Interpretation of figure 3.5

[holdpt]

We have B-L1a-F joints on a 304L hopper. There is a concern that the root openings may be excessive. I am trying to understand the fit-up tolerances in figure 3.5 of D1.6 (2007).
1/4" plate should have 1/4" root opening if detailed as such, plus 1/16" based on the equation? I question it because I am trying to understand where the less than or equal to comes into play. With a 3/8" max thickness limit, nothing would ever equal 1/4" so why not just say +T/4?

 

[Sammy19]

I just looked this up out of curiosity.... I'm a learner so I would be curious to see the answer here as well. If I am reading the formula correctly at maximum allowable thickness of 3/8" - "+T/4" would only be 3/32", nowhere near 1/4" ...

 

[Sammy19]

Speaking as a welder, tho, using the max root opening on 1/4" with FCAW as specified here, (whether it's 5/16" or 1/2" depending on the answer to your question) would be pretty a pretty big groove to fill on the edge of 1/4" stainless. The ends of those plates are going to get pretty hot. I would think blue-ing and distortion would become an issue toward the top of the tolerance here. If I were asked to weld this, I would definitely shoot for the inside of the tolerance at 3/16". Less than that and the torch angle would have to be near perfect to catch the bottom corners. Actually saying it like that makes the formula in the table make even less sense... At the top end of the tolerance you would have potentially a 1/2" root opening on a 1/4" butt joint, double the thickness of the material. That sounds excessive to me. It says more or less the same thing in D1.1 tho. "+1/4 - 1/16". Your assertion of "+T/4" sounds more reasonable to me. But again, I'm not an engineer, just a welder / CWI wanabee.

 

[DekDee]

holdpt,
I am not much good at imperial but I will try.
3/8" is maximum thickness of material.
So if you have 1/4" thick material the root opening is 1/4" minimum.
As Detailed allows the root opening to be 5/16" max (1/4 + 1/16") / 1/4" min
As Fit-Up allows the root opening to be 9/16" max (5/16" + 1/4") / 3/16" min (1/4 - 1/16")

3.13.1 Joint Dimensions. Dimensions of groove welds
specified in 3.13 may vary on design or detail drawings
within the limits or tolerances shown in the “As Detailed”
column in Figure 3.4. Fit up tolerance of Figure 3.4 may
be applied to the dimension shown on the detail drawing.

Hope that helps,
Cheers,
DD