CUI is a serious issue for energy facilities – and has been for as long as there has been insulation on steel equipment. Moisture gets into the insulation material due to condensation or external sources. Combined with high or cyclic temperatures, this creates optimal conditions for rapid corrosion development.

According to the Norwegian Petroleum Safety Authority, more than 20% of the major oil and gas accidents reported within the EU since 1984 have been associated with CUI. Furthermore, about 50% of the reported hydrocarbon leaks at onshore plants in that study are caused by CUI*. Thus, there is no doubt that CUI represents a major challenge for facilities that continuously focus on reducing risks and hazards.

Explaining the issue from a technical perspective Svein Jacob Kaspersen, R&D Manager Speciality Temp and Tank at Jotun Performance Coatings says; “standard carbon steel can be affected when moisture can infiltrate the insulation from sources such as precipitation or condensation in cyclical processes or when more stable systems are shut down for maintenance. Stainless steels can suffer external chloride-induced stress corrosion if contaminates, such as chlorides from the atmosphere and or the insulation, are present at the steel surface. Therefore, steel structures under insulation are normally protected with coatings to prevent corrosion-related damage during the operational life required of the equipment.”

But CUI is not something that has just been discovered, although the focus on the topic has increased rapidly during the last 50 years.

Insulation is also needed to maintain a steady temperature in some of the different processes that take place in refineries.

"This can require cool or cryogenic temperatures, as well as high temperature”.

A hidden threat

Despite the growing focus on CUI in the industry there does not appear to be a quick fix. One of the major problems is that discovering CUI is extremely difficult because of the various components involved. During the processes, the steel will expand and contract when exposed to temperature changes, but the coating protecting the steel may expand and contract at a different rate. This puts stress on the coating and could lead to cracking and flaking leaving the steel unprotected, and at high temperatures the coating itself could break down.

“For an uninsulated pipe this degradation of the coating would be visible during routine inspections. However, once a layer of insulation is placed around the pipe any such damage becomes invisible. There may be some signs in extreme cases such as staining or lifting of the insulation, but this cannot be relied upon. Furthermore, the insulation itself requires protection from the elements in exposed situations and there will be an outer jacket or casing covering it,” Svein Jacob Kaspersen points out.

Although the manufacturers of the various components; piping, coating, insulation, and casing may have worked and developed products aimed at reducing the incidence of CUI, they have mostly been doing so on a separate basis. Part of the challenge is therefore down to the fact that there has been less than ideal collaboration between the different parties. 

Working together to solve the problem

This state of affairs existed until 2018 when an ISO standard for testing coatings was published. ISO 19277 Qualification testing and acceptance criteria for protective coating systems under insulation (https://www.iso.org/) was considered a step in the right direction but the mandatory elements of it did not actually test the coating together with insulation.

That same year, a Joint Industry Project (JIP) was started up in the US, and phase 1 was finalised in 2023. The work was coordinated and carried out by Southwest Research Institute (SwRI) in San Antonio, Texas. The initial aim was to determine the durability of various coatings and insulation types applicable to CUI. Among those taking part were eight oil and gas operators, five coating manufacturers including Jotun and a number of insulation suppliers.

He continues: “This project took a systematic approach, examining how different coatings and insulation systems perform together - reflecting real-world scenarios where various coatings are used with different insulation types. Insights from both coating manufacturers and insulation manufacturers were invaluable in enhancing our understanding. Additionally, end users provided valuable perspectives from how these systems have performed in real life over the years. Collaborations like this are essential for deepening knowledge on complex topics like CUI. This advancement will greatly facilitate the development of new coatings and insulation products.”

The new standard test procedure is published by the Association for Materials Protection and Performance (AMPP) as AMPP TM21442 Test Method for Evaluation of Protective Coatings For Use Under Insulation (https://store.ampp.org/).

The AMPP document states the rationale behind it as, “CUI test methods currently available in industry do not mimic field conditions and are based on a pass-fail criterion conducted for a fixed exposure time and are unsuitable for estimating coating service life and performance. This AMPP standard provides a comprehensive test methodology to simulate field conditions under insulation in order to establish the performance of a coating in service."

During the SwRI JIP, coated pipe spools with different types of insulation were exposed to wet and dry testing at temperature cycles ranging from 21 °C to 80 °C through to 21 °C to 315 °C. Among the coatings tested were products from Jotun’s Jotatemp range which showed an overall very good performance.

Commenting on Jotun’s participation in the SwRI JIP, Ingrid Vee, Global Category Manager – Heat Resistance at Jotun says, “We are proud to have been an active contributor to the development of this new industry standard by providing support and information, and sharing our research expertise and experience.”

As the 2021 study by DNV for the Norwegian Petroleum Institute found that operators consider CUI as “the biggest threat to the mechanical integrity of oil and gas industry facilities”*, it is understandable why this topic now is a hot topic in the industry. A failure of any steel component in an energy plant would likely pose a threat to those in the immediate vicinity and could affect a wide area beyond the plant itself.

At the end of the day, it all comes down to how you protect your assets and properties.

*https://www.havtil.no/contentassets/9ec16fd263fc4a25a5b8e4fc20de33d3/maintenance-manegement---corrosion-under-insulation