August 01, 2025
Have you ever wondered how manufacturers ensure the performance of their pipeline? Once the ductile iron pipes manufacturing process is completed, to provide a leak-proof pipeline, hydrostatic testing is essential. Proof testing and field testing are both used for DI pipe testing, whether in the manufacturing stage or post-installation, following standards such as AWWA hydrotest standards and EN 545 guidelines.
Ductile iron pipes’ hydrostatic testing begins by filling the pipelines with water to remove air, followed by increasing the pressure to 1.5 times the working pressure using a calibrated pump. Maintain the pressure for a specific time, and to diagnose further leaks, use a double bump test. Follow AWWA hydrotest standards and use water for safety.
This guide explores hydrostatic testing, its diagnostic approach to DBT, and post-test procedures for ensuring safety improvements.
Before the pipeline testing, pipes should be flushed for hydrostatic testing of ductile iron pipes to clean and fill the pipes with water before the pressurization process. This process mainly goes for debris and trapped air removal.
There are several reasons that proper flushing is crucial in the ductile iron pipe testing process, such as debris clearance and air removal.
Debris clearance is required due to entering soil or sand particles during installation that can damage valves or fittings while decreasing the risk of operational issues post-commissioning.
Air removal happens considering how dense trapped air can get, unlike water, and can cause mishaps during the pressure testing. These fluctuations seem like leaks that continue with unnecessary maintenance, evaluations, or retests.
Industry standards provide clear guidance on flushing before pipeline testing to ensure consistency and reliability:
AWWA C600 Guidelines: This standard mainly indicates how important it is to slowly fill the pipes with clean water to remove air and debris. According to Scribd, via adding air release valves or cocks at high points for better water flushing performance and reducing safety risks.
EN 545 Guidelines: The European standards for the hydrostatic testing of ductile iron pipe rely on complete air removal before the primary process. Filling the entire pipeline from the lowest point to ensure all the air is released.
To succeed in the ductile iron pipe testing procedure, here are some valuable techniques that are highly recommended:
Slow Fill from Low Point: For natural and complete air removal, fill the pipeline slowly from the lowest point with water. The quicker water filling gets, the worse air traps, especially in complicated pipelines.
High-Point Air Release: Installing air release valves, corporation cocks, and fire hydrants to release trapped air at high points by keeping them open while flushing continues.
Flush Velocity ≥ 2.5 ft/s: As the AWWA does not mention a specific flushing velocity, a range of 2.5 ft/s (0.76 m/s) or more is suggested to move sediment with no cement lining damage.
Visual and Flow Checks: Controlling the flow rate is another key factor to ensure that air bubbles are entirely removed.
To ensure the proper performance and leak-free operation of ductile iron piping systems, the testing procedure includes a setup section for the test, applying certain levels of pressure, controlling the pressure, and final evaluation for standard compliance.
Test setup creates a reliable base for accurate and safe hydrostatic testing of ductile iron pipe by filling pipes with clean and potable water, including no trapped air, and controlling the whole process through correct installation. Below is an outline of the setup process:
Fill Line from Low Point: Filling the pipes with clean and potable water is the first step in setting up the line for the test. This process is operated gradually at the lowest point to remove air while ensuring complete filling. This helps expel air from high points like valves or fire hydrants.
Install Calibrated Gauge at Low End: Place a liquid-filled pressure gauge at the lowest point of the test section and at least 3 feet above grade to verify calibration at 0 psi (from 2 psi). This setup ensures correct measurement during the test, including pressure changes.
Prime and Isolate Pump: To deliver consistent pressure, pressurize the pipeline with a pump (whether hand- or motor-driven), then prime the pump and isolate the test section by closing the valves to avoid pressure changes during the test.
There are multiple rules to achieve safe testing for ductile iron pipe based on the AWWA C600 guideline.
The test pressure should be about 1.25 times the regular pressure tolerance of the pipeline at the highest points.
The test pressure is recommended to be 1.5 times the operating pressure at the lowest points where elevation changes the hydrostatic pressure.
For pipes with cement mortar lining, the same pressure rate as the operating pressure is recommended to avoid any damage to the linings.
The correct timing for hydrostatic testing of ductile iron pipes is essential to ensure long-lasting performance in harsh conditions. The hydrostatic testing of ductile iron pipes requires keeping the pressure test for at least 2 hours based on AWWA C600. During this time, the pressure shouldn’t change by more than five psi to account for temperature changes or other practical aspects.
Pro Tip: To succeed in the testing process, control the process continuously to achieve a stable pressure curve using a pressure recorder.
To clarify uncertain test results as a diagnostic pressure test for hydrostatic testing of ductile iron pipe, the double bump test (DBT) is mainly used. If the test results show >5 psi pressure drops or high make-up water, even suspecting the existence of trapped air, DBT helps engineers reshape the testing process.
Pressurize the pipeline up to 200 psi for 30 minutes and measure the recovery volume (e.g., using a 5-gallon bucket). Then, boost the pressure to 250 psi for another 30 minutes and record the recovery volume. Finally, increase the pressure to 300 psi for 30 minutes and measure the volume.
Interpretation: If the result shows a decrease in volume, trapped air is indicated, and if the volume increases, a probable leak is clarified.
After hydrostatic testing of ductile iron pipes, post-test procedures and best practices are necessary for pipeline integrity. Here are some additional tips following AWWA C600 and EN 545:
Use acoustic devices to detect leak sounds or visual inspections for wet spots.
Check joints and fittings first, as they are common leak points.
Log pressure curves with a recorder to verify stability (≤5 psi drop).
Note visual leak signs (e.g., water pooling) and recovery volumes.
Avoid using air for hydrotesting as it poses explosion risks.
Flush before and after testing to clear debris and protect cement-lined DI pipe.
Verify joint and thrust restraint design for test pressures (e.g., 1.5× operating pressure).
Hydrostatic testing of ductile iron pipe ensures pipeline integrity through systematic flushing, pressure testing, and diagnostics like the Double Bump Test. Following AWWA C600 and EN 545 standards, proper setup, leak localization, and documentation minimize failures and costs. Best practices, including water-only testing and robust thrust restraints, guarantee safe, reliable water systems, protecting infrastructure and public health.
