ASME B16.34 Section 6.1.2

[bumpjones]

I am working on a report for a class 3 valve and in reviewing B16.34 Section 6.1.2 to determine the minimum wall thickness required found the following, "the inside diameter d is taken as the minimum diameter of the flow passage but not less than 90% of the basic inside diameter at the valve end" This seems counter intuitive to me, the larger diameter flow path would require a larger minimum wall thickness to withstand the stresses due to the internal pressure in the valve. But the way I interperet the code is that the minimum diameter flow path determines the required wall thickness. How can this be?