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.
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.