Flame arresters installed in piping systems should always be tested to verify that the design would quench a flame front propagating within a closed piping system. if the conditions are not satisfied further testing is warranted before installing the particular flame arrester.
Deflagration and Detonation testing
Deflagration, Detonation and explosion tests for flame arresters are performed using propane. Some flame arresters pass detonation test but fails in deflagration test. If the process gas increases the rate of combustion, additional tests using the specific process gas are warranted.
Flame Retention Testing
Continuous burn and endurance test are done using gasoline vapor or n hexane to determine how the flame arrester will perform during flame retention. Arresters tested using these will go well with most common paraffin and aromatic hydrocarbon. If the gas to be transported in the piping support accelerated rate combustion reactions such as acetylene, hydrogen or olefinic hydrocarbons, additional tests using the specific process gas are warranted.
Significance of MESG
The Maximum Experimental Safe Gap (MESG) concept was developed for designing electrical equipment for use in hazardous atmospheres. MESG is defined as the maximum clearance between two parallel metal surfaces that has been found, under specified test conditions, to prevent an explosion in a test chamber from being propagated to a secondary chamber containing the same gas or vapour at the same concentration. If the MESG of the gas is less than 0.90mm, additional tests using the specific process gas are warranted. A list of hydrocarbon and chemical gases or vapors which have MESG less than 0.90mm is contained in appendix B. If the process gas contains some portion of a gas or vapor which has a MESG less than 0.90 mm ( like hydrogen ), it is advisable not to rely totally upon the MESG value as a determining factor as to the nature of a potential combustion wave within a piping system. The molecular structure of the gas or vapor can be an important factor, particularly if double or triple bonds exist. Turbulence generation can cause a combustion reaction to accelerate such that flame arrester design is challenged beyond its capability to interrupt a flame front and or a detonation occurs.
Only flame arresters, the design of which has been tested, should be installed and maintained in the exact mechanical form in which they were tested. This includes proper maintenance of the flame arrester element, housing and gaskets. Unless the flame arrester is installed at the end of a pipe open to atmosphere, flame arresters used in piping systems should be capable of withstanding and interrupting a propagating detonating flame front.
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