bevel weld detailing

[rllo]

I have a question about beveling specifically. a 1/4" bevel weld was called out to attach a HSS16x16x1/2 to PL. the shop drawings show a 3/8" chamfer (bevel?) on all 4 sides. why is that? I drew this up in CAD and don't see where my 1/4" bevel spec is. then I realized I don't really know what I'm doing - is the 1/4" bevel supposed to be the leg or hypotenuse distance, I wondered. this is why i'm here. thank you for your help.

 

[kingnero]

Depens on the welding process that will be used and the desired penetration.
A 45° prep is usually to small. Try to have "beta" between 50 and 55°.
My interpretation of the weld designation is 1/4" flat "in" the vertical part, and a fillet weld following on the first weld with a leg length of 1/4".
Hence the 3/8 chamfer, to ensure the weld goes to 1/4" deep. You foresee insufficient penetration this way...

 

[gtaw]

It depends on what your governing standard is. As indicated by the welding symbol you included in your post, the 1/4-inch dimension is the depth of the bevel. For the bevel, the depth would be measured through the thickness of the part being beveled. If AWS D1.1 is the governing standard, the maximum weld size for design purposes would be the depth of the bevel minus 1/8-inch for bevel angles less than 60 degrees.

If the designer requires a 1/4-inch weld size (joint penetration), the 1/4-inch dimension should be denoted as (1/4) [enclosed by brackets]. The depth of the bevel would have to be increased to produce the 1/4-inch weld size if partial joint penetration is expected.

Be aware that AWS D1.1 does not consider a weld made without backing or back gouged to be prequalified. To make a weld without backing or back gouging, it is considered partial joint penetration. The contractor would have to qualify the WPS and the welders without backing in order to comply with AWS D1.1.

Whether the weld is partial joint penetration or complete joint penetration determines the allowable stress permitted and the required weld size.

If you are working to a different fabrication standard, they could have something different.

 

[dauwerda]

is the 1/4" bevel supposed to be the leg or hypotenuse distance, I wondered.

The 1/4" is the leg size, but this is perhaps a bit more complicated answer than you realize (assuming AWS D1.1 is the design standard).
The welding symbol that you are showing is somewhat incomplete (putting the 1/4" dimension in parentheses would fix that). Typically as an engineer you are concerned about the strength of the weld, and not as much about how that is achieved. So the important issue would be to callout that you want a PJP groove weld with an effective throat of 1/4", this would be done by putting the dimension in parentheses. The fabricator would then pick their weld process (SMAW, GMAW, etc.), the bevel angle and bevel size to achieve required effective throat. For instance, for a prequalified PJP weld and a 45° bevel, if GMAW is used in the flat or horizontal position, the effective throat is equal to the bevel size (1/4" bevel gives 1/4" effective throat), but if SMAW it is 1/8" less than the bevel size (1/4" bevel gives 1/8" effective throat).

Without the parentheses around your 1/4" dimension, you are calling out a 1/4" bevel but you aren't dictating the weld process, so it isn't clear what effective throat is actually needed. I would guess the fabricator (conservatively) assumed your dimension was meant to be the effective throat size and they are using the SMAW process so to achieve the 1/4" effective throat they need a 3/8" bevel in order to be prequalified.

Be aware that AWS D1.1 does not consider a weld made without backing or back gouged to be prequalified. To make a weld without backing or back gouging, it is considered partial joint penetration. The contractor would have to qualify the WPS and the welders without backing in order to comply with AWS D1.1.

Perhaps it's the wording, but this doesn't ring true to me. PJP welds are absolutely prequalified and don't require backing or back gouging. I'm assuming you were talking specifically about CJP welds here? As the HSS sidewall is 1/2" thick and the OP only called for a 1/4" bevel, I think it's safe to assume they are going for a PJP.

 

[gtaw]

A double sided groove weld made without back gouging or a single sided groove weld made without backing without qualification by testing to be considered to be a partial joint penetration groove weld. Reference: AWS D1.1/D1.1M:2020 clause 5.4.2.1.

The work around is to qualify the WPS for single sided groove welds made without steel backing or back gouging or a double groove weld made without back gouging is to qualify the WPS by testing.

Other AWS welding standard may have similar wording regarding welds made without backing or back gouging are considered to be PJP unless qualified by testing.

ASME B&PV Code also have similar wording with regards to groove welds made without backing or back gouged to be PJP.

A PJP groove weld is considered to be welded with backing where the base metal is acting as backing.