Regarding 2009b Sec.Ⅷ Div.2 4.16 g0=g1 Integral Flange, there are no rules to decide stress factor V. On this part, the only formulas are indicated to calculate V when 0.1<Xh<2.0. In the case of g0=g1, Xh=0 because hub length h=0.
Although g0=g1 case is shown on the figure 4.16.1, the formula to calculate V at Xh=0 is not shown on Sec.Ⅷ Div.2 4.16 ”Design Rules for Flanged Joint” !!
Of course, I know that Div.1 has rules for g0=g1 Integral Flange. It says that V=0.550103 if g0=g1. But I have to use Div.2 to get U-2 stamp.

I have one opinion about this matter.
On Sec.Ⅷ Div.2 4.1.1.2, it says that “Part 4 does not provide rules to cover all loadings, geometries, and details. When design rules are not provided for a vessel or vessel part, a stress analysis in accordance with Part 5 shall be performed considering all applicable loadings specified in the User’s Design Specification.”
So, do I have to design g0=g1 Integral Flange by Div.2 Part 5?

Please advise me.

no.
in my opinion, Hub length is not Zero. entire straight length to be considered as hub. And Flange can be designed as per Part-4.