Hoop Stress on Circumferential welds?

[Patassa]

I'm working on a leak repair on a large cooling water line and the probable solution will be to weld on a full encirclement split tee. A more experienced engineer actually told me that the fillet welds (circumferential)would "push me into the next size pipe schedule" due to them being weaker in hoop stress than a butt weld. I stared at him blankly as I've never considered hoop stress for circumferential welds before. My supervisor who is even more experienced than the other guy said no, that I don't need to check the hoop stress on those welds (I think he may have even said there was no hoop stress on those welds).

It can't be both, which is it? I've reviewed my text books but can't find anything like this in them. If someone has an answer with a picture or reference that would be ideal. But a consensus would help too. Thanks

 

[LittleInch]

I'm struggling to understand what your colleague means.

If this is a repair to a leak then the repair sleeve becomes fully pressurized.

What he might be referring to is that the fillet weld can experience bending from the sleeve material being pressurized and creating forces on the weld from the sleeve expanding in a hoop direction and a large stress concentration at the inner toe of the fillet weld.

You probably need to make that weld a full penetration weld to give it more strength.

Alternatively if you can drain the pipe down is to look at grounted sleeves which are certified for through wall defects.

There are a lot of variables here so a good sketch and a blow up of what you're planning at the weld area would help.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BigInch]

Because of the fillet's right triangle geometry, the maximum shear stress occurs at the throat of the fillet, a thickness = 2 ^-1/2 x the thickness of the plate