Hello all!

ASME B31 codes use pad thickness when calculating the SIF of reinforced fabricated tees, but not the diameter of such pads. Is there any minumum required diameter of the pads to comply with B31? (let's assume that such pad is only required for SIF reducing, not for branch reinforcement according to section 104.3.1 of ASME B31.1).

Thank you for your help.

Best regards

I don't know of defined minimum, however there are common sense issues here. Consider what is achieved in terms of stress re-distrbution by adding a ring and altering the local flexibility of the connection.

A very small ring will not add any stiffness, and welds that are too close may make the situation worse.

Since the maximum size allowed to be considered for pressure ... although a ring could actually be larger diameter ... is clearly defined, I would aim for that figure. Then you can be confident that you will be in the geometry regime to which B31.3 pp D SIF's apply.

Babbo,

The notes to B31.1 Fig 104.3.1(D) state "Width to height of rings and pads shall be reasonably proportioned, preferably on a ratio as close to 4:1...". The other codes don't say very much on this point but, as pointed out already, common sense should prevail.

The criteria I was taught and used over my career was:

Minimum Pad Thickness = The wall thickness of the Header Pipe

Minimum width of the Pad "Ring" = 1/2 the Diameter of the Branch Pipe