Transmission, Distribution & Storage

The last twenty years of an intense research on metal hydroborates as solid hydrogen stores and solid electrolytes are reviewed. It is shown that from the most promising application in hydrogen storage due to their high gravimetric and volumetric capacities the focus has moved to solid electrolytes due to high cation mobility in disordered structures with rotating or tumbling anions-hydroborate clusters. Various strategies of overcoming the strong covalent bonding of hydrogen in hydroborates for hydrogen storage and disordering their structures at room temperature for solid electrolytes are discussed. The important role of crystal chemistry and crystallography knowledge in material design can be read in the cited literature.

High hydrogen content fuels can be used in gas turbine for power generation with CO₂ capture IGCC plants or with hydrogen from renewables. The challenge for the engine is the high reactive combustion properties making dilution necessary to mitigate NO_x emissions at the expense of a significant energy cost. In the concept analysed in this study high Exhaust Gas Recirculation (EGR) rate is applied to the gas turbine to generate oxygen depleted air. As a result combustion temperature is inherently limited keeping NO_x emissions low without the need for dilution or unsafe premixing. The concept is analysed by process simulation based on a reference IGCC plant with CO₂ Capture. Results with dry and wet EGR options are presented as a function EGR rate. Efficiency performance is assessed against the reference power cycle with nitrogen dilution. All EGR options are shown to represent an efficiency improvement. Nitrogen dilution is found to have a 1.3% efficiency cost. Although all EGR options investigated offer an improvement dry EGR is considered as the preferred option despite the need for higher EGR rate as compared with the wet EGR. The efficiency gain is calculated to be of 1% compared with the reference case.

As part of the LTS Futures HyTechnical project IGEM requested that DNV GL undertake an assessment of the possible impact of hydrogen transmission on BPDs to support the development of supplements to the existing suite of natural gas standards to accommodate the possible future use of hydrogen. The current state of knowledge of the behaviour of large scale high pressure hydrogen releases is limited in comparison with the considerable body of data from research and operational experience of natural gas but is adequate to undertake an impact assessment to take account of the different gas outflow and fire characteristics of 100% hydrogen vs. natural gas.<br/>Calculations of the BPDs for 100% hydrogen pipeline fires on an equivalent basis to those in IGEM/TD/1 for natural gas have been performed with a degree of confidence in the results and demonstrated that the equivalent BPDs for 100% hydrogen are approximately 10% smaller than for natural gas. The results are presented graphically in this report.<br/>However hydrogen introduces the potential for substantially higher overpressures than natural gas due to the higher flame speed and wider flammable limits if delayed ignition is a credible event. The overpressure estimates presented in this report are intended to be scoping calculations to put the likely overpressures into context. The results suggest that significant overpressures are possible at the BPDs but there is a lack of evidence to support the estimation of the overpressures following delayed ignition of a large turbulent hydrogen release in the open (in contrast to explosions in confined or congested regions) and there is a high degree of uncertainty in the predictions presented here. It is therefore recommended that large scale pipeline rupture experiments are performed similar to those undertaken previously for hydrogen natural gas and natural gas/hydrogen mixtures but with ignition engineered to take place after a short delay in order to measure the overpressures and provide the means to validate or refine the predictions made.<br/>The analysis has highlighted limitations in the original method of calculating BPDs in IGEM/TD/1 which reflects the techniques available at the time approximately 40 years ago. Since then understanding of the hazards from pipeline failures and the ability to model the consequences and predict the associated risks to people in the surrounding area have advanced very considerably facilitated by software tools and documented in standards such as IGEM/TD/2. These methods allow the highly transient nature of a high pressure gas pipeline rupture release to be modelled more accurately and for the thermal effects of fires on people and buildings to be calculated taking account of the time-varying thermal dose.<br/>For these reasons a simple comparison of the possible overpressure effects of delayed ignition of a 100% hydrogen release at the BPDs can be misleading and implies that the overpressure hazards could be more severe than those for fires which may not be the case. Example calculations have been performed for a representative pipeline case which indicate that using current methods the predicted thermal hazard distances for 100% hydrogen pipeline fires (house burning and escape for people) are substantially greater than those estimated for overpressures following delayed ignition for similar levels of vulnerability. This report addresses buried pipelines only – the potential for more severe explosion overpressure effects for hydrogen releases may be more significant for Above Ground Installations (AGIs) especially where congestion or confinement may be present. It is recommended that similar studies are conducted to quantify the effect of hydrogen conversion on the consequences and risks associated with hydrogen releases at AGIs.<br/>Finally it is stressed that the analysis in this report does not consider the relative risks for 100% hydrogen and the equivalent natural gas pipelines. There remain uncertainties in the failure frequencies for steel pipelines transporting hydrogen and particularly the probability of immediate and delayed ignition. The likelihood of delayed ignition of a large turbulent high pressure hydrogen gas pipeline rupture release may be very low due to the wider flammability limits and lower minimum ignition energy for hydrogen compared with natural gas. Additional research is currently ongoing or planned to address the gaps in knowledge for 100% hydrogen which should allow more robust comparisons of the relative risks to be made in the future.

This work discusses the design and demonstration of an in-situ test setup for testing pipeline steels in a high pressure gaseous hydrogen (H2 ) environment. A miniature hollow pipe-like tensile specimen was designed that acts as the gas containment volume during the test. Specific areas of the specimen can be forced to fracture by selective notching as performed on the weldment. The volume of H2 used was minimised so the test can be performed safely without the need of specialised equipment. The setup is shown to be capable of characterising Hydrogen Embrittlement (HE) in steels through testing an X60 pipeline steel and its weldment. The percentage elongation (%El) of the base metal was found to be reduced by 40% when tested in 100 barg H2 . Reduction of cross-sectional area (%RA) was found to decrease by 28% and 11% in the base metal and weld metal respectively when tested in 100 barg H2 . Benchmark test were performed at 100 barg N2 pressure. SEM fractography further indicated a shift from normal ductile fracture mechanisms to a brittle transgranular (TG) quasi-cleavage (QC) type fracture that is characteristic of HE.

Body-centered cubic (BCC) alloys are considered as promising materials for hydrogen storage with high theoretical storage capacity (H/M ratio of 2). Nonetheless they often suffer from sluggish kinetics of hydrogen absorption and high hydrogen desorption temperature. Carbon materials are efficient hydrogenation catalysts however their influence on the hydrogen storage properties of BCC alloy has not been comprehensively studied. Therefore in this paper composites obtained by milling of carbon catalysts (carbon nanotubes mesoporous carbon carbon nanofibers diamond powder graphite fullerene) and BCC alloy (Ti1.5V0.5) were extensively studied in the non-hydrogenated and hydrogenated state. The structure and microstructure of the obtained materials were studied by scanning and transmission electron microscopes X-ray diffraction (XRD) and Raman spectroscopy. XRD and Raman measurements showed that BCC alloy and carbon structures were in most cases intact after the composite synthesis. The hydrogenation/dehydrogenation studies showed that all of the used carbon catalysts significantly improve the hydrogenation kinetics reduce the activation energy of the dehydrogenation process and decrease the dehydrogenation temperature (by nearly 100 K). The superior kinetic properties were measured for the composite with 5 wt % of fullerene that absorbs 3.3 wt % of hydrogen within 1 min at room temperature.

We evaluated the strain rate sensitivity of the micro-damage evolution behavior in a ferrite/martensite dual-phase steel. The micro-damage evolution behavior can be divided into three regimes: damage incubation damage arrest and damage growth. All regimes are associated with local deformability. Thus the total elongation of DP steels is determined by a combination of plastic damage initiation resistance and damage growth arrestability. This fact implies that hydrogen must have a critical effect on the damage evolution because hydrogen enhances strain localization and lowers crack resistance. In this context the strain rate must be an important factor because it affects the time for microstructural hydrogen diffusion/segregation at a specific microstructural location or at the damage tip. In this study tensile tests were carried out on a DP steel with different strain rates of 10^{− 2} and 10^{− 4} s⁻¹. We performed the damage quantification microstructure characterization and fractography. Specifically the quantitative data of the damage evolution was analyzed using the classification of the damage evolution regimes in order to separately elucidate the effects of the hydrogen on damage initiation resistance and damage arrestability. In this study we obtained the following conclusions with respect to the strain rate. Lowering the strain rate increased the damage nucleation rate at martensite and reduced the critical strain for fracture through shortening the damage arrest regime. However the failure occurred via ductile modes regardless of strain rate.

The final session of the meeting consisted of a discussion panel to propose future directions for research in the field of hydrogen embrittlement and the potential impact of this research on public policy.

This article is a transcription of the recorded discussion of ‘Hydrogen Embrittlement: Future Directions’ at the Royal Society Scientific Discussion Meeting Challenges of Hydrogen and Metals Jan 16th–18th 2017. The text is approved by the contributors. H.L. transcribed the session and drafted the manuscript. Y.C. assisted in the preparation of the manuscript.

Link to document download on Royal Society Website 

High-strength steel fasteners characterized by tensile strengths above 1100 MPa are often used in critical applications where a failure can have catastrophic consequences. Preventing hydrogen embrittlement (HE) failure is a fundamental concern implicating the entire fastener supply chain. Research is typically conducted under idealized conditions that cannot be translated into know-how prescribed in fastener industry standards and practices. Additionally inconsistencies and even contradictions in fastener industry standards have led to much confusion and many preventable or misdiagnosed fastener failures. HE susceptibility is a function of the material condition which is comprehensively described by the metallurgical and mechanical properties. Material strength has a first-order effect on HE susceptibility which increases significantly above 1200 MPa and is characterized by a ductile--brittle transition. For a given concentration of hydrogen and at equal strength the critical strength above which the ductile–brittle transition begins can vary due to second-order effects of chemistry tempering temperature and sub-microstructure. Additionally non-homogeneity of the metallurgical structure resulting from poorly controlled heat treatment impurities and non-metallic inclusions can increase HE susceptibility of steel in ways that are measurable but unpredictable. Below 1200 MPa non-conforming quality is often the root cause of real-life failures.

Link to document download on Royal Society Website 

Numerous reviews on hydrogen storage have previously been published. However most of these reviews deal either exclusively with storage materials or the global hydrogen economy. This paper presents a review of hydrogen storage systems that are relevant for mobility applications. The ideal storage medium should allow high volumetric and gravimetric energy densities quick uptake and release of fuel operation at room temperatures and atmospheric pressure safe use and balanced cost-effectiveness. All current hydrogen storage technologies have significant drawbacks including complex thermal management systems boil-off poor efficiency expensive catalysts stability issues slow response rates high operating pressures low energy densities and risks of violent and uncontrolled spontaneous reactions. While not perfect the current leading industry standard of compressed hydrogen offers a functional solution and demonstrates a storage option for mobility compared to other technologies.

The report investigates a kickstart project that allows up to 10% hydrogen into gas distribution networks. It reviews the technical impacts and standards to identify barriers and develop recommendations.

You can see the full report on the Australian Government website here 

This report is developed in support of Australia's National Hydrogen Strategy