As we discussed in the previous post on CUI corrosion it can be very damaging to your plant equipment and an inherent risk to your plant for leaks, fires and explosions. Also, we discussed in the first CUI blog that there is a potential for corrosion between 10°F to 400°F and it is very dependent on insulation system quality and external conditions. Detecting CUI issues and knowing where to look cannot be done from the office, it will required your inspectors to be in the field looking for damaged insulation, wet insulation, vents and drains, steam tracing leaks and any complex joints where moisture can enter the insulation. One other location that must be reviewed are inspection ports in the insulation. (the very location used for monitoring internal corrosion can be creating a separate CUI issue!) Based on the field reviews and NDE techniques discussed below, the inspection should be completed to determine if external corrosion is present or if simply the damaged insulation needs to be repaired.
Normally CUI corrosion is localized to the area of insulation damage or ingress of moisture under the insulation, therefore basic Ultrasonic (UT) thickness measurements are of no value in finding CUI damage. There are a number of techniques available for inspecting for CUI damage and include the following:
- Use of an Infrared (IR) camera looking for wet insulation.
- Visual inspection of damaged area. This is generally cost prohibitive, but is very effective if the insulation is being removed for repair/replacement. Coordination/communication between your insulator and inspector is critical.
- Real Time Radiography (looking for corrosion scale with follow up inspection required)
- Guided Wave UT
- Pulse Eddy Current Testing
Additional and improved technology is continually progressing to detect this difficult to find, but dangerous corrosion mechanism. There is a current American Petroleum Institute project between industry and NDE technology companies to improve/develop better ways for detecting CUI. If you have had good success with any of the inspection techniques mentioned above, please share with others on this blog post.
Preventing CUI in the first place should be a consideration as well by reviewing and designing new process systems with prevention of CUI in mind. In the past, insulation was installed on process systems simply for personnel protection to prevent a potential burn to employees. Although positive for personal safety, alternate methods of personnel protection should be used in new designs. A bird cage type arrangement or thermal barrier coatings should be considered.
What should I do/Actions to Consider?
- Talk with your inspection department to determine how CUI inspection locations are determined. Determining the CUI locations from the office or looking in the easiest locations is compliance only and will not improve your plant reliability.
- Verify with your process engineer that the insulation is required for process reasons. If is not required, consider removing the insulation. Additionally, ensure that any new projects do not install insulation for personnel protection without investigating other alternatives.
- Keep up to date with industry NDE techniques for finding CUI damage.
- Verify that your CUI program includes inspection for corrosion under Fireproofing as well.
If you are interested in reading in detail about CUI issues and inspection techniques the following documents are available- API RP 583- Corrosion Under Insulation & Fireproofing, API-571 and NACE RP 0198.
