Failed solvent-welded joint on a 63 mm uPVC rising main
A six-storey apartment block in Kandy has a new 63 mm PN10 uPVC rising main from the ground suction tank to a rooftop tank. The run is 38 m with 22 solvent-welded joints. The contractor pressure-tested at 9 bar (1.5 times the 6 bar working pressure). The gauge held for eight minutes, then dropped 1.5 bar; water weeps from a joint near a fourth-floor 45° elbow. The pipe was stored uncovered in direct sun for three weeks. The solvent cement tin had been opened five months earlier and has no batch label. The plumber wiped the pipe with a dry rag, applied cement to the pipe spigot only, pushed the joint in, held it for five seconds, and tested one hour later. The ambient temperature is 32°C. The client wants the system handed over the next morning.
1. Diagnose the likely causes of the joint failure and rank them. Show how the evidence supports your ranking.
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The most likely cause is a defective solvent-welded joint, not a burst pipe. The leak is at a joint, the gauge dropped only after eight minutes, and cement was applied to the spigot only. Correct practice requires cleaner and cement on both spigot and socket, a full even coat, immediate assembly with a quarter-turn, and holding until initial set. The opened five-month-old cement is suspect because shelf life after opening is limited, and without a batch label it cannot be verified. Dry wiping leaves dust and grease; at 32°C the cement skins quickly, so a five-second hold may have seized before full insertion. Testing after one hour is too soon; solvent joints need cure per the manufacturer, often 24 hours at this diameter and temperature. Three weeks of direct sun may also have degraded the uPVC if it is not UV-stabilised, but that would not usually cause a single joint leak.
Rank: 1) poor jointing and cement application; 2) expired or contaminated cement; 3) inadequate cure before testing; 4) possible UV damage to the pipe, which should be checked for chalking and cracking.
2. Describe the repair and re-test procedure, including what you would verify before handing over.
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Cut out the failed joint plus at least one pipe diameter either side, using a proper cutter and allowing for the fitting length. Inspect the cut pipe for UV chalking, cracks, ovality and contamination; if suspect, replace the affected length. Use new PN10 fittings and fresh cement with a readable batch and date. Clean both surfaces with the manufacturer's cleaner, apply an even coat of cement to socket and spigot, assemble fully with a quarter-turn, hold, wipe off excess, and mark the joint. Support the pipe to prevent strain.
Cure according to the manufacturer's table: for 63 mm at 32°C, plan on at least 24 hours before a full pressure test, not one hour. Refill slowly and vent air. Re-test the section at 9 bar with a calibrated gauge for the specified duration, checking all exposed joints and the repair. Confirm no pressure drop, no weeping, correct support spacing and no UV exposure. Only then hand over, with the test record and cement batch details. If the client needs water sooner, provide a temporary supply rather than testing early.