Installation of flame arrestors

Specifically, please follow the requirements of HG/T 20570.19-1995 \"Technical Specifications for the Design of Process System Engineering – Installation of Flame Arresters\".

Flame arrestors are piping fittings that are frequently used in chemical construction projects, and the quality of their design and selection has a direct impact on the safety of chemical production operations. The design and selection of flame arrestors is an important and complex task. Today, we will introduce the flame arrestors; based on **standards**, we will discuss the steps for selecting flame arrestors, the principles for their installation, precautions during installation, as well as maintenance and anti-freezing measures. Provisions for the installation of flame arresters: 1. Installation of vent flame arresters. Vent flame arresters are installed on the vent pipes of storage tanks (or tank cars) to prevent external flames from entering the tanks (or tank cars); they come in end-type and standard types. Flame arresters for pipe-end venting are of the explosion suppression type, while flame arresters for regular venting are divided into those that suppress explosion ignition and those that suppress detonation. Flame arresters and breather valves shall be installed on fixed-roof tanks for Class A B and Class B liquids (GB50160-2008) ； The installation of flame arresters in oil storage tanks for petroleum is carried out in accordance with the provisions of the \"Code for Design of Oil Depots\" (GBJ74-84) ； Flame arresters shall be installed on the direct venting pipes (including those equipped with breather valves) of storage tanks (and tank trucks) for chemical oils whose flash point is ≤43°C ； When the maximum operating temperature of the material in the storage tank (and tank truck) is greater than or equal to the flash point of that material, a flame arrester is installed on its direct venting pipeline (including the venting pipeline equipped with a breather valve). The maximum operating temperature of a flame arrester must take into account factors such as changes in ambient temperature, sunlight exposure, and uncontrolled heating elements ； A flame arrester needs to be installed on the vent manifold of the online combustible gas analysis equipment ； Flame arrestors must be installed on the exhaust pipe of internal combustion engines entering explosive hazard areas, as well as in other situations where flame arrestors are necessary. 2. Installation of pipeline flame arresters: Pipeline flame arresters are installed in closed piping systems to prevent flames at one end of the system from spreading to the other end. They come in two types: those that prevent deflagration and those that prevent detonation. Piping that transports explosive mixtures capable of deflagration or detonation (accident conditions should be taken into account) is equipped with pipe flame arresters at the inlet to the receiving equipment ； Pipe flame arresters are installed at the inlet of the receiving equipment, or at the location determined through testing to be the most effective for preventing explosions, for those pipes that transport gases capable of self-decomposing and exploding, thereby causing flame spread ； A flame arrester or other fire suppression device should be installed before the flue gas enters the flare tip ； Other situations where pipe flame arresters should be installed. 3. Steps for selecting a flame arrester: The choice between an exhaust flame arrester and a pipeline flame arrester depends on the application scenario. Determine whether to choose an explosion suppression type flame arrester or an explosion deflagration type flame arrester. The propagation speed of flame waves within a pipe depends on the type of medium, the location within the pipe, as well as the shape of the pipe between the flame arrester and the ignition source. Therefore, the diameter of the passages in the flame arrester elements used must be sufficient to prevent the spread of flames under such conditions; this requires determining whether to use a flame deflagration-type or a flame detonation-type arrester (usually determined through testing or based on experience). The appropriate flame arrester should be selected based on the MESG value of the medium under actual operating conditions, which represents the technical safety level of explosive gas mixtures. The fundamental principle for selecting a flame arrester is to ensure that the MESG value of the medium under operating conditions is greater than the MESG value specified in the flame arrester’s certification. For flame arresters selected for mixtures composed of various flammable gases, tests must be conducted to determine the MESG value of the gas mixture. If no test conditions are available, the flame arrester is determined based on the smallest MESG value among the various components of the mixture. 4. Determine the flame speed of the flame arrester based on that of the medium. The flame speed refers to the velocity at the inlet of the flame arrester; it is influenced by the medium and operating conditions (temperature, pressure, pipe diameter, pipe length and shape, installation location, etc.). If such data are not available, actual testing is required. The certification document for the flame arrester should specify the maximum flame speed that the product is capable of preventing; the principle behind determining the flame arrester is that the flame speed of the medium must be lower than the maximum flame speed indicated in the certification document. 5. Verification of the pressure drop of the flame arrester: After initially selecting a flame arrester following the steps above, it is necessary to check, based on the model of the selected flame arrester and the flow rate of the medium in the pipeline, whether the \"flow-rate–pressure drop curve\" provided in the product specifications for that flame arrester meets the pressure drop requirements specified in the process. Principles for selecting flame arrestors: 1. The flame arrestor housing must be able to withstand the pressure and allowable temperature of the medium, as well as resist corrosion by that medium. 2. The filler should have sufficient strength and must not react chemically with the medium. 3. The structural type of the flame arrester is selected primarily based on the chemical properties of the medium, as well as temperature and pressure. For media for which the operating pressure is not greater than 1.0 MPa and the temperature is below 80°C, a flame arrester made of galvanized carbon steel wire mesh is used. Special media such as acetylene pipelines, especially those under high pressure of over 0.15 MPa, require special flame arresters; higher manufacturing standards are applied when the operating pressure can reach 2.5 MPa. 4. The safety flame arrestment speed of the selected flame arrester should be greater than the flame propagation speed that may occur at the installation location. 5. The combustible gas delivery pipeline connected to the burner shall be equipped with a flame arrester when no other backflow prevention devices are available. The selection principle is as follows: to prevent flames from propagating at subsonic speeds, flame arresters designed to suppress deflagration should be used, and they should be installed as close as possible to the source of fire ； To prevent flames from propagating at sonic or supersonic speeds, blast-resistant flame arresters should be used, and they should also be installed at a distance away from the source of fire. The minimum required installation distance from the fire source for flame arrestors of the blast suppression type with different nominal diameters can be referred to in the table below. Table of minimum installation distances from the ignition source for blast-proof flame arresters. Nominal diameter DN of the pipe, Minimum installation distance L (m): 15 – 0.5; 20 – 1.0; 25 – 1.5; 32 – 2.0; 40 – 3.0; 50 – 4.0; 65 – 6.0; 80 – 8.0; 100 – 10.0; 125 – 10.0; 150 – 10.0; 200 – 10.0. 6. When using flame arresters in cold climates, it is necessary to use housings with heating elements, either partially or entirely, or to employ other methods for providing heat. 7. In special cases, a flame arrester equipped with interfaces such as a flushing pipe, pressure gauge, and drain port can be selected as needed. 8. For flame arresters installed at pipe ends, threaded connections are recommended when the nominal diameter of the pipe is less than DN50 ； Flange connection is recommended when the nominal diameter of the pipe is greater than DN50. 9. Flame arresters installed in pipelines should preferably be connected using flanges. 10. The flame arrester installed at the pipe end shall be equipped with a rainproof ventilation cover that can be automatically opened or fixed in place. Basic performance of flame arresters: 1. For flame arresters installed on pressurized pipelines or equipment, their housings must be able to withstand a pressure not less than that of the pipeline’s pressure test, without any leakage, cracks, or permanent deformation ； For the flame arresters on oil storage tanks, their housings must be able to withstand a pressure of not less than 0.9 MPa, without any leakage, cracks, or permanent deformation. 2. The flame arrester should be able to prevent explosions continuously for 13 times, with fire suppression achieved each time. 3. The flame arrester shall be able to withstand a burn test for 1 hour without backfire during this period. 4. The pressure loss of the fluid through the flame arrester shall not exceed the values specified in the table below. Allowable pressure loss table: Pressure of pipes and equipment/Pa: 295, 540, 800, 980, 1300, 1765, 2000. Pressure loss/Pa: 10, 11, 16, 20, 26, 36, 40. (5) The ventilation capacity of the flame arrester shall not be less than the values specified in the table below. Minimum ventilation rate of flame arresters: Nominal diameter (DN): 50, 80, 100, 150, 200, 250. Ventilation volume (m3/h): 150, 300, 500, 1000, 1800, 2800

It is more reasonable to install it at the pipe outlet; by choosing a deflagration-type flame arrester, the requirements can be met. If it is difficult to install at the pipe outlet and installation is required in the middle of the pipe or elsewhere, it is necessary to determine whether an explosion-proof type flame arrester is needed.

If a pipe flame arrester is used, can it be installed at any position on the vent pipe? It doesn’t have to be the end of the vent pipe