How do you find corrosion under insulation (CUI) and what nondestructive testing (NDT) techniques are best? These are questions conscientious system operators should ask when trying to hold off the costly problem of hidden corrosion in their systems. CUI is one of the most difficult corrosion processes to prevent but adoption of proactive measures, such as the development of an inspection program intended to detect early signs of corrosion and mitigate potential piping failures, is critical.
In fact, corrosion is so costly that theNational Association of Corrosion Engineers (NACE)据估计，全球腐蚀成本约为2.5万亿美元。那么，对于系统操作员来说，限制腐蚀成本的关键是什么？如何发现绝缘下的腐蚀？
We wrote about theconditions under which corrosion is likely to be foundunder insulation in a previous blog post. If you’d like to learn about CUI risk factors and where you might find it, you might want to start there. However, if you are wondering how we locate corrosion in an insulated system using nondestructive testing techniques, read on.
Let’s look at the most common methods yourNDT consultantmay consider or rule out when building your inspection program:
Visual Inspection i.e. Insulation Removal
Visual inspection is one of the most effective NDT methods to locate corrosion but that comes with a couple big caveats. Removal of insulation is the most expensive and labor-intensive way to find corrosion. The logistics of this process can be made even more complicated by the presence of asbestos. What’s more, if your operation is in service during a visual inspection, it’s possible a system may experience process issues.
虽然非常有效，但目视检查最终更有助于为CUI检查建立基线和行动计划，该检查将与其他NDT方法配合使用。
剖面照相术
Profile radiography is a simple and effective technique to inspect piping that is vulnerable to corrosion though its ability to detect a reduction in internal wall thickness. This NDT technique has a few distinct advantages that include a high level of portability, the ability to scan piping without removing the insulation as well as relatively inexpensive and quick results.
However, this method can be limiting because it can only verify small areas and can be technically challenging when scanning piping greater than 10 inches in diameter. There also are safety concerns due to radiation which prevent others from working in the surrounding area during inspection. Depending on your system, this can lead to downtime or scheduling delays.
Ultrasonic Thickness Measurement
超声波测厚是一种基于超声波运动来测量固体元件厚度的技术。这是另一种有效的技术，可以通过各种内衬和涂层测量壁厚。这种技术的一个好处是，您只需要访问被检查管道的一侧。
However ultrasonic thickness measurement comes with its own set of limitations which include scans being limited to a small area and the complication of needing to cut small holes into the insulation to perform the technique which can be expensive and may compromise the integrity of the insulation (which can increase the CUI issues already under inspection).
Infrared Thermography
Infrared thermography is a technique that can detect moisture spots within the insulation of the piping. This method works by detecting the difference in temperature between the dry insulation and damp insulation. Where there is wet insulation, there likely (but not always) is corrosion. One benefit of this method is that infrared thermography can work without making direct contact with the piping being scanned which enhances safety as well as saving time and money. This method is generally faster and more sensitive than other moisture gauges.
Neutron Backscatter
中子背散射是另一种用来探测绝缘层内水分的技术。这种方法使用放射源，放射出高能中子进入绝缘层，对可能存在的水粒子作出反应。这些结果指出存在较高腐蚀可能性的区域。这个过程相对快速准确。然而，像中子背散射这样的方法，指向可能腐蚀的区域，会产生假阳性，因为水分的存在不能保证腐蚀也存在。
Real-Time Radiography
This technique, true to its name, provides a real-time look at the pipe’s outside diameter through insulation which produces an image an inspector can see on a TV monitor during inspection. Real-time radiography offers safety and speed enhancements relative to traditional radiography. This method is limited to small structures and requires access to both sides of the pipe under inspection.
脉冲涡流
脉冲涡流是一种无损检测技术，它利用电磁波来确定导电材料的壁厚，探头放置在被检测的管壁上。虽然该技术非常精确，但通常仅用作筛选方法，因为它仅提供平均壁厚。
Leverage NDT Methods for Your CUI Inspection Program
从无损检测顾问可用于检测和测量腐蚀的典型方法的优缺点可以看出，通常利用多种方法的组合来筛选系统中可能发生腐蚀的区域。然后，初始筛选指向需要额外检查和测量的管道目标区域。虽然布劳恩Intertec目前不提供中子背散射，实时射线照相，或脉冲涡流，重要的是要知道的范围内的选择。manbet体育滚球
作为我们之间拥有数十年经验的无损检测检查员，我们利用我们在复杂操作方面的专业知识和经验，帮助您找到最适合您的系统、预算和关注点的检查方法。
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