5.11.3(d) Valve ends. All valves of Classes I and II piping systems having nominal diameters exceeding 50 mm (2 in.) are to have flanged or welded ends. Welded ends are to be butt welding type, except that socket welding ends may be used for valves having nominal diameters of 80 mm (3 in.) or less (see 4-6-2/5.5.2).