Section 61(2)(a) in The Punjab Factory Rules, 1952
(a)In respect of pressure vessels of thin walls such as sizing cylinders made of copper or any other non-ferrous metals, the safe working pressure shall be reduced at the rate of 5 per cent of the original working pressure for every year of its use after the first five years and no such cylinder shall be continued to be used for more than twenty years after it was first taken into use.