COMPRESSED NATURAL GAS CYLINDER ( CNG )
Natural gas as alternative fuel has been used on the public vehicles since early 2000. More than hundred thousands of natural vehicles are travelling on the road on different countries although they will be added day by day regarding to the government policy. To ensure efficient and safe high pressure cylinder used in vehicles, having a safety standard is very important.
At first, the high pressure cylinders which used in vehicles were built and tested based on available industry standards. Therefore cylinders were produced very heavy. Accessing to new high strength steel and aluminum alloys, inspectors and suppliers of cylinders had to use the new standards according to new materials to achieve lighter tanks in spite of keeping safety in CNG vehicles. Therefore, a number of national and international standards have released to specify requirements for design, test, inspection requirement, and repair of cylinders. Cylinders are used on vehicles should be light and safe and satisfy the expected conditions. In design standards of cylinders such as ISO 11439, ECER110 and NGV2-20000, the mentioned criteria are as following cases.
üDetermine working conditions of cylinder
üEstimation of fatigue life with a series of designed tests
üIt is needed for destructive testing on the cylinders from the production series
üIt is needed for non destructive testing and inspection of all production cylinders
üNeed to have producers with a comprehensive quality system
üRequire periodic inspection according to instructions of cylinder manufacturer
üNeed to determine the safe working life of the cylinders that produced by the manufacturer as part of their design.
Main standards CNG cylinders have very comprehensive safety performance criteria such as burst pressure, or pressure cycle test, ability to resist extreme environmental damage. Safety performance criteria for all CNG cylinders in the form of this article is not expressed but in a few important criteria will be evaluated.
CNG cylinder design approval test and common 3rd party inspector’s quality plan for cylinder as per ISO 11439
Comet had more than 10 years experience with these type of inspection
- Permissible working pressure test as per standards
- Working conditions
- Burst pressure tests
- Dimensional measurements and cylinder weight should be within tolerances of design
- Confirm compliances with the final level specified in the design (deep drawn surfaces and laps in the necks and shoulder areas.
- Working life
- Penetration test
- Bonfire test
- Maximum allowable defects
- Environment test
- Batch test and periodic inspection of cylinders as per ECER 110 and ISO 11439 mandatory
- Mechanical test, hydraulic test, volumetric expansion value, coating and verification of labeling and marking,
The above scope of inspection shall be carried out in order to ensure the quality of the products manufactured, built or rebuilt equipment meet safety and quality standards. Continuous inspection of each step by visual or automated inspection procedures, testing, witnessing samples test, spare of final product assembly selected at a predetermined frequency.