Popularly known as CUI for “Corrosion Under Insulation,” the issue is more correctly related to Corrosion Under Inadequate And Poorly Installed Insulation, or CUIAPII.  The problem is rarely sought out, and only is realized after decades of hidden pipe deterioration results in the first failure.

Outer pipe corrosion at chill water and dual temperature systems is often far more severe than what is occurring internally, and is always more severe at the colder supply side.  Most cold water pipe is insulated using fiberglass, which only provides limited protection.  Installed using anything less than 2 in. thick insulation means even less protection.  Its paper/foil “moisture barrier” is mediocre to poor at best, as a review of our photographs below graphically prove.   Worse is soft foam insulation; many later finding that the superior foam insulation installed has actually caused more damage.  Cold pipe can be very well protected by the use of thick hard cell foam glass, mastic cement at each seam, and a hard shell outer covering, but is rarely installed.

The same level of damage is also common to exposed condenser water piping to and from the cooling tower.  Installed for the purpose of protecting the pipe, most outdoor insulation only conceals a very major hidden threat.  Water treatment chemicals are extremely corrosive and damaging to any aluminum covering – leaving those pipe runs vulnerable to over spray often in the worst condition.  Maintenance and service personnel walking all over the insulation will quickly add to that damage.

Fundamental to all forms of CUIAPII is the universal misunderstanding that insulation alone will protect the pipe, which it can’t.  For most of the worse cases we investigate, the simple 1st step of painting or coating the pipe with an effective waterproof paint or epoxy would have avoided almost all of the damage entirely.