UL 525:2008 pdf download – Flame Arresters.
10.1 The flow capacity of a flame arrester shall be determined at the operating pressures (both positive and negative) specified for the arrester by the manufacturer.
10.2 When a flame arrester is intended for use as an emergency vent, the flow capacity shall be determined at the pressure at which the valve reaches the full open position. If the pressure at full open position is greater than 2.5 psi, and the start to open pressure is less than 2.5 psi, the flow capacity shall also be determined at 2.5 psi.
11 Endurance Burn and Continuous Flame Tests
11.1 General
11.1.1 A Type I flame arrester shall be subjected to the Endurance Burn Test described in 11.2.1 — 11.2.9 and there shall be no passage of flame, both during the test and when the gas valve is closed at the conclusion of the test.
11.1.2 A Type II flame arrester shall be subjected to the Continuous Flame Test specified in 11.3.1 —
11.3.5 and marked in accordance with 24.1(e).
11.1.3 When a flame arrester is to be provided with cowls, weatherhoods, deflectors, and similar components, it is to be tested in each configuration in which it is to be provided.
11.2 Endurance burn test
11.2.1 The flammable mixture for the test is to be a 2.5 percent mixture by volume of n-hexane in air or a 1.9 percent mixture by volume of gasoline vapor in air.
11.2.2 The flame arrester is to be mounted on a tank so that the mixture emission is vertically upwards, or mounted in the position for which it is designed and which will result in the most severe heating of the arrester. When the arrester is provided with a vent valve, the valve is to be open for the test.
11.2.3 The tank mentioned in 11 .2.2 is to be provided with a burst diaphragm at one end and an inlet for the mixture at the other end.
11.2.4 The burst diaphragm is to be made of 0.0015- to 0.010-inch (0.038- to 0.2540-mm) thick cellulose acetate film, polyester film, polyethylene terephthalate film, or the equivalent.
11.2.5 The mixture is to be introduced into the tank and is to be ignited by a pilot flame or spark plug at the outlet of the flame arrester. The mixture may be reignited as necessary during the test.
11.2.6 Temperatures are to be measured on the surface of the protected side of the arrester element at its center, at its edge, and halfway between the center and the edge.
11.3.5 The flow of the mixture into the inlet is to be stopped for 15 seconds every 10 minutes after initiation of the test. There shall be no flashback, as determined visually, at any time during the test, including the 15 seconds following the final 10-minute burning interval.
12.2 Explosion tests
12.2.1 The flame arrester is to be subjected to explosion tests as described in 12.2.2 — 12.2.11 using propane-air mixtures at atmospheric pressure over the range specified in 12.2.2.
12.2.2 A series of at least 10 tests are to be conducted over the flammable range, which involves testing at 3.0, 3.5, 4.0, 4.2, 4.5, 5.0, 5.5, 6.0, 6.5 and 7.0 percent propane by volume in air.
12.2.3 The flame arrester is to be installed in a pipeline of the diameter for which it is designed. The pipe connected to the inlet (tank end) is to be at least 5 feet (1 .5 m) long. The outlet of the flame arrester, based upon the intended use, is to be connected to:
a) A vent line of the maximum length of pipe intended, if marked on the arrester in accordance with 24.1(a);
b) A 5-foot length of pipe, when it is intended to open directly to the atmosphere; or
c) The intended vent valve, with the valve open for the test.
12.2.4 The test installation, including the axes of the inlet and outlet pipes, is to be inclined from the horizontal with the inlet end higher than the outlet end unless the flame arrester is specifically designed for vertical use only, in which case the flame arrester is to be tested in that position. The angle of inclination of the test installation shall be such that the bottom edge of the opening of the tank end of the inlet pipe is above the top edge of the opening of the tank end of the flame arrester.
12.2.5 The diameter of each pipe’s open end is to be reduced by a donut-shaped ring loosely inserted into the pipe. The ring is to have a hole the size of the inlet or outlet line for the flammable mixture.