Ultrasonic testing is not appropriate for fillet welds? 1

[abusementpark]

I read somewhere recently that ultrasonic testing (UT)is not appropriate for fillet welds, but didn't get a further explanation as to why. Can anybody elaborate?

UT still seems to be fairly common in the structural engineering industry. What are some good alternatives if UT isn't valid?

 

[metengr]

Can UT be performed on fillet welds?

It is possible but not practical. Why? Because of geometry of the fillet weld. I have seen on larger fillet welds UT performed that was very complicated to perform with questionable results. At the end of the day, the NDT examiner must be able to interpret results and for fillet welds this can be difficult, at best.

 

[racookpe1978]

Well, it's pretty simple: A properly welded fillet weld will always have a "crack" in it.

Think about it: A (full-penetration) butt weld will be solid metal through the weld. A UT signal will go through the first metal, through the weld, through the second metal, then finally "reflect" from further down the second metal. You get a consistent signal rhough the "good" weld, and you hope to see a reflected or distorted signal from a crack inside a badly flawed weld or a weld that has cracked.

But the two pieces of metal on a fillet weld are NOT perfectly welded with a smooth weld bead. The weld spans a "corner", but the inside of a joint of a fillet weld is not joined metal-to-metal.

The UT result from a properly conducted UT test on a fillet weld will "always" find that crack, right? So how do you successfully run the UT test to find the flaw, if you are going to get an "echo" from the "crack"

 

[phighfill]

The only good that UT shearwave on a fillet weld is good for is to check the amount of penetration in the junction. I have used this many times to see how much penetration each leg has on very critical fillet welds.

 

[Metaljon]

Yes UT of fillet is not very practical. The geometry does not allow the ultrasonic signal to be received. Our policy is to only check for penetration if it is to be a full penetration weld or for cracking at the weld toes and not to inspect the weld volume.

 

[hom2color]

Depending on the throat thickness, large volumetric defects and penetration can be assessed by UT.