Firewater Distribution System
Publish Time: 2022-02-11 Origin: Site
When installing a firewater system, consideration should be given to the materials of construction and to the overall layout.
Materials of construction
Steel pipe should be used aboveground for firewater lines. Underground piping systems can be constructed of steel, cement-lined steel, or high-density polyethylene (HDPE). Concrete is sometimes used but is seldom economical except in large diameters. HDPE does not corrode, resists accumulation of scale, and is very ductile and lightweight. Because it fails when heated, HDPE pipe can only be used in buried installations. Burial also provides protection from mechanical damage.
Layout
The topic of equipment and piping layout is discussed in Chapter 11. Issues to do with the layout of a firewater system are described below.
In climates where freezing does not occur, above-ground installation of steel firewater distribution lines has the advantages of low first cost and ease of inspection and repair. In cold climates, distribution lines should be buried below the frost line.
When possible, firewater mains should be arranged in loops around process facility and tank farms. Shutoff valves should be located to allow isolation of system segments for maintenance while still providing water for all facilities. The minimum water rate with a section of pipe out of service should be at least 60% of the design rate at design pressure for that area. A firewater header should be provided in each process facility area to serve hose stations.
Deluge valves
High-performance butterfly valves and gate valves are recommended for block valves in firewater distribution systems. They should provide reasonably tight shutoff and use sealing materials that do not swell or deteriorate with age. Any valve that may be buried, and that may therefore not receive frequent maintenance should be very durable.
The operation of the deluge valves will be initiated automatically by the fusible plug fire detection systems, through direct action and through instrumentation. Zone valves should be able to be opened manually.
Hydrants
Hydrants should be located close to the buildings and structures that they are to protect, while being far enough away that operators and emergency responders can use them safely. Unless booster pumps are used, hydrants should not generally be more than 150 meters from one another.