Sandia National Laboratories in Livermore, California maintains unique, state-of-the-art research facilities to address both fundamental scientific and applied engineering questions related to the interactions of gaseous hydrogen with materials. Principal research staff engage in research programs addressing sustainable energy for next generation energy technologies, such as fuel cell technologies, as well as national security, manufacturing and materials development.

Capabilities and Core Competencies

The Hydrogen Effects on Materials Laboratory is the cornerstone of Sandia’s research expertise in hydrogen compatibility of materials and a core capability stewarded by EERE’s Fuel Cell Technologies Office at the U.S. DOE. The laboratory houses specialized assets for evaluating materials performance in high-pressure gaseous hydrogen.

  • Fracture and fatigue testing in high-pressure gaseous hydrogen – Standard tensile, fracture and fatigue test configurations are executed with concurrent gaseous hydrogen exposure at pressure up to 140 MPa.
  • High-pressure fracture and fatigue testing at temperature – New capability enables loading of a variety of test specimen configurations (standard tensile, fracture and fatigue tests) at controlled (constant) temperature in the range of 220K to 450K concurrent with gaseous hydrogen exposure at pressure up to 140 MPa.
  • Constant-displacement, environmentally-assisted crack growth testing – Instrumented fracture mechanics specimens are loaded to constant displacement and exposed to gaseous hydrogen at pressure up to 200 MPa. The temperature can be independently controlled (usually constant) in the range of 200K to 440K. Subcritical cracking threshold and crack velocity can be measured.
  • Pressure cycling in controlled temperature – New capability allows exposure of non-metals (and metals) to pressure cycles up to 100 MPa at controlled (constant) temperature within the range 220K and 400K.
  • Thermal precharging – Materials and test specimens are exposed to high-pressure gaseous hydrogen or deuterium (up to 140 MPa) at elevated temperature (up to 300˚C) to produce controlled hydrogen content within the specimens prior to evaluation.

For more details on the Hydrogen Effects on Materials Laboratory, see Somerday et al., Intern J Hydrogen Energy 42 (2017) 7314-7321.

Hydrogen transport and trapping determines many features of the interactions between hydrogen and materials. In particular, the effects of hydrogen on mechanical properties can be strongly influenced by transport (or diffusion) of hydrogen in materials on the time scale of testing.

  • Gas-phase permeation – Permeation and diffusion of hydrogen are measured in two instruments by exposing one side of a thin foils of material to deuterium at ~0.5 bar and measuring the deuterium molecules that evolve on the down-stream side of the foil, which is at ultra-high vacuum. These tests may be conducted at up to 1000˙C.
  • Thermal desorption spectroscopy (TDS) – In TDS, a gas-charged specimen is heated at a controlled heating rate to release the hydrogen, which is measured as a function of temperature. The resulting spectrum is analyzed to determine the amount of hydrogen in the material and characterize the “strength” of the interactions between microstructural features and the hydrogen.
  • Local-electrode atom probe (LEAP) – Atom-probe tomography enables atomic resolution reconstruction of microstructures, including identification of atomic sites of hydrogen bonding within bulk materials.

A formidable obstacle to our understanding of hydrogen-surface interactions lack of experimental surface science tools capable of directly detecting hydrogen. To address this gap, Sandia has developed an array of specialized capabilities that can be brought to bear on the problem. The first of these is an angle-resolved ion energy spectrometer (ARIES) for low energy ion beam analysis. This instrument was developed specifically for detection of light adsorbates such as hydrogen, and uses low energy ion beams (< 3 keV) to probe the surface. Scattered and recoiled particles then provide information on surface structure and composition; detection of hydrogen concentrations as low as 0.03 monolayers is possible.

Other advanced surface techniques under development address the long-standing problem of how to extrapolate experiments performed in ultra-high vacuum environments to more relevant high pressure regimes. To bridge this gap, we are developing an ambient pressure x-ray photoelectron spectroscopy (AP-XPS) and infrared absorption spectroscopy systems (IRAS) to system capable of operating at near-ambient pressures (~10 Torr.) Other advanced techniques such as Kelvin probe force microscopy and electron energy loss spectroscopy are also being exploited to study hydrogen on surfaces.

Challenges associated with experimental characterization of atomic scale hydrogen interactions necessitates the use of computational tools to inform the development of predictive models of hydrogen-assisted fatigue and fracture. Robust models must capture the hydrogen-surface interactions and hydrogen transport as well as the mechanisms of hydrogen interactions with microstructural features in the bulk, such as vacancies, dislocations, and grain boundaries. Sandia researchers model hydrogen interactions across multiple length scales, working closely with experimentalists to inform the macroscopic response of materials in hydrogen environments.

  • Density Functional Theory (DFT) – In DFT, the equations of quantum mechanics governing the behavior of electron orbitals are solved to compute the energetics and dynamics of atomic systems with very high fidelity. This approach provides fundamental insight into the atomistic details of hydrogen’s interactions in a material.
  • Molecular Dynamics (MD) – While DFT is a very accurate approach, its computational cost prohibits studies to a few hundred atoms. With MD, the interactions of millions of atoms can be studied over nanosecond time scales. MD provides a valuable tool for studying fundamental hydrogen-defect interactions (dislocations, grain boundaries, crack tips, …).
  • Dislocation Dynamics (DD) – A key feature of hydrogen embrittlement is the impact of hydrogen on plastic deformation. DD is a tool where the motion of large ensembles of dislocation lines—crystalline defects whose motion induces plastic deformation—is simulated. The time and length scale of these simulations allows for a stronger comparison with experiments than is possible with MD and DFT.
  • Crystal Plasticity (CP) – DD simulations are typically limited to single crystals. In contrast, CP is a tool for studying polycrystalline materials, where the response of ensembles of grains is simulated. Direct comparisons with high resolution strain mapping experiments is possible using CP.
  • Continuum Finite Element Methods (FEM) – Continuum FEM models are the work horse of engineering system design. Multiphysics tools have been developed at Sandia for studying coupled deformation and hydrogen diffusion. Multiscale methods allow concurrent coupling between continuum models and high resolution models (e.g., CP) in key regions of interest, such as a crack tip.

Research Programs

The Hydrogen Safety, Codes and Standards subprogram at Sandia includes several areas of research, including the compatibility of materials and components with high-pressure gaseous hydrogen. The materials and components compatibility program element has several broad objectives:

  1. optimize the reliability and efficiency of test methods for structural materials and components in hydrogen gas
  2. develop science-based understanding of the effects of dissolved high-pressure gases on the integrity of polymer materials and methods to evaluate performance characteristics in high-pressure gases
  3. generate critical hydrogen compatibility data for structural materials and polymers to enable technology deployment
  4. create and maintain information resources [link to resource page]
  5. provide international leadership in the harmonization of standards for qualifying materials and components for service with high-pressure gaseous hydrogen

Each of these objectives supports the development, optimization, or implementation of hydrogen containment codes and standards, such as ASME Article KD-10 for stationary and transport vessels, ASME B31.12 for piping and pipelines, CSA HPIT1 for industrial truck fuel systems, SAE J2579 for fuel systems in hydrogen vehicles, and CSA CHMC1 for hydrogen containment material qualification.

The Hydrogen Delivery program at Sandia focuses on the need for safe and reliable hydrogen transport pathways from centralized production facilities, e.g., pipelines. Carbon-manganese steels are candidates for the structural materials in hydrogen gas pipelines; however, it is well known that these steels are susceptible to hydrogen embrittlement, which compromises the structural integrity of steel components. One manifestation of hydrogen embrittlement in steel hydrogen containment structures subjected to pressure cycling is hydrogen-accelerated fatigue crack growth. Such pressure cycling represents one of the key differences in operating conditions between current hydrogen pipelines and those anticipated in a hydrogen delivery infrastructure. Furthermore, as a push to reduce costs, higher strength steel pipelines are of growing interest in attempt to facilitate cost savings. Recent work has been focused on higher strength steels to enable their use in the hydrogen infrastructure. Welds, in particular, present an added area of concern as often times residual stresses and microstructures can vary significantly compared to the base metal. Therefore, focus has been concentrated on understanding hydrogen accelerated fatigue crack growth behavior explicitly for the welds and heat-affected zone (HAZ) in high strength steels.

Applying structural integrity models in design codes coupled with measurement of relevant materials properties allows quantification of the reliability/integrity of steel hydrogen pipelines subjected to pressure cycling. Furthermore, application of these structural integrity models is aided by the development of physics-based material models, which provide important insights such as the effects of gas impurities (e.g., oxygen) on hydrogen-accelerated fatigue crack growth. Successful implementation of these structural integrity and material models enhances confidence in the design codes and enables decisions about materials selection and operating conditions for reliable and efficient steel hydrogen pipelines.

Components for high-pressure gaseous hydrogen service are generally manufactured from premium grade materials to ensure performance in demanding applications. Decisions about materials selection for these applications are often based on historical experience and not comprehensive understanding of materials performance in hydrogen environments. To support DOE targets for lower cost and superior performance in high-pressure hydrogen energy applications, Sandia has been demonstrating mechanical performance of austenitic stainless steels in these environments, exploring advanced test methods for evaluating materials, and developing foundational understanding of hydrogen-materials interactions to inform materials design tools. The Materials Design and Analysis Tool enables screening of thousands of materials compositions to evaluate the compositional trade space for austenitic stainless steels, while experimental fatigue studies are illuminating the importance of materials variables (composition and strength), environmental variables (hydrogen pressure and temperature) and mechanical variables (fatigue loads and frequency). Additionally, mechanisms of hydrogen embrittlement in the context of evolving fatigue microstructures are being studied, along with the initiation and growth of fatigue cracks and methods to monitor these processes during testing.

Passivation of metal surfaces to mitigate hydrogen embrittlement

Recent mechanical testing has shown that introducing ppm oxygen concentrations in hydrogen gas streams can drastically reduce fatigue crack growth, even down to levels encountered in inert atmospheres. Passivation of the crack tip surfaces has been proposed as the underlying mechanism, though rigorous models of this effect have yet to be developed. A team of researchers is working to decipher how oxygen and hydrogen compete for surface sites in a mixed gas environment and block transport of hydrogen into the bulk. The goal of this work is to establish the boundaries where surface passivation is effective, thereby strengthening the scientific basis for adopting natural-gas standards for hydrogen-pipeline design.

Hydrogen-assisted fracture of additively manufactured austenitic stainless steels

Additive manufacturing provides a platform to design components with novel structures and characteristics; however, additively manufactured steels feature unique microstructures that are distinct from conventional wrought materials. The unique characteristics of these microstructures can enhance hydrogen-enhanced fatigue and hydrogen-assisted fracture. This activity seeks to expand our knowledge of microstructure-property relationships in this class of materials.

Fundamental microstructure-hydrogen interactions in austenitic stainless steels

The basic interactions of hydrogen with discrete, fundamental microstructural elements are not well understood, while many hypotheses have been advanced to phenomenologically describe specific observations. An interdisciplinary team of materials scientists and mechanical engineers is deconstructing these interactions to build foundational understanding and models to predict microstructure-hydrogen interactions in austenitic stainless steels. This work includes design of critical experiments, such as evaluation of the effects of hydrogen on deformation of single crystals as well as development of atomic potentials for MD simulations of highly-alloyed systems and deployment of finite element machinery to capture multiscale, multiphysics models representative of the unique character of hydrogen.

Sandia National Laboratories in Livermore is internationally recognized for its capabilities and expertise on the topic of hydrogen and hydrogen isotope compatibility of materials. Sandia maintains active research activities with partners from the around the globe, providing materials expertise and leadership in many research and engineering communities, including foundational research, hydrogen safety, and fusion energy technologies Sandia staff also participate in committees at standards/codes development organizations, often contributing to the scientific basis for the deployment of hydrogen-specific testing methods. International researchers regularly visit Sandia to work collaboratively with research staff and advance the understanding of hydrogen effects in metals and polymers.

Resources

Handbook-style guidance on materials selection for hydrogen service, organized by materials class. [Learn more link]

Materials property database (using Granta MI) with emphasis on fracture and fatigue properties measured in gaseous hydrogen environments [Learn more link]

Materials property visualization tool to aid composition-property trade space for austenitic stainless steels [Learn more link]

International forum for advancing testing capability and testing methods in high-pressure gases [Learn more link]

  • International Hydrogen Conference series

This international conference, held approximately every 4 years, is the premier topical meeting on hydrogen effects on materials. The ninth conference in the series was held in September 2016; proceedings from 2012 conference.

  • Materials for Hydrogen Service

Sessions on this topic are held every year at the ASME Pressure Vessels and Piping (PVP) Division Conference in July; in recent years, more than 20 papers have been contributed per year. Papers for all years available from the ASME Digital Collection.

  • International Conference on Hydrogen Safety

International Association for Hydrogen Safety (HySafe) organizes this conference on odd years in September/October. It is the premier conference on hydrogen safety, including sessions on hydrogen compatibility of materials. Conference program from 2017, Hamburg, Germany; papers and presentations from 2015, Yokohama, Japan; program from 2013, Brussels, Belgium.

  • International Conference on Metals and Hydrogen

Held approximately every 3-4 years in Ghent, Belgium, this conference focuses on hydrogen compatibility of metals. May 2018 is the third in the series.

  • Asia-Pacific Symposium on Tritium Science (APSOT)

The APSOT conference series covers topics of tritium science related to fusion energy research. The objective of the symposium is to provide a forum for an exchange of information on tritium science, technology, engineering, and general experiences with safe tritium handling for fusion energy. This symposium will also offer a timely opportunity to discuss recent international developments. The APSOT intended to attract not only veteran tritium experts but also scientists, engineers and students who are new to the various fields of studying and handling hydrogen isotopes. Participants from other countries are also cordially welcomed to participate. Proceedings are published in Fusion Engineering and Design.

The first APSOT meeting was held in Mianyang, China 2015 (having originated from an earlier China-Japan tritium mini-workshop.) APSOT-2 is hosted by Sandia/CA and will be held in Pleasanton, CA in September 5-8 2017.

  • Gaseous Hydrogen Embrittlement of Materials in Energy Technologies

With its distinguished editors and international team of expert contributors, Gaseous hydrogen embrittlement of materials in energy technologies (volume 1 and volume 2) is an invaluable reference tool for engineers, designers, materials scientists, and solid mechanicians working with safety-critical components fabricated from high performance materials required to operate in severe environments based on hydrogen. Impacted technologies include aerospace, petrochemical refining, gas transmission, power generation and transportation.

  • Tritium Barriers and Tritium Diffusion in Fusion Reactors

A contribution to Comprehensive Nuclear Materials, this chapter provides the basic thermodynamics relationships that describe H-isotope transport in materials for fusion applications and an extensive review of the literature on tritium permeation characteristics.