to treat local areas where ALWC is occurring.
LATreat™ is an electrochemical process which
works in a similar way to CP simply using the
seawater and electricity to generate all the
necessary active agents.
The treatment comprises three optimised stages,
Cleaning, Sterilisation and Coating which are
typically carried out sequentially using BAC
equipment located within easy access of the
structure to be treated.
Following lengthy studies, the endurance of the
calcareous film has been evaluated the
treatment is now commercially available. A
Patent covering the UK has also been granted
for the process.
Cheaper than alternative solutions – no permanent equipment or associated cost
Short time to implement – around 100 hours for treatment per unit area
Minimum disruption to harbour activities
All equipment removed on completion
The treatment is environmentally friendly; chlorine generation is short term and
No external agents are used in the process, Mg2+ and Ca2+ are available in
Processes Involved
1. Cleaning - using cathodically generated hydrogen which removes the aggressive
surface foulant characteristic of ALWC.
2. Sterilisation - using anodically generated chlorine which is a known biocide used
to kill the bacterial infestations.
3. Coating - rapid in situ application of a protective alkaline coating deposited from
seawater dissolved salts using a pulsed current technique, which provides
optimum local protection whilst normal deposits reform.
Before Treatment
During the cleaning process
After coating treatment
The specialist Switch Mode Power (SMP) Supplies, developed
by BAC, offer the following advantages:
• Accuracy and linearity better than 0.1%
• Ripple amplitude much lower than conventional transformer
• Compact physical size
• Constant current/voltage/potential control
• Frequency modulated output
LATreat™ is not a replacement for other corrosion prevention
products, but is proving to be an environmentally friendly
alternative which may prove more effective and economical in
some situations
Stafford Park 11, Telford, Shropshire, TF3 3AY, UK
Tel +44 (0) 1952 290321
Fax +44 (0) 1952 290325
Email: [email protected]