Example calculation per B31.1 for required thickness of titanium NPS 4, with P= 740 psig, SE = 12.1 psi, A = 0 :
when y = 0.0, tm = 0.1376
when y = 0.4, tm = 0.1343
So, I see there is little difference, and y = 0 is more conservative. Non-ferrous metals (aluminum, nickel alloys, copper, and...