Undercut is when the edge of the weld pass does not fill the edges along the existing metal where the weld is placed. It does not always occur only in lap fillet welds against the base metal. In this article I give some clear tips and pointers on how to be aware of undercutting and how to prevent it.

First of all, you’d have to ask the question for general purposes only; Do you know what undermining is? When we talk about undercuts in the world of welding, what image immediately comes to mind?

No, silly, it’s not the missing money you thought was in your last check. You just didn’t add well.

Undercut is when the edge of the weld pass does not fill the edges along the existing metal where the weld is placed. It does not always occur only in lap fillet welds against the base metal.

Undermining the weld is not acceptable from an inspection standpoint and can eventually lead to weld failure. When welding under strict code or formal welding guidelines, this seemingly small welder error will almost always have to be repaired or corrected before the welding inspector will approve the weld.

Undercutting usually occurs on the top side of the weld. The reason for this is simply due to the pull of gravity on the molten pool when the following combination of elements is not set correctly: heat (amperage), travel speed, proper rod angle placement, or filler material.

Now that we have an understanding of what the problem is, what is the solution?

When trying to correct any welding problem, always start with one area and work from there.

When trying to correct undercut, the first area of ​​welding that comes to mind is the heat used in the process. That term, heat, refers to the amperage setting that is used to burn the rod or filler material. The size of the rod will dictate your welding amp range. You will not normally see undercutting on quick freeze rods like 6010 or 7010. You will normally see this type of problem occur on low hydrogen rods like 7018 or 8018.

When welding on material that is not extremely thick, your rod size or diameter should not be excessive. In other words, don’t use 5/32″ 7018 on 2″ pipe or anything like that. The wand is oversized for what the material can handle in terms of heat output and puddle size.

Burning the material you are welding is one of the main culprits for this problem.

There is no need to burn your material.

When I am welding a plate or pipe where I have to go uphill and fight gravity at some point in the welding process, I always try to use no more or less than 3/32″ rod when working with rod rod. we are working with TIG this is not the case but with electrodes it makes a difference.

Someone recently told me about their notch welding experience. I started asking questions to isolate the problem. The first question I ask is what is the material you are working on? carbon, stainless, etc. Carbon was the answer. Well, what position were you in? aerial, vertical, 6G, etc. Was it plate, pipe or tube? Pipe on a 6G. Good. What size was the pipe?

2″ schedule 40 they told me. Okay. What size rod were you using? 1/8″ he said.

I said that? Why would you use a 1/8″ rod on a material so small that it can’t handle that kind of heat?

That size of pipe can’t handle that kind of heat. I never use 1/8″ 7018 or larger on something this small. In the 6G setting, all the heat goes to the top of the pipe. By the time you get to the cap or the last set of weld passes, the pipe is extremely hot and at that point there is no longer any place for the heat to go.Gravity is pulling the weight of that big 1/8″ puddle off the top where it needs it to go so it doesn’t undermine the pipe.

If I used 1/8″ 6010 5p++++++ in the root and hot step and the amp draw is around 85 then the rod that would burn in that same heat range when going to the 7018 in the fill and cap would be 3 /32″. This is a good indicator when brazing from quick freeze to low hydrogen.

If the amps are too high for the material to handle, it will most likely undermine the material. This is also true on the plate. There is no real need to go below 3/32″. Drop five amps on the heat range if the problem persists.

The angle of the rod will also have a big influence on how the metal is placed in the step.

The angle of the rod should be close to a 90 degree angle compared to the pipe or plate. In any case, the bar should be larger than the estimate of 90 degrees, but almost never less. Of course, there are always some exceptions, but this serves as a general rule.

Travel speed will also make a difference. A slow travel speed will naturally result in excessive metal buildup and the heat at the top of the weld will cause it to sink. Gravity is working against you at this point. Too fast a travel speed will result in not enough weld metal being deposited when making the pass. Through proper heat (amps), bar angle, and bar placement. Test the settings within these three areas and go from there.

Thanks for your time, see you soon.