Inco 718 welded with AMS 5832 filler wire Per Mil. Spec. 1595a

Inco 718 wheather cast or sheet, has one very tenatious surface oxide and the scotch brite prep is my guess as to the cause of your indication during Xray inspection. This oxide is very strong and present even on freshly sheared test cupons. The oxide itself is so strong that its actually an asset in the working performance of the material in high temperature aircraft engine applications. A brite surface when preped is simply not enough! Mechanical abrasive prep is the best way to be sure you have an optimum surface. We often employ 1-1/2 inch 80-120 grit aluminum oxide disks driven by pnumatic angle grinders at apropreate rated rpm to remove the oxide. This is done immedatly prior to the weld. The scotch brite is fine for your <Properly stored and packaged > welding wire when followed by Achohol/acetone wipe on everything. This prep technique must also address the sheared faces of the cupons as we really don't know what was cut on that shear prior to your cupons or how clean the blade is.

Multi pass welds on alloy 718 require mechanical abrasive prep between passes to remove refractory oxide from the weld bead face to avoid "stringers" which will show on an Xray and are nasty stress risers. This consideration also needs to be kept in mind even in singe pass welds with several starts and stops. AWS Welding Handbook Vol. 3 8th edition provides good general information on the many variables encountered with inco 718 and its family of precipitation hardenalbe alloys.

Good luck with your certs and projects

Lawrence Bower
Education Development
United Airlines

And watch those pinholes <stress risers> as you tail off ever so slowly on the foot pedal. :)

I'm sorry I'm late in responding to your question CPLANE and I hope you do see this because I have had experience with BOTH discontinuities with many of the Inconels (600's including 690, & 800's) over the years.
Incomplete fusion (IF) between passes -Is very easy to allow to happen if the welder is a "cup-walker" and draws the filler metal straight off the wire instead of dipping and watching the front edge of the puddle fuse to the previous pass. The indication on the radiographs will actually appear to resemble the bottom of his filler rod (will have some width to the indication). The welder will not know this is occurring during the application because he has no visual aids that fusion is occurring. The indication on the radiograph will exhibit a "fading" (different desities) at it's edges and the length will usually not be perfectly straight.
Hollow bead -It's not really hollow-bead as is found with SMAW welding on pipelines (specificlly down-hilll welding) it has been my experience that it is really "worm-hole porosity". During the GTAW welding of the Inconels, if the amps are to hight a chrome oxide forms at the back of the molten puddle. A gas bubble gets trapped under the sheets of chrome oxide (you can actually scrape the oxide off the molten puddle with the filler rod during the welding) in the semi-molten stage and gets dragged along as the welder welds his pass. This indication will resemble just what it's called a "worm-track". The edges of the indication in the radiograph will appear distinct and little change in density will be observed across the indication. The edges of the indication usually appear very straight with little variation.
It is very true with ALL nickel-base alloys, "cleanlyness is next to godlyness"
Again, sorry for being late.