Section 56(7) in The West Bengal Factories Rules, 1958
(7)Every pressure vessel or plant in service shall be thoroughly examined by a competent person-(a)externally, once in every period of six months;(b)internally, once in very period of twelve months;Provided that if by reason of the construction of a pressure vessel or plant, a thorough internal examination is not possible, this examination may be replaced by a hydrostatic test which shall be carried out once in every period of two years;(c)hydrostatically tested once in every period of four years:Provided that in respect of a pressure vessel or plant within walls such as sizing cylinder made of copper or any other non-ferrous metal, periodic hydrostatic test may be dispensed with subject to the condition that the requirements laid down in sub-rule (8) are fulfilled:Provided further that when it is impracticable to carry out thorough external examination of any pressure vessel or plant every six months as required in clause (a) of this sub-rule, or if owing to its construction and use the pressure vessel or plant cannot be hydrostatically tested as required in clauses (b) and (c) of this sub-rule, a thorough external examination of the pressure vessel or plant shall be carried out at least once in every period of two years, and at least once in every period of four years a thorough systematic non-destructive test, like ultrasonic test, to detent defects of all parts shall be carried out.
