Importance of Hydro testing in CNG Cylinders

Hydrotesting is an essential component of the periodic examination of applicable CNG cylinders because it provides a controlled way to assess pressure-retaining behaviour and, where required, measure total and permanent expansion. It can reveal unacceptable permanent deformation, leakage, pressure loss and visible abnormality before a cylinder is returned to service. Its contribution to safety depends on correct cylinder identification, visual examination, approved equipment, calibrated instruments, careful removal of trapped air, use of the prescribed test pressure and hold time, accurate evaluation and complete documentation. Hydrotesting should not be treated as an isolated activity or as a replacement for other inspection requirements. The safest approach is a lifecycle-based programme in which cylinders are used, inspected, retested, marked and withdrawn strictly in accordance with their design approval, applicable Indian Standards and current PESO requirements. Only approved testing facilities and trained personnel should perform the work.

  [1] International Organization for Standardization (ISO), ISO 11439:2013, Gas cylinders — High pressure cylinders for the on-board storage of natural gas as a fuel for automotive vehicles, Edition 2, including Amendment 1:2021. ISO catalogue: https://www.iso.org/standard/44755.html [2] Bureau of Indian Standards (BIS), CNG Cylinders — technical explanatory material, including description of hydrostatic stretch and volumetric expansion. [3] Government of India, Ministry of Commerce and Industry, The Gas Cylinders Rules, 2016, particularly Rule 35 and Schedule IV (Examination and Testing of Cylinders). Petroleum and Explosives Safety Organisation (PESO): [4] Bureau of Indian Standards, Standard details and catalogue information, including IS 16299:2014 (periodic inspection and requalification of high-pressure steel CNG cylinders) and IS 7241:2024 (hydrostatic stretch testing recommendations). [5] Compressed Gas Association (CGA), CGA C-1, Methods for Pressure Testing Compressed Gas Cylinders and Tubes, 12th Edition, March 2022.  [6] Government of India, Ministry of Commerce and Industry. Gas Cylinders Rules, 2016. Petroleum and Explosives Safety Organisation (PESO). [7] Bureau of Indian Standards. IS 5844: Hydrostatic Stretch Testing of Compressed Gas Cylinders. Consult the current applicable edition. [8]  International Organization for Standardization. ISO 11439:2013 — Gas Cylinders: High Pressure Cylinders for the On-Board Storage of Natural Gas as a Fuel for Automotive Vehicles, including applicable amendments. [9] Sharma, P., Chugh, P., and Neogi, S. (2021). “Study to methodize the design of a safe Type-4 CNG storage vessel using finite element analysis with experimental validation.” International Journal of Pressure Vessels and Piping, 192, Article 104425. [10]  Bureau of Indian Standards. CNG Cylinders: Technical educational material on cylinder testing and hydrostatic stretch