The latest DVGW Guideline G221 gives recommendations for preparation of the obligatory risk assessment (Gefährdungsbeurteilung) which must be carried out prior to operation of existing or new infrastructure using hydrogen.

Note: This article is translated from the original German text and considers the German regulatory framework. Nevertheless, many of the themes in relation to hydrogen are considered applicable in the international context.

European Hydrogen Backbone (Source: EHB Initiative)

The new coalition government in Germany has reinforced the national hydrogen strategy as part of the aim of achieving CO2-neutrality by 2045. This includes planning for 10GW domestic electrolytic hydrogen generation capacity (green hydrogen) by 2030, facilities for hydrogen import, and a corresponding expansion of the inland hydrogen transport and distribution infrastructure.

In addition to new hydrogen pipelines, this will require the repurposing of a significant portion of the existing German natural gas pipeline network for hydrogen transport. FNB (German association of gas transmission companies) estimates that up to 90% of the future hydrogen network shall comprise repurposed natural gas pipelines. The GET H2 consortium has proposed an initial ‘hydrogen backbone’ comprising 5,100 km new and reassigned pipelines to be in place by 2030, and this has been adopted into the official Network Development Plan (NEP 2022-2032) of the Bundesnetzagentur. The German hydrogen network shall eventually be extended and integrated into an overall European Hydrogen Backbone (EHB) estimated to comprise around 40,000km by 2040.

These ambitious goals require careful technical analysis, as well as minimisation of the associated risks. In Germany, the DVGW is responsible for the development of corresponding Technical Rules and Guidelines relating to hydrogen transport. This includes recent publications, such as DVGW G655, G463, G409 which are designated as “H2 Ready”. The latest Guideline DVGW G221 (Guideline for the Application of the DVGW Codes of Practice to the Pipeline Bound Supply of the General Public with Hydrogen-containing Fuel Gases and Hydrogen), issued in December 2021, provides guidance for preparation of the obligatory risk assessment (Gefährdungsbeurteilung) which must be carried out by the Owner prior to operation of existing or new infrastructure using hydrogen. Note: the term ‘Gefährdungsbeurteilung’ (Risk Assessment) is mentioned 41 times in the new standard!

First step: up-to-date risk analysis of existing operation

The requirement to evaluate operational risks is well established and legally anchored (in Germany, as per ArbSchG, BetrSichV, GefStoffV). What is less well known, or at least not so well implemented in practice, is that such risk analyses should be regularly updated considering, for instance: altered process fluids or operating parameters; modified plant systems / components; ‘lessons learned’ based on root cause analysis of accidents or near-misses; updated risk acceptance criteria; and so on (see TRBS 1111 §4.1 “Erstellung und Aktualisierung der Gefährdungsbeurteilung“). It is recommended to update risk studies latest every 5 years, for instance, using the DHAZOP methodology which focuses on the changes since a previous analysis. In regard to hydrogen operation, DVGW G221 assumes that the existing plant / system risk analysis is up-to-date. As per section 10, only then is “The risk assessment(s) of the affected gas infrastructure … to be revised and adapted specifically to hydrogen.” Apart from an up-to-date risk analysis of existing operation, additional documentation pre-requisites for the hydrogen risk analysis are given in DVGW G 221 Attachment F and H.

Key factors to be considered in a hydrogen HAZOP

The HAZOP Methodology is well known and defined in various standards, such as DIN EN 61882 “HAZOP-Verfahren”, and TRBS 1111 “Gefährdungsbeurteilung”. Guidewords for evaluation of new or “re-purposed” hydrogen projects are similar to those used for natural gas infrastructure projects (see guidewords table). Nevertheless, during the HAZOP the Team shall be aware of specific issues related to hydrogen, noting that these may potentially be outside the current operating experience. DVGW G221, section 10, highlights hydrogen-specific themes, including:

  • Modified gas compositions, including range of variable hydrogen compositions
  • Changed physical-chemical properties and effects on people, the environment, pipelines, assemblies, components and systems
  • Effectiveness of protective systems, including functionality, set-points and response behaviour of safety devices
  • Blow-down behaviour
  • Changed fire and explosion risk during operation and maintenance
  • Flow noise and vibration
  • Modified solid residues

According to PSC’s experience, the following additional issues should be considered during the ‘hydrogen’ HAZOP:

  • Potentially reduced pipeline MAOP required for H2-operation (e.g. acc. to ASME B31.12), and corresponding impact on existing overpressure protection systems
  • Existing pipeline condition, e.g. wall thickness reduction, weld anomalies, and so on, as per intelligent pig reports, CP surveys, etc
  • Need for lifecycle calculations considering pressure cycling, hydrogen embrittlement / crack development and fracture toughness
  • Material compatibility and H2-permeability of existing materials, in particular, be aware of the ‘material mix’ for existing fittings, equipment, gaskets, lubricants. Consideration of missing documentation/certification of “H2-Readiness” Alternatively, ‘proven in use’ confirmation may be required and / or need for material samples to establish chemical analysis, fracture mechanics, hardness of existing components
  • Changed flow characteristics of hydrogen (in particular, increased velocity), with consequent impact on control elements (control valves, orifices) and safety devices (PSVs, SSVs)
  • Combustion characteristics of hydrogen
    • Stoichiometric concentration of hydrogen
    • Ignition properties
    • Lower and upper flammability limits (LFL and UFL)
    • Detonation limits
    • Flame quenching and blow-down limits
    • Micro-flames
  • Changed hazardous zones and ATEX requirements (e.g. methane – LFL/UFL: 2-16.6 Mol% and ATEX class: IIA T1 compared to hydrogen: LFL/UFL: 4-77 Mol% and ATEX class: IIC T1)
  • Changed F&G detection and protection requirements
  • Changed consequences of flash fire, Deflagration-Detonation-Transition (lower radiation energy, higher pressure wave)
  • Positive JT-effect (changed pre-heating requirements)
  • Impact on or influence from upstream source and downstream connected customers (critical sensitivity to H2)
  • Higher risk of cyber attack of H2-infrastructure leading to increased consequences (Keyword: ‘worst-case scenario’)
  • Suitability of existing vent and flare systems (height, sterile area, Ex-zone)
  • Special criteria in relation to gas storage systems (Keyword: hydrate formation)
  • Custody transfer metering standards, calibration

Other codes and standards can be used to extend the H2-HAZOP Brainstorming Checklist, e.g. ISO/TR 15916; DGUV 203-092, ASME B31.12, EIGA 121_14, ANSI/AIAA G-095.

Safeguards for Hydrogen Application

When considering appropriate safeguards and protection measures, those typically already existing for natural gas systems generally still apply (with necessary modification). However, as per DVGW G221 §10, hydrogen-specific mitigation measures may be required, including consideration of:

  • Hydrogen-specific training for staff and/or service providers
  • Adapted operating instructions for, but not limited to: first fill, commissioning, external and internal leak test, decommissioning, inertisation/flushing, maintenance, repair, emergency response, adaptation of explosion protection measures (avoidance of dangerous explosive and ignition sources)
  • Hydrogen-specific signage and labelling
  • Adapted proof test requirements
  • Qualifications for test personnel and inspectors
  • Hydrogen compatible monitoring systems including portable and fixed gas detectors and instrumentation
  • Checking and adjustment of the settings and the response behaviour of existing safety devices, respectively installation and commissioning of additional protections as required
  • Exchange or adaptation of components and line sections in the event of material incompatibilities
  • Redefinition of the Ex zones and adaptation of the explosion protection document
  • Use of hydrogen-compatible odorants

Need for experienced personnel

A significant issue addressed in the standard is the potential lack of experience in the operation of hydrogen systems. DVGW G 221, section 5.2 states:

“The operator must ensure that the assigned service providers and installation contractors, as well as its own personnel, are suitable and competent for the hydrogen-specific tasks and … ensure that the technical specialists and experts are trained and instructed regarding hydrogen.”

Appendix I gives recommendations in regard to the themes that should be subject of further training.

Finally, it should be noted that a change from natural gas to hydrogen transport is certainly to be considered as a “significant change” (wesentliche Änderung) as per the High Pressure Gas Pipeline Ordinance (GasHDrLtgV). Therefore, in accordance with German regulations, it is necessary to obtain the appropriate ‘expert opinion’ (gutachterliche Äußerung) from the independent expert and fulfil approval requirements of the responsible authority. It is recommended to involve the assigned expert (Sachverständiger) into the risk analysis process at an early stage (e.g. HAZOP participation) in order to identify potential approval issues.

PSC has provided independent Chairman and Scribe services for >100 HAZID, HAZOP (including HAZOP revalidation) and LOPA studies. PSC experts are certified according to IChemE and the Exida CFSE program. Here you will find information on some of the hydrogen-related projects we have worked on.