D1.1 - Minimum Fillet Weld Size

Date 11-13-2024 20:03

Sorry if this is a re-tread, I can’t find this in any previous discussion since at least 2015. Any input you can provide would be appreciated.

I am working with D1.1-2020. We wish to bring our fillet weld sizes down as far as possible to avoid over-welding. The bulk of our welding is in the 1/8” to 1/4” range, although some components are lighter or heavier. Engineering suspects that many of our welds are oversized for the load they are required to handle and wishes to employ 1/8" welds where they can.

4.4.2.8 – says “the minimum size fillet weld shall not be smaller than the size required to transmit the applied load nor that provided in 7.13”

7.13 points to table 7.7, which says that for materials ≤1/4”, the minimum fillet weld size is 1/8”– This would put many of our fillet welds at 1/8” according to the engineers

I also read 4.18.3 - Prohibited Joints and Welds saying “fillet welds less than 3/16” shall be prohibited

How can this prohibition be understood? My gut tells me that 3/16” should be the minimum designed weld size (even though some of the materials are under 3/16”) and that 1/8” will be the absolute minimum in the as-welded condition if a 3/16” fillet is undersized (ex: for 10% length).

I am left with a couple of questions:
- Is the minimum “as-designed” fillet weld size 1/8” or 3/16”?
- Why didn’t they include the 3/16” limit under 4.4.2.8? They don’t point to it in the index either.
- Table 7.7, note “B” says “except that weld size need not exceed the thickness of the thinner part joined”
   - Are they only referring to materials ≥3/16”?
   - Does this mean that we can use 1/8” fillet welds on 1/8” materials? How do we square that with “fillet welds less than 3/16” shall be prohibited”?
   - Does this mean that we are allowed to weld materials under 1/8” to code? How do we handle thin attachments (≤1/8”) to heavier materials? Can I write D1.1 WPS’s that cover 1/16” attachments (I believe I would have to qualify that WPS)?

By Lawrence (*****)

Date 11-14-2024 13:55

In no particular order.

Base metals thinner than 1/8" are outside the scope of D1.1. AWS D1.3 structural code for sheet is one option that includes sheet steel welded to supporting structural members.

Note that the 3/16" minimum fillet size is published in Clause 4.18.3. Now scroll up and note that this clause falls under "Part C" which is design for cyclical loading. Your engineer can determine if their designs fall into this category or not.

Now validate that by looking at Table 7.7 footnote "c". which states: "Minimum size for cyclically loaded structures shall be 3/16 in"

So if your fillets are statically loaded, the minimum weld sizes in the table are kosher for both design and execution.

Having said that... Have you actually tried to make a 1/8" fillet with Spray Transfer GMAW or FCAW? It's not such an easy thing to do even if it is possible, and allowable.

On the other hand.. Making right sized welds is super smart and if you have the conditions to make the smaller size welds and your engineering is behind specifying them... It will save a lot of time... A LOT

By dhagfors (*)

Date 11-14-2024 18:49

Thank you Lawrence, I'm not sure how I missed that. I'll read more carefully. I am concerned about bringing welds down to 1/8" as they're going to have to run such a precise bead and quality is already a concern. They're running GMAW-P with .035". We'll see how the samples go. I appreciate the response.

By Lawrence (*****)

Date 11-14-2024 20:09

I've had similar teachable moments.

Not many of us spend a lot of time in the design clause, and it's easy to overlook the separation of static and cyclic "parts".

If your are using Lincoln power supplies, take a look at "RapidArc" waveforms. The arc length is very short which helps get a smaller fillet. Also Lincoln has a subroutine for GMAWP called "Ultimarc" which I've found to be helpful with both spatter control and mill scale conditions. Ultimarc goes from -10 to +10 so there is a wide functional range, but yet does not have a noticeable impact on current or arc voltage, Meaning you can set it where it works best and not worry about straying from WPS ranges.

By jwright650 (*****)

Date 12-03-2024 13:01

I've seen 1/8" fillets called out, but never really tried to strictly adhere to it. Lawrence, you are correct in saying that it is difficult to run an 1/8" fillet consistently with FCAW. Never really looked into smaller electrodes, so do they even make a D1.1 compliant electrode under .035"? I came from a structural fab shop where we used large electrodes looking to maximize deposition, so trying to weld these small fillets hasn't been on my radar before.

By Lawrence (*****)

Date 12-03-2024 13:41

Hi Gerald

I did a quick search and looked at Hobart Fabshield 21B which is an E71T-1 that has been around a long time.

They do indeed have an .030 diameter all position electrode.

The D1.1 Prequalification clause has a maximum FCAW electrode diameter noted (Table 5.1), but no minimum.

So I guess if the electrode wire has the A520 blessing it's good to go.