Pipe Fittings

1.      Flanged Pipe Fittings

A pipe “flange” is a ring of metal, usually welded to the end of a pipe, with holes drilled in it parallel to the pipe centerline to accept several bolts.

Flange joints are made pressure-tight by inserting a donut-shaped gasket between the flange pairs prior to the tightening the bolts. A common method of installing such a flange gasket is to first install only half of the bolts (in the holes lower than the centerline of the pipe), drop the gasket between the flanges, then insert the rest of the bolts.

2.      Tapered thread pipe fittings

For smaller pipe size, threaded fittings are commonly used to create connection between pipes and between pipe and equipment. The intent of tapered thread is to allow the pipe and fitting to “wedge” together when engaged, creating a joint that is both mechanically rugged and leak free.

When male and female tapered pie threaded are first engaged, they form a loose junction

After tightening, however, the tapered profile of the threads acts to wedge both male and female pieces tightly together as such :

In the united States, the most common tapered thread for general-purpose piping is NPT, or National Pipe Taper Design. NPT threads have an angle of 60^o and taper of 1.7833^o

NPT pipe threads must have some form of sealant applied to assembly to ensure pressure tight sealing between the threads. Teflon tape and various liquid pipe “dope” compounds work well for this purpose.

Sealant are necessary with NPT threads fore two reasons:

·        To lubricate the male and female pieces

·        To fill spiral gap formed between the root of the female thread and the crest of the male thread.

Another tapered-thread standard is the BPST, or British Standard Pipe Tapered, BSPT threads have a narrower thread angle than NPT threads (55^o instead of 60^o) but the same taper of  1^o 47 ‘ (1.783^o).

3.      Parallel  thread pipe fittings (SAE straight thread)

Since parallel threads are incapable of forming pressure-tight seal on their own, the sealing action of a parallel thread pipe fitting must be achieved some other way.

This function is usually meet with an O ring or gasket.