Corrosion under insulation (CUI) is a form of corrosion resulting from water trapped under insulation. CUI is a main asset integrity threat to many processing facilities. CUI damage is not readily identifiable and hidden underneath the insulation.
Product Number:
MECC23-20377-SG
Author:
Muhammad Zaid Kamardin, Muhammad Afiq Mansor, Hambali Chik, Azniza Azmy
Publication Date:
2023
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Corrosion Under Insulation (CUI) is a main asset integrity threat to many processing facilities. CUI damage is not readily identifiable and extensive insulation removal for inspection is often uneconomical. As a result, most organizations rely on Visual Examination (VT) with Partial Removal of Insulation method where locations to be opened for CUI detailed inspection rely on predicted susceptible CUI locations and risk. In some cases, non-destructive examinations (NDE) techniques, such as Guided Wave Testing (GWT), are employed to improve the identification of corroded locations.
However, the selection of inspection and NDE technique is often not guided by robust methodology. This paper proposes and evaluates a methodology based on Cost of Corrosion model where both proactive cost and reactive cost are considered. The proactive cost is divided into the cost of true positive and cost of false positive. These costs are a function of quality of risk assessment, and NDE techniques’ Probability of Detection (PoD) and False Call Probability (FCP). In terms of reactive cost, the monetary value of residual risk after inspection completed is also quantified. In addition to underprediction due to gaps in corrosion and risk assessment, NDE techniques with poor PoD will lead to higher reactive cost due to misinspection or false negative result.
An optimum CUI program is a program that leads to the lowest total cost by balancing both proactive cost and reactive cost. Based on a case study conducted at a petrochemical plant, the Cost of Corrosion model has demonstrated value in reducing the Cost of Corrosion by 10% when compared with alternative strategies.
