How to Inspect for Corrosion Under Insulation


How to Inspect for Corrosion Under Insulation

The best and most pragmatic approach to addressing corrosion under insulation (CUI) issues is to follow a mitigation strategy. This involves the implementation of multiple layers to separate the insulation from the pipe surface coupled with drainage and venting systems to allow any excess trapped moisture to escape. This has proven to be the most successful long-term strategy available in the industry today. With Distribution International and Crossroads C&I supporting these exciting solutions, you can rest assured we have your back!

Inspection at First Glance

Corrosion under insulation is a major risk factor for both the environment and operational life of assets (pipelines, equipment, etc.). One of the most common consequences of corrosion is thinning of assets, which leads to product leaks and significant maintenance spending. In fact, studies have shown that CUI is the cause of 40-60% of the money spent on piping maintenance in the oil and gas industry. Products that wear thin and begin to deteriorate cause leaks and slow down the entire production process. Extreme contamination causes a facility to shut down entirely.

To inspect for CUI, watch for damaged and stained jacketing as well as general and/or localized metal loss underneath the insulation. The extent of the damage determines the mitigation strategy: to either replace the asset or fix it by using reasonable measures followed by re-insulation. This is especially true in most common carbon steels and 300 series stainless steel. 

The most significant concern in steel is temperatures between 32-300 degrees Fahrenheit (0-149 degrees Celsius). Be especially careful when dealing with steam vents, deluge systems, spill locations, ingress points of moisture and acid vapors. Areas exposed to these conditions are particularly susceptible to CUI. 

In order to prevent future instances of CUI, companies overdesign their assets by keeping a corrosion allowance to compensate for some level of corrosion. However, this is costly and wastes valuable time and resources. Over time, the manufacturing process as a whole lurches to a halt, damages equipment and leads to permanent product loss — including the invested capital. Product leaks from failed assets lead to an increased carbon footprint and may even cause catastrophic fires, endangering employees’ health and welfare. 

Criteria must be established to determine the degree of damage that will be replaced and the degree that will be tolerated. After inspections are complete, the item is either marked for future replacement or is coated and reinsulated. To mitigate the risks of CUI, watch for signs of general metal loss or the entire affected surface losing thickness and take into account these methods of inspection. 

How to Inspect Using Radiography

Radiography is one of the best methods used to inspect CUI when small sections of piping are exposed. The comparator block is used to calculate the thickness of the pipe’s wall, which you can execute using the Ricki T tool, as one example. 

The challenge here is that radiography is most effective only when the piping has a diameter of 10 inches (25.4 cm) or less. As a result, this method only verifies the presence of CUI in relatively small areas. It’s not, for example, able to detect chloride stress corrosion cracking (Cl-SCC) in stainless steel. Another major concern is radiation safety. Radiography cannot be conducted with workers present. In the long term, this leads to major inefficiencies and complicated workflows among employees. 

Moisture detection imaging (MDI) offers a noninvasive, preventative approach to CUI. MDI detects the presence of moisture without removing insulation. Unlike some conventional inspection methods, MDI is data-driven, reliable and highly efficient. Low labor and material costs make this an affordable option. High detectability, detailed reporting (within 24 hours) and real-time data acquisition promise high-level productivity and consistency over time.

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How to Inspect Using an Ultrasonic Thickness Measurement

Another method of inspection is known as ultrasonic thickness measurement. Unfortunately, this method presents many drawbacks. Just as with radiography, it’s limited to small areas. It’s expensive to cut insulation holes and seal them with caps or covers, and once the holes are cut, you run the risk of compromising the integrity of the insulation still intact. In cases where the corrosion isn’t fully recovered, this strategy could actually exacerbate CUI. Similar to radiography, the ultrasonic thickness measurement isn’t able to pick up on Cl-SCC in stainless steel. 

How to Inspect Using Insulation Removal

One of the most effective ways to prevent CUI is by using insulation removal techniques. This method stands apart from the rest since insulation removal allows you to detect Cl-SCC in stainless steel. The first step is to remove the insulation. Second, you inspect the surface condition of the pipe. Then, you replace the existing insulation with new material. 

Of course, even the best insulation techniques come with their own set of challenges. For starters, insulation removal is expensive. In some cases, installers must also be wary of removal that may involve asbestos. 

How to Inspect Using Infrared

In situations where corrosion is likely hiding under layers of wet insulation, infrared is one of the best ways to detect CUI. Infrared technology detects damp spots underneath insulation. 

In one study conducted by The International Society for Optical Engineering, infrared technology was used to inspect oil pipelines on Alaska’s North Slope. The goal was to detect water trapped between foam materials and the steel pipe. This technique is particularly useful because it scans piping quickly and detects both water and pipe wall thinning.

How to Inspect Using a Neutron Backscatter

The neutron backscatter system detects wet insulation on pipes and vessels, A radioactive source emits high-energy neutrons into insulation. The count displayed to the inspector is proportional to the amount of water in the insulation. According to the measurements, low counts indicate low moisture presence. 

Each method for inspecting corrosion under insulation is unique. It’s important to consider the specific project at hand and the resources available to you to carry out the inspection. Distribution International has the insulation solutions you need to make any project a success. From products and accessories to MRO solutions, we’re confident that our robust inventory will meet your demands. To find out more about our industry-leading selection, visit DI’s insulation product page.

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