single bevel groove weld with a fillet weld over it 3

[matschka]

A new QC engineer here has said that the fillet weld on top of a single bevel groove weld specified on the drawing is not necessary because it does not add or increase the strength of the weld joint. He said that the fillet weld is only for cosmetic purposes or to increase fatigue strength.Looking for some technical guidance on this issue.

 

[Ron]

Please post a sketch of the weld. It depends on the stress orientation as to the benefit of the fillet weld. Most likely it provides some level of reinforcement.

Is there a fatigue consideration for the weld?

 

[metengr]

Incorrect. The fillet weld used for nozzle and other structural attachments in vessels or objects is required because it will provide some additional load-carrying capacity AND is typically used to reduce stress concentration in an otherwise sharp geometric transition.

 

[DVWE]

Most of the ASME joints in section UW have fillet welds for additional reinforcement.

Why don't you ask him for his source?

 

[HgTX]

It's typically not included in the strength calculation, but it does increase capacity and reduces stress concentration as metengr says.

Not cosmetic. More dispensable in a static than cyclic situation, but not cosmetic.

And it may not be a prequalified joint detail without it, depending on what code you're working with.

Hg

Eng-Tips policies: faq731-376

 

[EngAddict]

Well he is right, 95% of the time it is cosmetic. I agree with metengr, it can be used for fatigue, also additional strength and area reinforcing (however small it may be). Same goes for strength really not much improvement, Dependant upon the size, but a cover weld, not really for strength. Stress concentration is a big one, but again the majority of the time this is only needed for fatigue assessment, otherwise peak stresses can be omitted.

 

[dhengr]

matschka:

Believe it or not, welds are designed so welders can make them, and we can have some degree of confidence in their strength. Metengr has it right. AWS calls the fillet weld over a beveled groove weld, a reinforcement weld, because it increases the capacity of that weld. Fatigue and stress concentrations at sharp corners are another issue. It’s a good thing your QC guy isn’t designing your welds, and he could use some more training if he’s responsible for welding QC.

Many engineers draw that weld as if a welder could make a weld, with a weld face which perfectly aligns with the face of the grooved pl., as if a machinist cut that corner perfectly square, it can’t be done. They are not showing a real world weld, they are showing what they don’t know about welding and weld joint design. So, a good welder will give you a slightly convex face on that groove weld and probably a slight reinforcement fillet at the base of the weld. Many times a simple fillet weld will accomplish the same thing as your groove weld much more economically.

I am assuming a Tee joint, flange pl. horiz. and vert. web pl. with grooves. For your beveled groove weld, either you or the code make some judgement about the quality of your weld root (root pass) and that determines the center point for the effective throat radius. For what the welder would do, as I mentioned above, the effective throat for weld design will be the groove depth. If I tell him to put a 1/4" reinf’mt. fillet at the base corner; the effective throat will be the hypotenuse of the triangle with groove depth (horiz. leg) and 1/4" (vert. leg), a greater effective throat than the first case. If I tell the welder to make the reinf’mt. weld the same height as the groove opening, it does not have to be a 45° fillet, theoretically the fillet has to have a large enough base dimension so that I can swing a compass about the center point and to the point the groove opening and the reinf’mt. weld meet, and the weld face must be out beyond that arc wwhich is now the effective weld throat. The weld will theoretically fail along that new min. effective throat, irrespective of the loading being tension or shear btwn. the flange and the web. Obviously, the reinf’mt. improves fatigue conditions over the ill detailed square corner. And, some loading conditions can will load the joint in a less favorable way, it’s the designers job to minimize this likelihood.

 

[EngAddict]

Why would the engineer or drafter draw in every weld pass with a convex finish then a convex or concave fillet over the top? May as well draw in the weld splatter too.. It is technical drawing not impressionism.

Lets put this in perspective. If I weld a 32mm thick nozzle into a 50mm thick pressure vessel with full penetration welds then the 9mm cover fillet does bugger all for strength, it is there for fatigue and cosmetics only.
If I weld a lug to a plate where the full pen or partial pen depth is the same as the fillet leg then this cover fillet is designed for strength, not cosmetics.

Either way it is good practice to use a cover fillet in all cases but it is better practice for the engineer to actually understand why.