An introduction to Corrosion Under Insulation (CUI)

To any corrosion engineer the CUI corrosion mechanism is basic stuff. However many asset-owners keep reinventing the wheel by finding technical solutions for this problem that’s known over 40 years. Also there is a big focus on surface protection and metallurgic (piping, equipment materials) and very little on insulations. Remarkable, because a lot of people follow the idea that thermal insulation is root cause. And in CUI projects often the old insulation is replaced by the same system as before. And little to no energy is put into evaluate a fit-for-purpose insulation system.

It’s a widely accepted fact that asset-owners have not enough knowledge about technical industrial insulation systems. Sharing specific experience and expertise about CUI is Temati’s key success factor and explains our excellent track record in providing solutions for CUI. We build long term relationships with asset-owners e.g. maintenance managers, inspection engineers, RBI engineers, asset integrity managers, design engineers etc. This contributes to more CUI awareness and emphasizes on how to mitigate CUI by engineering and implementing fit-for-purpose insulation systems.

Want more insights on Temati products and their contributions in mitigating CUI? visit frequently asked question about CUI

Specific solutions for specific problems


Temati DrainplugThe best practice to mitigate CUI is a system approach by designing a fit-for-purpose coating, insulation material and jacketing that minimizes water or moisture ingress. But it’s a general accepted fact that in the long run water or moisture ingress can’t be avoided and steps need to be taken to limit the consequences. There are several well documented insulation systems that minimize water or moisture accumulations and allow the system to dry out. One of these systems is installing drainplugs.

Damaged or missing insulation and or jacketing needs to be repaired within a reasonable time frame. This will limit the amount of moisture or water ingress and subsequently the risk of CUI.

TEMATI drainplugs can only drain moisture and water to a certain extend and functionality is subject to the insulation’s technical condition. TEMATI drainplugs are not a safety net for anomalies in insulation systems, but will mitigate the effect of water or moisture ingress. If an insulation system which is in a good condition internal condensation cannot accumulate inside. Learn more about Drainplugs

Protectem* Flangebelt™

In general asset-owners are reticent to insulate flanges. This is often based on bad practices where leakages have resulted in wet insulation, HSE issues or fire hazard (when it’s related to chemical products). But also in having un-insulated flange pairs there are critical spots. For instance end-caps. The level of design, fabrication and installation of these end-caps determines if water ingress can occur. Also vibrating pipes or using wrong sealant/calking are critical aspects that plead for insulating completely.

Flangebelt applicationAnother argument not to insulate often used by mechanical engineers is flange-integrity. If flange-pairs are insulated, stud-bolts temperatures get too high. This results in extra expansion and consequently lower bolt-tension, which could cause leakages. Thermographic inspections have shown that the temperature inside the flange only drops a couple degrees (depending on the environmental temperature). In other words the temperature drop does not justify the argument of not insulating. In some cases bolts are being post tightened after commissioning, when pipe lines are running at service temperature. This means flange pairs have to be insulated after this.

Also insulated flanges provide a good weather protection and avoid corrosion of threaded ends, which contributes to loosening stud-bolts during maintenance.

There are several fundamental reasons for insulating flanges:

  • process control (traced systems)
  • prevent heat loss
  • save energy
  • reduce CO2

Protectem Flangebelts - equipped with a drainpipes or sniffer tubes and optional sample bottles – prevent leakages from affecting the insulation.

This drainage system is also documented for removable insulation boxes in the CINI insulation for industry manual. Learn more about Flangebelts


CUI can happen when wet and saturated insulation materials are in contact with a pipe or equipment (substrate). From a corrosion prevention point of view the most logical solution is to disconnect insulation from the substrate. A method that is described in CINI but originates from Shell and Equinor (formerly Statoil) is called Non-Contact. This can easily be achieved by using spacers or special designed rings as shown below.

However, from a thermal insulation point of view the so called chimney effect can occur and cause extra heat loss. Therefore Non-Contact needs to be carefully considered in the design phase.

Another system that is described in the CINI manual is to create an air cavity at the outside of the insulation system. By using a studded foil like Temafol the cladding/jacketing is detached form the insulation material.

This system enables two basic physics principals. Within the cavity a draft allows moisture to evaporate. The cladding/jacketing is always colder, which allows moisture to condensate against its inside and freely drain from the system.

Learn more about Temafol

insulated pipes