Section 18(2) in The Static And Mobile Pressure Vessels (Unfired) Rules, 1981
(2)Pressure relief .-(i) Every vessel shall be provided with two or more pressure relieving devices in accordance with the provisions of the Design Code referred to in rule 12;[(i-a) for cryogenic pressure vessels, the outer vessel shall be provided with a vacuum valve and safety relief device (disc) to release internal pressure. The discharge area of such device shall be at least 0.34 sq mm/litre of water capacity of the inner vessel. The relief device shall function at a pressure not exceeding the internal design pressure of the outer vessel;] [ Inserted by G.S.R. 372(E), dated 17.5.2002 (w.e.f. 17.5.2002).](ii)the relief valves shall be spring loaded and shall be set-to-discharge and reach full flow conditions as required by the Design Code referred to in rule 12;(iii)weight loaded relief valves shall not be permitted;(iv)the relief valves shall be so designed that they cannot be inadvertently loaded beyond the set pressure;(v)the design of the valves shall be such that the breakage of any part will not obstruct free discharge of the liquid under pressure;(vi)safety relief valves on any vessel shall be set to start-to-discharge at a pressure not in excess of 110 per cent. of the design pressure of the vessel and shall have a total relieving capacity sufficient to prevent the maximum pressure in the vessel of more than 120 per cent. of the design pressure;[(vi-a)in case of cryogenic pressure vessels, the safety relief devices shall be set to discharge in such a manner that at least one such device shall be set at a pressure not higher than the maximum allowable working pressure and the other device may be set at a pressure not higher than 110% of the maximum allowable working pressure; ] [Inserted by G.S.R. 372(E), dated 17.5.2002 (w.e.f. 17.5.2002). ](vii)each safety relief valve shall be plainly and permanently marked with the pressure in kg/cm2 at which it is set to discharge, with the actual rate of discharge of the device in cubic metres per minute of the gas at 150C and at atmospheric pressure, and with the manufacturer's name. The rated discharge capacity of the device shall be determined at a pressure of 120 per cent. of the design pressure of the vessel;(viii)connections of safety relief devices shall be of sufficient size to provide the required rate of discharge through the safety relief valves;(ix)safety relief valves shall be so arranged that the possibility of tampering is minimised and if the pressure setting or adjustment is external, the safety relief valve shall be provided with suitable means of sealing adjustment;(x)each safety relief valve shall be provided with shut-off valve between it and the vessel. The arrangement of the shut-off valve installed between the safety relief valve and the vessel shall be so designed as to afford full required capacity flow through at least one of the safety relief valves;(xi)safety relief valves shall have direct communication with the vapour space of the vessel;(xii)for vessels other than those mounted on the vehicles of over 4500 litres water capacity, relief valves shall be fitted with extended vent pipes adequately supported and having outlets at least 2 metres above the top of the vessel and at least 3.5 metres above the ground level and the vent pipes shall be fitted with loose-fitting rain caps;(xiii)[ relief valves shall be tested by a competent person for correct operation not less than once in a year and a record of such test shall be maintained. The test certificate shall be issued in the prescribed pro forma .] [ Substituted by G.S.R. 264(E), dated 10.3.1993.]
