Weld neck flange Main feature:

Carbon Steel: ASTM A105, A350 LF1, LF2 CL1/CL2 LF3 CL1/CL2, ASTM A 694 F42, F46, F48, F50, F52, F56, F60, F65, F70
Stainless Steel: ASTM A182 F304/304L, F316/316L, F316H, F316Ti, F321, F44 (UNS S31254)
Alloy Steel: ASTM A182 F1, F5/A, F9, F11, F12, F22, F91
Size: 1/8" NB TO 48"NB.
Rating: 150#, 300#, 400#, 600#, 900#, 1500#, 2500#

Uses:
The weld neck flange is very resistant to dishing and has a very sturdy connection because it has the pipe along with the tapered hub.
The flanges are ideal for extreme fluctuations of temperature.
They are ideal in environments where there may be a lot of bending and handling of the flanges.

Preferred in an environment with extreme temperature conditions.
This type of flange is preferred for every severe service condition_resulting from high pressure or from sub-zero or elevated temperature.
They are used in situations where loading conditions are substantially constant or fluctuate between wide limits.

This is probably the best welding flange available because of its high, heavy neck.
Highly recommended wherever a sound welded joint connection is needed.