In short
- The hydrostatic test pressurises a capped, water-filled sample of pipe in a heated bath and checks that it neither bursts nor leaks within the test time.
- NS 40:2079 requires one sample from every production batch to pass 48 hours at 80 °C.
- A batch is pipe of one designation, from one machine and one batch of raw material, over up to 48 hours of production.
- If a sample fails, twice as many are retested; if the retest fails, the batch is rejected.
- Longer tests — 100 h at 27 °C, 165 h and 1,000 h at 80 °C — run on a set schedule.
What is a hydrostatic pressure test for HDPE pipe?
It is the test that proves a pipe can carry pressure. A length is cut from the production batch, fitted with pressure-tight end caps and filled with water. It is then held in a test bath at the test temperature while a pressure unit keeps the inside of the pipe at a constant test pressure. The sample passes if it survives the full test time without bursting or leaking.
The test pressure is not a single figure. It is calculated for each size and wall thickness so that the pipe wall carries the hoop stress the standard sets for the material grade and test temperature:
test pressure = 2 × hoop stress × wall ÷ (outside diameter − wall)
That is why the test is equally demanding for a small, thick pipe and a large, thin one: both walls are loaded to the same stress.
- A sample length cut from the production batch, filled with water.
- Pressure-tight end caps seal both ends.
- The sample sits in a test bath held at the test temperature: 80 °C for the batch test.
- A pressure unit holds the internal pressure that produces the hoop stress NS 40:2079 sets for the material grade.
- The pressure is held for the full test time: 48 hours for the batch test. The sample must not burst or leak.
Why test at 80 °C?
Heat speeds up the slow processes by which plastic pipe could eventually fail under pressure. A test at 80 °C shows in 48 hours what a test at everyday temperature would take far longer to reveal, which makes it practical to test every batch. NS 40:2079 also includes a 100-hour test at 27 °C — the reference temperature Nepal’s standard uses for its climate — and longer 80 °C tests of 165 and 1,000 hours.
What counts as a batch?
The Nepal Bureau of Standards & Metrology calls a batch a control unit. Its product manual for NS 40:2079 defines it as pipes of the same designation from a continuous extrusion run of one machine, made from the same batch of raw material, up to a maximum of 48 hours. Change the size, the pressure class, the machine or the raw material batch, and a new control unit begins — with its own samples and its own tests.
Which tests run on every batch?
The pressure test is one of several that NBSM’s scheme requires on every control unit:
| Test | Samples per batch | What it proves |
|---|---|---|
| Internal pressure, 80 °C for 48 h | One | The pipe wall holds pressure without bursting or leaking |
| Dimensions, appearance, length or coiling | Ten | Diameter, ovality and wall are within the standard |
| Identification stripes | Ten | The blue stripes that identify water pipe are correct |
| Longitudinal reversion | One | The pipe does not shrink excessively when heated |
| Carbon black content and dispersion | One (composite) | Enough carbon black, evenly spread, for UV protection |
| Melt flow rate | One (composite) | The material is the grade it should be and processes consistently |
| Oxidation induction time | One | The material is stabilised against heat and oxidation |
| Density | One | The polyethylene is the specified type |
| Yield strength and elongation at break | One | The pipe is strong and ductile, not brittle |
Alongside these, the scheme sets a schedule for longer tests: 100 hours at 27 °C and 165 hours at 80 °C whenever the resin or manufacturing method changes, with every pressure class and grade covered in rotation; 1,000 hours at 80 °C at least once every two years; and a 48-hour pressure test on fusion joints when the resin or method changes.
What happens if a sample fails?
The rules are strict. If a sample from a batch fails any requirement, double the original number of samples is taken and tested again. If the retest also fails, the whole control unit is rejected. For the long-term pressure tests, a failure means NS marking stops immediately and NBSM is informed; marking resumes only after corrective action and three further samples pass.
Factory test or site test: do you need both?
Yes. The factory test proves the pipe. A pressure test on the finished pipeline after installation proves the joints, fittings and installation — things no factory test can check. Follow the test procedure in your project specification or your consultant’s instructions for that site test.
Ask for the test report
You can ask for the test report that goes with your consignment. A useful report shows the batch details that match the marking on the pipe, the size, pressure class and grade, and the measured results: dimensions, the pressure test outcome, melt flow rate, density, carbon black and oxidation induction time. Contact our team to request one, or read how to check a supplier’s NS licence.
Sources
Frequently asked questions
What is the hydrostatic test pressure for HDPE pipe?
There is no single figure. The test pressure is calculated for each size and wall thickness so that the wall carries the hoop stress NS 40:2079 sets for the material grade and test temperature: test pressure = 2 × hoop stress × wall ÷ (outside diameter − wall).
How long does the HDPE pipe pressure test take?
The test on every production batch lasts 48 hours at 80 °C. Scheduled long-term tests run for 100 hours at 27 °C, and for 165 and 1,000 hours at 80 °C.
Is every batch of Maruti HDPE pipe tested?
Yes. Every production batch is sampled and tested in our in-house laboratory to the NBSM scheme for NS 40:2079, including the 48-hour internal pressure test at 80 °C.
Can I get the test report for my pipe?
Yes. Ask for the test report with your consignment; it shows the batch, size, pressure class, grade and measured results.
Do I still need to pressure test the pipeline on site?
Yes. The factory test proves the pipe; a site test after installation proves the joints, fittings and installation. Follow your project specification for the site test.
Written by the technical team at Maruti Pipes Pvt. Ltd., Nepalgunj, Nepal. See our HDPE pipe range for Nepal.