6.1.4 The minimum thickness tb, of a straight seamless copper or copper alloy pipe to be used for a pipe bend is to be determined by the formula below, except where it can be demonstrated that the use of a thickness less than tb would not reduce the thickness below t at any point after bending:
where
symbols are as defined in 4.1.1
c and σ are obtained as in 6.1.3 in general, R is to be not less than 3D.
6.1.5 Pipes are to be seamless, and branches are to be provided by cast or stamped fittings, pipe pressing or other approved fabrications.
Table 1.6.2 Copper and copper alloy pipes