Screening an offshore heat exchanger at risk of CUI
24/04/2026
During the summer of 2025, Subtera travelled offshore to a floating production, storage and offloading (FPSO) vessel operating in the North Sea to screen a heat exchanger for corrosion under insulation (CUI) and moisture using the scan, track, analyse, report (STAR) technology.The heat exchanger was known to be at risk of CUI due to its operating temperature and insulation arrangement. Previous inspections had been carried out by cutting inspection hatches into the insulation to allow ultrasonic testing (UT) measurements. This approach damaged the insulation system and required additional repair work after each inspection.
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| Weep hole |
During the activity, Subtera engineers worked closely with the asset integrity team and also with team members from the on-asset service provider.
Subtera’s STAR technology detects CUI and locates moisture on operational insulated assets protected by polymeric cladding. STAR enables safe screening of operational assets, while the cladding and insulation remain in situ, helping to reduce costs and maintain productivity.
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| CUI located beneath calcified insulation |
In preparation for the asset screening, Subtera worked closely with the operator to confirm the details, scope out the planned activity, gather all relevant asset information, plan logistics and ensure that all relevant health & safety information was communicated and understood.
The scope of work was approved in advance of Subtera arriving at the FPSO vessel. Where necessary, scaffolding was erected to ensure safe and secure access to all scan sites contained within the scope.
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| THz image of screened heat exchanger showing how the intensity increases with process temperature |
Subtera’s STAR sensor passively measures terahertz light naturally radiating from the operational asset being screened. The diameter of each asset governs the number of angles at which the asset should be assessed using STAR.
Non-intrusive screening was performed while the asset remained in operation. The objective was to identify localised areas of suspected CUI or moisture beneath the insulation to support targeted intrusive inspection.
The screening identified one localised area of suspected CUI and several areas of suspected moisture. These locations were stripped back; corrosion was identified under calcified insulation and moisture was located. Sections not flagged during screening confirmed an absence of CUI when the insulation was removed, thereby validating the STAR data.
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| STAR thermal sensors measure cladding temperature during screening |
Subtera is an ISO 9001- certified organisation that provides non-intrusive CUI and moisture detection solutions to help industry reduce emissions, extend the life of existing assets and maximise process availability.
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