Threaded flanges, also sometimes referred to as companion flanges / screw flanges / NPT flanges, contain a female NPT thread in the center for connection to male NPT threaded piping. Threaded flanges are common when creating reducing connections. Other thread styles are available for machining, aside from the standard NPT form as designated by the ASME B16.5 specification.
The most popular threaded flanges range in ½ inch to 6” nominal pipe size, but we are able to offer NPT threaded flanges up to 24” if necessary. The amount of additional machining and labor hours which go into producing a larger diameter threaded connection make them less popular than a slip on or weld neck configuration. It may be of significantly beneficial use for an application which requires connecting and disconnecting from time to time. The male pipe end is joined to the flange without a weld connection required but can be sealed with a weld if necessary. This weld seal would defeat the purpose of a threaded flange as a structural option, as its primary advantage is to assemble and disassemble the connection. For the purposes of pressure vessel equipment, the weld seal can be applied if the user is certain they would like to keep the pipe and flange assembly sealed permanently.
Threaded flange connections are often a requirement when a male NPT pipe connection is utilized and the media in question is highly reactive or explosive in nature, which is why NPT/threaded companion flanges are commonly utilized in API oilfield service. This API 6A specification also allows for a male thread flange connection, but this is much less common than the female NPT in the center.
For dimensional data on the NPT itself, refer to the chart below: