Corrosion Under Insulation (CUI) is the cause of many of the Oil & Gas industry’s most serious problems including forced shutdowns, lost production, early repair and replacement, as well as safety and environmental consequences that can cost millions of dollars.
CUI maintenance can be extremely costly, taking up >50% of a typical Oil & Gas facility’s maintenance budget, as well as posing various challenges for asset owners and applicators. Typical considerations which can add cost for CUI maintenance:
- Stripping/recladding of insulation
- Surface preparation
One asset owner in Indonesia advised “It costs us $1,100 per square meter to scaffold, open up the insulation, prepare the surface, apply a protective coating, then make good the insulation”
Due to the high cost of CUI maintenance, it is especially important that applied coatings can be relied upon for long term service. For many years, Epoxy Phenolic technology has been a common solution specified to protect pipework operating at high temperatures. These coatings evolved from linings used for the internals of storage tanks, where a highly crosslinked film was advantageous to resist the damaging effects of strong chemicals or high temperature service. Over time, it was realized that the high crosslink density also provided an effective barrier to mitigate the damaging effects of CUI.
Challenge of DFT Control
Typically used in new construction, one of the major downsides of traditional epoxy phenolic technology is that it is very sensitive to overapplication. Overapplied coatings become highly stressed during heating and cooling, which can rapidly lead to cracking during high temperature service. This causes particular challenges at maintenance, as dry film thickness (DFT) control becomes much more difficult when applying outside a controlled paint shop environment.
The action of the CUI corrosion mechanism causes pitting in steel. When a protective coating such as a traditional epoxy phenolic is applied to the pitted surface, a higher thickness will collect in the pits. The higher thickness in the pits and the potential stress concentration will reduce lifetime versus a uniform and flat-blasted substrate. Add to this the fact that maintenance applications can be made more difficult due to access constraints and the overall risk of overapplied coating becomes unexpectedly high!
High level pipe racks require scaffolding for access, and the frequency of maintenance turnarounds can dramatically affect lifetime costs.
Tolerance to DFT Over-application For a Traditional Epoxy Phenolic Coating
- Light grey – good, no visible defects
- Medium grey – cracking and defects observed around weld only
- Dark grey – cracking and defects observed around face of panel
Based on alkylated amine epoxy technology, Interbond 2340UPC is a next generation epoxy phenolic coating for high temperature applications from AkzoNobel. Interbond 2340UPC delivers excellent tolerance to over application, fast cure even at sub-zero temperatures and unrivaled impact and damage resistance. This reduces the need for remedial work, minimizing overall application costs whilst maximizing productivity. The DFT tolerance greatly reduces the potential for cracking in service, helping to ensure excellent resistance to CUI and aggressive cyclic conditions. Table 2 shows the tolerance of alkylated amine epoxy technology to higher DFT.
Tolerance to DFT Over-application of DFT For an Alkylated Amine Epoxy
Interbond 2340UPC shows robust crack resistance even at thicknesses up to 2 x 350µm.
CUI maintenance can be highly costly. In order to minimize the cost of maintenance and reduce the frequency of maintenance turnarounds, effective CUI maintenance coatings need to be suitable for the ‘real world’ maintenance process. Interbond 2340UPC shows excellent tolerance to overapplication and has a strong track record in highly aggressive maintenance scenarios all over the world.