For corrosion of steel to occur, four factors need to be present: (1) water; (2) oxygen; (3) corrosive chemical(s); and (4) a suitable temperature. Since only a small percentage of pipes actually operate in this range, CUI is only likely to occur when a pipe operating at an above-ambient service temperature is shut down for service. That happens to all pipes sooner or later. As water vapor does not lead to corrosion, liquid water must be present for CUI to occur. That will be the case at 50°C to 140°C.

Corrosion will not occur on a 315°C pipe, at least not while it is operating at that temperature. It will occur when the pipe is shut down, is in the process of being shut down, or is being brought back to temperature.

If a pipe operates continuously at a temperature where water is likely to be present much of the time , the probability of CUI occurring is much greater. For a carbon steel pipe with a process temperature between 37°C and 100°C water that leaks into the insulation system will sooner or later find its way to the interface between the pipe and the insulation.

Invariably, there will be some chlorides or other corrosion-causing chemicals in the environment that will dissolve in the water that gets to the pipe. Consequently, for a low operating temperature, with an insulation system that leaks and an uncoated pipe, the conditions for CUI are close to ideal. STOPAQ immersion grade coating systems can protect carbon steel pipe from water, air, and corrosive chemicals.

With those three elements, as well as time and a certain temperature range, corrosion will occur. The first line of defence against CUI is up to STOPAQ. The second line of defence is insulation system maintenance. The third line of defence is a suitable insulation material such as Aerogel.


STOPAQ Wrappingband CZH + insulation according to spec