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Understanding acceptable welding undercut

Q: I find myself rejecting a lot of welds. I don't want to fail them and find out that I misinterpreted something. When there are small amounts of undercut throughout the length of the weld, I'm still not clear on what AWS means by "... in 2 inches up to 12 inches" [AWS D1.1, Table 6.1(7)]. So I find myself pretty much disregarding the 1/32 undercut rule, unless the weld is less than 2 in. long, and just using 1/16.

A: All right, here we go. Table 6.1 (7), “… undercut shall not exceed 1/32 in., with the following exception: undercut shall not exceed 1/16 in. for any accumulated length up to 2 in. in any 12 in. ..."

Depth of undercut that is not more than 1/32 in. is acceptable, period! Also, undercut greater than 1/32 in. deep that does not exceed 1/16 in. deep and its accumulated length comes to 2 in. or less is also acceptable.

Example 1

You've got a 3-in. weld and it has 1/16 in. of undercut (depth) for 2 in. of its length. It's acceptable.

Example 2

A 3-in. weld is part of a 3-on-6 intermittent fillet weld. Imagine if three of those fall within 12 in. One 3-in. weld has undercut and the undercut is 1/16 in. deep for ¾ in. of its length. Another 3-in. weld is undercut at two places. The undercut is 1/16 in. deep for ¾ and again for ½ in. of its length. The last 3-in. weld has 1/32 in. for its entire length. If each of these three welds fall within the same 12 in. of a joint length, it is acceptable. The total length of the undercut greater than 1/32 in. deep is equivalent to 2 in.

Example 3

If you have a weld that is 8 in. long, the same rules apply. If the weld has undercut its entire length that did not exceed 1/32 in. deep, it's acceptable. If along that same weld at one location the undercut is 1/16 in. deep for ¼ in.; then at another location, 1/16 in. deep for ½ in.; then again for 1 in.; then again for ¼ in., that weld would still be acceptable (as long as the individual undercuts greater than 1/32 in. deep but not over 1/16 in. deep do not total more than 2 in. of length in any 12 in.)

Now my head hurts.

David N.’s response:

Holy crap! I understand even better now! So, the length they are talking about is how far along the weld the undercut runs. That is the most important part that I wasn't grasping before. That's so simple, and now quite embarrassing. I understand now why no one could explain it to me—it should have been obvious. Every time I read about the 2 in., I was thinking it had something to do with the weld length, not the length of the undercut portion.

I couldn't get past my initial understanding, kind of like when you learn the words to a song incorrectly and even after you find out the correct words, you still sing them wrong out of habit ... OK, fine. Maybe it's nothing like that!

PWC’s response:

That is exactly what it's like.

About the Author
Braun Intertec

Paul Cameron

Braun Intertec

4210 Highway 14 East

Rochester, MN 55904