4.2 Hydrogen containment and piping

Measures to prevent the release of dangerous substances should be given the highest priority. The likelihood of a leak occurring can be minimised by using high quality engineering.

Particular attention should be paid to the design, installation, operation and maintenance of hydrogen handling equipment in order to reduce the likelihood and size of any leak [19]. The following points should be taken into account as recommended best practices [2]:

• Ensure that the storage equipment, pipe work and connections conform to an approved standard for hydrogen equipment [25];
• Ensure that maintenance work if effectively controlled and is only carried out by authorised competent people;
• Minimise the frequency with which connections are made and broken;
• For gaseous supply, use appropriate refillable stationary storage in preference to regularly replacing large numbers of separately connected cylinders;
• Use the minimum amount of storage that is practical without disproportionately increasing other hazards, such as those associated with moving gas cylinders;
• Use the minimum length and size of pipe work that is appropriate;
• Use the minimum length of high pressure pipe work, from the pressure source to the high pressure regulator;
• Where possible, use as small a diameter and operating pressure as possible, flow restriction may also be used on high pressure pipe work, in order to minimise mass flow of hydrogen and hence the consequences of any unintended releases, (see Figure A.1 Appendix 6);
• Minimise hydrogen inventories where possible (Appendix A6);
• Minimise the number of joints by using continuous lengths of pipe work wherever practicable;
• Where possible use fusion joints (welded or brazed) to join pipe work, flange/threaded connectors may be used where necessary;
• Give due consideration to the risk of fatigue due to vibrations in pipes;
• Ensure that the system is leak tested before use in a manner appropriate to hydrogen systems [25];
• Use a high pressure relief valve downstream from the high pressure regulator that is able to vent into a ‘safe’ place where hydrogen gas cannot accumulate but can freely disperse;
• Suitable isolation valves, with locking facilities, should be used to enable isolation of sections of pipe work/system for routine maintenance and in emergencies;
• All hydrogen handling equipment and piping shall be identified and appropriately labelled;
• Carry out appropriate inspections of the system at suitable regular intervals and record the results;
• Review the operation and maintenance history at suitable intervals.

When high-pressure storage is used, it should be designed and built to an appropriate design code or standard and located in a secure open-air compound [25]. Measures appropriate to the location should be taken to prevent unauthorised access, vandalism and impact from vehicles.

Cryogenic hydrogen storage installations should be constructed to an appropriate code and located in a suitable open-air position and not within an occupied building [29]. Low temperature storage installations should incorporate suitable measures to prevent oxygen-rich liquid air, a powerful oxidising agent, from condensing on uninsulated surfaces exposed to liquid hydrogen temperatures. To avoid the risk from fire, potentially flammable materials, including asphalt and tarmac, should not be present beneath pipe work where condensation may occur.

Only appropriate pipe work and fittings for the supply of hydrogen should be used [8, 25]. Cupro-nickel and stainless steel are preferred materials for high-pressure pipe work whereas copper can be used for lower pressures. All pipe work joints should be brazed or welded where possible. Flanged or screwed joints may be used where necessary. Suppliers should be able to provide information on the operating parameters of pipe work and fitting, and the standards used for their manufacture.

Compression joints are generally not recommended for use on hydrogen systems as it is difficult to achieve and maintain these in a leak-free condition. Where their use is considered essential, such as on small-bore pipe work, they should be suitable for the duty and used in strict accordance with the manufacturer’s instructions.

Particular attention should be given to the design and location joints in the system that may require regular maintenance, or where mechanical joints will be frequently disturbed or made/broken as the likelihood of leaks in these areas is increased. The connection between the cylinder and the manifold is typical of these and should be checked with a suitable detection solution or suitable electronic gas detection device whenever the cylinder is changed [30].

Pipe routing should reflect consideration of factors such as risk from impact damage, formation of flammable mixtures in poorly ventilated areas, heat sources etc. Consequently, where pipe work passes through enclosed ducts, cavity walls etc, there should be no mechanical joints.

Piping should preferably be routed above ground; if underground pipe work is unavoidable, it should be adequately protected against corrosion. The position and route of underground piping should be recorded in the technical documentation to facilitate safe maintenance, inspection or repair. Underground hydrogen pipelines should not be located beneath electrical power lines.

Pipe work should be cleaned before being place into service using a suitable procedure for the type of containment, which provides a level of cleanliness required by the application.

Systems should be suitably purged using an inert gas (i.e. nitrogen) to prevent the existence of a hydrogen/air mixture. Purging can be by sweep purging, evacuation or repeated pressurisation and venting cycles, using appropriately engineering and sited vent and purge connections. Also, consideration should be given to the asphyxiation hazards of using inert gases.