For an example, let's use a 3" 150 pound slip-on pipe flange. According to ASME B16.5, it must be .88" thickness (tF). However, I've noticed ASME B16.34 valves bolted to these flanges that are substantially thinner, approximately .750"-.780".
According to ASME B16.34, 6.2.2 Flanged Ends...