ASME SEC. XII Forming strain requirement for High Alloy steel such as SA 240 TYPE 304

There are threads on this. My recollection of ASME VIII is that there are no requirements. If you want to derive some fibre elongation numbers for your own peace of mind, you can reverse engineer Div 1 Appendix 44 (cold stretched pressure vessels). Cold stretched vessels don't required PFHT. Formed heads are essentially cold stretched.
It is the nature of the material.

The 2XX alloys work harden much more than the 3XX ones.
They are also significantly less corrosion resistant.
Likely this combination lead to the limits.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed