6.3.5 Header branch thickness
The branches can be considered as cylindrical pressure vessels and the formulae from Clause 18.104.22.168 (given in (d) above) used:
The bore of the branch must be found first: if a velocity of 3 m/s is assumed, the cross-sectional area is 0.32/3.0 = 0.107 m2, giving a 0.37 m bore. Therefore,
The thickness calculated is that needed for pressure considerations alone. In practice, the branch wall thickness is increased to compensate for the opening needed (see Clause 3.5.4 of BS5500 ) and also to ensure that it is adequate to withstand the forces imposed on it by the pipework to which it is attached. The end of the branch is reduced to a thickness suitable for welding to the HP feed pipework, which has a typical wall thickness of 32 mm (see Figs 3.47 and 3.48).