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An Insight to the RBI of Corrosion under Insulation (CUI) and Corrosion under Fireproofing (CUF)

This paper covers the risk-based inspection (RBI) practices to address external corrosion under insulation (CUI) and corrosion under fireproofing (CUF). The paper discusses risk-based inspection practices of the external corrosion of carbon and low-alloy steels under insulation and fireproofing and the external chloride stress corrosion cracking (ECSCC) of austenitic and duplex stainless steels under insulation, and the external stress corrosion cracking of carbon steel under mineral wool insulation. The RBI methodology described consists of 4 steps, including unit level prioritization, challenging the need for insulation, data validation, and detailed RBI analysis. These steps work together to identify units at higher risk of CUI and CUF, develop an appropriate inspection plan to mitigate CUI and CUF, enhance personnel safety, and reduce unnecessary expenditures. The risk of CUI and CUF failure can be quantified by considering the likelihood of occurrence and severity of consequence.
Product Number: 51324-21057-SG
Author: Yashar Behnamian; Duane Serate; Gordon Cheuk Hei Ho; Aaron Mcdonald; Simon Yuen
Publication Date: 2024
$40.00
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Comprehensive Corrosion under Insulation (CUI) Management for Cryogenic Service: A Facility-Specific Approach with Broad Industry Implications

Product Number: 51324-21071-SG
Author: Abdullah M. Alratoee; Ricardo S. Costa; Meshary A. Al-Bahli; Faisal M. Al-Mutahhar; Mohamed A. Ahmed
Publication Date: 2024
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Picture for Pitfalls in the Typical RBI Methodology for CUI Management Programs
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Pitfalls in the Typical RBI Methodology for CUI Management Programs

Product Number: 51324-20894-SG
Author: Ahmad Raza Khan Rana; Joel Chapman; Touqeer Sohail; Syed Umair Niaz Bukhari; Graham Brigham
Publication Date: 2024
$40.00
Modern-day risk-based inspection (RBI) platforms are designed to evaluate the safety and/or financial risk of assets using industry-recommended RBI methodologies (e.g., API 581). There are cases where the RBI methodology does not represent the true risk profile of the asset, despite implementing the best possible inspection programs and careful input of inspection data. One of the main pitfalls present is the inherent limitation in the risk calculation methodologies that makes no or little use of the inspection data. An example of such a situation is the CUI risk assessments that are subjected to uncertainties due to numerous scientific parameters that are partially addressed (or even unaddressed) in modern-day RBI approaches. This work addresses two case studies of external corrosion rates due to CUI for two pairs of test rigs made with small bore piping deployed with two different insulation designs, namely conventional design, and moisture egress design. The assemblies were tested using two different methods for CUI simulation and testing conditions. The first pair was tested per ASTM G189-07 under isothermal wet-dry conditions at 100 °C (212°F) for three days, while the second pair was submerged under water for two days followed by outdoor exposure for one year. The experimentally determined corrosion rates were compared to those calculated using API 581-compliant RBI software. The comparisons of resulting corrosion rates are complemented by an explanation of the deviations and pitfalls.