Design of stand pipes.-The design of the branches and standpipe shall be regulated in the following manner:

(a)  in order to withstand the maximum working pressure or design pressure, the     minimum thickness of branch and standpipe shall be determined in accordance with the provisions specified in sub-regulation (a) of regulation 338;

(b)  compensation requirements for openings in the main pressure parts shall be determined in accordance with the provisions of regulation 279;

(c)  the additional thickness shall be considered to withstand superimposed loading due to connecting pipe-work or fittings.

The minimum thickness of the branch or stand-pipe shall be the greatest of the values required above and shall not be less than 0.015 d_o + 3.2 mm where d_o is the outside diameter of the branch (in mm.):

Provided   that the provisions of the regulations shall not apply to such tube stub which have been designated as tubes.