Branch Connection Reinforced Pad Calculation

Hi,

I am fairly new with this calculation.

This is 18 x 18 at 45° wye lateral.

Dh = 18 in, Th= 0.562 in

Db = 18 in, Db = 0.562 in

Design pressure 550 psi, corrosion = 0.1, Design Temp = 160° F

Material = A106-B, Allowable = 19,000 psi.

Calculated Result for Design thickness of the pad.

th = 0.258 in, tb = 0.258 in

When I model this Wye Lateral using FEA.

I need to use at least 1" thick material to meet the allowable of 19000 psi.