Groove welds between "thin" steel

[MacGruber22]

I recently specified a C6x8.2 channel to have a moment connection to another C6x8.2 (as a backspan member for a cantilever). I specified a CJP weld at each flange. My senior engineer said he doesn't trust groove welds of any kind on material less than 1/2" thick (C6x8.2 has a t_f = 0.343); due to experience observing welders burning through the steel. Is there some merit to what he is saying? I can imagine it happening, but I am reluctant to re-configure my framing for this reason alone. My logic is that what is stopping a bad welder from burning through "thinner" material when it is a fillet, plug, etc.? We specify sheet metal welding and fillet welds on thinner structural steel all the time without a care. I don't understand his logic, but maybe someone can convince me otherwise.

"It is imperative Cunth doesn't get his hands on those codes."

 

[metengr]

My senior engineer said he doesn't trust groove welds of any kind on material less than 1/2" thick (C6x8.2 has a tf = 0.343); due to experience observing welders burning through the steel. Is there some merit to what he is saying?

No.

 

[MacGruber22]

Fair enough. That is what I suspected.

"It is imperative Cunth doesn't get his hands on those codes."

 

[gtaw]

The AWS structural codes require the use of backing to ensure CJP and to prevent the problem of excessive melt through. The alternative to the use of backing is to weld one side and then back gouge and back weld the second side.

If the connections are subject to static loads, PJP groove welds are acceptable. An alternative is the fillet weld the members to plates connections.

Best regards - Al

 

[MacGruber22]

gtaw - thanks, I am well-aware of those methods. I pushed him for why, but he kept with the same reason about "things he has seen".

"It is imperative Cunth doesn't get his hands on those codes."

 

[Mr168]

Also keep in mind that AWS D1.1 has provisions in it for CJP/fillet welding of structural steel members down to 1/8" in thickness, and even that is considered a "nominal" dimension with some flexibility for tolerance (e.g. unistrut welding, etc.)

 

[Ron]

The only reason this might give a little pause is that ultrasonic flaw detection (UT) could not be used since the web is less than 5/16" thick, unless a specific calibration procedure was developed. For a CJP weld, you would want NDT done, so that would limit you to radiographic testing (RT), which might have geometric issues with this configuration. Otherwise, the comment is BS.

 

[weldstan]

Full penetration welds are routinely made in thickness < 1/2"; in fact, the bulk of full penetration welds are made in such thickness, especially in tubular connections.

 

[MacGruber22]

Ron - I appreciate the affirmation from another structural guy. I think the senior engineer's reasoning comes from his bitterness in dealing with crappy welders.

"It is imperative Cunth doesn't get his hands on those codes."

 

[Ron]

MG22...Yep! Trusting the weld vs. the welder is a bit different! If the welder is certified, he should be able to put a good butt weld in place.....good welder>>>>>>good weld. Had lots of years as a certified welding inspector and in nondestructive testing.

 

[MacGruber22]

Ron, I think that was the problem with me posting it in this particular forum, as experience with workmanship quality can vary wildly. I can't speak for the other industries, but there seems to be a lot of inherent laziness in building structures field-welding. Yet, the problem I still have with my senior engineer's opinion, is that it still seems that a crappy welder is going to produce a poor fillet weld just as likely as a PJP or CJP weld. Maybe the only thing we have going for us with fillet welds, is that sometimes you can achieve more redundancy through fillet weld length. Every text and specification preaches not to specify weld capacities greater than the demand. I have a hard time trusting that advice for field-welding. Also, when designing a welded structure (particularly retrofits) I spend way more brain energy thinking about welding position and simplicity of installation, than I do in calculating the theoretical weld capacity.

The irritation for me with the CJP welds I specified, was that I had to reconfigure the stability of the frame since those CJP welds were critical in my initial framing layout. And the re-configuring resulted in more work for me and the installer. Oh well. Thank you for the comments.

"It is imperative Cunth doesn't get his hands on those codes."

 

[Ron]

MG22....exactly on target with your last comments! No reason you couldn't use a CJP weld in that configuration.

 

[MacGruber22]

I will end this thread with one of the surprising quantity of welding memes

"It is imperative Cunth doesn't get his hands on those codes."