A Review of Corrosion under Insulation: A Critical Issue in the Oil and Gas Industry

Abstract

Corrosion under insulation (CUI) is defined as any form of external corrosion that occurs on the underlying metal beneath insulated equipment, due to water ingress through the insulation layer. This type of corrosion is frequently observed in oil and gas production, where insulated piping is prevalent, and has historically remained a predominant materials integrity issue. The prediction and direct visualisation of CUI are challenging tasks because of the coverage of the insulation layer(s) and any external jacketing or cladding. Several factors, including the local/ambient environment, system design, and the piping installation process, can influence how CUI initiates and propagates. In this review, CUI background, CUI monitoring, and CUI mitigation strategies are discussed.

Corrosion under insulation of pipeline steel in groundwater containing sulphate-reducing bacteria

“…This is evidence that the diffusion of corrosive species from the bulk solution to the deeper areas under the insulation affects the morphology of corrosion products formed on the steel surface. This result agrees with findings from prior studies on the CUI of steel [3][4][5]30] In the SRB inoculated medium, the sample in the bulk solution presented more bacterial cells and corrosion products than the insulated steel (Figure 8a-f). At the base of the insulated steel are carbon-rich membranes of irregular shapes (Figure 8c and d), which could originate from ruptured biofilm or extracellular polymeric substances (EPS).…”

“…Insulation is applied on steel pipes to avoid energy losses from temperature fluctuations. But the external corrosion of steel pipes under wet insulation is accompanied by severe localised perforation and failure of piping systems [3][4][5]. Moreover, early detection of corrosion under insulation (CUI) is difficult, which makes mitigation tasking and could result in undesirable consequences [4][5][6].…”

Study on the Effect of Metal Mesh on Pulsed Eddy-Current Testing of Corrosion under Insulation Using an Early-Phase Signal Feature

“…Corrosion under insulation (CUI) is a form of external corrosion that occurs on the underlying metal beneath the thermal-insulated coating [ 1 ]. It stems from the accumulating electrochemical corrosion due to ingress of water/moisture into the insulation.…”

Imaging corrosion under insulation with a mechanically-translatable atomic magnetometer

“…The assessment of the corrosion level of pipelines is an important problem in the Oil & Gas Industry. Corrosion Under Insulation (CUI) typically occurs as a localized corrosion damage determined by moisture trapped between the insulation and the pipe to which the insulation is applied [1]- [3]. CUI often leads to catastrophic failure of the equipment, hence its early identification is of paramount importance to the Industry.…”

“…Current approaches for CUI assessment include infrared thermography, neutron backscattering, radiography, pulsed eddy current testing, and various forms of ultrasonics techniques. Each of these CUI monitoring techniques has drawbacks [3], and efficient large-scale monitoring of CUI in pipelines is still an open problem.…”