ASME UW-20

Hi!

I am trying to make a fixed tubesheet calculation based on ASME UHX Sec. 8 Div. 1 2010 ed. but i have some problems in calculating Lmax in step 9 UHX-13.5.9 b1 and b2. In the case of full strenght weld and partial strength weld, Lmax Can be calculated in UW-20. In UW-20, Design Strength Fd is required in calculating Lmax but ASME Din not Specify formula in calculating Fd.

Question.

1. Can i use Wt in UHX-13.5.9 b1 as Fd?

2. If Wt can be use as Fd,(Wt values are different from loading case 1-7) should i use value of Wt in each loading case? or the maximum value of Wt form loading case 1 to 7 to be used?

Thanks..