D1b.1 internal static electricity and ignition in hydrogen distribution pipelines

This HyDelta study (WP1B.1) focuses on gaining more insight into the role of electrostatic charging and discharging as a potential ignition source in hydrogen distribution pipelines, with the aim of better assessing the associated risk.

The research is structured based on a combination of practical knowledge, theoretical considerations and experimental research. During daily operation, static electricity poses no risk as a potential ignition source. In collaboration with the Expert Assessment Group (EAG), relevant field scenarios have been identified in which the fire triangle may be completed and where electrostatic charge might play a role. This applies particularly during unusual (non-standard) circumstances, such as maintenance work and incidents. A selection of these scenarios (including excavation damage and blow-off) was subsequently used as the starting point for a systematic analysis of the underlying physical mechanisms.

Based on literature and existing knowledge, it was determined how electrostatic charging arises from interactions between dust particles and pipeline materials and what role variables such as gas velocity, dust concentration, humidity, geometry and material properties play in this process. These theoretical insights were subsequently investigated experimentally using a dedicated linear test setup, in which these parameters were varied in a controlled manner. The experiments were supplemented with simplified modelling to place the measured charge buildup and discharge energy in context and relate them to potential ignition criteria.

The analysis shows that ignition by electrostatic discharge is physically possible, but only when a specific and simultaneous combination of preconditions occurs. In addition, there are factors such as low dust concentrations in accordance with the gas quality regulations, the presence of local grounding, and variable environmental conditions that limit the build-up and retention of charge. This means that the risk of ignition due to electrostatic charging is assessed as negligible in practice, although it cannot be completely ruled out.

Material properties play a major role in electrostatic charging and discharging. Gasunie (TSO) operates high-pressure pipeline networks and uses only steel pipes. The regional network operators (DSOs) primarily use PE and PVC materials in existing gas distribution networks. However, in new industrial projects, a new gas distribution network is almost always constructed, in which steel pipes are often used. The steel pipes are conductive materials, whereas the DSOs mainly use insulating materials in their gas network distribution systems, which influences the behavior of electrostatic discharges.

For steel pipes, a spark can jump from a person to the pipe (the electrostatically charged person discharges), and the presence of dust in pipes is not necessary; for PE and PVC pipes, the flashover must originate from the pipe and jump towards the earth (or to a person) (whereby the electrostatically charged plastic inner wall discharges). This is fully elaborated on in the report's synthesis.

Under the circumstances described in the “excavation damage” scenario, it is expected that several of the required conditions will not occur simultaneously. In particular, dust concentrations in the distribution network are generally low and are limited by the application of filters, while other factors such as geometry, relative humidity, and gas flow conditions do not continuously occur in an unfavourable combination. The same reasoning applies to the “blow-off” scenario.

Therefore, although ignition cannot be physically ruled out entirely, the probability of all necessary conditions occurring simultaneously is assessed as being low in practice for both scenarios because:

·        Dust concentrations in the distribution network are generally low;

·        The presence of dust is limited as much as possible by the application of filters in gas pressure regulating stations;

·        Insulating materials can conduct poorly charged particles toward the earth;

·        Flow velocities are limited by the structure of the gas distribution network;

·        The wearing of PPE by technical personnel during work activities and incidents is required, and in the event of a measured gas concentration exceeding 10% of the lower flammability limit, the workplace must be evacuated immediately in accordance with the VWI (G21). Specific work instructions aimed at the application of hydrogen have been drawn up for all hydrogen pilot projects, as well as specific VWI’s. The content of these dedicated VWI’s has not been addressed in this study. 

The situation in which electrostatic charging and discharging of a person may lead to ignition is further investigated in the report on the second part of the study (WP1B.2. - The occurrence of electrostatic discharge outside hydrogen distribution lines and the possible risks) [1].