Ensuring Joint Integrity in Large‐Diameter Sewer Systems
Infrastructure Demands
As America’s infrastructure expands, the demand for reliable sewer systems is growing rapidly—industry forecasts suggest over 700 million linear feet of sewer pipe installations by 2026.
For larger-diameter systems (say 30 inches and up), ensuring the integrity of pipe joints becomes both more important and more challenging. In sewer design, the term “watertight” is often used, but per industry standards "watertight" really means meeting a defined leakage rate under pressure—not zero leakage everywhere.
For example, under ASTM International D3212 (for flexible‐seal plastic pipe joints) the lab test might call for 10.8 psi of pressure for 10 minutes—but that lab result doesn’t automatically translate to perfect field performance over miles of pipeline. Typical acceptable leakage rates for sanitary sewers run from about 10 to 200 gallons per inch‐mile per day depending on the agency; for storm sewers the number is often 200-300 gal/inch‐mile/day.
How are installed joints tested?
There are three main field methods:
- Low‐pressure air testing – A run of pipe is isolated (via plugs in the upstream and downstream manholes and laterals) and then pressurized (typically 2-4.5 psi) and monitored for an allowable pressure drop over a set time.
- Hydrostatic exfiltration (draw-down water test) – Similar to the above, the run is filled with water to an elevation above the pipe crown, stabilized, then monitored for water level drop over time as an indicator of leakage. This method becomes impractical for long runs and large diameters due to water volume and time involved.
- Visual inspection/CCTV – For very large diameters or where air/water testing is too risky or expensive, visual methods (entry walkthroughs or remote CCTV) are used. While useful, they cannot verify long‐term joint integrity.
For diameters of 48 inches and up – and especially 72 inches or greater – the traditional low-pressure air test becomes more difficult, unsafe, and expensive. Inflated plugs in large diameters must resist enormous thrust forces (for example tens of thousands of pounds) and logistics can be problematic.
As a result, many agencies shift to visual inspection or specialized joint‐isolation equipment: devices that isolate a single joint (via bladder or inflatable seal), pressurize the void between two gaskets, and measure leakage locally. These allow for more controlled testing of individual joints but can be time-consuming and costly.
Takeaway
Designers and owners of large‐diameter sewer systems must weigh the tradeoffs between test rigor, cost and practicality. While lab spec tests like ASTM D3212 are useful references, field‐testing in large‐diameter applications requires adapted strategies. The choice between air, hydro, visual or isolation methods comes down to diameter, site conditions, groundwater, contamination risk and budget. With growing emphasis on performance and durability, specifying appropriate joint testing early in design helps ensure the system meets expectations in service.