From 2013 nfpa 13d
see 5.2.2.2
5.2.2.2* Pipe used in sprinkler systems other than those addressed in 5.2.2.3 or 5.2.2.4 shall be designed to withstand a working pressure of not less than 175 psi (12.1 bar).
AHJ FAQ Can the authority having jurisdiction allow the installation of pipe/tube rated for less than 175 psi (12.1 bar) in a stand-alone system?
ANSWER: The NFPA 13D requirements for allowable pipe/tube have been significantly changed for the 2013 edition. In paragraphs 5.2.1, 5.2.2.3, 5.2.2.4, 5.2.2.4.1, 5.2.5.3, 5.2.5.4, and 5.2.5.4.1 – where supply pressures are limited – pipe/tube, fittings, and sprinklers are permitted to be rated for lower pressures than those typically required for fire protection systems. If the authority having jurisdiction is not allowing these new provisions, then the jurisdiction may not have adopted the 2013 edition. The standard was changed for this edition to recognize that nonmetallic pipe with ratings of less than 175 psi (12.1 bar) have traditionally been used on domestic plumbing systems where other codes restrict the maximum pressures in the system. If there is no fire department connection, and the domestic and fire systems share the same water supply, then the maximum pressures in the fire protection system will be the same as that for the domestic system. Domestic plumbing fixtures and system components are typically limited to 80 psi (5.5 bar).
A.5.2.2.2 In most installations, pressure increases due to temperature fluctuations or pressure surges do not cause the system pressure to exceed the pressure rating of the pipe. In situations where the system pressure has the potential to exceed the pipe pressure rating, installation of a relief valve should be considered. Where a relief valve is installed, consideration should be given to making sure that an adequate drain is available to handle the anticipated discharge.
5.2.2.3 Nonmetallic pipe used in multipurpose piping systems and passive purge systems not equipped with a fire department connection shall be designed to withstand a working pressure of not less than 130 psi (8.9 bar) at 120°F (49°C).
AHJ FAQ Is it the intent of 5.2.2.3 to allow the installation of a pressure-reducing valve on a stand-alone fire sprinkler system so that lower pressure–rated pipe/tube can be used?
ANSWER: No. It is the intent of this section to allow lower pressure–rated pipe/tube for a stand-alone fire sprinkler system when it is supplied by the same service as the domestic and when the supply pressures do not exceed 80 psi (5.5 bar) (or there is a pressure-reducing valve installed in the common supply for the purposes of limiting domestic system pressures). The introduction of a pressure-reducing valve in the fire sprinkler system piping solely for the purposes of using a lower pressure–rated sprinkler pipe/tube introduces an unnecessary failure point and complicates the maintenance requirements.
Paragraph 5.2.2.3 provides reduced system working pressure criteria and temperature criteria for piping used in multipurpose and passive purge systems. The justification for allowing the pressure to be lower for the pipe material in multipurpose and passive purge systems is that higher pressures do not often get trapped in the system. If a pressure surge from the water supply traps a high pressure in the piping system, the high pressure will be relieved when a person uses a plumbing fixture such as a sink, shower, or toilet.
The pressure criterion in 5.2.2.3 was developed from the maximum pressure requirement of 80 psi (5.5 bar) for plumbing fixtures, as provided by the International Plumbing Code and the Uniform Plumbing Code. The Technical Committee on Residential Sprinkler Systems believes that a safety factor should be included over and beyond 80 psi (5.5 bar) because of the associated life safety objectives. The technical committee chose a pressure rating of 130 psi (8.9 bar) at 120°F (49°C) for piping used in multipurpose systems where specific conditions exist. (See the commentary following 5.2.5.) The temperature criterion of 120°F (49°C) is consistent with the minimum requirements referenced in UL 1821, Standard for Safety-Thermoplastic Sprinkler Pipe and Fittings for Fire Protection Service.
A study conducted in 1977 by the National Bureau of Standards, which is now the National Institute of Standards and Technology, measured the attic temperatures of a house in Houston, Texas, to investigate potential temperature profiles for warm-weather areas. The maximum temperature was 115°F (46°C) at the top of the peak and 84°F (29°C) at the attic floor on the insulation’s underside. This temperature criterion also prompted new requirements concerning the installation of plastic pipe in attics. (See Section 7.7.)
Note that the pressure requirement is tied directly to a temperature. This is important when dealing with plastic materials. Any plastic material loses its ability to hold pressure as the material heats up. Therefore, just listing a pressure rating is insufficient for dealing with piping materials made of plastic. The pressure requirement needs to be tied to a temperature.
5.2.2.4 Nonmetallic pipe used in wet pipe sprinkler systems not equipped with a fire department connection and provided with a pressure-reducing valve set no higher than 80 psi (5.5 bar) shall be designed to withstand a working pressure of not less than 130 psi (8.9 bar) at 120°F (49°C) and 100 psi (6.9 bar) at 180°F (82.2°C).
This text, which permits pipe to have a minimum pressure rating of 130 psi (8.9 bar) under the specified conditions, was added in the 2013 edition. The requirement allows 130 psi (8.9 bar) rated pipe to be installed in stand-alone sprinkler systems as well as with the multipurpose and passive purge systems referenced in 5.2.2.3. The philosophy associated with this allowance is described in the commentary for 5.2.2.3.
A secondary pressure/temperature rating of 100 psi (6.9 bar) at 180ºF (82.2ºC) is intended to provide a level of assurance that the piping system will perform as intended when exposed to temperatures greater than 120ºF (49ºC), which is possible in attics located in certain geographic regions. The secondary pressure rating of 100 psi (6.9 bar) at 180ºF (82.2ºC) is consistent with the existing pressure rating requirements in the plumbing product standards.
5.2.2.4.1 If the maximum static pressure from the water supply is less than or equal to 80 psi (5.5 bar), pipe designed to withstand a working pressure of not less than 130 psi (8.9 bar) at 120°F (49°C) and 100 psi (6.9 bar) at 180°F (82.2°C) shall be permitted to be used without a pressure-reducing valve.
This text, which permits pipe to have a minimum pressure rating of 130 psi (8.9 bar) when the maximum static pressure from the water supply is not greater than 80 psi (5.5 bar), was added in the 2013 edition. The requirement allows pipe rated at 130 psi (8.9 bar) to be installed in all types of systems, including stand-alone sprinkler systems, when the supply pressure will not exceed 80 psi (5.5 bar). This applies to municipal water supplies and could also apply to water supplied by a tank and pump when the static pressure does not exceed 80 psi (5.5 bar). The philosophy associated with this allowance is described in the commentary provided for 5.2.2.3.
A secondary pressure/temperature rating of 100 psi (6.9 bar) at 180ºF (82.2ºC) is intended to provide a level of assurance that the piping system will perform as intended when exposed to temperatures greater than 120ºF (49ºC), which is possible in attics located in certain geographic regions. The secondary pressure rating of 100 psi (6.9 bar) at 180ºF (82.2ºC) is consistent with the existing pressure rating requirements in the plumbing products standards.
5.2.2.4.2 If a pressure-reducing valve is used to comply with 5.2.2.4, an automatic means of pressure relief shall be installed on the sprinkler system side of the pressure-reducing valve.
