I have worked with three (3) organizations in the past 5 years on their efforts to make H2 an everyday fuel for household appliances, vehicles, and industrial fuels. Each project was a huge learning experience for everyone! But I am a lover of “codes” to establish the baseline design, construction, operation, and maintenance. I looked to my IFC for guidance, and I was not let down. For those dabbling in H2, here are the fundamentals:
5806.3 Above-ground tanks for liquid hydrogen.
Above-ground tanks for the storage of liquid hydrogen shall be in accordance with Sections 5806.3.1 through 5806.3.2.1.
Section 5806.3 introduces provisions that address the requirements for above-ground tank construction in greater detail than Section 5003.2.1. The requirements for the construction of above-ground tanks parallel those for underground tanks, except that the vacuum jacket (outer tank) is NOT required to meet the requirements of the ASME BPVC. The vacuum jacket provides an improved insulating barrier around the inner storage vessel by using a vacuum and an insulating layer. The vacuum jacket space is also designed to contain and relieve hydrogen should a leak occur into the annular space. The jacket is designed to a safety factor of two (2). For underground tanks, the safety factor is 3.5.
Design criteria for such tanks can be found in CGA H-3, which, while not referenced in the code, is available to those seeking more detailed design requirements than would otherwise be available through Section 5003.2.1. The minimum design requirements established by Section 5806.3, coupled with the general requirements of Chapter 55 applicable to all cryogens, result in greater consistency and increased public safety.
5806.3.1 Construction of the inner vessel.
The inner vessel of storage tanks in liquid hydrogen service shall be designed and constructed in accordance with Section VIII, Division 1, of the ASME Boiler and Pressure Vessel Code and shall be vacuum jacketed in accordance with Section 5806.3.2.
Hydrogen in the liquid state must be stored in insulated tanks at very low temperatures, usually at or below -423°F, to maintain that temperature. The inner vessel of the assembly must be constructed as a pressure vessel in accordance with the ASME BPVC, Section VIII, Division 1, to withstand the liquid hydrogen pressures. Liquid hydrogen storage tanks are designed and manufactured as double-walled tanks equipped with a layer of insulation between the inner tank and the outer jacket. Additionally, the annular space between the inner tank and outer jacket is held under a vacuum for further insulation. Leakage of either the outer jacket due to external corrosion or the inner tank due to an internal crack will result in a loss of vacuum and early detection of the leak.
5806.3.2 Construction of the vacuum jacket (outer vessel).
The vacuum jacket used as an outer vessel for storage tanks in liquid hydrogen service shall be of welded steel construction designed to withstand the maximum internal and external pressure to which it will be subjected under operating conditions to include conditions of emergency pressure relief of the annular space between the inner and outer vessel. The jacket shall be designed to withstand a minimum collapsing pressure differential of 30 psi (207 kPa).
For above-ground liquid hydrogen vessels, the requirements in this section are applicable. Above-ground vacuum-jacketed vessels must be designed to withstand the maximum internal and external pressure to which they may be subjected. Because the primary inner vessel is designed as a pressure vessel, the vacuum jacket must be designed to withstand a collapse due to the loss of vacuum and be capable of withstanding the pressure that can result in the event the liquid hydrogen vessel becomes involved in a fire or is subjected to the radiation energy of an exposure fire. While the probability of such an event is low, hydrogen could leak from the primary pressure vessel into the annular space created by the vacuum jacket. This section requires that the outer vessel be designed for a minimum collapse pressure differential of 30 psig (207 kPa) and with a means of pressure relief to ensure that the inner primary vessel and the outer jacket safely relieve any pressure in the event the vessel is subjected to fire exposure.
5806.3.2.1 Vacuum-level monitoring.
A connection shall be provided on the exterior of the vacuum jacket to allow measurement of the pressure within the annular space between the inner and outer vessels. The connection shall be fitted with a bellows-sealed or diaphragm-type valve equipped with a vacuum gauge tube that is shielded to protect against damage from impact.
This section requires a means of monitoring the hydrogen tank’s vacuum jacket to ensure that the vacuum is maintained. Loss of vacuum will increase the heating of the primary vessel, thereby increasing the pressure inside the inner vessel. This will eventually cause the pressure relief device to operate. For above-ground liquid hydrogen tanks, a connection with a tube or pipe terminating in the vacuum space must be equipped with a vacuum pressure gauge to monitor pressure. This section specifies the use of a bellows-sealed or diaphragm valve. A bellows valve is constructed with a steel bellows welded to the valve stem and bonnet. This bellows creates a multilayer barrier that prevents the release of any product around the valve packing or gasket. Bellows valves are generally specified based on the number of cycles they are expected to undergo over their service life, which can range from 2,000 to 10,000 cycles. A diaphragm valve is constructed similarly, with an internal diaphragm that isolates the valve’s working parts from the cryogenic hydrogen and the valve inlet from the valve outlet.
5806.4.2 Location. Storage tanks shall be located outside in accordance with the following: 1) Tanks and associated equipment shall be located with respect to foundations and supports of other structures such that the loads carried by the latter cannot be transmitted to the tank. 2) The distance from any part of the tank to the nearest wall of a basement, pit, cellar or lot line shall be not less than 3 feet (914 mm). 3) A minimum distance of 1 foot (305 mm), shell to shell, shall be maintained between underground tanks.
Underground tanks must be located away from a building or structure so that the tank does not inadvertently bear the weight of structures it was not designed to support, which could cause the underground tank to rupture. Similarly, underground tanks are to be at least 3 feet (914 mm) from the nearest below-grade wall or property line to prevent leakage from migrating through the soil and entering an adjacent basement, cellar, or pit. Further, the location of an underground storage tank should not pose a risk of affecting adjacent property. To provide physical independence between underground tanks so that they share no common or projected loads, a minimum shell-to-shell clearance of 1 foot is required between adjacent tanks.
5806.4.3 Depth, cover, and fill.
The tank shall be buried such that the top of the vacuum jacket is covered with not less than 1 foot (305 mm) of earth and with concrete not less than 4 inches (102 mm) thick placed over the earthen cover. The concrete shall extend not less than 1 foot (305 mm) horizontally beyond the footprint of the tank in all directions. Underground tanks shall be set on firm foundations constructed in accordance with the International Building Code and surrounded with not less than 6 inches (152 mm) of noncorrosive inert material, such as sand.
Exception: The vertical extension of the vacuum jacket as required for service connections.
Excavation for underground tanks must not damage existing adjacent structures and must provide a sound foundation for the underground tank. The use of 6 inches (152 mm) of well-tamped, noncorrosive material (e.g., sand or clean pea gravel) around an underground tank prevents concentrated loads from being applied to the tank. These concentrated loads can be caused during backfilling when a hard, solid object, such as a rock, comes in contact with the underground tank. Soil pressures on the rock can be concentrated over a small contact area with the underground tank, leading to a leak in the vacuum jacket.
While the 1 foot of earth cover plus a 4-inch (102 mm) concrete slab will provide physical protection for the tank from most predictable load scenarios, it would not alone provide adequate protection from the imposition of vehicular loads on the tank. However, the provisions of this section and those for vacuum jacket construction in Section 5806.4.8 are intended to work together to provide adequate protection from all anticipated loads, including vehicle loads. The exception recognizes the practical limitations of maintaining the required burial depth and cover on vertical vacuum jacket extensions used to provide above-ground control and monitoring points, such as for vacuum and liquid level gauges, manually operated valves, controls, pressure relief devices and instrumentation. Such extensions must be readily accessed by mobile supply equipment at ground level and by authorized personnel.
5806.4.4 Anchorage and security.
Tanks and systems shall be secured against accidental dislodgement in accordance with this chapter.
Sections 5503.5.2 and 5504.3.1.1.4 detail the provisions for the security of cryogenic fluid containers. See the commentaries to those sections for further information.
5806.4.5 Venting of underground tanks.
Vent pipes for underground storage tanks shall be in accordance with Section 5503.3.
Section 5503.3 regulates pressure relief vent piping. Note that the provisions of Chapter 8 of NFPA 2 also apply in accordance with Section 5801.1. For further information, see the commentaries to Sections 5503.3 through 5503.3.2.
5806.4.6 Underground liquid hydrogen piping.
Underground liquid hydrogen piping shall be vacuum jacketed or protected by approved means and designed in accordance with Chapter 55.
Piping associated with underground liquid hydrogen storage tanks must be provided with the same level of design integrity as the tank that it serves. If the piping is not designed with a vacuum jacket, an engineered design complying with the performance requirements of Chapter 55 and approved by the fire code official must be provided.
5806.4.7 Overfill protection and prevention systems.
An approved means or method shall be provided to prevent the overfill of all storage tanks.
The purpose of spill and overfill protection equipment is to reduce the potential for a hydrogen release during deliveries by stopping or reducing product flow, or alerting the delivery person before the tank becomes full and begins releasing hydrogen into the environment. The equipment must be maintained in proper working order and used properly to provide adequate protection from overfills.
5806.4.8 Vacuum jacket construction.
The vacuum jacket shall be designed and constructed in accordance with Section VIII of ASME Boiler and Pressure Vessel Code and shall be designed to withstand the anticipated loading, including loading from vehicular traffic, where applicable. Portions of the vacuum jacket installed below grade shall be designed to withstand anticipated soil, seismic and hydrostatic loading.
This section, along with Section 5806.4.3, requires that the design of the tank’s vacuum jacket, burial depth, and cover work together to provide a tank installation unlikely to be affected by any anticipated loading conditions, including the possibility of vehicles being driven over the installation site.
5806.4.8.1 Material.
The vacuum jacket shall be constructed of stainless steel or other approved corrosion-resistant material.
Soil and environmental conditions can initiate or accelerate corrosion, which can weaken the tank and create a potential for leaks. The tank must be protected from corrosion by use of corrosion-resistant material, coatings, cathodic protection, or alternative methods approved by the fire code official.
5806.4.8.2 Corrosion protection.
The vacuum jacket shall be protected by approved or listed corrosion-resistant materials or an engineered cathodic protection system. Where cathodic protection is utilized, an approved maintenance schedule shall be established. Exposed components shall be inspected not less than twice a year. Records of maintenance and inspection events shall be maintained.
Corrosion-induced deterioration of tanks, piping, and components can lead to leaks and spillage of liquid hydrogen. Using noncorrodible materials of construction or cathodic (galvanic) protection can protect the tank, piping, and components from deterioration and failure caused by corrosion.
Cathodic protection uses a sacrificial anode to prevent the corrosion of the tank’s metal vacuum jacket. The need to replace the sacrificial anode will depend on the corrosion rate. While not specifically prohibited by this section, the joining of dissimilar metals in system construction should also be avoided because of the localized galvanic action that could occur between them. This localized galvanic action can cause metals to corrode to the point of failure.
Because cathodic protection systems are more complex than other corrosion protection methodologies, and in order to verify that the system is functioning properly, a fire code official’s approved maintenance and inspection schedule must be established with all activities recorded. Records must be retained and made available for examination by the fire code official upon request.
5806.4.8.3 Vacuum-level monitoring.
An approved method shall be provided to indicate loss of vacuum within the vacuum jacket(s).
For vacuum-jacketed tanks to effectively maintain liquid hydrogen at the required temperature, the vacuum level must be maintained. This section requires that an approved method of monitoring the integrity of the vacuum jacket be provided. Where an electronic monitoring and alarm system is not employed, administrative procedures are required to ensure regular checking of the vacuum level to prevent the loss of the liquid hydrogen (see commentary,
Section 5806.3.2.1).