Steel pipes

Steel pipes to BS 1387 are normally specified in the nominal bore sizes given in Table 1. Finishes can be black or galvanised, the latter being preferred for corrosion resistance.

TABLE 1. Nominal bore size steel tubes to BS 1387

Nominal size Actual bore Approximate o.d.
Medium Heavy
in in mm in mm in mm
1/8 0.226 5.77 0.178 4.52 13/32 10.3
1/4 0.338 8.59 0.290 7.37 17/32 13.5
3/8 0.476 12.09 0.428 10.87 11/16 17.5
1/2 0.623 15.82 0.575 14.60 27/32 21.5
3/4 0.839 21.31 0.791 20.09 1.1/16 27
1 1.060 26.92 0.996 25.30 1.11/32 34
1.1/4 1.401 35.59 1.337 33.96 1.11/16 43
1.1/2 1.633 41.48 1.569 39.85 1.29/32 48
2 2.066 52.48 2.002 50.80 2.3/8 60

Steel pipes are normally used with threaded connections. Above 65 mm nominal bore, welded fittings to BS 1965 are recommended, although cast iron pipes with integral flanges or steel pipes with welded-on flanges may be used. In sizes smaller than 65 mm malleable iron fittings conforming to BS 143 and BS 1256 may be used for pressures up to 10 bar.

Screwed connections, to BS 21, are restricted to metallic tubes with thick walls.