Though threaded pipe flange is available in different dimensions, threaded fittings mostly is used in small diameters pipeline. (Below 4 inch normally.)
On the other hand, it is not compatible with a pipe system in thin wall thickness, since there is no space for doing the threading.
The threaded flange is screwed to the threaded pipe by the thread, which is processed in the inner hole of the flange. So It does not need to be welded. Therefore, it became so convenient for installation and maintenance comparing with other flange types, such as slip on flange, socket weld flange etc.
Threaded flanges are used where it is difficult to weld or cannot be welded, such as threaded flanges used to protect the galvanized layer of pipes. In addition, It should not be used on pipes with repeated temperature fluctuations or above 260 ℃ and below -45℃ as well.In ASME B31.3 standard it defines: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.
