Flame arresters function by interrupting the combustion wave as it progresses through the flame arrester. Typical flame arresters accomplish this by quenching the flame front using a heat sink with high surface-to-volume ratio and narrow passageways, such as a wire screen, woven wire gauze, metal honeycomb, parallel metal plates, or a porous metal plate. The metal absorbs heat from the flame and quenches it, thus preventing it from the flame and quenches it, thus preventing it from passing through the flame arrester. Various types of flame arresters and potential problems associated with their use in piping systems are discussed in the following sections.
Pressure Concerns and Maintenance
High pressures developed in piping, especially during a detonation, may damage the element in a flame arrester or even rupture the housing. Flame arresters should be included in periodic maintenance checks. After interrupting a flame front, flame arrester elements should always be inspected for possible damage. A flame arrester should be designed and installed in piping so that maintenance can be done without the need to completely remove the flame arrester. Some high risk systems use parallel flame arresters to enable one at a time to be taken out of service for maintenance. For these systems, the effects of piping configuration should be evaluated to determine if there has been an influence on flame speed.
Typical flame arresters with elements will cause a pressure drop and high surface area of the elements, condensation can readily occur. Gases that have a high carbon content or that can polymerize can plug the elements. Or, if the gas mixture contains sulphur or hydrogen sulfide, deposition of sulphur compounds may occur. It may be necessary to heat or heat trace the flame arrester to reduce the potential for condensation, deposition and plugging of the element. Some facilities install pressure gauges upstream and downstream of a flame arrester to monitor changes in pressure drop and facilitate determining if elements have become plugged. Where condensation is a concern, it may be appropriate to install normally closed, valved drains on the housing of the flame arrester to enable draining of accumulated condensed liquids.
The manufacture should be consulted if it is necessary to heat or heat trace a flame arrester for the service conditions it will experience. The test results for the flame arrester should be reviewed to ensure that the specific heating conditions envisioned for operation of the flame arrester will not cause it to be incapable of quenching a flame front. This review should take place before the changed conditions are implemented. For installations under Coast Guard jurisdiction the vapor control system must be separated or insulated from external heat sources to limit vapor control system piping surface temperature to not more than 350*F during normal operation.
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