CUI stands for Corrosion Under Insulation. The surface of an insulated steel pipe corrodes beneath the insulation layer, out of sight, until the damage has already progressed far.
It is exactly this invisibility that makes CUI expensive. The surface looks intact from the outside, but the steel thins under the insulation. The damage is often discovered only when the insulation is opened or the pipe leaks.
How CUI forms
Moisture reaches under the insulation from rainwater, condensation, steam or washdowns. When water stays against the steel surface and cannot evaporate, corrosion advances.
Particularly vulnerable is the temperature range in which moisture condenses on the pipe surface but does not dry off. The damage concentrates at points where the tightness of the insulation is weakest.
The compound stays soft and repairs itself from minor damage, so no space is left for moisture between the steel surface and the protection.Stopaq, viskoelastinen suojaus
Joints and fittings are the risk points
CUI typically strikes where the insulation has been interrupted or had to be worked: field-made joints, bends, flange connections and valves.
These are exactly the points where moisture most easily reaches the steel surface. That is why protection is worth directing to them first.
Viscoelastic protection
Stopaq's technology is a viscoelastic polyisobutylene compound (PIB) that is applied cold. The compound stays soft, flows into the irregularities of the surface, and repairs itself from minor damage, so no space is left for moisture between the steel surface and the protection.
Stopaq Wrappingband adheres without a primer and does not require sandblasting; wire brushing is sufficient. Its operating temperature is -45 °C to +70 °C, and it is ISO 21809-3 and EN 12068 compatible. A mechanical protective tape, Stopaq Outerwrap, is applied over the top.
For the annular space of casing pipes, for example at road and railway crossings, Stopaq Casing Filler is used, which is pumped in hot and displaces water and oxygen.
Cathodic protection is preserved
Underground steel pipes are often protected with cathodic protection. According to the manufacturer, Stopaq's viscoelastic compound does not interfere with cathodic protection, so the two protection methods can be used side by side.
