Plastics Pipe Selection, Handling, Storage and Installation for Potable Water Supplies Code of Practice: Part 3 - Laying and Jointing of UPVC Pipes
2003 Edition

IS 7634 Part 3 specifies several approved jointing techniques for UPVC pipes including solvent welded joints—which are strongly recommended especially for above-ground and duct installations—integral elastomeric sealing ring joints, mechanical compression joints, flanged joints, threaded or screwed joints, and union coupled joints. Solvent cement joints are preferred for their capacity to withstand axial thrust from internal pressure and should comply with IS 14182. Threaded joints require PVC to be the male component or special care to avoid over-tightening. Mechanical compression and flanged joints are also viable depending on application requirements.

To ensure quality preservation onsite, UPVC pipes and fittings must be stored shielded from heat sources and kept away from contact with substances like diesel, paints, and solvents. Fittings and ancillary components should remain in their original sealed packaging until use, avoiding premature jointing. Pipes and fittings should be stored separately to prevent damage. Solvent cement must be kept in cool locations in airtight containers, as non-hermetic containers such as HDPE screw lids are unsuitable. Cement showing viscosity changes or gel formation should be discarded, and thinners must not be added to restore viscosity. Application temperatures between 0°C and 45°C are recommended, with joints made during cooler periods in fluctuating climates.

Trench width requirements vary depending on pipe diameter and soil stability. Unsupported trenches typically require widths from about 2 to 7 times the pipe diameter, whereas supported trenches may be wider to prevent soil collapse. For example, a 110 mm pipe may have a minimum unsupported trench width of 450 mm (around 4 times the pipe diameter) and a supported trench width of 900 mm. Bedding must provide firm, stable, and uniform support along the pipe length, with removal of stones larger than 20 mm. The recommended bedding thickness is between 100 and 150 mm under the pipe. For pipes with diameter 100 mm or greater, bell holes must be provided beneath socket joints to accommodate joint assembly.

Pressure testing is conducted by filling the pipeline slowly with potable water at a velocity not exceeding 0.6 m/s. The test pressure is generally the nominal pressure rating or 1.5 times the actual operating pressure, whichever is higher. The test setup includes flanged tees, air release cocks, sampling points, and temporary thrust blocks to prevent pipe movement. The success criteria involve no visible leaks, stable pressure readings without abrupt drops, and proper operation of valves after pressurization. Pressure gauges with ±0.2 bar accuracy are recommended, and a minimum curing period of 24 hours before testing ensures joint integrity.

To prevent joint separation caused by axial thrust in buried UPVC pipes, it is essential to install concrete anchor blocks at critical locations such as bends, reducers, and closed ends to resist thrust forces generated by internal pressure. Axial thrust values provided in IS 7634 Part 3, Table 3, should be used to design these anchors. Leave sufficient clearance around joints free of backfill for inspection and testing. In above-ground installations, solvent cemented joints capable of sustaining axial thrust are recommended. Additionally, surge pressure analysis should be conducted to account for transient forces that may increase axial loads on joints.