Reinforcement of multiple openings shall be subject to the following provisions:
Where two or more adjacent branch pipes are spaced between centres at less than 2 times their average outside diameter (so that their effective areas of reinforcement overlap), the group of openings shall be reinforced as specified in Clauses 4.3.18 and 4.3.19. The reinforcing metal shall be added as a combined reinforcement, the strength of which shall be at least equal to the combined strengths of the reinforcements that would be required for the separate openings. Portions of cross-sections shall not be considered to apply to more than one opening, or be evaluated more than once in a combined area.
Where possible, where more than two adjacent openings are to be provided with a combined reinforcement, the minimum distance between centres of any two of these openings shall be equal to at least 1.5 times their average outside diameter and the area of reinforcement between them shall be at least 50% of the total required for these two openings on the cross-section being considered.
Where two adjacent openings, as described in Item b), have a distance between centres less than 1.33 times their average diameter, no credit for reinforcement shall be given for any of the metal between such openings.
Any number of closely spaced adjacent openings, in any arrangement, may be reinforced as if the group were treated as one opening of a diameter enclosing all such openings.