American Welding Society Forum
For many years we have fought this battle in SAW weld repair of rotor shafts. We build up an OD to machine back at .140" over the finish dia. for UT("They cant UT in the near field").
many times when the UT is done they find indications .200" or deeper.
I say that they are the results of the heat input. These are top qualilty forgings but any where from 1 to 30 years old. Our tolerance's are very tight (we repair any thing greater than 1/32"). We seldom get indications in the weld metal. Am I correct in assumeing that the indications existed prior to the weld but were very minute untill they incountered the heat of the Arc?
You are more than likely correct. I require some jobs (base metal) to be NDT clean before you weld. Then if the defects show up after welding you have a clearer picture. UT IS VERY SENSATIVE AND CASTED/FORGED PARTS CAN HAVE SMALL INDICATIONS BEFORE WELDING. AND WELDING COULD MAKE THEM STAND SHOW UP AFTER WELDING.
One thing I learned a long time ago - it is extremely difficult, if not almost impossible to determine the real cause of a weld defect without putting your eyes on the part, observing the weld process, looking at material chemistry data, looking at thermal history of the part, cutting it up for failure analysis, or some other method that gives reliable data. I can only speculate that since you are using SAW, and it is a deep penetrating process when performed correctly, that you may have some inclusions at the weld fusion line area, or the UT is seeing the interface between the dendritic weld microstructure and the grain structure of the base metal, or the heat input from welding is actually causing microcracking in the heat affected zone, or you have some hot cracking going on in the weld metal. What you really need to do is make some similar welds on a discarded shaft of the same material and have them examined by a local test lab.
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