The examination of pipes’ walls is a central area in the NDT industry due to the fact that even a small change in the pipe’s wall thickness may have grave repercussions on the pipe’s ability to withstand pressures and meet preset standards. Two techniques are generally used to conduct wall thickness measurement – the Tangential Technique and the Double Wall Technique. Both of these techniques contain inherent obstacles that must be overcome in order to achieve accurate and reliable measurements. In this advertorial we will focus on using Vidisco’s portable digital radiography system for conducting a pitting measurement using the Tangential Technique. Vidisco’s main contribution to measurement lies in the development of automatic processes which eliminate the user’s need to mark the measurement points manually and allow for complicated calculations required when measuring. These automatic processes are now available in the Vidisco proprietary XbitPro software and they ensure accurate and consistent replication of the measurements even when they are performed at different times and by different users. When attempting to measure wall thickness at the pitting site on the outer side of the wall (external pitting) or the inner side of the wall (internal pitting) using the Tangential Technique, we encounter a problem regarding how to clearly identify the exact location where the pitting measurement should be conducted. This is due to the fact that the X-ray image received does not contain a clean image of the pitting. In order to explain the reason for the unclear image of the pitting when using the Tangential Technique let’s study the following sketch (see fig. 1), which clearly shows that in the external pitting (and similarly in the internal pitting) we unavoidably penetrate some of the pipe material on the way. Another fundamental problem is that we need to position the pitting in an exact position, parallel (top or bottom) to the DDA imager due to the fact that if it is not properly positioned, the material projection will block out the pitting to the extent that it may be totally missed. In order to overcome the first problem of the “halfshadow” effect on the X-ray image of pitting, special algorithms have been developed which take these factors into consideration and calculation, and enable us to measure the pitting accurately within the limitations of the pipe’s diameter and wall thickness; this technique is generally more effective in small bore pipes with relatively thinner wall thickness. The second problem - when you cannot see the defect (internal pitting or when the pipe is covered with insulation) - is more acute. In this case we will need to apply trial and error, by taking X-ray shots and adjusting the positioning of the DDA imager and X-ray source until reaching the desired position. It seems probable that the right/easiest way to measure pitting is by using the Double Wall Technique. Digital radiography makes “trial and error” in X-ray inspection an easy and fast process. Because the images are generated on the laptop screen in seconds, adjustments to DDA and X-ray source placements can be made immediately and the correct inspection location is determined on the spot. With Vidisco’s portable digital X-ray systems you can ensure that the inspections are completed on site without the need to scan or develop film or image plates in the lab. Our systems are truly portable and can be brought to any location. Highest quality images are available immediately in situ, the thin flat panels can fit into tight places and the NDT operator can easily find the ideal positioning for any specific NDT RT inspection. Vidisco’s XbitPro software enables a fully automatic, intuitive and accurate Wall Thickness Measurement, while overcoming the related challenges. It serves as a userfriendly, optimal tool for both Tangential and Double Wall Techniques, according to the user’s chosen method. For more information go to: http://www.ndt.net/article/ndtnet/2012/59_Kleinberger.pdf http://www.ndt.net/search/docs.php3?SearchDocs=vidis co&searchmode=and and http://www.vidisco.com/RayzorXPro.asp Vidisco www.vidisco.com http://www.vidisco.com/NDTMain.asp email: email@example.com
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