In the calculation report the allowable stresses in Case 1(OPE) W+T1+P1, are 0. Why? For other cases it is okay. The pipe material is A106B. Its density is 0.00783 kg/cu cm. Inside the pipes flows flue gas. density of the flue gas is small.
I have clicked two times on box called allovable stresses. On the left side of the input sheet, there are Code 31.3, SC 137.892.... Box called Eff is emty, so are the boxes F1 to F9