GB/T 42626-2023Periodic inspection and evaluation of fully wrapped fibre reinforced composite gas cylinders of compressed hydrogen gas for automotive vehicles (English PDF)

4.1 Types and Descriptions of Gas Cylinder

4.1.1 Type 3 gas cylinder Fully-wrapped carbon fiber reinforced cylinder with an aluminum alloy liner.

4.1.2 Type 4 gas cylinder Fully-wrapped carbon fiber reinforced cylinder with a plastic liner.

4.2 Inspection Tools and Devices The inspection institution shall be equipped with at least the following tools and devices:

a) Explosion-proof lamp: used to inspect the inner and outer surfaces of gas cylinders and the surface of accessories. The voltage shall not exceed 12 V, and shall satisfy the requirements of explosion-proof level II class C and group T1 in GB/T 3836.1;

b) Inspectoscope and endoscope: used to inspect the surface of gas cylinder and the inner surface of gas cylinder (including the inner surface of the neck) that are partially obscured due to installation. The endoscope shall be in high-definition color and have the function of storage;

c) Special tools, for example, torque wrench: used for the disassembly and installation of gas cylinders, cylinder valves or TPRD end plugs;

d) Depth gauge: used to measure the depth of damages, such as: scratches, dents and abrasions, etc.;

e) Length measurement tools: including rulers, squares and tape measures, which are used to measure the length of damages, etc.;

f) Hydrostatic test device: used for hydrostatic test of gas cylinders;

g) Air-tightness test device: used for air-tightness test of gas cylinders;

h) Air-tightness helium leak detection device: used for helium leak detection of gas cylinders;

i) Hydrogen venting / recovery device: used for the discharge or recovery of hydrogen gas;

j) Cleaning device: used for the cleaning of contaminants and corrosion products on the inner and outer surfaces of gas cylinders;

k) Portable pumping-type hydrogen leak detection device: used to detect hydrogen

5.1 Pre-inspection of Hydrogen Storage System

5.1.1 Overview The pre-inspection of the hydrogen storage system includes appearance patrol inspection and hydrogen leak detection.

5.1.2 Appearance patrol inspection Before the appearance patrol inspection, it shall be confirmed that the on-board hydrogen system has been powered off. In the appearance patrol inspection, the gas cylinders, cylinder valves, connecting pipelines, fixing brackets or fastening belts shall be inspected. If the following conditions are satisfied, the inspection result is qualified:

a) The fixing bracket or fastening belt of the gas cylinder is intact, and not loosening or deformed;

b) The cylinder valves and hydrogen pipelines of the cylinder group or a single cylinder are not loosening or damaged, and there are no obvious signs of gas leakage;

c) There is no abnormality on the surface of the gas cylinder and cylinder valve.

5.1.3 Hydrogen leak detection

5.1.3.1 After the appearance patrol inspection, hydrogen leak detection shall be carried out one by one on the gas cylinders, cylinder valves / TPRD end plugs, connecting pipeline joints on the hydrogen storage system and other parts where leaks may occur.

5.1.3.2 The detection pressure of hydrogen leakage shall not be lower than 20% of the nominal working pressure.

5.1.3.3 A portable pumping-type hydrogen leak detection device shall be used for detection. The resolution of the instrument shall not be lower than 1 mL/m3, and the minimum detection concentration shall not be greater than 100 mL/m3.

5.1.3.4 Thoroughly rotate the end of the detection head of the instrument in the site to be detected to find the maximum leakage point, and read the hydrogen concentration value at that location. When there may be condensation water dripping from the detection area, it is advisable to install a detection head shield with a lateral opening on the detection head of the instrument.

5.1.3.5 If leakage is found through detection, the actual measured hydrogen concentration shall not be greater than 300 mL/m3.

5.1.3.6 The hydrogen leak detection device shall be regularly verified or calibrated, and the verification or calibration cycle shall comply with the relevant stipulations.

5.2 Information Query and Recording

5.2.1 Before the inspection of the gas cylinder, the following information shall be consulted:

a) Relevant information provided by the gas cylinder manufacturing organization, including gas cylinder supervision and inspection certificate, instructions for use and certificate of conformity, etc.;

b) Relevant information provided by the vehicle manufacturing organization (when the on-board hydrogen system is installed by the vehicle manufacturing organization) or on-board hydrogen system integration organization (when the on-board hydrogen system is installed by an organization other than the vehicle manufacturing organization);

c) Registration certificate for gas cylinders for automotive vehicles;

d) Previous inspection reports;

e) Filling records of gas cylinders after the last inspection, daily maintenance records, emergency measures and handling records of accidents or abnormal situations, etc.

5.2.2 Check and record the manufacturing mark and inspection mark of gas cylinders. The recorded content shall at least include license number or organization code of the manufacturing organization, gas cylinder manufacturing standard, gas cylinder serial No., manufacturing year and month, nominal working pressure, hydrostatic test pressure, nominal water capacity, design service life, design cycle times, REE, manufacturing organization and model of cylinder valve and TPRD end plug (if present, the same below), the date of the last inspection and the name or code of the inspection institution, etc. For imported gas cylinders, the nationality shall be recorded.

5.2.3 Gas cylinders manufactured by manufacturing organizations that have not obtained When it is confirmed that the known chemicals, by which, the gas cylinder is contaminated, will not cause damage to the gas cylinder, it shall be determined as level 1 damage; spots, blistering, softening, resin falling-off, fiber breakage or looseness caused by chemical erosion of the gas cylinder shall be determined as level 3 damage; when the type of chemical cannot be determined, or the impact on the gas cylinder material cannot be confirmed, it shall also be determined as level 3 damage.

6.3.5 Ageing When a gas cylinder is exposed to sunlight and atmospheric environment for a long time, the glass fiber protective layer on the outer surface of the gas cylinder will be damaged and aged, which may cause discoloration or degradation of the outer surface material. If only the surface layer of resin is pulverized, and no fiber in the wrapping layer is broken or loosened, it shall be determined as level 1 or level 2 damage; otherwise, it shall be determined as level 3 damage.

6.3.6 Impact damage Impact damage is caused by a strong impact on the surface of the gas cylinder. Impact damage may cause permanent deformation and dents on the surface of the gas cylinder, and may also cause delamination of the wrapping layer and fiber breakage. Surface damage related to impact damage includes: scratch, scuffing, bruise, fiber breakage or looseness, resin cracking, discoloration, dent or cylinder body deformation. When the above-mentioned damage exists, the surface of the gas cylinder shall be meticulously inspected, and the impact damage to the gas cylinder can be tested by tapping. If a small metal hammer is used to gently tap the surface of the wrapping layer to test the impact-damaged area, the sound emitted by the impact- damaged area will be significantly different from the sound emitted by the undamaged area. Meanwhile, an emphasis shall be placed on the following aspects.

a) Inner wall damage: the known impact area, surface damage area and inner wall of the gas cylinder shall be inspected to determine whether the inner wall has been damaged. If there is permanent deformation on the surface of the gas cylinder or any inward bulge on the inner wall, it shall be determined as level 3 damage.

b) Gas cylinder color: there may be local color changes on the surface of the impacted gas cylinder. Such changes are caused by delamination, cracking or cracks of the wrapping layer material, and bruises on the outer surface. Delamination of the wrapping layer shall be determined as level 3 damage.

c) Surface cracks: the impacted gas cylinder may manifest circular, oval or linear local surface cracks on the surface of the wrapping layer material. Cracks as deep as the carbon fiber layer shall be determined as level 3 damage.

6.3.7 Stress corrosion cracking The stress corrosion cracking of the gas cylinder may be caused by erosion by the environment (for example, carbonic acid or other acidic materials leaking from vehicle components). The stress corrosion cracking on the wrapping layer usually appears as cracking or collective cracking perpendicular to the fiber direction. Gas cylinders with cracking or collective cracking shall be determined as level 3 damage.

11.1 Method and Requirements for Drying

11.1.1 Gas cylinders that have passed the hydrostatic test shall be internally dried one by one.

11.1.2 Turn the cylinder upside down for a period of time or use special water drainage equipment to drain the remaining water in the cylinder, then, use dry air or nitrogen to blow it, or adopt other appropriate methods to dry the interior.

11.1.3 During internal drying, the temperature shall not exceed 70 C; the time shall be long enough to ensure that the inside of the gas cylinder is completely dry.

11.2 Inspection of Drying Condition With the help of an endoscope, observe the drying condition and cleanliness inside the gas cylinders. The inside of the gas cylinders shall be free of visible particulates, metal shavings and other impurities. The inner wall shall be completely dry and have no particulate impurities 100 m. Instruments, such as: particle detectors or particle size detectors can be used to detect the particulate impurities.