Gasketed PVC pipe is very popular today in North America for groundwater mains as well as sewer mains. As is the case with all piping, regardless of material, post-construction testing is generally required to ensure that all new lines have been installed correctly.
One test that is common for gasketed pipes, such as PVC, is the combined “leak and pressure” test. This test is intended to simultaneously check the pressure capacity and the tightness of the joints of the piping system.
The procedure for this test is to first fill a section of the line with water. Additional water is then pumped into the line until the section reaches the desired test pressure. The system is then shut down and maintained for a specified test period, typically 2 hours.
During these 2 hours, the system pressure may drop. If the pressure drop is rapid during the test, there is likely a major leak in the system. In most cases, this could be attributed to improper assembly of a fitting, pipe joint, or service connection.
However, assuming proper installation and mounting has been done, a slight drop in pressure may occur over the 2 hours. To set a limit for an allowable pressure drop, a table of ‘Allowable Leakage Volumes’ was created. This chart indicates the maximum volume of water that is allowed to be added back into the system after a pressure/leak test has indicated a slight drop in pressure. (The actual value table can be found in the IPEX PVC Pressure Pipe Installation Guide or in AWWA C605).
For example, for 1000m of PVC water main pipe with 300mm joints, it is allowed to add a maximum volume of 7.6L of make-up water (theoretically, the leak that occurs during the test) for a leak test. 1035 kPa (equivalent to 2.0 US gal. for 3300 ft of 12″ pipe tested at 150 psi). If higher volumes of water are required, the test is considered failed and the installer must locate and repair any deficiencies in the system.
As a result of this table of ‘leakage’ assignments, many people have the perception that gasketed PVC joints always leak to some degree. Indeed, a properly assembled PVC pipe will be airtight.
This statement is verified by rigorous testing performed on the gasketed joint at the manufacturing plant. Gasketed PVC pressure joints, to be certified to CSA B137.3 and comply with ASTM D 3139, must undergo the following 2 tests:
(a) 60 minutes at 2.5 times rated pipe pressure (i.e. 588 psi for DR18)
(b) 60-70 seconds at 3.2 times rated pipe pressure (ie 755 psi for DR18)
Both tests are conducted while the joint is traveling at its maximum recommended angle to simulate a worst case field condition. Zero joint leakage is allowed during these tests. The consistency and precision found in PVC pipe extrusion, coupled with very tight dimensional tolerances, ensure that the gasketed joint will be as reliable in the field as it is demonstrated in the plant.
An example of PVC’s joint tightness was illustrated on a recently completed project outside of Vancouver in Delta, British Columbia. B&B Contracting of Surrey was contracted to construct 15,000ft (4,500m) of 16″ (400mm) PVC DR18 water pipe as the main supply line to the newly constructed DeltaPort container terminal.
After completing the installation, project superintendent Rollie Knackstead showed great confidence in his team’s workmanship, as well as the pipe, by deciding to pressure test the entire 15,000 feet of pipe at once. The results were exceptional. B&B successfully tested the line at 200 psi for 2 hours without a drop leaking. The pressure gauge did not exceed the 200 psi level. PVC airtight joints helped turn an already successful installation into a very successful overall project.
If during a pressure/leak test on PVC, the pressure drops slightly (within allowable make-up water volumes), does this mean there has been a leak? Perhaps, but tests at the PVC pipe plant, as well as numerous case histories, such as the B&B Contracting project in Delta, seem to indicate that properly assembled PVC pipe will not leak.
So why is it occasionally necessary to have small volumes of make-up water after a pressure test? Here are 4 possible reasons:
(a) trapped air
(b) displacement of tees or elbows before joint restraint function
(c) faulty connections for valves, fittings, hydrants, or services
(d) radial expansion of PVC pipe
In fact, radial expansion is such a significant factor with another thermoplastic pipe material (HDPE) that its test limit is specifically identified as an “expansion allowance”, rather than a “leakage allowance”. It is also interesting to note that if a comparison is made, the actual allowable make-up water values are found to be significantly higher with butt-fused HDPE than those for PVC pipe with gaskets for equivalent pipe sections and test pressures.
In summary, the reader is cautioned that often times a more appropriate term for ‘Leakage’ is ‘Apparent Leakage’ or ‘Makeup Water Allowance’ when analyzing PVC pressure pipe test results. Evidence suggests that properly assembled gasketed PVC pipe will have virtually zero leaks. The fact that PVC does not weaken over time due to corrosion attacks will ensure that today’s airtight joints remain so for many years to come.