ASME B16.1:2020 pdf free download.Gray lron Pipe Flanges and Flanged Fittings.
7.5 Threaded FLanges
7.5.1 GeneraL. Flanges shall have a standard taper pipe thread in accordance with ASME H 1.20.1. The thread shall be concentric with the axis of the flange, and variations in alignment shall not exceed 5.00 mm/rn (0.06 in./ft).
7.5.2 CLass 125. Threads shall be countersunk a distance not less than one-half of the pitch of the thread at an angle approximately 45 deg with the axis of the thread for the purpose of easy entrance in making the joint and protection of the threads. Countersinking shall be concentric with the threads. The length of the threads shall be measured to include the countersink.
75.3 CLass 250. Hub may be recessed. When not recessed, threads shall be countersunk a distance not less than one-half of the pitch of the thread at an angle approximately 45 deg with the axis of the thread at the back of the flange. If hub is recessed, threads shall be 45 deg countersunk to diameter of recess. The purpose is for easier entrance in making a joint and for the protection of the threads. Countersinking shall be concentric with the threads. The length of threads shall be measured to include the countersink.
7.6 FLange Bolt HoLes
7.6.1 Flange Bolt HoLes. Flange bolt holes shall be in accordance with the dimensions shown in Tables 7.61-1 through 7.6.1-3. Pairs of bolt holes shall straddle the centerline.
8 BOLT, NUT, AND GASKET DIMENSIONS
8.1 Bolting
(a) All bolting materials shall have square, heavy hex, or hex heads and square, heavy hex, or hex nuts with full flat bearing faces as specified in ASME B18.2.1 for bolts and ASME B18.2.2 for nuts. Threads shall be UNC or UN8 and have a thread fit class of 2A for bolts and 2B for nuts.
Washer faced bolts or washer faced nuts are prohibited.
(b) Carbon steel bolts 1 in. and smaller shall have square heads (ASME B18.2.1] or heavy hex heads (ASME B18.2.1) and shall have square or heavy hex nuts (ASME B18.2.2).
(c) Carbon steel bolts 1 %g in. and larger shall have square heads (ASME B18.2.1), hex heads (ASME B18.2.1), or heavy hex heads (ASME B18.2.1) and shall have hex nuts (ASME B18.2.2) or heavy hex nuts (ASME B18.2.2) or square nuts (ASME B18.2.2). For bolt sizes 1%2 in. and larger, stud bolts with a nut on each end are recommended.