Since CNG cylinders are considered as high priority safety elements in cars, they need to comply with the requirements assigned in national and international standards such as ISO 11439, ECE-R110 and ISIRI 758. Compliance with these standards is checked during production inspections, testing all cylinders throughout the production line and examining a number of randomly chosen samples out of any product batches by the use of advanced equipment and under supervision of authenticated inspectors of the Institute of Standards and Industrial Research of Iran. The examinations must be programmed in such discipline that the results could account for the natural characteristics, service life and physical and chemical specifications of the product with an appropriate confidence level. CNG cylinders are designed in observance of some technical aspects such as the cylinder’s pressure in function, number of fill-empty cycles in its service life and its exposure to flammable natural gas. Also, the useful time of the cylinder needs to be longer than the vehicles.
Asia Nama’s laboratory is equipped as to fulfill the company’s QC requirements. Licensed as a “Cooperating Laboratory in CNG Cylinder Manufacturing Industry” by the Iranian Standard Institute, the facility is capable of accomplishing all the required tests regarding the cylinders’ mechanical, metallurgical, functional and chemical specifications, as explained below:
Mechanical tests are accomplished by the use of the following devices:
- “Charpy Impact Tester” can be used by up to 500 Jules of power to measure the amount of energy a cylinder absorbs in a breakage.
- “Universal Testing Machine” is capable of accomplishing a variety of tests such as tensile test, three-point bending test and pressure test on the samples with a 100 ton capacity. It can also analyze parameters such as tensile strength, compressive strength, yield strength and relative length increase percentage.
- “Bending Test Machine” is for inspection of the bending pattern of cylinders.
- “Brinell Hardness Tester” is also another machine for accomplishment of the mechanical tests.
Metallurgical tests are conducted by the use of the following devices:
- Cutting machine
- Hot Mount
- Metallurgical Microscope
Chemical tests are performed by the use of the following device:
- “Desktop Metal Analyser (ARUN)” can be used to analyze and determine the type and components of steel.
There are also other chemical inspections to control the chemical processes during the production of cylinders.
Specific functional tests are as follows:
The test is performed to determine the service life of the cylinders. In the test, the cylinders are pressured by an alternating pressure of 20-260 bar in ambient temperature. In this condition, the cylinder is expected NOT to leak or break before it completes 15000 cycles (which is an average service life for CNG cylinders).
The test is performed to determine the resistance of cylinders against hydrostatic pressure before breakage. The cylinders are supposed NOT to break under a pressure lower than 450 bar.
Penetration (Gunfire) Test:
The test is performed to make sure the cylinders won’t burst or break against penetration of a bullet. In the test, a cylinder pressurized under 200±10 bar with compressed gas is gun-fired by a single bullet of 7.62 mm or bigger. The cylinder is supposed NOT to burst or rupture.
The bonfire test is performed to make sure of the appropriate function of the cylinder’s safety valve and its timely pressure relief of the cylinder when in bonfire. The cylinder is supposed NOT to burst in this condition.
Leak before Break (LBB) Test:
The test is performed to make sure the cylinders would not rupture as pressurized under high pressure cycles. The test is accomplished by the use of cycling test machine through 20-300 pressurized cycles which continue until the cylinder starts to leak.
Before the production is officially launched, any cylinder type in question needs to achieve the type approval certificate on the basis of a number of specific tests. Also, the product batches need to be tested under supervision of an internationally authenticated company’s delegates during the mass production process.
Type Approval Tests
Type #1 CNG cylinders are to be evaluated by a number of particular tests such as below:
- Chemical Analysis of Steel: The test is performed to determine the type and components of steel.
- Tensile Test: The tests is performed in ambient temperature in accordance to standard ISO 6892-1 in order to evaluate the physical parameters such as tensile strength, compressive strength, yield strength and relative length increase percentage of the sample.
- Charpy Impact Test: The test is accomplished in accordance to standards ISO 148 in -50°C.
- Sulfide Stress Cracking Test (SSC): The tests is performed in accordance to NACE TM0177 in order to evaluate the resistance of cylinders in a corrosive sulfide environment.
- Ambient Temperature Pressure Cycling Test
- Hydrostatic Test
- Leak before Break Test
- Penetration Test
- Bonfire Test
Coating Tests include:
- Paint Adherence
- Chemical Resistance
- Salt Spray
- Exposure to UV Emission
- Exposure to Pressurized Spray of Particulates
All Inclusive Tests
After type approval, during mass production, the following tests are accomplished on every cylinder on the line:
- Brinel Hardness Test: The test is accomplished in accordance to ISO 6506 standard.
- Hydrostatic Pressure Burst Test: The test is accomplished to measure the permanent volume increase of the cylinder as pressurized under 1.5 times higher than its normal operational pressure.
- Leakage Test: The test is to inspect any possible leakage out of the cylinder’s end.
- Non-Destructive Ultrasonic Inspection: The test is to inspect the thickness of the cylinder wall and ensure the wall is clear of any cracks and defects.
- Non-Destructive Magnetic Inspection: The test is to ensure that the cylinder is clear of any cracks and defects in bends and head-thread.
- Measurement of Dimensions, Marking and Appearance Evaluation.
Product Batch Tests
Product Batch tests are accomplished on randomly chosen cylinders out a group of produced ones. These tests include:
- Tensile test in ambient temperature
- Charpy Impact Test in -50°C
- Hydrostatic Burst Test
- Ambient Temperature Pressure Cycling Test
- Paint Adherence Test
- Paint Thickness Test
- Dimension Checks in Accordance to Manufacturing Drawings
Mandatory Standard Sign Application license
After successful completion of all tests, the result sheets, the drawing documentation, the stress analysis reports and all related drawing are confirmed by the official supervisor and delivered to the Institute of Standard and Industrial Research of Iran where the company’s Mandatory Standard Sign Application License for mass production is issued. For the time being, Asia Nama Company has obtained the Iranian standard sign application licenses for the production of cylinders with 35, 52, 57, 60, 62, 75 and 113 units of capacity which are all approved by TUV NORD COMPANY.