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Butt Weld Penetration Depth

Butt Weld Penetration Depth

Butt Weld Penetration Depth

Can anyone tell me approximately what thickness material can be butt welded from one side without any edge preparation and still acheive full penetration (or close to it).  Is this value dependant on the material or  process that is used?  I am primarily interested in structures made from low carbon steel or aluminum square tubing and welded using commonly available equipment (TIG, MIG or stick).


RE: Butt Weld Penetration Depth

I stick with about 1/8" for GTAW on CS if I can't get to the backside to see how I'm doing. A little practice on flat stock with variations in the root opening may let you know more.

I've done 1/4" with SMAW and GMAW with a 1/8"-3/16" root opening with visually acceptable roots on the back side.

If your talking about a joint closed up tight, I have no idea as I have never done that.

Have a nice day

Gerald Austin
Iuka, Mississippi

RE: Butt Weld Penetration Depth

Pipewelder covered the steel part, but on aluminum, depending on the function of the part, I've gotten
complete root penetration on up to 1/4" using DC- Tig with
Helium as the shield.
When i did this at Northrop and Boeing it was for ground
support equiptment or tooling and we still had to certify
in that process, like we did for the class A applications.
All critical Aluminum was done AC. Even the auto seam welds
done on 2219 satelite fuel tanks.
So, What ya building?

RE: Butt Weld Penetration Depth

Hi atlarson:

Where I live the welder himself must have the appropriate ticket before he can make a CP weld from one side only, or he must use a backing plate.  In the structural trade, very few welders carry this kind of ticket.  So it is very much a welder ability issue.  Any reason you would not use a backing plate?

RE: Butt Weld Penetration Depth

If you are welding structures to be used for something other than a home project, decoration or temporary supporting during fabrication then I perplexed as to why any welding would be accomplished without joint preparation, especially if the completed weld is to be subjected to loads and stresses.

The ability to accomplish a full penetration weld is governed by the welding process, the filler metal, the base metal and the joint type. Additional limitations maybe defined by the governing organizations and jurisdictional authorities (AISC, ASME, AWS, ANSI, DOD, etc).

You have identified some processes and some base materials. What is the filler metal type and diameter (E7018, ER70-S-3)? What is the joint type (butt joint, tee joint, corner joint, lap joint or an edge joint)?

Generally speaking I would not exceed a base material wall thickness of 1/8”. Depending on the application and significance to the operation a square groove may not be recommended.

RE: Butt Weld Penetration Depth

The real way to assure you obtain what you need is a "test"
with the variables you wish to use. See ASME SecIX,Article II,the QW-200 section.

The welder must then be qualified to the WPS you have written. ASME SecIX,Article III,the QW-300 section.

There are other codes that address the same thing. If your work is critical and your quality important,you should perform the qualifcation tests for the procedure and the welder.

RE: Butt Weld Penetration Depth

Joint design and addition and deletion of backing are "NON ESSENTIAL" variables as far as ASME SEC IX goes however codes of construction do indicate the need to prove procedures used for one sided welding without backing.

Since you indicated square tuing I doubt you are working to ASME. AWS D1.1 is much more restrictive on joint design variations than ASME and I think for good reasons.

Have a good day

Gerald Austin
Iuka, Mississippi

RE: Butt Weld Penetration Depth

Deletion of backing is an essential varible for performance,see SecIX QW-350 SMAW,GMAW,GTAW,PAW

However my point was that if you have questions such as this,why not,as a minimum, run a example,section it and look.

This may only be square tubing,but what a way to learn.

RE: Butt Weld Penetration Depth


The reference to QW 200 threw me off. I thought you were referring to procedure qualification and backing and not performance.

Good point about the testing though as far as seeing what you can do. Wether it be for the shop or the house.

Another item which I am sure you were aware of but might be read by others another way:

A welder does not "QUALIFY TO" a WPS. One is used during qualification . I may use a WPS that is written for All positions to test flat. I am not qualified to use that procedure within all of its ranges. In addition I could use a WPS with a Max "T" of 3/4" for a 3/4" plate test. My qualified range would extend beyond that of the original WPS.

Good day

Gerald Austin
Iuka, Mississippi

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