Corrosion under insulation (CUI) is a financial burden to our insulation
industry; millions of dollars are spent annually to remediate, replace,
and
re-insulate corroded systems. To compound these costs, plant shut-downs
to repair and remediate far out-cost the actual remediation costs.
To understand corrosion
under insulation, we must understand the mechanics of the corrosion
process.
Metal corrosion begins when four ‘ingredients’ are
present:
- An Anode
- A Cathode
- An electrical
path connecting the anode and cathode
- An Electrolyte
(e.g. moisture)
Three of these ‘ingredients’ are inherent in all metals;
an anode, a cathode, and an electrical path connecting them. The only ‘ingredient’ missing
is the electrolyte; normally water, but it can be other liquids or solutions,
or chemical compounds.
The anode is where corrosion occurs, the anode sacrifices itself to
protect the cathode, releasing positively charged metal ions into the
electrolyte and electrons are left behind in the metal. These electrons
flow through the metal to protect the cathode.
An electrolyte is a solution capable of conducting electrical current
in the form of ionic flow. The electrical path is a connection between
the anode and cathode where current in the form of electrons can flow.
Free electrons do not flow in the electrolyte, only in a metal path.
Anodic and cathodic areas develop where chemicals have been deposited,
where there are temperature differences, and in areas where moisture
is present. Chlorides and other industrial contaminants in the electrolyte
can also cause an area to become anodic. The contamination may be present
on the metal surface before it is coated or insulated. Once these areas
become wet, corrosion begins.
Quite simply, three
of the four elements for corrosion to occur are inherent in all metals,
it’s like the simplicity of a boxed cake
mix; “just add water” and corrosion will occur. Corrosion
can be accelerated by cyclic temperature changes or the presence of chlorides
or other elements.
For more information on CUI, other page links discuss remediation and
prevention.
