Section 18 in The Static And Mobile Pressure Vessels (Unfired) Rules, 1981
18. Fittings .-(1) General .-(i) Fittings .-Each vessel shall be provided with each of the following fittings all of which should be suitable for use with the gas at pressures not less than the design pressure of the vessel to which they are fitted and for temperatures appropriate to the characteristics of the gas and operating conditions, namely,-
-Pressure relief valve connected to the vapour space;-Drains;-Contents gauge or maximum level indicator;-Pressure gauge connected to the vapour space;-Means of measuring the temperature of the contents of the vessel.(ii)[ Vessel connections .-Connections of vessels shall be designed and attached to the vessel in accordance with the Design Code specified under rule 12. All static vessels for storage of corrosive, flammable or toxic gas in liquefied state shall not have more than one pipe connection at the bottom for inlet or outlet, apart from the drainage. The drainage pipe, if provided, shall be extended beyond the shadow of the vessel and provided with two shut-off valves. No drainage pipe shall be provided direct from spherical vessel. The bottom inlet or outlet pipe for spherical vessel shall be integrally welded to the vessel and extended up to three metres beyond the shadow of the vessel, at the end of which, combination of manual and remote operated valve shall be provided.](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.](3)Shut-off and emergency shut-off valves .-(i) all liquid and vapour connections on vessels, except those for relief valves, plugged openings, and those where the connection is not greater than 1.4 mm diameter opening shall have shut-off valves located as close to the vessel as practicable;(ii)all liquid and vapour connections on vessels, except those for relief valves, and drainage connections of small diameter, shall have an emergency shut-off valve, such as, an excess flow valve, an automatically operated valve or a remotely controlled valve. The emergency shut-off valve shall be in addition to the shut-off valve referred to in clause (i), unless the emergency shut-off valve is a remotely controlled valve which can be operated from a safe area and shall be of a type which shall not fail:[Provided that the emergency shut-off valve is not required in cases where the connection to a vessel is not greater than three millimetre in diameter for liquid and eight millimetre in diameter for vapour, or for vessels meant for storage of non-corrosive, non-flammable or non-toxic gas;] [ Substituted by G.S.R. 141(E), dated 14.2.2000 (w.e.f. 18.2.2000).](iii)where the emergency shut-off valve is of the excess flow type, its closing rate of flow shall be below the rate which is likely to result from a fracture of the line it is protecting, calculated under the most adverse weather conditions likely to be experienced. Excess-flow valves shall have a rated flow capacity sufficiently above normal flow requirements to prevent valve chatter.(4)Liquid level gauging device .-(i) a vessel used for liquefiable gas or dissolved gas shall be equipped with a liquid level gauging device to afford ready determination of the amount of liquid in the vessel at any time;(ii)all liquid level indicators shall be suitable for operation at the design pressure of the vessel;(iii)every vessel shall, in addition, be equipped with a fixed maximum level indicating device depending upon the liquefiable gas or dissolved gas filled in the vessel;(iv)gauging devices that require bleeding of the contents of the vessel, such as, a rotary tube, fixed tube and slip tube shall be designed in such a manner that the same cannot be completely withdrawn in normal gauging operations.(5)Pressure gauge .-Every vessel shall be provided with at least one pressure gauge.
