Metode Test (uji Tabung CNG) Sesuai ISO 11439

A.1 Tensile tests for steel and aluminium cylinders and liners

A tensile test shall be carried out on material taken from the cylindrical part of the finished cylinder or liner using a rectangular test piece shaped in accordance with the method described in ISO 9809-1 for steel and ISO 7866 for aluminium. The two faces of the test piece representing the inside and outside surface of the cylinder shall not be machined.
The tensile test shall be carried out in accordance with ISO 6892.
The tensile strength shall meet the manufacturer’s design specifications.
For steel cylinders and liners, the elongation shall be at least 14 %.
For aluminium alloy cylinders and liners of type 1 or type 2 construction, the elongation shall be at least 12%.
For aluminium alloy liners of type 3 construction, the elongation shall meet the manufacturer’s design
specifications.

A.2 Impact test for steel cylinders and steel liners

The impact test shall be carried out on material taken from the cylindrical part of the finished cylinder or liner on three test pieces in accordance with ISO 148.
The notch shall be perpendicular to the face of the cylinder wall. For longitudinal tests the test piece shall be machined all over (on six faces). If the wall thickness does not permit a final test piece width of 10 mm, the width shall be as near as practicable to the nominal thickness of the cylinder wall. Test pieces taken in the transverse direction shall be machined on four faces only, the inner and outer face of the cylinder wall shall be unmachined.

A.3 Sulfide stress cracking test for steel

Testing shall be conducted in accordance with Method A - NACE Standard Tensile Test procedures, as described in NACE Standard TM0177-96. Tests shall be conducted on a minimum of three tensile specimens with a gauge diameter of 3,81 mm (0,150 inches) machined from the wall of a finished cylinder or liner. The specimens shall be placed under a constant tensile load equal to 60 % of the specified minimum yield strength of the steel, immersed in a solution of distilled water buffered with 0,5 % (mass fraction)
sodium acetate trihydrate and adjusted to an initial pH of 4,0, using acetic acid. The solution shall be continuously saturated at room temperature and pressure with 0,414 kPa (0,06 psia) hydrogen sulfide (balance nitrogen). The tested specimens shall not fail within a test duration of 144 hours.

A.4 Corrosion tests for aluminium

Corrosion tests for aluminium alloys shall be carried out in accordance with annex A of ISO 7866:1999 and meet the requirements therein.

A.5 Sustained load cracking (SLC) tests for aluminium

A.6 Leak-before-break (LBB) test

Three finished cylinders shall be pressure cycled between 20 bar and 300 bar at a rate not to exceed 10 cycles per minute in accordance with A.13.
All cylinders shall either fail by leakage or exceed 45 000 pressure cycles.

A.7 Extreme temperature pressure cycling

Finished cylinders, with the composite wrapping free of any protective coating, shall be cycle tested, as follows:
a) condition for 48 h at zero pressure, 65 °C or higher, and 95 % or greater relative humidity. The intent of this requirement shall be deemed met by spraying with a fine spray or mist of water in a chamber held at 65°C;
b) hydrostatically pressurize for 500 cycles multiplied by the specified service life in years between 20 bar and 260 bar at 65°C or higher, and 95 % or greater relative humidity;
c) condition the cylinder and fluid at – 40 °C or lower as measured in the fluid and on the cylinder surface;
d) pressurize from 20 bar to 200 bar for 500 cycles multiplied by the specified service life in years at – 40°C or lower. Adequate recording instrumentation shall be provided to ensure the minimum temperature of the fluid ismaintained during the low temperature cycling.

The pressure cycling rate of b) shall not exceed 10 cycles per minute. The pressure cycling rate of d) shall not exceed 3 cycles per minute unless a pressure transducer is installed directly within the cylinder.
During this pressure cycling, the cylinder shall show no evidence of rupture, leakage or fibre unravelling.

Following pressure cycling at extreme temperatures, cylinders shall be hydrostatically pressured to failure in
accordance with A.12, and achieve a minimum burst pressure of 85 % of the minimum design burst pressure. For type CNG-4 designs, prior to the hydrostatic burst test the cylinder shall be leak tested in accordance with A.10. NGV Community (Non-Commercial Library Distribution Only)

A.8 Brinell hardness test

Hardness tests shall be carried out on the parallel wall of each cylinder or liner in accordance with ISO 6506-1 at
the rate of one test per metre length of parallel wall. The test shall be carried out after the final heat treatment and
the hardness values thus determined shall be in the range specified for the design.

A.9 Coating tests

Coatings shall be evaluated using the following test methods, or using equivalent standards acceptable to the
Inspector in the country of use:
a) adhesion testing, in accordance with ISO 4624:—, using method A or B as applicable. The coating shall exhibit an adhesion rating of either 4A or 4B, as applicable;
b) flexibility, in accordance with ASTM D522-93, using test method B with a 12,7 mm (0,5 in) mandrel at the specified thickness at 20 °C. Samples for the flexibility test shall be prepared in accordance with ASTM D522-93. There shall be no visually apparent cracks;
c) impact resistance, in accordance with ASTM D2794-93. The coating at room temperature shall pass a forward impact test of 18 J (13,3 ft lbs);
d) chemical resistance, in accordance with ASTM D1308-87 except as identified in the following. The tests shall be conducted using the open spot test method and 100 h exposure to a 30 % sulfuric acid solution (battery acid with a specific gravity of 1,219) and 24 h exposure to a polyalkalene glycol (e.g. brake fluid). There shall be no evidence of lifting, blistering or softening of the coating. The adhesion shall meet a rating of 3 when tested in accordance with ISO 4624:—;
e) minimum 1 000 h exposure, in accordance with ASTM G53-93. There shall be no evidence of blistering, and adhesion shall meet a rating of 3 when tested in accordance with ISO 4624:—. The maximum gloss loss
allowed is 20 %;
f) minimum 500 h exposure in accordance with ISO 9227. Undercutting shall not exceed 2 mm at the scribe
mark, there shall be no evidence of blistering and adhesion shall meet a rating of 3 when tested in accordance
with ISO 4624:—;
g) resistance to chipping at room temperature, in accordance with ASTM D3170-87. The coating shall have a rating of 7A or better, and there shall be no exposure of the substrate.

A.10 Leak test

Type CNG-4 designs shall be leak tested using the following procedure (or an alternative acceptable to the
Inspector in the country of use):
a) thoroughly dry the cylinders;
b) pressurize the cylinders to working pressure with dry air or nitrogen containing a detectable gas such as
helium. Any leakage detected shall be cause for rejection.

NOTE Leakage is the release of gas through a crack, pore, unbond or similar defect. Permeation through the wall in compliance with A.21 is not considered to be leakage.

A.11 Hydraulic test

Any internal pressure applied after autofrettage and prior to the hydrostatic test shall not exceed 90 % of the
hydrostatic test pressure. One of the following two options shall be used:

Option 1. Volumetric expansion test
a) The cylinder shall be hydrostatically tested to at least 1,5 times working pressure. In no case shall the test
pressure exceed the autofrettage pressure.
b) Pressure shall be maintained for 30 s and sufficiently longer to ensure complete expansion. Any internal
pressure applied after autofrettage and prior to the hydrostatic test shall not exceed 90 % of the hydrostatic
test pressure. If the test pressure cannot be maintained due to failure of the test apparatus, it is permissible to
repeat the test at a pressure increased by 7 bar. No more than 2 such repeat tests are permitted.
c) Any cylinders not meeting the defined rejection limit shall be rejected and rendered unserviceable.

Option 2. Proof pressure test
The hydrostatic pressure in the cylinder shall be increased gradually and regularly until the test pressure, at least 1,5 times working pressure, is reached. The cylinder test pressure shall be maintained for at least 30 s to establish that there are no leaks.

A.12 Hydrostatic pressure burst test

The rate of pressurization shall not exceed 14 bar/s at pressures in excess of 80 % of the design burst pressure. If the rate of pressurization at pressures in excess of 80 % of the design burst pressure exceeds 3,5 bar/s, then either the cylinder shall be placed schematically between the pressure source and the pressure measurement device, or there shall be a 5 s hold at the minimum design burst pressure.
The minimum required (calculated) burst pressure shall be at least 450 bar, and in no case less than the value
necessary to meet the stress ratio requirements. Actual burst pressure shall be recorded. Rupture may occur in either the cylindrical region or the dome region of the cylinder.

A.13 Ambient temperature pressure cycling

Pressure cycling shall be performed in accordance with the following procedure:
a) fill the cylinder to be tested with a non-corrosive fluid such as oil, inhibited water or glycol;
b) cycle the pressure in the cylinder between 20 bar and 260 bar at a rate not exceeding 10 cycles per minute.
The number of cycles to failure shall be reported, along with the location and description of the failure initiation.

A.14 Acid environment test

On a finished cylinder the following test procedure shall be applied:
a) expose a 150 mm diameter area on the cylinder surface for 100 h to a 30 % sulfuric acid solution (battery acid with a specific gravity of 1,219) whilst the cylinder is hydrostatically pressurized to 260 bar;
b) pressurize the cylinder to burst in accordance with the procedure defined in A.12.
The burst pressure shall exceed 85 % of the minimum design burst pressure.

A.15 Bonfire test

A.15.1 General
The bonfire test is designed to demonstrate that finished cylinders, complete with the fire protection system
(cylinder valve, pressure relief devices and/or integral thermal insulation) specified in the design, will prevent the rupture of the cylinder when tested under the specified fire conditions.
Precautions shall be taken during fire testing in the event that cylinder rupture occurs.

A.15.2 Cylinder set-up
The cylinder shall be placed horizontally with the cylinder bottom approximately 100 mm above the fire source. Metallic shielding shall be used to prevent direct flame impingement on cylinder valves, fittings, and/or pressure relief devices. The metallic shielding shall not be in direct contact with the specified fire protection system (pressure relief devices or cylinder valve).
Any failure during the test of a valve, fitting or tubing that is not part of the intended protection system for the design shall invalidate the result.

A.15.3 Fire source
A uniform fire source of 1,65 m length shall provide direct flame impingement on the cylinder surface across its entire diameter. Any fuel may be used for the fire source provided it supplies uniform heat sufficient to maintain the specified test temperatures until the cylinder is vented. The selection of a fuel should take into consideration air pollution concerns. The arrangement of the fire shall be recorded in sufficient detail to ensure that the rate of heat input to the cylinder is reproducible.
Any failure or inconsistency of the fire source during a test shall invalidate the result.

A.15.4 Temperature and pressure measurements
Surface temperatures shall be monitored by at least three thermocouples located along the bottom of the cylinder and spaced not more than 0,75 m apart. Metallic shielding shall be used to prevent direct flame impingement on the thermocouples. Alternatively, thermocouples may be inserted into blocks of metal measuring less than 25 mm square.
Thermocouple temperatures and the cylinder pressure shall be recorded at intervals of every 30 s or less during the test.

A.15.5 General test requirements
The cylinder shall be pressurized to working pressure with natural gas or compressed air and tested in the
horizontal position at working pressure and at 25 % of working pressure if a thermally activated PRD is not used.
Immediately following ignition, the fire shall produce flame impingement on the surface of the cylinder along the 1,65 m length of the fire source and across the cylinder diameter.  Within 5 min of ignition the temperature at least one thermocouple shall indicate a temperature W 590 °C. This minimum temperature shall be maintained for the remainder of the test.
For cylinders of length 1,65 m or less, the centre of the cylinder shall be positioned over the centre of the fire
source.
For cylinders of length greater than 1,65 m, the cylinder shall be positioned as follows:
a) if the cylinder is fitted with a pressure relief device at one end, the fire source shall commence at the opposite end of the cylinder;
b) if the cylinder is fitted with pressure relief devices at both ends, or at more than one location along the length of the cylinder, the centre of the fire source shall be centred midway between the pressure relief devices that are separated by the greatest horizontal distance;
c) if the cylinder is additionally protected using thermal insulation, then two fire tests at service pressure shall be performed, one with the fire centred midway along the cylinder length, and the other with the fire commencing at one of the ends of a second cylinder.

A.15.6 Acceptable results
The cylinder shall vent through a pressure relief device.

A.16 Penetration tests
A cylinder pressurized to 200 bar 10 bar with compressed gas shall be penetrated by an armour piercing bullet with a diameter of 7,62 mm or greater. The bullet shall completely penetrate at least one side wall of the cylinder.
For type CNG-2, CNG-3 and CNG-4 designs, the projectile shall impact the sidewall at an approximate angle of 45°. The cylinder shall not rupture.

A.17 Composite flaw tolerance tests

For type CNG-2, CNG-3 and CNG-4 designs only, one finished cylinder, complete with protective coating, shall have flaws cut into the composite in the longitudinal direction. The flaws shall be greater than the visual inspection limits as specified by the manufacturer. As a minimum, one flaw shall be 25 mm long and 1,25 mm in depth, and another flaw shall be 200 mm long and 0,75 mm in depth, cut in the longitudinal direction into the cylinder sidewall.
The flawed cylinder shall then be pressure cycled between 20 bar and 260 bar at ambient temperature, initially for 3 000 cycles, then followed by an additional 12 000 cycles.
The cylinder shall not leak or rupture within the first 3 000 cycles, but may fail by leakage during the further
12 000 cycles. All cylinders which complete this test shall be destroyed.
A.18 High temperature creep test
This test is required for all type CNG-4 designs, and all type CNG-2 and CNG-3 designs in which the glass
transition temperature of the resin matrix does not exceed 102 °C. One finished cylinder shall be tested as follows:
a) the cylinder shall be pressurized to 260 bar and held at a temperature of 100 °C for not less than 200 h;
b) following the test, the cylinder shall meet the requirements of the hydrostatic expansion test (A.11), the leak test (A.10) and the hydrostatic pressure burst test (A.12).

A.19 Accelerated stress rupture test

For type CNG-2, CNG-3 and CNG-4 designs only, one cylinder shall be hydrostatically pressurized to 260 bar at 65 °C. The cylinder shall be held at this pressure and temperature for 1 000 h. The cylinder shall then be pressured to burst in accordance with the procedure described in A.12, except that the burst pressure shall exceed 85 % of the minimum design burst pressure.

A.20 Impact damage test

One or more finished cylinders shall be drop tested at ambient temperature without internal pressurization or
attached valves. The surface on to which the cylinders are dropped shall be a smooth, horizontal concrete pad or flooring. One cylinder shall be dropped in a horizontal position with the bottom 1,8 m above the surface on to which it is dropped. One cylinder shall be dropped vertically on each end at a sufficient height above the floor or pad so that the potential energy is 488 J, but in no case shall the height of the lower end be greater than 1,8 m. One cylinder shall be dropped at a 45° angle on to a dome, from a height such that the centre of gravity is at 1,8 m; however, if the lower end is closer to the ground than 0,6 m, the drop angle shall be changed to maintain a minimum height of 0,6 m and a centre of gravity of 1,8 m.
Following the drop impact, the cylinders shall then be pressure cycled between 20 bar and 260 bar at ambient temperature, initially for 3 000 cycles, then followed by an additional 12 000 cycles.
The cylinder shall not leak or rupture within the first 3 000 cycles, but may fail by leakage during the further 12 000 cycles. All cylinders which complete this test shall be destroyed.

A.21 Permeation test

This test is only required on type CNG-4 designs. One finished cylinder shall be filled with compressed natural gas
to working pressure, placed in an enclosed sealed chamber at ambient temperature, and monitored for leakage for
500 h. The permeation rate shall be less than 0,25 ml of natural gas per hour per litre water capacity of the cylinder.
The cylinder shall be sectioned and the internal surfaces inspected for any evidence of cracking or deterioration.

A.22 Tensile properties of plastics

The tensile yield strength and ultimate elongation of plastic liner material shall be determined at 50 °C in
accordance with ISO 527-2.
The test results shall demonstrate the ductile properties of the plastic liner material at temperatures of 50 °C or lower by meeting the values specified by the manufacturer.

A.23 Softening temperature of plastics

Polymeric materials from finished liners shall be tested in accordance with a method described in ISO 306.
The softening temperature shall be at least 100 C.

A.24 Coating batch tests

A.24.1 Coating thickness
The thickness of the coating shall be measured in accordance with ISO 2808 and shall meet the requirements ofc the design.

A.24.2 Coating adhesion
The coating adhesion strength shall be measured in accordance with ISO 4624:—, and shall have a minimum
rating of 4 when measured using either test method A or B, as appropriate.

A.25 Boss torque test

The body of the cylinder shall be restrained against rotation and a torque of twice the valve or PRD installation torque specified by the manufacturer shall be applied to each end boss of the cylinder. The torque shall be applied first in the direction of tightening a threaded connection, then in the untightening direction, and finally again in the tightening direction.
The cylinder shall then be subjected to a leak test in accordance with A.10.

A.26 Resin shear strength

Resin materials shall be tested on a sample coupon representative of the composite overwrap in accordance with ISO 14130, or an equivalent standard acceptable to the Inspector in the country of use. Following 24 h boiling in water the composite shall have a minimum shear strength of 13,8 MPa.

A.27 Natural gas cycling test

Special consideration shall be given to safety when conducting this test. Prior to conducting this test, cylinders of this design shall have successfully passed the test requirements of A.10 (leak test), A.12 (hydrostatic pressure burst test), A.13 (ambient temperature pressure cycling test) and A.21 (permeation test).
One finished type CNG-4 cylinder shall be pressure cycled using compressed natural gas between less than 20 bar and working pressure for 1 000 cycles. The filling time shall be 5 min maximum. Unless otherwise specified by the manufacturer, care should be taken to ensure that temperatures during venting do not exceed the defined service conditions.
The cylinder shall be leak tested in accordance with A.10 and meet the requirements therein. Following the
completion of the natural gas cycling the cylinder shall be sectioned and the liner and liner/end boss interface
inspected for evidence of any deterioration, such as fatigue cracking or electrostatic discharge.