SOLVING THE PROBLEM OF CORROSION UNDER PIPE INSULATION
By: Brian Courtright
With insulated metallic piping, the phenomenon known as corrosion under insulation (CUI) is a problem that is hard to quantify. The presence of moisture between insulation and pipe is hidden from view unless a facility adopts a fairly radical approach to detection. If moisture is present between the steel surface and insulation, then corrosion is practically a certainty.
CUI can lead to prolonged downtime due to equipment failure, severe catastrophic leaks or explosions, and general safety and environmental concerns. The problem is common to insulated carbon steel, low alloy steel, galvanized, and stainless steel piping operating in all different temperature conditions.
Causes of CUI in Piping
When equipment and pipe operate cyclically, either because of maintenance or as part of their process, CUI can form in several ways.
The insulation material itself may be water absorbent and hold trapped condensation in contact with the steel substrate.
The piping system design may not adequately provide reliable drainage for condensation to escape, leaving it to pool locally.
The insulation may have been improperly installed or a break in the vapor barrier from holes or tears may have occurred some other way.
Corzan® CPVC Won’t Corrode
None of these issues need be an ongoing concern with CPVC piping. Thermoplastic piping made of Corzan® CPVC is inherently corrosion resistant. While CPVC’s lower thermal conductivity inhibits heat loss compared to metal, insulation may still be needed for code compliance. Corzan piping will not corrode even if there is a break in the insulation vapor barrier, or if it is installed incorrectly.
For instances of system piping not being driven by a plumbing, mechanical, or energy code, insulation may not be needed or could be reduced, because CPVC will remain condensation-free under most environmental conditions that would cause copper tube to sweat and drip. In those situations, such as hot and cold water supply lines within conditioned buildings, water temperature can be calculated versus the dewpoint to determine the best solution.
In short, without significant investments in condensation detection methods and resources devoted to systematic monitoring, CUI rarely is discovered before extensive damage is done. Corzan CPVC is the thermoplastic CUI solution, eliminating the worry of trapped condensation under insulation altogether.
