Can anybody suggest Best Method to detect localised internal corrosion in boilar water wall tubes?
What is the best way to make "mosaic" UT probe? Or is it available in maket ready made? Suggestion Please.
My first try would be an ultrasonic thickness gauge. If for some reason that doesn't work, I have used radiography. The down side to radiography is, you can't give an exact measurement of the wall thickness, but you can see the corrosion as dark spots on the film.
Envision Product Design has developed a digital x-Ray automated boiler waterwall inspection system with backing from EPRI. This system is now ready for commercial application with the 1st prodution unit going to EPRI in October 2009. Http://cmosxray.com
For reliable detection of localized/pitting corrosion I would suggest application of ultrasonic corrosion mapping system with semi continues thickness data collection and C-scan display of measured wall thickness. There are several systems of this type available on the market. They may be equipped with mechanized, semi mechanized or manual scanners. The main drawback of this type of systems is time consuming scanning.
To overcome this problem when testing large scale objects you can sometimes adopt a statistical approach based on the Statistical Theory of Extreme Values. With this methodology you can obtain quite reliable evaluation of corrosion damage of big structures on the bases of actual scanning of only small fraction (e.q. 2%) of their total area.