(7)Service test and examination. - Every pressure vessel or plant in service shall be thoroughly examined by a competent person-(a)externally, once in every six months;(b)internally, once in every twelve months;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 two years :Provided that for a pressure vessel or plant process which can not be frequently opened, the period of internal examination may be extended to four years; and(c)hydrostatically tested once in every four years :Provided that in respect of pressure vessel or plant with thin walls such as sizing cylinder made of copper or any other non-ferrous metal periodic hydrostating test may be dispensed with subject to the conditions 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 by clause (a) or if owing to its construction and use a pressure vessel or plant can not be hydrostatically tested as required in sub-rule (b) of this clause thorough external examination of the pressure vessel or plant shall be carried out atleast once in every two years, and atleast once in every four years a thorough systematic non-destructive test like ultrasonic test for metal thickness or other defects of all parts the failure of which might lead to eventual repture of the pressure vessel or plant shall be carried out.(d)the hydrostatic test pressure to be carried out for the purposes of this rule shall be 1.25 times the design pressure or 1.50 times the maximum permissible working pressure vessel whichever is less.
