Posted on Mon Oct 22, 2007 01:22 AM
Post Subject: RE: Welcome to the NDT forum
Thank for the introduction.
I have a quick question about the CUI (corrosion under insulation) what is the best method for:
1- Identify the damaged insulation area
2- Identify the corrosion extent under the insulated piping/vessel section.
I post this in the discussion since I'm not sure to which part this thread belongs to.
Posted on Mon Oct 22, 2007 10:27 AM
Post Subject: RE: Welcome to the NDT forum
I am afraid that typical pipe insulation materials do not support high frequency sound waves. Thus it is necessary to remove the insulation at measurement points when using conventional ultrasonic corrosion gages. It is possible to detect pipe corrosion from greater distances, with less insulation removal but also with somewhat less resolution, using guided wave techniques, which typically use high energy EMAT arrays to generate a 360-degree wave. I'm afraid that Olympus NDT does not offer that sort of equipment at this time.
Posted on Tue Oct 23, 2007 04:46 AM
Post Subject: RE: Welcome to the NDT forum
Tom Nelligan wrote:
I am afraid that typical pipe insulation materials do not support high frequency sound waves. Thus it is necessary to remove the insulation at measurement points when using conventional ultrasonic corrosion gages. It is possible to detect pipe corrosion from greater distances, with less insulation removal but also with somewhat less resolution, using guided wave techniques, which typically use high energy EMAT arrays to generate a 360-degree wave. I'm afraid that Olympus NDT does not offer that sort of equipment at this time.
Posted on Tue Oct 23, 2007 02:23 PM
Post Subject: RE: Welcome to the NDT forum
There are a number of methods of finding CUi, and the first two are not particularly good.
1. Pulsed eddy current. This was developed several years ago, and hasn't taken off despite support.
2. Radiography: this has severe technical limitations, plus all the problems with dealing with RT (licensing, safety, chemical waste).
3. The newest appraoch is microwave NDT. Check the Evisive web site at www.evisive.com.
As Tom Nelligan points out, ultrasonics (conventional or phased arrays) doesn't do well through insulation. If you want to remove the insulation, there are many techniques for measuring and sizing pits, but that may not be cost-effective.
Posted on Thu Oct 25, 2007 07:46 PM
Post Subject: RE: Corrosion under insulation (CUI)
You might consider tangential x-ray as a methodology, it will alert you to the exfoliation corrosion areas, however, you will still have to remove the insulation to quantify the amount of actual corrosion at each location. There are small portable instruments on the market that offer real-time viewing as the inspector scans along the pipe and observers the shadowing of the exfoliation on the tangent of the pipe.
