I can assure you that if a mag particle test or a dye penetrant test were performed on a damascus barrel that it will not show the welds between the ribbons unless they were not fused. It will only show where a flaw is such as a crack or lack of fusion between the welds. These two tests can be used on a damascus barrel but can only tell you if flaws exist where the barrel is visible. You cannot check between the ribs. One way to check the barrels with the dye penetrant method is to dye the inside of the barrels, let the dye penetrate,clean off the dye and then spray the developer on the outside of the barrels. If you get some red indications on the developer it means that you have a porous spot in your barrel. This may be a crack,lack of fusion, or a small hole. There is a test method called an eddy current that can be used to test tubing but it's probably used by seamless tubing manufacturers in the quality control process. You should be able to look in your phone book and look for a testing company in your area. The more industry you have around you the more you will find. If you live way out in farm country they may be a bit scarce. I'd bet that there are some really suitable test methods available in this computer age that I am not aware of that could be used to get a really good test on some old damascus barrels. Xray has sum limitations and probably would only have limited use in this application.