GB/T 29729-2022Essential requirements for the safety of hydrogen systems (English PDF)

5.2 Combustion characteristics

5.2.2 The detonation limit of hydrogen in air at normal temperature and pressure is within the flammable limit range, and the detonation velocity is 1480 m/s~2150 m/s.

6.1 Leakage and seepage

6.1.1 Hydrogen can easily leak through porous materials, assembly surfaces, or sealing surfaces. After hydrogen leaks, it will spread rapidly, causing the flammable and explosive areas to expand continuously, and the diffusion process is invisible to the naked eye. The main factors affecting the spread of hydrogen leakage include the leakage location, ambient temperature, ambient wind speed, ambient wind direction and obstacles.

6.1.2 After a leak occurs in a liquid hydrogen or slush hydrogen system, the liquid hydrogen will evaporate and diffuse rapidly, forming a visible explosive mist cloud, which may cause negative pressure in the system and cause the surrounding air to enter the system and condense into solid particles, which may clog the system's pipes, valves and other components.

6.1.3 Hydrogen can easily penetrate into certain non-metallic materials and cause hydrogen seepage. If hydrogen seepage occurs in a liquid hydrogen system, it may lead to hydrogen loss or damage to the vacuum insulation layer.

6.2 Hazards associated with combustion

6.2.1 Leaked hydrogen can easily cause combustion or explosion. Hydrogen combustion may cause the performance of hydrogen system materials to deteriorate and may cause the hydrogen system to fail due to overpressure that results from a sharp increase in internal temperature and pressure.

6.2.2 Hydrogen deflagration may lead to the rapid expansion of the combustion area and the rapid increase of the pressure in the confined space. The high-speed detonation wave generated by hydrogen detonation may have a huge impact on the environment outside the combustion area, accompanied by the rapid spread of high-temperature gas.

6.2.3 Hydrogen flames are difficult to detect and shall be detected using ultraviolet detectors or ultraviolet/infrared composite multi-band detectors.

6.3 Stress-related risk factors

6.3.1 Failure of the hydrogen system may result in the rapid release of stored energy in the high-pressure hydrogen, forming a shock wave and damaging surrounding facilities.

6.3.2 Heat leakage in liquid hydrogen and slush hydrogen systems will cause thermal stratification and hydrogen evaporation, resulting in a sharp increase in the volume of hydrogen in the system. If the pressure relief device does not operate in time, it may cause the system to fail due to overpressure.

NOTE: Thermal stratification refers to the fluid stratification phenomenon in which the cold fluid is at the bottom and the hot fluid is at the top due to the difference in fluid density caused by different temperatures in the direction of gravity.

6.3.3 Solid hydrogen particles in slush hydrogen tend to accumulate and precipitate, thus blocking pipes, valves and other components of the slush hydrogen system.

6.3.4 When the system for hydrogen storage in solid state overheats, the hydrogen pressure in the system may rise sharply, causing the pressure vessel to fail due to overpressure.

6.3.5 During the use of containers for hydrogen storage in a solid state, hydride powder may form a local accumulation of powder due to vibration or hydrogen flow, resulting in stress concentration.

6.4 Temperature-related risk factors

6.4.1 The temperature drops sharply during the hydrogen liquefaction process, which may cause the material to shrink. The different shrinkage degrees of hydrogen system materials may cause the system structure to deform in an uncoordinated manner, thereby causing increased stress in the structure or leakage on the sealing surface.

6.4.2 The low-temperature environment of liquid hydrogen and slush hydrogen systems may cause the toughness of the material to decrease and increase the crack sensitivity of the material. When the temperature of the liquid hydrogen and slush hydrogen system is lower than the ductile-brittle transition temperature of the material, the material will change from a ductile state to a brittle state.

6.4.3 When a high-pressure hydrogen cylinder is filled with hydrogen quickly, the temperature inside the cylinder will rise, which may cause the cylinder's carrying capacity to decrease or leakage.

6.4.4 If gases such as air with a freezing point higher than the temperature of liquid hydrogen are mixed into the liquid hydrogen and slush hydrogen systems, solid

a) Control the amount of hydrogen used in storage and operation while meeting demand;

b) Formulate corresponding operating procedures;

c) Reduce the number of people in hazardous environments and shorten their exposure time;

d) Avoid accumulation of hydrogen/air (oxygen) mixture in confined spaces;

e) Install hydrogen and flame detection and alarm devices;

f) Ensure that there is no open flame source in the explosion hazard area of the hydrogen system;

g) Determine the explosion hazard area of the hydrogen system. The definition of the explosion hazard area level shall comply with the provisions of GB 50058;

h) Ensure that there is no other debris in the explosion hazard area of the hydrogen system and that the passages are unobstructed.

7.2 Risk control in design

7.2.3.1.10 The design, manufacture, inspection and testing of hydrogen cylinders shall comply with the requirements of GB/T 5099(all parts), GB/T 33145, etc. The aluminum liner carbon fiber fully wrapped gas cylinders for compressed hydrogen for vehicles shall comply with the requirements of GB/T 35544.

7.2.3.1.11 The gas cylinders, pipelines, valves and other accessories of the hydrogen gas cylinder group shall be securely fixed, and the pipelines, valves and other accessories shall be equipped with protective facilities to prevent collision damage.

7.2.4.2.2 The hydrogen pipeline shall be equipped with a vent pipe, analysis sampling port, and purge port; their positions shall meet the requirements of gas discharge, sampling, purge and replacement in the pipeline.

7.2.1 Basic requirements

7.2.1.1 The hydrogen system design shall meet the following basic requirements. a) Fail-safe design.

1) Install safety accessories such as safety relief devices and flame arresters;

2) Set single fault tolerance or double fault tolerance.

b) Automatic safety control.

1) Remotely monitor the security status of the system in real-time;

2) Automatically control operating parameters such as pressure and flow rate;

3) When hydrogen leakage or flame is detected, the equipment can automatically take corresponding safety measures, including closing the stop valve, opening the ventilation device, shutting down the equipment, etc.

c) When the hydrogen system has an abnormality, fault or malfunction, the alarm device can give an alarm in time.

7.2.1.2 A safety integrity assessment should be performed.

7.2.2 Reasonable material selection

7.2.2.1 The following factors shall be evaluated when selecting materials for hydrogen systems.

-- Compatibility with hydrogen;

-- Compatibility with adjacent materials;

-- Compatibility with the use environment;

-- Toxicity;

-- Failure mode;

-- Processability;

-- Economy.

7.2.2.2 Metal materials used in hydrogen systems shall meet strength requirements and have good plasticity, toughness and manufacturability. They shall also have good low-temperature toughness when used in low-temperature conditions, and their ductile-brittle transition temperature shall be lower than the operating temperature of the system.

7.2.2.3 Non-metallic materials used in hydrogen systems shall have good resistance to hydrogen penetration.

7.2.2.4 Materials in direct contact with hydrogen in hydrogen systems shall have good compatibility with hydrogen. The compatibility test of metal materials with the hydrogen environment shall comply with the requirements specified in GB/T 34542.2, and the hydrogen embrittlement sensitivity test shall comply with the requirements specified in GB/T 34542.3.

7.2.2.5 For hydrogen systems, steel with low carbon content or steel containing strong carbide-forming elements should be used.

7.2.2.6 For commonly used metal materials and non-metal materials in hydrogen environments, see Appendix D. To reduce the hydrogen embrittlement sensitivity of metal materials, the following measures shall be taken.

a) Control the material hardness and strength to an appropriate level;

b) Reduce residual stress;

c) Avoid or reduce cold plastic deformation of materials;

7.2.3.2 Liquid hydrogen storage containers

7.2.3.2.1 Liquid hydrogen storage containers shall be equipped with an insulation system with good insulation effect. Both the inner container and the vacuum interlayer shall be equipped with a safety relief device. The relief volume design shall evaluate the overpressure hazard caused by the rapid phase change of liquid hydrogen.

7.2.3.2.2 The support and foundation of liquid hydrogen storage containers shall be insulated and non-combustible and ensure they are firm.

7.2.3.2.3 The vent pipe of the liquid hydrogen storage container shall be installed at the top of the container, and the speed of hydrogen discharge should be controlled to prevent accidents such as fire and explosion.

7.2.3.2.4 The liquid outlet pipe of the liquid hydrogen storage container should be led out from the bottom of the container, and a shut-off valve shall be installed on the liquid hydrogen pipeline.

7.2.3.2.5 The coating and transport packaging of stationary liquid hydrogen storage containers, mobile liquid hydrogen storage containers and their components shall comply with the requirements specified in NB/T 10558 and the technical requirements of the drawings.

7.2.3.2.6 The rated filling rate of liquid hydrogen pressure vessels shall not be greater than 90% of the geometric volume of the inner container.

7.2.3.2.7 Liquid hydrogen pressure vessels shall be equipped with pressure and liquid level measuring instruments in the control room and on-site respectively.

7.2.3.3 Slush hydrogen storage containers

In addition to complying with the relevant provisions in 7.2.3.2, slush hydrogen storage containers shall also meet the following requirements.

a) Prevent pollutants from entering the container and promptly handle the accumulation of solid hydrogen particles in the container;

b) Replenish or concentrate slush hydrogen in a timely manner to ensure that the mass fraction of solid hydrogen in the container meets the requirements.

7.2.3.4 Solid-state hydrogen storage containers

7.2.3.4.1 The technical requirements, testing and inspection, marking, packaging, etc. of solid-state hydrogen storage containers shall comply with the requirements of GB/T 34544, GB/T 33292, etc.

7.2.3.4.2 In addition to complying with the relevant provisions of 7.2.3.1.4 and 7.2.3.1.5, solid-state hydrogen storage containers shall also meet the following requirements.

a) Prevent local accumulation of solid fillers during use;

b) A filter with a filtration accuracy matching the particle size of the solid-state hydrogen storage material is installed at each end of a single tube or a row of tubes.

7.2.3.4.3 Depending on the size of the hydrogen storage capacity and the thermal effect of the solid-state hydrogen storage material, the solid-state hydrogen storage container should be equipped with a heat exchange structure.

7.2.3.5 Pumps and compressors

7.2.3.5.1 The type and quantity of hydrogen compressors shall be determined based on the inlet pressure, exhaust pressure, hydrogen purity and hydrogen consumption or usage characteristics.

7.2.3.5.2 The model and exhaust volume of the compressor used for hydrogen filling shall be determined according to the specifications and quantity of the filling station or filling container, filling time, intake pressure and exhaust pressure.

7.2.3.5.3 The type and quantity of liquid hydrogen booster pumps shall be determined based on the liquid inlet pressure, liquid discharge pressure and hydrogen consumption or usage characteristics.

7.2.3.5.4 The hydrogen-related components of hydrogen compressors and liquid hydrogen booster pumps shall have good hydrogen compatibility under the conditions of use.

7.2.3.5.5 A hydrogen tank should be installed in front of the compressor that is used to transport hydrogen, and a hydrogen buffer tank shall be installed after it.

7.2.3.5.6 When several hydrogen compressors are connected in parallel to draw air from the same hydrogen pipeline, measures shall be taken to ensure that the hydrogen pressure on the suction side is positive. of GB 50177; when hydrogen pipelines are laid together with other pipelines or arranged in layers, they shall comply with the requirements of GB 4962.

7.2.4.3 Liquid hydrogen and slush hydrogen pipelines

7.2.4.3.1 Pipeline insulation shall adopt high vacuum multi-layer insulation, vacuum powder insulation or other insulation methods with excellent insulation effect.

7.2.4.3.2 When using corrugated expansion joints, the piping system shall have sufficient elasticity to avoid failure or leakage of the piping due to thermal expansion and contraction.

7.2.4.3.3 Threaded connections should not be used.

7.2.4.3.4 Liquid hydrogen and slush hydrogen pipelines shall be equipped with safety relief devices at locations where liquid may be retained, and liquid discharge pipelines shall be provided with slopes.

7.2.4.3.5 Liquid hydrogen and slush hydrogen pipelines shall be kept away from flammable materials such as asphalt, and materials around the pipelines that are prone to low-temperature embrittlement shall be protected.

7.2.4.3.6 Liquid hydrogen and slush hydrogen pipelines should not be used for long-distance transportation. Slush hydrogen pipelines shall prevent the precipitation of solid hydrogen particles and flow stratification.

7.2.5 Attachments

7.2.5.1 Safety relief devices

7.2.5.1.1 Safety relief devices (including safety valves, bursting discs and auxiliary pressure relief devices) shall meet the following basic requirements.

a) The unit that manufactures the safety relief device holds the corresponding special equipment manufacturing license;

b) The safety relief device can ensure that the system pressure is always no higher than the maximum allowable working pressure of the system, its size is adapted to the maximum flow of the pressure source, and it still has sufficient relief capacity under extreme conditions;

c) If the low-pressure hydrogen system is connected to the high-pressure hydrogen source through a pressure regulator, and the upper-pressure limit of the low-pressure hydrogen system is lower than the pressure of the high-pressure hydrogen source, a safety relief device shall be installed in the low-pressure hydrogen system to prevent overpressure;

d) The material of the safety relief device can adapt to the operating temperature of the hydrogen system and has good compatibility with hydrogen;

e) When multiple safety relief devices are installed on a liquid hydrogen or slush hydrogen pipeline, each safety relief device does not affect the pipeline flow rate, and does not affect the opening pressure of other safety relief devices during operation;

f) No stop valve is installed between the safety relief device and the protected container or pipeline.

7.2.5.1.2 The safety valve shall also meet the following requirements.

a) The movable part of the safety valve is flexible and can move when unevenly heated or cooled, and no packing that may prevent the normal operation of the safety valve is used;

b) A fall lift safety valve with a product certificate or quality certificate is used, and it is only installed after it has been calibrated and sealed;

c) The safety valve is installed vertically on the discharge pipeline where it is easy to observe and inspect and close to the protected container.

7.2.5.1.3 The bursting disc shall also meet the following requirements.

a) The bursting disc does not produce sparks or metal fragments when it explodes;

b) The bursting disc is replaced regularly according to its service life;

c) The bursting disc is equipped with a safety protection cover.

7.2.5.1.4 When designing and installing auxiliary pressure relief devices, transient pressures caused by liquid hammer, cavitation, etc. shall be evaluated.

7.2.5.2 Valves

7.2.5.2.1 The hydrogen overflow valve shall adopt a self-starting device. When the flow rate reaches the preset maximum value, the overflow valve shall close automatically.

7.2.5.2.2 The shut-off valve for the hydrogen pipeline should be a ball valve or a stop valve.

7.2.5.2.3 Valve materials and sealing packings should be selected based on the working […]