API RP 2028:2002 pdf download
API RP 2028:2002 pdf download.Flame Arresters in Piping Systems.
5.3 POTENTIAL EFFECTS OF INSTALLATION GEOMETRY
The geometry, size, and length of piping and piping systems are important to consider when selecting a flame arrester. It is possible that the level of turbulence generated by combinations of these factors may render a flame arrester incapable of quenching a flame front. Studies have noted that a correlation of the performance of a flame arrester and piping size is not always possible. It may be necessary to have tests performed for the particular size of flame arrester proposed for use. This is particularly relevant as piping diameter increases. For piping systems, it is advisable to install only flame arresters that have been designed and tested for detonations. In some situations, this is required for regulatory compliance.
Placing two or more flame arresters in series is not advisable. It has not been demonstrated that additional protection would be provided. If the flame front propagates through the first flame arrester, it can be expected to propagate through the second flame arrester.
Pipe diameter going into and out of a flame arrester should he kept constant. Proprietary testing indicates that changes in diameter can cause flame fronts to accelerate through an arrester.
5.4 FLAME ARRESTERS NOT USING METAL ELEMENTS
Some standards and testing laboratories have provided for flame arresters that have a design that does not use metal elements. Examples are hydraulic (water) type flame arresters in CEN-EN 12874 and in the FM Approval Guide. The performance of these flame arresters must be demonstrated by testing.
In certain situations, the USCG regulations allow the installation of “water seals” and quick closing valves for mechanical interruption of the flame path. These devices must meet USCG certification requirements. Demonstration of the suitability of these devices may require performance testing of the design. By contrast, emergency shutdown valves required by the USCG regulations for oil or hazardous material transfer lines and cargo vapor shutoff valves arc not intended to act as flame arresters and arc not required to function as quickly.
Flame arresters using devices and techniques other than metal elements are available and in use within the hydrocarbon industry. Some of these flame arresters have been in service for years without incident; however, without proof of performance of the design by testing, it should not be assumed that the flame arrester will he capable of performing properly. Examples of flame arresters with designs that do not use metal elements are discussed in the following sections.
5.4.1 Water Seals
Water (hydraulic) seals are often installed to prevent reverse gas flow. Their design is capable of interrupting a flame front. The gas mixture is bubbled through a reservoir of water (or sometimes another liquid). Passage of the flame front is prevented because each gas bubble is isolated by the liquid water. There is no standard design for water seals. Each installation presents a specific design problem involving the rate of gas flow, the depth of the seal, and the size and configuration of the vessel containing the water. If composition of the process gas is such that a flame arrester using a metal element could become frequently plugged, using a water seal may be appropriate. If a water seal is used as a flame arrester, some important design considerations are:
a. The water seal must be capable of withstanding the pressures developed. Water seals are typically used immediately adjacent to ignition sources such as flare stacks. In such a case, the water seal would most likely have to withstand only a deflagration. If a water seal is installed within a closed piping system. it should be designed to withstand a detonation.
b. The water must remain in the seal for it to function as a flame arrester. Automatic water level control and low level alarms are desirable. It is doubtful that it is possible to design for the water to be retained within the seal in the event of a detonation and its accompanying pressure.
c. In cold climates, the water seal must he protected against freezing which may require being heated or heat traced. In some instances, anti-freeze has been added to water, or lower freezing point materials (such as glycerine) have been used as the fluid for hydraulic seals.
