The battle against corrosion under insulation

The hidden dangers of corrosion under insulation (CUI) span the oil and gas industry from upstream operations to midstream infrastructure and downstream applications, including the production of LNG. CUI is a severe form of localised corrosion that occurs when water, inorganic salts, and other contaminants become trapped beneath insulation covering pipes, valves, tanks, and other assets, leading to the formation of corrosion cells that are hidden from view and can spread unnoticed.

In oil and gas operations, elevated process temperatures may accelerate corrosion rates, leading to pitting and metal loss that may cause leaks and potentially catastrophic failures, with the potential to harm personnel and, in extreme cases, cause the loss of life. Yet, in LNG operations, cold/cryogenic temperatures can also contribute to increased CUI risks. A perfect recipe for corrosion – moisture, oxygen, and chlorides – exists in both temperature scenarios, but moisture from condensation can be especially prevalent under insulation in cryogenic LNG operations due to the extreme temperature differentials with ambient air. Studies show that moisture causes 85% of insulation system failures in LNG operations. At the same time, some LNG applications also operate at high heat, compounding CUI threats across entire facilities.

Because cryogenic temperatures are required for numerous LNG refinery applications, most assets are made from stainless steel rather than the carbon steel that is commonly used in other oil and gas refining operations. Stainless steel provides added strength, hardness, and corrosion resistance, helping LNG facilities better protect their production assets, including at very low temperatures. However, stainless steel is still susceptible to corrosion, with chloride stress corrosion cracking (CSCC) being especially virulent when chlorides from salts are in contact with the metal, whether it is exposed or covered with insulation. Such CSCC causes tiny surface cracks to develop in stainless steel, weakening its structure. These cracks may become so pervasive that there could be potential for gas leaks to develop and explosions to occur.

Given the corrosive threats associated with insulated assets used in LNG production, facility operators are best served by covering assets with protective coatings that create a barrier between the metal substrate below and the chlorides, moisture, and other exposures on the surface. Such coatings should be considered an integral part of a robust insulation system, as they help to mitigate the corrosion process and enable assets to operate longer before requiring maintenance. Still, a faulty insulation system may lead to corrosion taking place and can put an asset out of commission prematurely.

Traditional organic coatings in CUI service range from only 5 – 13 years before facilities need to proceed with costly inspection and repainting activities. However, more advanced coating technologies are being formulated to properly address typical coating failure mechanisms, offering improved performance and thereby extending the lifetime of coated assets. Those formulations are engineered to better withstand the varied exposures assets may face before and after they are insulated, including elevated and extremely low operational temperatures, exposure to chlorides before and during service, rough handling during transport, outdoor storage prior to installation, and high moisture conditions from humidity and condensation. Not only are some of these new liquid coatings performing better than traditional CUI coatings, but they are also faster, easier, and more economical to apply compared to thermal sprayed aluminium (TSA), which is sometimes used in LNG applications.

LNG production environments are ripe for CUI

LNG facilities operate at approximate temperatures as low as -162°C (-260°F) and require an effective thermal insulation system on assets to prevent them from excessive heat gain and to maintain these temperatures to ensure effective and safe operation. The need to better address CUI in LNG refining applications is pressing. The world is in a grip of geopolitical turmoil and therefore global LNG demand is rising, with numerous projects planned to meet growing needs. As existing facilities expand and new ones are constructed, LNG operators will need proven, cost-effective CUI-mitigation solutions that improve the safety and long-term productivity of their facilities.

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Read the article online at: https://www.lngindustry.com/special-reports/09102023/the-battle-against-corrosion-under-insulation/