Test procedures for flame screens and flame arresters located at openings to the atmosphere;-
(1) The test rig shall consist of an apparatus producing an explosive mixture, a small tank with a diaphragm, a flanged prototype of the device a plastic foil bag and an ignition source in three positions, other test rigs may be used, provided that the test are deemed to be equivalent by the Director General.
(2) A flash back test shall be carried out as follows;
(a)The tank and the plastic foil bag shall be filled with the most easily ignitable propane/air mixture.
- The plastic foils bag enveloping the prototype device. The dimensions of the plastic foil bag are dependent in those of the device but for the devices normally used on tankers the foil bag shall be a circumference of 2 meters and a length of 2.5 meters and a wall thickness of 0.05 millimetres.
- These ignition sources shall be installed in the bag, one close to the device, one as far away as possible therefrom, and the third at the midpoint between those two.
- These three sources shall be ignited in succession during the three tests.
(b)If a flash-back occurs the tank diaphragm will burst and this will be audible and visible to the operator by the emission of a flame . Flame, heat and pressure sensors may be installed as an alternative methods of detecting a flash back.
(3) An endurance burning test shall be carried our as follows, in addition to the flash back test for flame arresters at outlets where flows of explosive mixtures are foreseen :-
- The flame arrester shall be so isolated that the mixture emission is vertical . In this position the mixture shall be ignited . Thermocouples shall be installed not he flame arresting element.
- Flash back shall not occur during this test. Endurance burning shall be achieved by using the most easily ignited gasoline vapour/air mixture with the aid of a pilot flame at the outlet.
- When the highest obtainable temperature of the exposed parts of the element is reached, by varying the proportions of the flammable mixture and the flow rate, the temperature shall be maintained for 10 minutes after which the flow all be stopped and the condition of the device observed .
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Test procedures for flame arrester located in line.-
- A flame arrester shall be installed at the end of pipe of suitable length and of the same diameter as the flange of the flame arrester. A plastic foil bag shall be secured to the exposed flange. The dimensions of the plastic foil bag shall be at least 4 meters circumstances, 4 meters length and material wall thickness of 0.05 millimetres. The pipe shall be filled with the most easily ignitable mixture of propane and air, which shall then be ignited. The velocity of the flame near the flame arrester shall be measure and shall have a value or that for the detonation velocity.
- A typical test rig should be used , other test rigs may be used provided the tests are equivalent.
- Three detonation test shall be conducted.
- No flash back shall occur through the device and no part or the flame arrest shall be damaged or show permanent deformation.