BS 3799:  Steel pipe fittings, screwed and socket-welding for the petroleum industry

This British Standard specifies requirements for forged carbon and alloy steel screwed and socket -welding fittings for use in the petroleum and petrochemical industry.

Screwed fittings specified in this standard are intended for assembly with pipe threaded in accordance with API Std. 5B or ANSI B2.1 (N.P.T.)
Socket-welding fittings specified in this standard are primarily intended from assembly with plain end pipe dimensioned in accordance with BS 1600 and API Std. 5L. It should be noted ， however， that with the exception of the nominal size 2-1/2（65mm）the socket dimensions are also suitable for use with plain end pipe dimensions in accordance with BS 3600( ISO/R 64).
BS 3799 provides for the following
(1) Screwed fittings:
Elbow， 90°and 45 °
Crosses
Tees
Couplings and half-couplings
Caps
Square, hexagonal and round head plugs
Hexagonal and round nipples
Unions
Welding bosses
Swage nipples
(2) Socked-welding fittings:
Elbow， 90°and 45 °
Crosses
Tees
Couplings and half-couplings
Caps
Unions
Welding bosses
Swage nipples