crack detector

I requested a dye penetrant test (Zyglo) on a slightly damaged aluminum bulkhead the other day. I prepped the metal by removing all finishes down to bare smooth metal. The technician arrived, but not with the Zyglo kit, but with a small electronic ocilliscope box with a probe smaller than a pencil. He ran the probe arond the area in question for a few seconds and pronounced it fit.

He explained to me that not only was it more accurate than the penetrant, it didn't even require removal of the finish to use it. Pretty amazing!

What the tech was using is Ultrsonic testing and yes I agree that UT is alot better than DP or MP.

Both DP and MP only check for discontinuity's with-in 1/16" of the surface. A deeper problem would not show up with either of these two NDT methods.

UT then would be the next best as the UT sound waves travel the full metal thickness. The problem here is that were open to discussion of just what the scope reads. A "very" experienced tech would be a asset in this case. I don't know if the newer UT scopes have a memory function to where the data could be reviewed by a metallurgist or welding engineer at a latter time.

X-ray NDT is always #1 when it comes to 100% metal thickness testing as there is a film that can be seen by many experts in that field. Back in the days, only a field engineer could make the call if there appeared to be a problem and only then would a metallurgist/welding engineer be called to the field for final determination of the flim.

The testing company is taking a huge risk by letting a field engineer make that call! As a AWS/CWI, I always liked going to the field to look at the films as it got me out from behind the desk. :)

T_Bone

He told me it was Eddy Current, but I thought it was strange that he claimed it would go right through the paint. I'd think the paint wouldn't allow conduction.

I really thought it was more like an ultrasound test.

I really desired the penetrant test myself, because thats what the MRB engineer ordered. This guy assured me that what he did was better anyway. I never did get an answer from him as to whether there was any authorization to do another type of test.

I wasn't really concerned with there being a crack since the defect was only .011 deep. The guy signed off on it, so its all on him now.