A hydrostatic test is a test of a previously isolated network and its accessories, which consists of subjecting the network to increased internal pressure for a set period of time in order to check its integrity and identify leaks.
Why are hydrostatic tests required by NFPA standards?
A fire protection system or part of a fire protection system is exposed to operating pressure during its service life. Even if it is not exposed (deluge system), it will be in the event of a fire.
The hydrostatic test is one of the key tests for ensuring that the system is correctly installed and sealed.
The main errors observed before hydrostatic testing are as follows:
Poorly placed couplings or seals
Insufficient head tightening
Defect on a welded connection
Example of a leak on a network exposed to pressure Leaks on underground pipes exposed to pressure
When to test?
The network must be tested when the installation is complete and before flushing operations.
A hydrostatic test must be carried out per system, i.e. per main control station.
The most difficult test to plan is for the underground network, as installation is usually planned long before the overhead networks are laid.
It is essential to carry out hydrostatic tests before flushing operations. Any leakage could compromise the behavior of the pipes during flushing operations.
What is required by NFPA standards and APSAD regulations?
All pipes must be hydrostatically tested at a gauge pressure of 13.8 bar (200 psi) or 3.4 bar (50 psi) above the system working pressure. Whichever is higher, they must maintain this gauge pressure at 0.35 bar (±5 psi) for two hours.
APSAD rule R1 sets this value at 15 bar or 1.5 times the working pressure.
For buried networks, the best engineering practice is to backfill the trench between the joints before testing, to avoid any movement of the pipe.
What are the best engineering practices?
Filling a large, long-installed above-ground network with pressurized water without leak testing is risky.
To prevent water damage, the best engineering practice is to perform pneumatic tests before hydraulic tests.
A successful pneumatic test is one carried out with an air pressure of 2.7 bar (40 psi) and a measurement drop not exceeding 11/2 psi (0.1 bar) in 24 hours.
APSAD rule R1 sets slightly different values (2.5 bar) and only requires this test to be carried out over a 2-hour period, without any drop in measurement.
During pneumatic testing, leaks cannot be observed visually, but can be heard by an often high-pitched whistling sound, the intensity of which depends on the size of the leak. It is therefore essential that the site is not in production or operation during this operation, and that the entire network is inspected (above the ceiling, technical rooms, etc.).
During hydrostatic testing, the system should be pressurized gradually, as certain elements, such as hemp, may expand.
Certificates and proofs
Evidence must be kept for examination. It is preferable for a customer representative to witness the operation.
Examples of evidence are photos or graphs used to record pressure gauge readings.
Photographic evidence of the start and end of the trial Recording pressure gauge evidence
Test certificates must be completed (see example in NFPA standard) and attached to the technical file (dossier des ouvrages exécutés or DOE) submitted to customers.
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