Ideas to Determine Weld Root Opening Size
Ideas to Determine Weld Root Opening Size
(OP)
On weld joints that are highly restrained, such as a partial penetration all-around fillet weld on a T-joint, a root opening is often recommended, presumably to minimize shrinkage stress in the cooled filler material and/or to avoid lamellar tearing in the base metal. What size root opening should be used? I have searched and cannot find this guidance anywhere. AWS D1.1 commentary C-2 make mention of the above concern but offers no guidance on utilizing root opening or what size it shoud be.
So I am thinking a simple linear expansion calculation is all that is needed to determine a logical size of the root opening. By choosing as delta T, the difference between molten steel temperature (~2800 deg F)and minimum service temperature (say 70 deg F) and plug this into:
dL = L x dT x alpha (where alpha = expansion coef. of steel)
we get dL = .75 x (2800 - 70) x (.00000633) for a specified fillet weld size of 3/4-inch leg.
Therfore dL = root opening = .013" = ~1/8"
Does this make sense? I don't know. We wouldn't place a 3/4 inch fillet weld at one shot, it would be built up in several passes probably using ~3/16" thick beads. Should the 3/16" bead size be used for the above calculation? Then we would get dL of .003" and that doesn't seem like much of a root opening an why bother?
So what thoughts does anyone have on how to determine root opening size?
So I am thinking a simple linear expansion calculation is all that is needed to determine a logical size of the root opening. By choosing as delta T, the difference between molten steel temperature (~2800 deg F)and minimum service temperature (say 70 deg F) and plug this into:
dL = L x dT x alpha (where alpha = expansion coef. of steel)
we get dL = .75 x (2800 - 70) x (.00000633) for a specified fillet weld size of 3/4-inch leg.
Therfore dL = root opening = .013" = ~1/8"
Does this make sense? I don't know. We wouldn't place a 3/4 inch fillet weld at one shot, it would be built up in several passes probably using ~3/16" thick beads. Should the 3/16" bead size be used for the above calculation? Then we would get dL of .003" and that doesn't seem like much of a root opening an why bother?
So what thoughts does anyone have on how to determine root opening size?





RE: Ideas to Determine Weld Root Opening Size
What you have done and explained makes perfect sense. By the way, you will not find any specific Code information related to root opening because this is a process function. The proof for process functions related to welding is in the qualification of the weld procedure with the stated root opening range.
RE: Ideas to Determine Weld Root Opening Size
Hg
Eng-Tips policies: FAQ731-376: Eng-Tips.com Forum Policies
RE: Ideas to Determine Weld Root Opening Size
Met, what is your rule of thumb for root openings in this type of T-joint?
RE: Ideas to Determine Weld Root Opening Size
If the root opening doesn't shrink shut - that is a good thing because then we wouldn't have the joint restraint condition that I am worrying about. Did you mean to say "we can't safely assume the root opening WON'T shrink shut"?
How are you specifying root opening size?
Thanks
RE: Ideas to Determine Weld Root Opening Size
RE: Ideas to Determine Weld Root Opening Size
D1.1 section 5.22.1 controls fillet weld root opening and adjustment of fillet weld size to accomodate the root opening.
Hg
Eng-Tips policies: FAQ731-376: Eng-Tips.com Forum Policies
RE: Ideas to Determine Weld Root Opening Size
I understand that once a root opening is incorporated, either by design or as a consequence of mill irregularities then Codes require fillet weld sizes to be adjusted.
But for the purpose of offsetting shrinkage stresses in a Tee-joint, do you folks not require an intentional root opening? If you do, what is your practice or method to determine size of the root gap?
Thanks
RE: Ideas to Determine Weld Root Opening Size
Best regards - Al