Partial Pen welds vs fillet welds

By KRDC Date 03-13-2002 23:59

I am designing a tube flange to an endplate and have a required load that the weld needs to carry. the tube is a 3/8" thk tube to an 1" thk endplate. if I were to use fillet welds the capacity would be =.3*Fu(filler matl)*.707*E( or weld size)*Length of weld. Correct? and if I were to use a partial pen weld the capacity would be (based on joint designation from AWS BTC-P4-GF, on pg 54 of AWS D1.1:2000 and allowable stress pg. 13, tension normal to effective area) = .3*Fu(filler matl)*E(or S or weld size, all the same, correct?)*Length of weld. Correct? For a 3/8"tube, and according to the joint, I need to have min 1/8" material left after the groove, which would leave 1/4" for the weld size(E). If I were to use a fillet weld the size of the weld could be 3/8" and I would have to reduce that by the .707 factor which leaves me with 0.265". That is larger, and therfore sronger, than if I were to use a partial pen. Correct? Why would partial pen welds be used with any thicknesses that are less than 1"? There does not seem to be a bennifit for groving if the material is less than 1" thk. Am I simplifing this, or only looking at my particular situation and generalizing to much? Any responses would be appreciated.
Thanks, A frustrated EIT

By CHGuilford (****)

Date 03-14-2002 15:02

If I understand your question, you are comparing the differences between making fillet welds and groove welds assuming both can achieve equal strength.
Fillet welds are usually easier to make because there is less preparation to do.
Groove welds require the groove to be prepared AND filler metal welded in. More time and labor is needed than for a fillet.

It is wise to look at the required weld cross section to make a good comparison. As I said fillets are usually easier but what if the required size means a large volume (more passes, more filler, more heat , more distortion, etc.) compared to a smaller but equal strength groove weld cross section? Or could a combination groove weld with fillet reinforcement be substituted?

Another consideration is access and ergonomics to do the actual welding. You have to consider if the welder can get the electrode into the joint at the right angle without being at risk of injury.

Sometimes a fillet will interfere with the fit of another part where a flush surfaced groove won't.

Having said all that, I believe the main reason for PJP grooves is to have versatility in welding applications.

Hope this helps,
CHGuilford