Piping systems
All piping systems must be seismically restrained, unless:
- the pipes have a diameter less than 50 mm, or
- the pipework is suspended by individual hangers less than 150 mm long from the top of the pipe to the supporting structure.
Piping systems that do not require restraint.
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Restraint requirements
Pipes should be restrained where:
- they connect to branch pipes
- they connect to equipment
- they use flexible couplings
- the free swaying of the pipe may damage other building elements.
Water supply piping shall be considered as at least category P5. Steam piping and gas piping shall be classified as category P1, P2 or P3.
All piping systems with pipes greater than 200 mm in diameter require specifically designed restraints.
For installations with a gas consumption exceeding 700 kW, the design should include a seismically operated shut-off valve. Note, however, that these devices are not recommended for sites with numerous small gas appliances because of the need to purge and recommission the system before the service can be restored.
See NZS 5601 Gas installations for more information. This standard cites NZS 4219:2009 for the seismic design requirements for gas systems.
Horizontal pipes
Each straight length of horizontal pipe shall have at least two transverse restraints and one longitudinal restraint. Continuous lengths of pipe with an offset along the length that is less than the corresponding maximum spacing given by NZS 4219:2009 may be considered as a single length of pipe for the purposes of longitudinal restraint.
Longitudinal restraint of a pipe length can be provided by transverse restraint of connected perpendicular pipes at elbows, bends or tees. This is as long as the connected pipes are of the same size or no more than one nominal size smaller. The transverse restraint of the connected pipe must be located within 600 mm of the elbow, bend or tee.
Where restraints are required, horizontal piping systems should use both transverse and longitudinal restraints.
Vertical pipes
Each length of vertical pipe shall have at least two transverse restraints in each orthogonal direction.
All restraints on vertical pipes shall be installed within two pipe diameters of a vertical support. Transverse restraints shall be installed perpendicular to the pipe axis, with the centre line of the restraint as close as possible to intersecting the pipe axis. Longitudinal restraints shall be aligned with the axis of the pipe.
The consequences of leakage from pipes and vessels should be assessed. Where gas or other hazardous substances may leak, consider installing seismically operated shut-off valves. Where electrical supply substations, main switchboards and emergency standby power plant are subject to flooding risk, consider locating them on or above ground floor level.
Vertical piping should use transverse restraints.
Underground pipes
Small underground pipes should be installed inside larger diameter pipes that pass through the foundations. Where pipes enter a building through the foundation, the design should account for relative movement between the pipe and building. The design should include a clearance of at least 25 mm between the pipe and the foundation.
Underground pipes that pass through soils of widely different density (that may experience differential movement in an earthquake) should have flexible connections immediately on either side of the soil boundary.