ASSET INTEGRITY
Corrosion under insulation: where it starts and what a bonded coating changes
Corrosion under insulation starts where water gets behind the jacketing and stays against the steel, most often at seams, penetrations, supports, insulation ends and low points. A bonded insulative coating over prepared, primed steel leaves no gap for that water to sit in, which reduces the conditions behind CUI; it does not repair corrosion that is already there or replace inspection.
Where CUI usually shows up
Start a review at the places water enters the insulation or cannot drain out.
| Location | Why water collects | What to look for |
|---|---|---|
| Jacket seams and overlaps | Rain and washdown water get past failed sealant or loose bands. | Rust streaks, staining, open seams, loose bands. |
| Penetrations, supports and hangers | The jacket is cut or pinched around the attachment. | Gaps around the attachment, dents, rust at the support. |
| Insulation ends at flanges and valves | An open or damaged end lets water into the insulation. | Missing end caps, damp or crushed insulation. |
| Low points and the bottom of vertical runs | Water inside the insulation drains down and sits. | Bulging or stained jacketing, wet insulation at the base. |
| Cold lines that sweat | Condensation forms on the steel under the insulation. | Drips, ice, damp jacketing. |
| Lines that run intermittently or sit idle | Moisture gets in while the line is cool and is not driven off. | Standby equipment and lines that cycle between hot and cold. |
| Jacketing damaged by foot traffic or impact | Dents and tears open a path for water. | Crushed sections, punctures, missing jacketing. |
How CUI is found
Inspection usually starts with a walk-down of the jacketing, then insulation is removed at the suspect locations so the steel can be examined. Your inspector chooses any non-destructive screening used to decide where to open first.
Coating does not end the need for inspection. It changes what is inspected: the coated steel itself, rather than the outside of a jacket.
Surface preparation and primer come first
Existing corrosion is removed and the steel prepared to the manufacturer's specification before any coating goes on. Carbon steel takes NanoTech Zinc Primer; non-ferrous metals need no primer.
Application needs dry conditions: surface, air and material at 40°F (4°C) or warmer, relative humidity at 70% or lower, and the surface at least 5°F above the dew point. Pipe that has already lost wall thickness goes to your integrity or engineering review before any coating decision.
What a bonded coating changes
Cool Touch is sprayed directly onto the primed surface and builds a continuous film with no space between insulation and pipe. In salt-spray (ISO 9227) and condensation (ISO 6270-1) exposure testing, the system showed no blistering, rusting, cracking or flaking.
Like any coating, it is maintained: areas damaged by impact or cut out for work are repaired to the same system. Where a fitting has to be opened often, a removable blanket can still be the better choice; the coating or blankets guide covers that decision.
Your next step
Send the lines and equipment involved, operating temperatures, where corrosion has been found and any recent inspection findings. We will review where a bonded coating fits and what preparation it needs.
Questions
Does an insulative coating prevent corrosion under insulation?
No coating can promise that. A bonded coating over prepared, primed steel removes the gap where water collects under jacketing, which reduces the conditions behind CUI. Inspection and repair of damaged areas still apply.
Can you coat a pipe that already has CUI?
Not as found. Corrosion is removed and the surface prepared to the manufacturer's specification first. Pipe that has lost wall thickness needs an integrity or engineering review before any coating decision.
Where should a CUI review start?
At the places water gets in and stays: jacket seams, penetrations and supports, insulation ends at valves and flanges, low points, and cold or intermittently used lines.