Codes not sure but, ANSI B 16.34 and API 600 are couple of Design Standards which are generally followed. Here detailed (Component wise) design is not delt. Generally, Valve manufacturers obtain thickness of the castings based on ASME Sec VIII Div 1, whether it is domed or flat Bonnet.
Blind Flange having Centre Hole is delt in Sec VIII Div 1 Appendix.