by Emily Newton
Corrosion under insulation (CUI) is a hidden hazard that can eat away at crucial equipment long before any damage is apparent. Insulation aids effective operation, but any moisture trapped within it can set the stage for corrosion beneath. This makes early detection an ongoing problem for oil and gas plants. Imaging advances for nondestructive testing (NDT) are providing inspection teams with a more accurate way to identify and mitigate risk.
Why CUI is a Top-Priority Challenge
CUI is a bigger problem than just maintenance. Hidden damage can cause leaks or equipment failures and contribute to a substantial risk of accidents. The 2024 Norwegian Ocean Industry Authority reported several CUI-related accidents, including a hydrogen leak and various naphtha leaks. The regulator had also probed cracks in a gas cooler linked to the problem.
Corrosion can be dispersed across large areas of insulation, and detecting this damage can be costly. “It takes a lot of inspection to find the scattered most severe CUI, which is why the cost of inspection is so high,” said Dr. Clare Watt of the Institute of Corrosion. An inexpensive approach to detecting these sites could reduce inspection costs by 80% to 90%, she noted. The potential of enhanced NDT imaging and diagnostics makes it a significant area of innovation for oil and gas facilities.
The Digital Evolution of Radiographic Testing Equipment
Traditional film radiography has long been used to inspect industrial equipment, but the procedure can be slow. Film requires chemical operations after exposure, and the images produced can be difficult to keep or retrieve. Longer exposure times can also be a limiting factor for inspection efficiency in oil and gas operations.
Computed radiography (CR) was a significant step toward digital examination. CR captures the radiographic image using reusable imaging plates rather than film. The plate is subsequently scanned, and the data can be viewed and stored digitally by NDT professionals.
This intermediate scan is eliminated with direct radiography (DR). Flat-panel detectors capture radiation and convert it into a digital image that appears almost immediately on the attached workstation. This speedier process allows specialists to evaluate image quality on-site and make modifications as needed. It also enables faster examination of potential wall loss under insulation, allowing facilities to move from picture acquisition to maintenance decisions with less delay.
DR vs. CR Radiography for NDT in Oil and Gas Inspections
Both CR and DR support digital inspection, but their workflows differ significantly. Comparing systems in terms of speed, image quality, and field adaptability can also help oil and gas facilities determine the optimal system for each inspection setting.
Workflow and Speed
Computed radiography involves multiple phases between exposure and image viewing. After removing a reusable imaging plate, the NDT specialist must take it from the cassette and scan it with a scanner. It must then be cleared before it may be used again. This technique is faster than film development, but can still be a bottleneck in high-volume inspection systems.
For direct radiography, the image is acquired by an array of digital detectors and transferred directly to a networked workstation. Technicians can see the outcome very immediately after the exposure and can evaluate if they need another image while the equipment is still in place. A shorter feedback loop can enable inspection teams to cover more components per shift.
Image Quality and Advanced Capabilities
DR systems often offer superior signal-to-noise ratio and better dosage efficiency than CR systems. The system’s large dynamic range also allows one to capture relevant detail across components with different material thicknesses. Fujifilm says, “With increased dynamic range, direct digital radiography can allow multiple thicknesses to be inspected at once.” This function is useful for examining complex piping arrangements where wall thickness or shape changes within a single exposure.
Digital images can also be zoomed or manipulated to allow technicians to examine questionable regions of metal loss. However, image quality still depends on correct exposure settings, detector placement and the component being inspected.
Portability and Deployment
CR is still practical for field inspections because its lightweight imaging plates can be more easily positioned around curved pipes or in tight spaces. Several plates can also be exposed before technicians return to a scanner to process them. This strategy slows image evaluation and may require the technician to return to the inspection area if the exposure is unsatisfactory.
DR provides instant findings in the workplace, but its flat-panel detectors are generally more inflexible and require careful handling. So the selection of equipment should be based on access conditions and the volume of inspection. If flexibility of placement is the key, CR may be the better choice. On the other hand, DR may provide a more efficient approach for repeated or high-throughput inspections.
Advanced Workflows and the Future of NDT
In conjunction with good inspection software, the detectors enable a connected workflow from exposure to final reporting. NDT technicians can view images at the inspection site, use measuring tools and sort data without transmitting physical film or scanning imaging plates. Digital files are also easier to communicate with off-site professionals if further investigation is required.
These capabilities are part of a larger transformation in the oil and gas industry toward data-driven maintenance. Inspection teams can compare current radiographs with prior images to assess changes in wall condition over time. Consistent digital records may also assist facilities in prioritizing follow-up inspections based on detected damage, rather than on fixed schedules.
The next stage of this progression is assisted defect recognition (ADR). ADR software can be used to highlight locations that may need more careful inspection rather than replacing the NDT technician. The technician is still required to evaluate the image and determine if an indication is significant. This human-led technique can help handle large volumes of images while providing the oversight required for industrial inspection.
Companies in the industrial imaging sector, such as Fujifilm, continue to design nondestructive testing solutions to support digital and connected inspection workflows. As detector technologies and software tools advance, oil and gas operations can utilize radiographic data to inform maintenance scheduling and risk management.
Frequently Asked Questions
The following common questions explain how digital radiography supports corrosion and weld inspections in oil and gas facilities.
What is the main difference between computed radiography and direct radiography?
CR uses reusable imaging plates that must be scanned after exposure. DR captures images on a digital detector and displays them almost immediately.
Why is CUI such a difficult problem to manage?
CUI develops beneath insulation, where it can remain hidden until significant metal loss occurs. Its scattered distribution also makes affected areas difficult to locate.
Is DR technology suitable for inspecting welds in the field?
Yes, DR can inspect many field welds when the detector, exposure setup and component geometry meet applicable requirements. Suitability should be evaluated for each inspection.
Is DR better than CR for a weld inspection?
DR often provides faster image acquisition and a higher signal-to-noise ratio, making it efficient for many weld inspections. However, CR may be more practical when flexible plate placement is needed, so the better option depends on the weld geometry and field conditions.
Gaining Clarity and Control Over CUI
CUI is a major concern since it can harm key equipment with no warning and no visual signs. New NDT approaches, such as direct radiography, provide inspection teams with a clearer look under insulation. Modern imaging procedures can help boost asset integrity while making oil and gas examinations safer and more efficient.
