#1 Stub End

A Stub End always will be used with a Lap Joint flange, as a backing flange. These flange connections are applied, in low-pressure and non-critical applications, and is a cheap method of flanging. In a stainless steel pipe system, for example, a carbon steel flange can be applied, because they have not come in contact with the product in the pipe.

Stub Ends are available in almost all pipe diameters. Dimensions and dimensional tolerances are defined in the ASME B.16.9 standard. Light-weight corrosion resistant Stub Ends (fittings) are defined in MSS SP43.

#2 Threaded Flange

Threaded Flanges are used for special circumstances with their main advantage being that they can be attached to the pipe without welding. Sometimes a seal weld is also used in conjunction with the threaded connection.

Although still available in most sizes and pressure ratings, screwed fittings today are used almost exclusively in smaller pipe sizes.  A threaded flange or fitting is not suitable for a pipe system with thin wall thickness, because the cutting thread on a pipe is not possible. Thus, the thicker wall thickness must be chosen...what is thicker?

ASME B31.3 Piping Guide says:

Where steel pipe is threaded and used for steam service above 250 psi or for water service above 100 psi with water temperatures above 220° F, the pipe shall be seamless and have a thickness at least equal to schedule 80 of ASME B36.10.

#3 Blind flange

Blind Flanges are manufactured without a bore and used to blank off the ends of piping, Valves and pressure vessel openings. From the standpoint of internal pressure and bolt loading, blind flanges, particularly in the larger sizes, are the most highly stressed flange types.

However, most of these stresses are bending types near the center, and since there is no standard inside diameter, these flanges are suitable for higher pressure temperature applications.