Pressure Test Failure on a Sprinkler Main
A 150 mm fire protection main in a new warehouse is undergoing a hydrostatic test at 1.5 times working pressure, held for two hours per the applicable standard. The gauge reads a drop from 1,380 kPa to 1,310 kPa over the hold period. The installing contractor proposes to add make-up water and continue, stating that the drop is due to air entrapment and thermal contraction of the fill water. Ambient temperature dropped 6 degrees Celsius overnight. You observe no visible leakage at joints, but one mechanical coupling at grid line C is damp. The building owner's insurer requires a witnessed passing test before occupancy in nine days. The contractor asks you to record the test as passed with a note about the gauge drop.
1. How do you handle the request to record a pass with a note?
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Decline. A witnessed test either meets the acceptance criteria or it does not; a 'pass with note' converts a failed test into an ambiguous record that misleads the authority having jurisdiction and the insurer. The 70 kPa drop exceeds normal gauge tolerance and is unexplained. The damp coupling is physical evidence of leakage, which is itself a failure independent of the pressure trend. Air entrapment and thermal effects are plausible contributors but must be eliminated by test, not accepted by assertion. Record the test as failed or inconclusive, note the gauge drop, the ambient temperature change, and the damp coupling, and notify the contractor and owner in writing the same day.
2. Describe the corrective action and retest plan you would require, including how to separate air and thermal effects from real leakage.
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First, repair or replace the suspect coupling at grid line C and inspect adjacent joints. Second, purge air at high points and verify venting is complete. Third, refill slowly and allow the system to stabilize to ambient temperature before pressurizing, recording water and ambient temperatures at start and end. Fourth, use a calibrated gauge of appropriate range (a gauge reading near mid-scale) and record gauge serial and calibration date. Fifth, conduct the hold with the specified duration and require the pressure to remain within the allowed tolerance without make-up water. If a drop persists with stable temperature and no visible leak, isolate sections to localize it. Only after a clean witnessed retest should a pass be recorded. Notify the owner that the nine-day occupancy target is at risk so scheduling decisions are made with accurate information.