The CNG cylinder hydro testing actually done in testing stations👇

1. Cylinder identification & documentation
Record manufacturer name, serial number, water capacity, working pressure, test pressure, and last test date.
Verify cylinder is within allowable service life as per PESO / ISO / EN norms.
Reject immediately if markings are missing or tampered.

2. Valve removal & gas depressurization
Ensure the cylinder is completely depressurized (zero gas pressure).
Remove the CNG valve using proper tools (no hammering or heating).
Check valve threads for damage.
⚠️ Safety note: Gas must be vented in a designated safe area.

3. Internal cleaning & drying
Drain any moisture, oil, or contaminants.
If required, flush with clean water or air.
Internal cleanliness is critical to avoid false expansion readings.

4. External visual inspection
Cylinder is placed on a rotating vise and inspected for:
Corrosion, pitting, dents, gouges
Bulging or out-of-roundness
Fire/heat damage
Weld seam defects
Base and neck cracks
❌ Cylinder is rejected if defects exceed permissible limits.

5. Internal visual inspection
Use a borescope / internal inspection lamp & mirror.
Check for:
Internal corrosion
Liner damage (for composite cylinders)
Scale or deep pitting

6. Weighing (empty weight check)
Cylinder is weighed empty.
Compare with original tare weight.
Excessive weight loss indicates metal thinning → rejection.

7. Filling cylinder with water
Fill the cylinder completely with water, ensuring no trapped air.
Air pockets can cause dangerous energy release and inaccurate results.

8. Mounting on hydro test machine
Cylinder is fitted with hydro test adapter.
Placed in a water jacket system or connected to a direct expansion test setup.
Pressure gauges and expansion measuring devices are zeroed.

9. Pressurization to test pressure
Gradually pressurize with water up to test pressure
(typically 1.5 × working pressure, e.g., 300 bar → 450 bar).
Hold pressure for the specified time (usually 30 seconds).

10. Measurement of expansion
Two values are measured:
Total expansion – expansion under pressure
Permanent expansion – expansion remaining after pressure release
Acceptance criteria:
Permanent expansion must be within allowable percentage of total expansion.
No leakage, sweating, or abnormal deformation allowed.

11. Pressure release & final inspection
Slowly release pressure.
Recheck cylinder for:
Cracks
Bulges
Leakage
Any visible deformation = fail.

12. Drying of cylinder
Drain all water.
Dry using:
Hot air blower, or
Vacuum drying system
Moisture left inside leads to internal corrosion.

13. Valve refitting & leak test
Reinstall approved CNG valve with correct torque.
Perform leak test using air/nitrogen and soap solution.

14. Marking & certification
Stamp or label:
Test date
Next due date
Testing station ID
Update records and issue hydro test certificate.

15. Acceptance or rejection
Accepted cylinders → cleared for service
Rejected cylinders → condemned, cut, or destroyed as per regulations

• High pressure capacity
• Heavy-duty industrial design
• Reliable & accurate testing
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