Photo Gallery B3: Corrosion Under Insulation
CUI, otherwise known in the trade as “Corrosion Under Insulation,” represents one of the most damaging forms of corrosion to any piping system operating under cold temperatures – such as chill water, dual temperature, and domestic cold water. It develops slowly over decades hidden from view, with few building owners or operators actively seeking to identify its presence. It can also develop under insulated pipe exposed to outdoor weathering, although that is technically a different condition.
The impact from CUI is directly related to pipe temperature, area humidity, the type and thickness of its insulation, and an effective moisture barrier. Supply pipe at typically 10° F lower temperature always suffers the worst. Contrary to claims by the insulation industry, fiberglass insulation provides a very poor barrier to moisture by its paper foil covering. Proof positive to this fact is provide in just some of the examples we have documented in this gallery. Although the level of deterioration to the pipe does not equal the thickness of rust product, it can often well exceed internal corrosion levels. And unlike internal corrosion which is typically uniform for most cold water systems such as chill water – external corrosion levels will vary dramatically.
To be honest. CUI should be re-titled as CUIPIPMI – for “Corrosion Under Inadequate, Poorly Installed, and Poorly Maintained Insulation.” Most examples of severe external corrosion loss under insulation are of no surprise. Obvious deficiencies such as 1 in. or even 1/2 in., insulation thickness, standard fiberglass in severe humidity areas such as Miami, Houston, and New Orleans rather than closed cell foam, trampled insulation due to lacking maintenance – all result in an accelerated external wall loss. The use of soft foam insulation presents an entirely different threat due to its potential to itself deteriorate; documented in another Photo Gallery.
Covering insulation with a metal or vinyl protective covering, while producing a very attractive result, will often fill with water as a result of the failure to silicone seal every joint and seam. For clamped cold water piping systems, condensate and water at the unprotected retaining bolts have failed long before the pipe itself – causing catastrophic damages. The absolute most basic front line preventative of painting the pipe with a high solids waterproof marine type coating is rarely performed prior to insulation under the flawed assumption that insulation is all that is required.
In short, most insulation will produce some level of hidden corrosion impact within 20 years or often sooner depending upon a wide variety of factors.
