Sheet Metal Plug Weld (AWS D1.3)- What size in the symbol? 1

[P1ENG]

I frequently specify fillet and groove welds, but plug welds are a little foreign to me yet so bear with me. Base material is HRS steel of nominal thickness.

AWS A2.4:2012 Section 9.2 says: "Plug weld size is the diameter of the hole at the faying surface."
AWS D1.3:2008 Section 2.2.6 says: "Arc plug welds (see figure 2.6) shall be specified as the minimum effective diameter at the faying surface (de)."

As I understand figure 2.6, the actual diameter of the hole in the member being attached is of no concern as long as the minimum diameter of 2.3.7.2 is met.

So real world application: There are 1/2" holes in 11 GA (0.120") material for plug welding. 1/2" meets the minimum required hole size per 2.3.7.2. Solving for the visible diameter, d, using de = 0.375" [minimum allowed] and the equation found in Figure 2.6 (de = 0.7d-1.5t), the minimum visible diameter of the weld needs to be 0.793". So what size should the plug weld be in the symbol: 13/16, 1/2, 3/8, or 1/2 (3/8)? Since the visible weld size needs to be 0.793", how is the welder supposed to know this?

If the hole is filled only to the size of the hole (i.e. the visible diameter of weld is the same size as the hole), then calculating for de gives a value less than the allowed minimum of 3/8".


Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[Duwe6]

The 'size' of a plug weld is the leg length of the fillet weld. Without any 'tail notes', a plug hole requires weld all around the perimeter.

 

[P1ENG]

A fillet weld all around a hole is not a plug weld... it is a fillet weld. A plug weld is a weld in a hole that is filled to some depth. Per AWS A2.4:2012 9.1.4: "The plug weld symbol shall not be used to designate fillet welds in holes"

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[48v]

P1ENG - I just reviewed both documents and agree that there's a conflict. I think the least ambiguous way to show it would be 1/2(3/8) to address the hole size and the effective weld size respectively. Only the inspector really needs to know the visible diameter requirement (and even that isn't explicitly referenced in chapter 6) so I'd either hope they check the book, or put that information in a note or tail.

 

[P1ENG]

48v - I was thinking the same way: 1/2 (3/8). My only problem is the welder still doesn't know how big the weld pool is to be. If they only fill the hole, the inspector should say, "Hey, your weld isn't big enough for this to go get the minimum effective diameter." To which the welder replies, "How was I to know how big the pool should have been?"

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[48v]

P1ENG - I think the best option would be to put a note in the tail. Something like '13/16" Weld Pool DIA' (if your welders are likely to actually be paying attention.)

 

[Ron]

Plug welds of sheet metal to a thicker base metal, such as a roof deck to joists, are bit different than a plug weld of two similar thickness base metals.

For sheet metal plug welds, the weld must be reinforced, meaning it must be above the surface of the surrounding sheet metal. It is specified by the diameter of the weld since the procedure is to burn through the sheet metal. If you are using weld washers, then the hole diameter of the weld washer should be completely filled.

The strength of a sheet metal plug weld comes from the fusion at the edge of the burn circumference. In addition, there is lap at the top of the sheet metal thickness provided by the reinforcing puddle. This creates a "clamping" of the sheet metal from the top as well as the shear from the fused edge.

In uplift both the clamping action and the shear can be mobilized for resistance; however, only the shear is calculated. For diaphragm shear, the clamping action helps prevent localized buckling at the circumference of the weld thus keeping the thickness of the sheet metal in a consistent plane.

 

[48v]

Ron, can you point us to that requirement? AWS D1.3 6.1.1.3 (I'm working out of the 2008 edition) requires 1/32" of reinforcement for arc spot welds, but makes no such requirement for plug welds sheet to sheet or otherwise. Just to be clear, an arc spot weld is when you melt the top sheet to a bottom member. A plug weld means that a hole was drilled/punched in the top sheet before welding was performed. D1.3 only allows arc spot welds between a top sheet and a bottom structural member, but it allows plug welds between two sheet metal members or a sheet metal and a structural member.

 

[P1ENG]

Ron,

My original thought was that the plug weld should be called out as the visible weld pool diameter. The engineer calculates the strength on this diameter, the welder knows how big the final weld should be, and the inspector can easily check this diameter. Everyone is on the same page and no one but the engineer has to do any math!

However, that is not what AWS A2.4:2012 Section 9.2 says: "Plug weld size is the diameter of the hole at the faying surface." Perhaps this should only be applicable to AWS D.1 and another definition is needed for sheet steel.

Sometimes what makes sense isn't backed by the code or standard. If I get a consensus, then I will call out the visible weld diameter. But this also brings up another question. Why bother putting in the 1/2" holes and how do the structural drawings indicate that the holes are 1/2"... in the tail, in a part drawing?

I have no doubt that this matters very little as a welder that "knows what to do" is going to do it regardless of what the prints say, whether right or wrong. So my quest is so that I am covered by properly calling out the weld as it should be on a print that I will be sealing.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[P1ENG]

Still looking for an answer. I have posed this question to AWS technical support and they forwarded my question on to some engineers or a committee with no response yet. I was told this might fall under consultation which AWS does not provide. I will report back if I get a response, but in the mean time I still welcome someone with more experience on this subject to chime in.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[gtaw]

A size of a plug weld is based on the diameter of the hole at the faying surface as mentioned already. The definition works for drilled holes, punched holes as well as for plug welds that employ a countersunk hole. AWS D1.1 does address countersunk plug weld holes. The hole diameter is a function of the material thickness (that has the hole) plus 5/16 inch to provide sufficient clearance for the welding electrode, gas nozzle, etc.

The diameter of the hole is indicated to the left of the weld symbol. The diameter symbol is placed to the immediate left of the hole size to indicate the size is the diameter of the hole.

The assumption is the hole is filled flush with the surface of the base metal in which the hole is place unless there is a fraction, indicating depth of fill, is placed inside the plug weld symbol.

AWS A2.4:2012 shows how the plug weld is specified.

Best regards - Al

 

[P1ENG]

gtaw: To understand my confusion, please try to calculate the strength of the 1/2" plug weld per AWS D1.3:2008 Section 2.2.6.

A 1/2" diameter hole is sufficient for the 11 GA sheet steel per 2.3.7.2. CHECK

Filling the 1/2" hole will produce a 1/2" diameter visible weld (d). CHECK

Nothing in the code limits the visible weld diameter​

Calculating de = 0.7*d-1.5t = 0.7*1/2-1.5*(0.12) = 0.17". FAIL

This does not meet the minimum effective diameter (3/8") of 2.2.6.​

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[gtaw]

I'm vacationing this week, so I don't have my copy of the code handy. Sorry.

Best regards - Al

 

[dhengr]

P1ENG:
What we need is a whole bunch more code formulas/equations which have no intuitive meaning and nobody can tell you were they came from. The strength of a plug weld is essentially based on the circumference of the weld around the hole, times the fillet weld size cap’y. If you want to be conservative take the circumference at about the mid height of the throat of the fillet weld. That you do or don’t fill the entire hole with weld metal doesn’t add much to the weld strength beyond a good quality fillet all the way around. On thinner material you will likely melt a larger hole during the welding process (thus, a slightly larger circumference) and there is more chance that you will start to fill the original hole, full depth. On thicker material, the code says the max. fillet size should be 1/16th or 1/8th inch smaller than the thickness of the metal part being welded. And now, your hole size has to be large enough so you can physically get down in there with a properly oriented welding rod (welding head and wire) to make a proper weld at the root. I don’t have the last couple AWS codes, or the special variations of the code, so I don’t know all the latest variations on the weld symbols, etc. But, I’d piece detail to top piece with the size and spacing of the holes I needed, this determines the weld circumference and then use a fairly generic plug weld symbol just showing the fillet size, all around.

 

[gtaw]

Sounds like you are confusing the restriction on the fillet weld size for a lap joint with a plug weld.

The minimum diameter of the hole for a plug weld (per D1.1) is the thickness of the part plus 5/16 inch. The strength of the plug weld is based on the area in shear, i.e., the area of the hole at the faying surface.

The length of the curved fillet weld, around the inside circumference, is the length of the throat along the centerline of the weld.

Best regards - Al

 

[48v]

The OP said that this question is specifically for D1.3 on 11 ga material. I think the question still stands that according to fig 2.6, the visible face of the plug weld should be larger than the hole size. 2.2.6 also says that the weld should be specified (via symbol) by the effective diameter, which is smaller than the hole diameter. Effective diameter = .7 * visible weld diameter - 1.5 * thickness. So according to D1.3, the hole size doesn't get included in the symbol at all. This is in direct conflict with A2.4 9.2.

I think the best way to make it clear on the drawing is to use the hole diameter in the symbol, and explain the visible size in the tail. But doing so is necessarily in conflict with one of the two codes.

 

[P1ENG]

dhengr: I read somewhere (can't try to find the source until tomorrow)about the stress distribution of a plug weld. It said something to the affect that for shear, one side of the weld is in tension because of local buckling or something. I'm leery of doing just a fillet weld with a length equal to the circumference.

gtaw: As 48v said, my concern is with sheet steel (D1.3). Also, enjoy your vacation! I'm in the midwest and a warm place to vacation would be welcomed but the plug weld woes of the world require I suck it up.

48v: Thanks for being on my side! My side:

To be clear: The weld strength is overkill for my specific application, so I am not too concerned whether the weld, in reality, will act like a plug weld, fillet weld, or etc. The connection will not fail. Rather, this is a quest in academia and clarification on a code that I have so far found to be redundant, confusing, and contradictory (AWS). If it were not a plug weld, I would use AISI or AISC for calculating the weld strength. And while I know that AWS calculates the weld strength the exact same for a spot weld or plug weld (same exact equations), AISI only gives the strength equation for a spot weld. Yes, I could argue that I could use the AISI spot weld calculation for the plug weld since they are the same in AWS, but I should verify first that AISI did not purposely omit plug welds.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant