Deflagration flame arresters

This book makes reference to flame arresters, deflagration flame arresters, and detonation flame arresters. Flame arresters is the generic term for both deflagration and detonation flame arresters. Deflagration flame arresters are nsed when a flame only propagates at snbsonic velocity, whereas detonation arresters are nsed when a flame can propagate at all velocities inclnding snpersonic velocities. 

Kirby (1999) reports two snccessful applications of deflagration flame arresters. In one incident, a deflagration flame arrester was installed near the junction of a collection header from an ethylene oxide process nnit with a flare stack. Although this type of flame arrester was really inappro-... 

FIGURE 3-1. End-of-line deflagration flame arrester locations. 

FIGURE 3.2. In line deflagration flame arrester location. 

As mentioned earlier, flame arresters can be classified as either deflagration or detonation type. Deflagration flame arresters on tanks are designed to stop a flame from propagating into a tank from an unconfined atmo-... 

Since gauzes have limited effectiveness in quenching high-velocity flames, they are only used as end-of-line deflagration flame arresters. 

The flame propagation direction affects the type of flame arrester selected. An end-of-line or in-line deflagration flame arrester used for the protection of an individual tank may be of a unidirectional design because the flame will only propagate from the atmosphere towards the tank interior. A bidirectional flame arrester design, however, is needed for an in-line application in a vapor recovery (vent manifold) system because the vapors must be able to flow from the tank interior into the manifold, or from the manifold into the tank interior. Consequently, flame may propagate in either direction. 

It has been shown by Palmer at the Fire Research Station (FRS) that a crucial variable governing the performance of a flame arrester is the flame speed incident on the arrester. The critical flame speed (minimum speed at which the flame can pass through the arrester) is discussed by Phillips and Pritchard (1986), drawing largely on the FRS work on propane-air mixtures at atmospheric pressure. A simple model based on heat removal from the flame yields the following relation for deflagration flame arresters ... 

Location and piping configuration must consider the possibility of DDT. For example, for end-of-line and in-line deflagration flame arresters, the location must be identical to the test piping configuration or a DDT may occur. 

The USCG classifies deflagration flame arresters in two categories as follows ... 

Type II Flame arresters acceptable for in-line applications. Type II arresters shall be specifically tested widi the inclnsion of all pipes, tees, bends, cowls, weather hoods, etc., which may be fitted between die arrester and the atmosphere. Owing to the prohibitive cost of testing deflagration flame arresters for each particular installation, the Type II (in-line) category is generally not enconntered. 

Appendix B to Part 154 is a standard specification for tank vent (end-of-line) deflagration flame arresters. It does contain test procedures for these types of flame arresters. An end-of-line flame arrester mnst be able to arrest three atmospheric deflagrations as well as to withstand two honrs of continnons bnrning withont flashback. 

The deflagration flame arrester must he subjected to a series of at least 10 explosion (deflagration) tests in a rig with a pipe at least 5 feet (1.5 meters) long with various mixtures of propane in air and different test conditions to test the entire spectrum of possible deflagrations. Also, a series of 3 flashback tests, using a mixture of 4.2 volume percent of propane in air, must be conducted. 

A UL Type 1 deflagration flame arrester must undergo an endurance burn test while a UL Type 11 deflagration flame arrester must be subjected to a continuous flame test. The test conditions for the endurance burn test and the continuous flame test for a deflagration flame arrester are the same as for a detonation flame arrester. 

The deflagration flame arrester must be hydrostatically tested to 250 psig for one minute without rupture or permanent damage. 

ASTM published a standard specification F 1273 for tank vent flame arresters (end-of-line deflagration flame arresters) in 1991 (reapproved in... 

The test gas may be propane, hexane, or gasoline vapors. Eor end-of-line deflagration flame arresters, tests shall be performed twice each for three ignition sources, for a total of six tests. Eor in-line detonation flame arresters three detonation tests are required. 

Comparison of Test Parameters of Various Standards for End-of-Line and In-Line Deflagration Flame Arresters (Adapted from Lapp and Werneburg 1999)... 

Example 2—Sizing of an End-of-Line Deflagration Flame Arrester... 

Size an end-of-line deflagration flame arrester for the normal vent nozzle of a 126,000 gallon API-type atmospheric pressure storage tank for the following conditions ... 

Figure 3-1 (page 19) shows where an end-of-line deflagration flame arrester should he located. It preferably should be installed on a nozzle that is near the outer edge of the tank/vessel roof for ease of accessibility for maintenance and removal. 

The length of installed pipe between the ignition source and the flame arrester is critical to the proper performance of end-of-line and in-line deflagration flame arresters. Line lengths greater than those used in the test allow higher flame speeds and pressure to... 

FM will condnct tests at their own test facilities nsnally only for deflagration flame arresters, following their Class 6061 test procednre. They will also observe and approve tests done at a hame arrester mannfactnrer s own test facility for both dehagration and detonation type hame arresters. For detonation hame arresters FM will accept tests that are done in accor-... 

Deflagration Flame Arrester A flame arrester used to prevent the transmission of a deflagration. 

End-of-Line Flame Arrester A deflagration flame arrester that is installed on atmospheric pressnre tank vent nozzles, having only one pipe connection. It is also called a tank vent deflagration flame arrester. 

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