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

1.1 Scope 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 for 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 nominal size 2 1/2 in (65 mm) the socket dimensions are also suitable for use with plain end pipe dimensions in accordance with BS 3600 (ISO/R 64). See Notes to Purchaser. This standard provides for the following:

BS 3799 - steel pipe fittings, screwed and socket-welding pipe fittings

BS 3799 – steel pipe fittings, screwed and socket-welding pipe fittings

1.1 Screwed and socket weld fittings:

90 deg and 45 deg Elbows,



Couplings and half-couplings


Square, hexagonal and round head plugs

Hexagonal head bushings

Hexagonal and round nipples .


Welding bosses

Swage nipples·

1.2 Sizes and size identification

The size of a fitting is identified by the nominal size of the pipe with which it is to be used. For reducing fittings, the openings are given in the alphabetical sequence shown in Fig. 1, the run openings being stated first, followed by the outlet opening(s). In each case, the larger opening is specified first.

1.3 Designation

Fittings to this standard shall be designated as 3000 lb and 6000 lb. These designations represent the maximum cold non-shock working pressures of the fittings in pounds force per square inch. For convenient reference schedule numbers of pipe normally used with these fittings are as follows:

Designations Screwed fittings Socket-weldlog fittings 3000 lb Schedule 80 Schedule 80 6000 lb Double extra strong Schedule 160 Bore dimensions given in the relative tables for 3000 Ib socket-welding fittings correspond to Schedule 40 Pipe.

1.4 Pressure/temperature ratings

Pressure/temperature ratings are listed in Table 1. Solid plugs and bushings do not carry specific ratings and are intended for use with screwed fittings of any of the designations shown in 1.3.

1.5 Manufacture

Fittings may be produced by any of the following recognized processes:

(1) Forging: elbows, crosses, tees.

(2) Forging or machining from bar stock: caps, bushings, hexagonal nipples. pipe plugs, unions.

(3) Forging, or machining from bar stock or seamless pipe: couplings, half·couplings, welding bosses, round and swage nipples.

1.6 Certification

By agreement between the purchaser and the manufacturer, the basis of acceptance by the purchaser of the fittings covered by his order may be a certificate stating that such fittings comply with the requirements of this standard, and that the material from which they are made has the chemical and physical characteristics specified in the appropriate standards listed in Table 3. 2. Design 2.1 Screwed fittings Screwed fittings shall be designed to withstand the stresses resulting from assembly.

For this purpose, elbows, tees and crosses shall be designed with wide reinforcing bands of heavy section connecting at the crotch of the fitting, resulting in additional wall thickness over the full length of the tapped ends. Screwed couplings, caps and similar fittings may have this additional wall thickness provided oyer their full length.

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