RT indications on Inconel alloys

Date 07-18-2003 12:45

Well, if you have been following this subject, it has been a long time coming but we do now have a final report. The false indications created on RT film are commonly called "ghost lines" or "density lines." I like the ghost line one myself, because they aren't really there! Anyway, on Inconel materials, less than .060" thick, a condition called epitaxial grain growth occurs in the center of the weld. Enlarged grain size, dendrite formations running in a totally different plane and the presence of Ti and Al migration all contribute to "beam diffraction" during the RT exposure. This creates the false images commonly interpreted as lack of fusion in the weld. I want to thank everyone who assisted me in finding the answer to this issue. Special Metals and CBI especially. If you ever have a job like this one, tell the RT evaluators before hand that they will see centerline indications which look like lack of fusion. Then when they do read the film, they will take you seriously and think you are very very good and wonder "How'd he/she know that?"

Thanks again,

Alan

By - Date 07-20-2003 05:27

Mr. Riddle,
Did this phenomenon create any anxiety that an actual centerline discontinuity could possibly be masked by a 'ghost line'?
Mankenberg

By ALAN RIDDLE (*)

Date 07-21-2003 09:50

It certainly did. In the beginning of this particular job the parts were rejected for L of Fusion, the welds were ground out in the area of interest and rewelded. Sometimes this took more than one attempt to get a acceptable weld according to the RT folks. When I was ask to get involved we started taking the production parts that were rejected and for various reasons couldn't be saved, we cut them up and started performing various destructive testing and found the welds to be fine. Over the past several months I have talked with many professional organizations that confirm the false images and how they now deal with them. At anytime, if we believe there may be more to an indication than just a "ghostline" or "density line" we rework the weld. Weld quality is number one.