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Corrosion Under Insulation (CUI)

Please contact Kod Pojtanabuntoeng for more information on CUI research and services.

Corrosion under insulation (CUI) is caused by water entrapped within thermal insulation. The presence of insulation, and in particular jacketing, slows down water evaporation, prolongs wetting period and allows corrosion to proceed undetected. The hidden nature of the CUI challenges the industry when it comes to inspection and monitoring. Detection of CUI can be too late; hence, resulting in disastrous outcomes such as leakage, loss of containment, and even fire and explosion. A recent study has shown 10% of the maintenance and repair budget for a piping system and pressure vessels in the petrochemical industry is spent on CUI alone.

CCEIC is actively engaging with the industry in this topic. The CUI test rig initially funded by Santos was designed and constructed for a hot service up to 80 oC. The rig is housed in the chamber in which the relative humidity and environmental temperature are controlled. CCEIC has developed procedures which is a combination of weight loss, 3D profilometry, an in-situ insulation dry-out monitoring, and corrosion product characterization to provide valuable information with respect to CUI behaviour.

Key projects

1. Investigation of corrosion under insulation

Project objectives

  • To develop an experimental test rig and experimental procedure to study CUI
  • To conduct series of validation tests to demonstrate the suitability of the method to investigate CUI at varying conditions.

Project summary

A CUI test rig with an associated environmental chamber have been developed and commissioned. A test procedure has been established allowing CUI to be appropriately investigated under laboratory-controlled conditions. Various modifications have been made to the existing standard (ASTM G189-07) to study CUI.

Using the developed CUI test rig and experimental procedure, validation tests on the effect of jacketing and drain holes were conducted. The presence of jacketing on the insulation delays the evaporation of water and enhances both uniform and localized corrosion. The introduction of drain holes facilitates the insulation dry out and allows the diffusion of oxygen into the insulation. As a result, uniform distribution of oxygen within the insulation leads to the increase in general corrosion rate in the short term but decreases localized corrosion rate. In longer term exposure, which better simulates actual field conditions, both WL and localized corrosion decreased. Therefore, the introduction of drain holes seems to be a promising technique to mitigate CUI.

2. Investigation of insulations and its role on CUI (ongoing)

Project objectives

  • To compare the performance of insulations against CUI
  • To determine the water uptake and dry-out of insulations with and without heat treatment.