Tapered pipe fittings

Brass pipe fittings

 
Stainless steel pipe fittings

Iron pipe npt fittings

Aluminum pipe fittings

Appearance of tapered pipe fittings
The male and female threads have a tapered flank and controlled truncation at the crest and root to assure metal to metal crest-root contact just as the male-female thread flanks make contact. Upon further tightening, the thread crests flatten out and allow the flanks to make full contact. This full thread profile contact theoretically give the tapered threads self-sealing ability. However, variations in condition of mating threads, fitting and port materials, assembly procedures and operating conditions make self-sealing highly unlikely without the aid of paste, tape, or pre-applied thread sealants.

Suggested applications for tapered pipe fittings
Tapered pipe fittings are prone to leakage because they are torque-sensitive. Over-tightening can distort the threads too much and create a leakage path. Also, tapered pipe threads are prone to loosening when exposed to high vibration and wide temperature variation. Repeated assembly and disassembly only aggravates the leakage problem by distorting the threads further. Tapered pipe threads are not to be used for mechanically joining components in a system where load would be placed perpendicular to the plumbing line. This weight will further weaken the sealing joint. In light of its sealing mechanism, assembly restrictions and design limitations, pipe thread connections are optimal only when the following conditions exist:
1. Minimum hydraulic shocks or vibration
2. The fitting is limited to one or two re-uses
3. The system utilizes low pressure; or few operating cycles (static condition) for higher pressure service
4. Skilled workers trained in the pros and cons of pipe fitting assembly are present

For these reasons, tapered pipe threaded connections are not recommended for dynamic pressure systems.

Tapered pipe fittings are still widely used in industry, though, because of their relative low-cost, widespread familiarization among users, lack of alternative port designs offered by many component manufacturers, and/or when exposed to more caustic media which requires the corrosion resistance of metal-only seals.
 

Hydraulic Supply Co. is located in Florida and Georgia, and is a distributor for Eaton Aeroquip, Eaton, SSP Fittings Corp. and Ward Manufacturing, leading manufacturers of pipe fittings
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