The Static and Mobile Pressure Vessels 
(Unfired) Rules, 1981

12. Design Code

1. vessels shall be designed, constructed and tested in accordance with the Indian standard 2825, as amended from time to time or such other standard or code approved by the chief controller.
   

2. A test and inspection certificate issued by the manufacturer of the vessel duly countersigned by an inspector that the vessel meets with the requirements of the standard or code referred to in sub-rule (1) shall be furnished to the chief controller.

13. Design Pressure

The design pressure of vessel shall not be less than: -

1. The vapour pressure of the gas in the vessel at 55d c if the vessel is meant for the storage of liquefiable gases : Provided that if the vessel is insulated the vapour pressure of the gas in the vessel shall correspond to the maximum temperature that is likely to be attained by the gas in the vessel;
   

2. The developed pressure of the gas in the vessel at 55dc if the vessel is meant for the storage of a permanent gas.

14. Design Of Vessels for Gases At Low Temperature

1. Refrigerated vessels: -

1. Vessels used for storage of refrigerated gases shall be designed in accordance with low temperature requirements under the design code referred to in sub-rule (1) of rule 12.

2. The capacity of the refrigeration system shall be adequate to maintain the gas in the vessel at a temperature so that its vapour pressure does not exceed the design pressure of the vessel and shall also remain below the pressure setting of the relief value on the vessel.

2.  Insulated vessels :-

1. The shell of the vessel and its manhole nozzle shall be insulated with a material approved by the chief controller. The entire insulation shall be covered with a metal jacket of a thickness not less than 3 mm. nominal and flashed all openings so as to be weather tight.

2. The insulation shall be of sufficient thickness so that the thermal conductance at 15dc (expressed in calories or sq. cm. per hour per limit prescribed by the chief controller.                 

15.  Filling Capacity And Filling Pressure.

1. The maximum quantity of liquefiable gas filled into any vessel shall be limited to the filling density of the gas and shall be such that the vessel shall not be liquid-full due to expansion of the contents with rise of the temperature to 55dc. If vessel is uninstalled or to the highest temperature, which the contents are likely to reach in service if, the vessel is refrigerated or insulated. The requirement shall be applicable irrespective of the ambient temperature of the product at the time of filling.
   

2. No vessel shall be filled with any permanent gas in excess of its design pressure

16. Markings On Pressure Vessels

Every vessel shall have a metal plate permanently fixed to it showing the following particulars which shall be visible from the ground level namely :-

1.  Manufacturer’s name and identification marks;

2.  The standard or code to which the vessel is constructed

3. Official stamp of the inspector;

4.  Design pressure in kg/cm2

5. Date of initial hydrostatic test and the subsequent test;

6.  Hydrostatic test pressure in kg/cm2;

7. Water capacity in litres;

8. Gas capacity, if filled with liquefiable gas ; and

9. Name or chemical symbol of the gas for which the vessel is to be used.

17. Painting Of Vessels.

Vessels shall be adequately painted externally to prevent corrosion and shall have a reflecting surface.

18. Fittings

1. General :-

   1. Fittings .- Each vessels 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 temperature 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.

2. Vessel connection. – Connections of vessels shall be designed and attached to the vessel to the vessel in accordance with the design code referred to in rule 12.

2.  Pressure relief :- 

1. Every shall be provided with two or more pressure relieving devices in accordance with the provisions of the design code referred to in rule 12;
   

2. 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;
   

3. Weight loaded relief valves shall not be permitted;
   

4. The relief valves be so designed that they cannot be inadvertently loaded beyond the set pressure;
   

5. The design of the valves shall be such that the breakage of any part will not obstruct free discharge of the liquid under pressure;
   

6. Safety relief valves on any vessel shall be set to start-to-discharge at a pressure not in excess of 110 percent 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 percent of the design pressure;
   

7. 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 meters per minute of the gas at 15dc 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 percent of the design pressure of the vessel;
   

8. Connections of safety relief devices shall be of sufficient size to provide the required rate of discharge through the safety relief valves;
   

9. Safety relief valves shall be so arranged that the possibility of tampering is minimized and if the pressure setting or adjustment is external the safety relief valve shall be provided with suitable means of sealing adjustment;
   

10. Each safety valve shall be provided with shut-off valve between it and the vessel. The arrangement of the shut-off valve installed between the 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;
    

11. Safety relief valves shall have direct communications with the vapour space of the vessel;
    

12. 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 meters above the top of the vessel and at least 3.5 meters above the ground level and the vent pipes shall be fitted with loose-fitting rain caps;
    

13. 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 proforma.

3. Shut-off and emergency shut-off valves :-

1. 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;
   

2.  all liquid and vapour connections on vessels except those for relief valves and drainage connections of small diameter shall have an emergency operated valve or a remotely controlled flow valve. the emergency shut-off valve referred to in clause  (i) , unless the emergency shut-off valve as a remotely controlled valve which can be operated from a safe area and shall be of a type which shall not fail :
   

3. 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 be experienced. excessflow valve shall a rated flow capacity sufficiently above normal flow requirements to prevent valve chatter.

4. Liquid level gauging device :-

1. A vessel used for liquefiable gas or dissolved gas shall be equipped with a liquid level gaugine device to afford ready determination of the amount of liquid in the vessel at any time;
   

2. All liquid level indicators shall be suitable for operation at the design pressure of the vessel;
   

3. 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;
   

4. 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.

19.  Periodic Testing Of Pressure Vessel In Service

1. All vessels shall be hydraulically tested by a competent person at a pressure marked on the vessel at intervals of not more than five years after the date of first test provided that in the case of vessels containing corrosive or toxic gases the periodic test shall be done at an interval of two years.

In case of vessels which are so designed constructed or supported that they cannot be safely filled with water or liquids for hydraulic testing or which are used in services where traces of water cannot be tolerated Chief Controller may permit pneumatic testing along with non-destructive tests instead of hydraulic testing as per procedure laid down in vessels fabrication code; after satisfying himself about the adequacy of the safety precautions undertaken.

2. The competent person carrying out the test as required under sub-rule (1) shall issue a certificate of test in prescribed proforma.

20. Precautions to be observed in carrying out hydraulic test.

in carrying out the hydraulic test referred to in rule 19 the following precautions shall be observed namely :-

1. Before the test is carried out each pressure vessel shall be thoroughly cleaned and examined externally and as far as practicable internally also for surface defect corrosion and foreign matter. During the process of cleaning and removal of sludge if any all due precautions shall be taken against fire or explosion if such sludge is of pyropheric nature or contains spontaneously combustible chemicals;
   

2. As soon as the test is completed the vessel shall be thoroughly dried internally and shall be clearly stamped with the marks and figures indicating the person by whom test has been carried out and the date of test and a record shall be kept of all such tests;
   

3. Any vessel, which fails to pass the hydraulic test, or which for any other reason is found to be unsafe for use shall be destroyed or rendered unsuitable under intimation to the chief controller