D1C.4 Domestic pressure regulators

A study was carried out on the risks involved in not replacing a domestic pressure regulator as part of the conversion from natural gas to hydrogen. The potential risks were inventoried and, in consultation with the guidance group and sparring group, the risks requiring further investigation were identified. A test programme has been determined based on the findings, also in consultation with the guidance/sparring group.

The distribution network operators have been removing pressure regulators from their networks, some due to complaints and some without complaints being received. 40 of these regulators were tested with hydrogen. Based on the findings, 10 regulators were selected and subsequently also tested with natural gas.

The general conclusion based on the studies is that there are no safety risks when the existing domestic pressure regulators are used in converting the pipeline network from natural gas to hydrogen. Nevertheless, there is a chance of more failures occurring due to the more sensitive (earlier) intervention of the UPSO (under-pressure shut-off) valve. The valve shut-off pressures will also increase by a few millibars when hydrogen is used.
This does not give an urgent reason to replace all pressure regulators, seeing as all hydrogen appliances will be equipped with a flame protection device that mitigates the safety risk. If a network operator chooses to replace the pressure regulators in homes as part of the conversion to hydrogen, there is no need to replace them immediately. New pressure regulators can be installed at a later stage and are not necessarily needed at the time of conversion.

• In a relatively large number of the regulators tested with hydrogen, the under-pressure protection (UPSO valve) closes prematurely. This occurs especially when lowering the inlet pressure to 17.5 mbar. It is worth noting that the failure behaviour of the UPSO valve during these tests was the same for natural gas and hydrogen. The minimum required supply pressure is 23.4 mbar, which in practice means that it is highly unlikely that the device is prematurely triggered because the inlet pressure is too low. Even if this were the case, closing the valve too soon will not lead to a dangerous situation. However, supply disruptions may occur sooner due to the more sensitive UPSO valve operation with hydrogen.
• The pre-closed UPSO valve can also open unintentionally in some regulators when the inlet pressure increases to 200 mbar. This could possibly be a safety issue in 200 mbar networks, were it not for the fact that the hydrogen systems will always have protection devices installed because of the requirement since 2010 that all new cookers must be fitted with a flame failure device.
• In all regulators that were tested with natural gas as well as with hydrogen, the regulating characteristics of hydrogen at inlet pressures of 37.5 mbar and 100 mbar were only a fraction (in the order of a few tenths of mbar) below the regulating characteristics of natural gas. No consequences are expected in practice from this marginal effect.
• No irritating noises or vibrations were discerned in any of the tested regulators. There are no indications that using hydrogen will cause more problems than when natural gas is used.
• No external leakage was observed in any of the regulators tested. If a regulator does not show external leakage with natural gas, it is also not likely that the same will happen with hydrogen.
• The shut-off pressure is several millibars higher with hydrogen than with natural gas. Only in highly exceptional cases could this lead to a higher chance that the gas valve of a hydrogen boiler doesn't open at start-up. (N.B. For most gas valve units, the manufacturer prescribes a maximum inlet pressure of 60 mbar).
• The probability of internal leaks from pressure regulators is greater with hydrogen than with natural gas. This effect translates into higher shut-off pressures.

The following is recommended to distribution network operators:
When converting to hydrogen, a choice should be made based on one's own considerations as to whether or not to replace the existing pressure regulators, with or without a UPSO valve that is or is not equipped with a bypass. This choice can be made using the decision tree in figure 6, based on the arguments for and against the various options given in table 11.