High pressure gaseous hydrogen has detrimental effects on the fracture toughness of Low Alloy High Strength (LAHS) steels and its effects needs to be evaluated. On one side, ASME Code, Sec VIII, Div 3 art. KD-10 indicates ASTM-E1681 as the fracture toughness testing procedure for material evaluation in gaseous hydrogen applications. Due to the comparative simplicity of testing self-loaded Wedge Opening Load (WOL) specimens from ASTM-E1681 in constant displacement, this type of test has become a “standard” for the industry. On the other side, fracture toughness evaluation of materials for OCTG applications in sour service is usually performed following Method D of NACE TM0177. This is also a test procedure that employs self-loaded double cantilever beam (DCB) specimens. In the present study a LAHS steel for seamless pressure vessels applications was tested in H2 gas at 550 bar and in sour environment (NACE Solution A with 1 bar of H2S and SR39.3 (pH 3.5) with 0.07 bar of H2S and N2 balance to reach 1 bar total pressure). The results allow the comparison of both testing techniques and the relative severity of gaseous H2 against usual environments for sour performance evaluation.

Hydrogen is increasingly gaining momentum as energy carrier and is expected to be one of the key ingredients in decarbonization and energy transition process. Hydrogen has the potential to lower emissions in emerging and hard-to-abate industries such as refineries, steelshops or ammonia plants and can also be used to buffer the variability in renewable sources such as wind and solar. In this scenario, hydrogen storage systems with large volumes will be needed and, as such, large, welded vessels become the preferred option. Traditionally, gaseous hydrogen has been stored in integrally forged (i.e. seamless) pressure vessels made of low alloy high strength ferritic steels such as Cr-Mo and Ni-Cr-Mo. For high pressure service fracture mechanics provides the engineering framework for the design and calculation of fatigue life of these vessels. In recent years, these materials have been extensively investigated and characterized for fatigue crack growth and fracture toughness in the expected target hydrogen environment. Traditional seamless pressure vessels are intrinsically limited by the production of a single seamless forging and consequently, a large number of pressure vessels may be required for a single installation depending on the size of the energy storage system required. For welded vessels, however fracture and fatigue resistance in the welding region need to be properly investigated by identifying and testing the most critical portion of the weld. This work provides an overview of recent results of fracture toughness and fatigue crack growth rate tests conducted in gaseous hydrogen for base metal and welded joints on a high strength, quenched and tempered P690 QL2 fine-grained steel for pressure applications, made according to EN 10216-3. The steel is a candidate to be used for design and construction of medium-high pressure containers for large hydrogen storage systems.

Hydrogen is expected to play a major role in the decarbonization of the energy grid. As a fuel, it possesses an elevated energy density per unit mass, about twice as much as natural gas but also a very low mass density; for this reason, it is preferably stored and transported at elevated pressures in the gas phase to achieve a comparable volumetric energy density. High strength quenched and tempered ferritic steels are widely used for gaseous hydrogen storage despite the fact that hydrogen affects material properties and result in higher fatigue crack growth rate and lower fracture toughness.This work presents the results of a comprehensive fracture toughness test program in gaseous hydrogen for the characterization of base metal, heat affected zone and weld metal on a high strength, quenched and tempered steel, suitable for the construction of hydrogen pressure equipment.Full penetration, butt welded joints were made using partly mechanized gas metal arc welding technique on a weldable, high strength steel, namely EN 101216-3 grade P690 QL2. Two different welding procedures were evaluated, and fracture toughness tests were conducted according to ASTM E1820 requirements, in high purity (99.9995%) hydrogen gas at a pressure of 200 bar on specimens extracted from base metal, heat affected zone and weld metal. While base metal and weld metal exhibited stable crack growth behavior, heat affected zone showed variable behavior as a function of the post-weld heat treatment conditions. It was found that local micro-hardness spots are a concern and should be controlled through dedicated post weld heat treatment operation to limit hardness values for use of welds in H2 gas conditions.

High-strength ferritic steels are widely used in the current hydrogen infrastructure for the construction of seamless and welded high-pressure vessels. In mobility applications (such as refueling stations), hydrogen is stored in the gaseous state at high pressures (typically between, 500 bar and 1000 bar for refilling of fuel cell vehicles), and seamless vessels are currently the only viable solution. To lower emissions in emerging and hard-to-abate industries, hydrogen storage is expected at lower pressures ( up to 350 bar) but in much larger volumes. In this scenario, large, welded vessels are required. The fracture toughness of these welds in hydrogen is a primary concern, as welding is known to produce microstructural and property gradients across the joint, potentially resulting in highly variable fracture resistance. In a previous work, the fracture resistance of welds fabricated from a high strength, EN 10216-3 grade P690 QL2 steel was investigated [1], showing greatly reduced fracture resistance due to the presence of local hard spots in the heat affected zone. This current work complements previous work with new fracture results for welds in gaseous hydrogen at pressure of 200 bar. Tests were conducted under rising displacement conditions as per ASTM E1820 standard [2], similar to the previous study, except that the crack extension was monitored with (singlespecimen) potential difference measurements for comparison to the previous study using unloading compliance. While the Jintegral resistance curve can be determined by both methods, the potential difference method, when properly implemented, can resolve the initiation of crack extension more precisely than the unloading-compliance technique, but the potential difference method is more difficult to implement and interpret. Additionally, displacement rate effects were investigated and compared between the two methods for crack-extension monitoring. The advantages and appropriateness of each test methodology are discussed in the context of structural integrity of welded pressure vessels.

High strength ferritic steels are very commonly used for construction of pressure vessels for hydrogen storage and transportation, thanks to the combination of affordable cost and availability of material for construction. As hydrogen becomes more and more important as a carbon-neutral energy vector, the number and size of installations for hydrogen storage are expected to grow, and large vessels fabricated by welding are among the possible solutions to meet this increasing demand of storage capacity. Ferritic steels suffer from hydrogen assisted cracking, and therefore safe design requires reliable knowledge of their fracture and fatigue properties when exposed to pressurized hydrogen environment. Thankfully, this information is today available for most commonly used steel grades ([1], [2]). However, these known design curves are specific for wrought products, whose microstructure is achieved by precise heat treatment conditions, typically, quenching and tempering. Welding, however, inevitably produces a local transformation of the material's microstructure, and a gradient of properties in the volume surrounding the solidified pool. Therefore, fabricating any high strength steel pressure equipment that includes welds, requires characterization of the fracture and fatigue properties of the different microstructural regions. Previous work from the same authors ([3]) demonstrated the variable performance of high strength steel welds in gaseous hydrogen, and thus the effect of welding parameters. This paper expands the previously published information, presenting new experimental findings on the FCGR behavior of welded joints made from a low a carbon weldable high strength steel, P690 QL2 ([4]).

A new model is presented to predict hydrogen-assisted fatigue. The model combines a phase field description of fracture and fatigue, stress-assisted hydrogen diffusion, and a toughness degradation formulation with cyclic and hydrogen contributions. Hydrogen-assisted fatigue crack growth predictions exhibit an excellent agreement with experiments over all the scenarios considered, spanning multiple load ratios, H2 pressures and loading frequencies. These are obtained without any calibration with hydrogen-assisted fatigue data, taking as input only mechanical and hydrogen transport material properties, the material's fatigue characteristics (from a single test in air), and the sensitivity of fracture toughness to hydrogen content. Furthermore, the model is used to determine: (i) what are suitable test loading frequencies to obtain conservative data, and (ii) the underestimation made when not pre-charging samples. The model can handle both laboratory specimens and large-scale engineering components, enabling the Virtual Testing paradigm in infrastructure exposed to hydrogen environments and cyclic loading.

Emerging hydrogen technologies span a diverse range of operating environments. High-pressure storage for mobility applications has become commonplace up to about 1,000 bar, whereas transmission of gaseous hydrogen can occur at hydrogen partial pressure of a few bar when blended into natural gas. In the former case, cascade storage is utilized to manage hydrogen-assisted fatigue and the Boiler and Pressure Vessel Code, Section VIII, Division 3 includes fatigue design curves for fracture mechanics design of hydrogen vessels at pressure of 1,030 bar (using a Paris Law formulation). Recent research on hydrogen-assisted fatigue crack growth has shown that a diverse range of ferritic steels show similar fatigue crack growth behavior in gaseous hydrogen environments, including lowcarbon steels (e.g., pipeline steels) as well as quench and tempered Cr-Mo and Ni-Cr-Mo pressure vessel steels with tensile strength less than 915 MPa. However, measured fatigue crack growth is sensitive to hydrogen partial pressure and fatigue crack growth can be accelerated in hydrogen at pressure as low as 1 bar. The effect of hydrogen partial pressure from 1 to 1,000 bar can be quantified through a simple semi-empirical correction factor to the fatigue crack growth design curves. This paper documents the technical basis for the pressure-sensitive fatigue crack growth rules for gaseous hydrogen service in ASME B31.12 Code Case 220 and for revision of ASME VIII-3 Code Case 2938-1, including the range of applicability of these fatigue design curves in terms of environmental, materials and mechanics variables.

Hydrogen is widely expected to become every day’s fuel in a decarbonized energy economy. Owing to its very low mass density, storing hydrogen efficiently in gaseous form requires significantly more elevated pressures than hydrocarbons. However, contact and interaction with hydrogen are known to be detrimental for container material properties, causing a decrease in ductility and toughness as it diffuses into the container walls. In this context, high strength materials with good resistance to hydrogen embrittlement are desirable. Ferritic steels are widely used thanks to their availability and competitive cost; it is known, however, that a ferritic steel’s sensitivity to hydrogen embrittlement generally becomes worse as its strength increases. The magnitude of such phenomenon nonetheless varies with the selection of the alloy and its manufacturing process parameters; as such, it is possible to identify high strength steels that are more or less suitable for the construction of pressure equipment for hydrogen storage and transportation. This work introduces a comparative assessment of different quenched and tempered, low alloy ferritic steels’ performance in a pressurized pure hydrogen gas environment, in terms of measured fracture toughness and fatigue crack growth rates. The findings are then discussed in comparison to similar alloys and manufacturing conditions.

Low alloy, quenched and tempered Cr-Mo and Ni-Cr-Mo steels are commonly used for construction of seamless pressure vessels for hydrogen gas storage. Designing such vessels for high-pressure gaseous hydrogen service requires knowledge of fatigue crack growth rates and fracture toughness in the service environment at the design pressure. Measurement of these properties is challenging, and only a few laboratories in the world are equipped to make these measurements at very elevated pressure up to 103 MPa (15,000 psi) which are of interests for pressure vessels to be used as buffers in hydrogen refueling stations. In recent years, these properties for common low alloy steels were published in the ASME Boiler and Pressure Vessel Code Case 2938-1, therefore allowing design and construction without the need for dedicated testing. However, the fatigue crack growth rate curves published in the CC were determined from test data at 100 MPa and above and may be over-conservative for lower pressure applications. Prior publication PVP2019-93907 ([1]) in fact, already proposed a correction factor of fatigue crack growth rates based on hydrogen fugacity. Since then, new data were generated at lower pressures i.e. 55 MPa (8,000 psi). This paper presents the new findings and discusses the applicability of the previously proposed equation, which could allow reducing conservatism in current design of pressure vessels.

Following the ASME codes, the design of pipelines and pressure vessels for transportation or storage of high-pressure hydrogen gas requires measurements of fatigue crack growth rates at design pressure. However, performing tests in high pressure hydrogen gas can be very costly as only a few laboratories have the unique capabilities. Recently, Code Case 2938 was accepted in ASME Boiler and Pressure Vessel Code (BPVC) VIII-3 allowing for design curves to be used in lieu of performing fatigue crack growth rate (da/dN vs. ΔK) and fracture threshold (KIH) testing in hydrogen gas. The design curves were based on data generated at 100 MPa H2 on SA-372 and SA-723 grade steels; however, the data used to generate the design curves are limited to measurements of ΔK values greater than 6 MPa m1/2. The design curves can be extrapolated to lower ΔK (< 6 MPa m1/2), but the threshold stress intensity factor (ΔKth) has not been measured in hydrogen gas. In this work, decreasing ΔK tests were performed at select hydrogen pressures to explore threshold (ΔKth) for ferritic-based structural steels (e.g. pipelines and pressure vessels). The results were compared to decreasing ΔK tests in air, showing that the fatigue crack growth rates in hydrogen gas appear to yield similar or even slightly lower da/dN values compared to the curves in air at low ΔK values when tests were performed at stress ratios of 0.5 and 0.7. Correction for crack closure was implemented, which resulted in better agreement with the design curves and provide an upper bound throughout the entire ΔK range, even as the crack growth rates approach ΔKth. This work gives further evidence of the utility of the design curves described in Code Case 2938 of the ASME BPVC VIII-3 for construction of high pressure hydrogen vessels.

The design of pressure vessels for high-pressure gaseous hydrogen service per ASME Boiler and Pressure Vessel Code Section VIII Division 3 requires measurement of fatigue crack growth rates in situ in gaseous hydrogen at the design pressure. These measurements are challenging and only a few laboratories in the world are equipped to make these measurements, especially in gaseous hydrogen at pressure in excess of 100 MPa. However, sufficient data is now available to show that common pressure vessel steels (e.g., SA-372 and SA-723) show similar fatigue crack growth rates when the maximum applied stress intensity factor is significantly less than the elastic-plastic fracture toughness. Indeed, the measured rates are sufficiently consistent that a master curve for fatigue crack growth in gaseous hydrogen can be established for steels with tensile strength less than 915 MPa. In this overview, published reports of fatigue crack growth rate data in gaseous hydrogen are reviewed. These data are used to formulate a two-part master curve for fatigue crack growth in high-pressure (106 MPa) gaseous hydrogen, following the classic power-law formulation for fatigue crack growth and a term that accounts for the loading ratio (R). The bounds on applicability of the master curve are discussed, including the relationship between hydrogen-assisted fracture and tensile strength of these steels. These data have been used in developing ASME VIII-3 Code Case 2938. Additionally, a phenomenological term for pressure can be added to the master curve and it is shown that the same master curve formulation captures the behavior of pressure vessel and pipeline steels at significantly lower pressure.

International standards and codes dedicated to design of pressure vessels are still unable to competitively ensure safe design and fitness for service of steel vessels for high pressure gaseous hydrogen. Emptying and shallow pressure cycles subject the material to hydrogen enhanced fatigue. A pre-normative project, MATHRYCE under the EU joint research program focused in this subject through material and component testing, analytical work, review of design methodologies and international collaboration. An easy to implement, safe and economically competitive vessel design methodology is targeted. Steps towards this goal were taken by deepening our understanding on hydrogen enhanced fatigue in different kinds of laboratory specimens and real vessels designed for hydrogen service at maximum 45 MPa pressure. This included cyclic pressure testing of artificially notched vessels both in hydrogen and inert environment. The effect of hydrogen pressure, frequency and mechanical loading parameters (ΔK, Sa) on fatigue crack initiation and propagation was analyzed. Attention was paid on the definition of “initiation” and influence of hydrogen on the relative parts of initiation and propagation on the fatigue life of a component. A good correlation between results with various test types was found. Particularly promising was the match between the measured — and estimated — crack growth rates in laboratory specimens and vessels. This supports our proposal for a safe design procedure based on crack growth and defect tolerant approach. Recommendations for implementation in a new international standard, on how to properly address hydrogen enhanced fatigue based on laboratory tests, were given and will be summarized in this presentation. Our results indicate that crack initiation from inclusions or other small microstructural features is not necessarily affected by hydrogen to a similar extent as crack growth, but when initiated, the remaining life may be short due to fast growth. This is challenging for design and inspection rules to allow economically competitive construction of hydrogen equipment without compromising safety.

A pre-normative project, “Material testing and recommendations for hydrogen components under fatigue, MATHRYCE” under the EU joint research program dealt with hydrogen enhanced fatigue in Q&T (YS=600MPa) low alloy Cr-Mo steel and pressure vessel design. The project was concluded by cyclic testing of pre-notched vessels by hydraulic and hydrogen pressure loading. This paper display part of the fatigue tests performed under hydrogen pressure, including fatigue crack initiation analysis from 0.5MPa H2 to 103MPa H2. Notable differences, but explainable correlations between results of various test types were found. Some implications to possible improvements of hydrogen pressure vessels design standards are also presented.

This study investigates the fatigue life of Cr-Mo pressure vessels for hydrogen storage by hydraulic and hydrogen pressure cycle tests. Two different sized cylinders have been tested; 35 L inner volume and 28 MPa working pressure (WP) and 198 L volume and 41 MPa WP. On the inner surface of the cylinders U-shaped notches of different depths were machined by electro discharge machining technique. The initial notch sizes were designed based on a two stage fatigue predictive model based on fracture mechanics to develop through wall cracks in the deepest notches after about 50,000 hydraulic cycles together with crack propagation of the intermediate notches and crack initiation in the smallest. The cylinders were cycled between the nominal pressure of 2 MPa and the WP until leak before break (LBB). Strain gauges were placed at the external surface of the cylinders in correspondence of the internally machined notches. On the notches which developed through wall, the strain showed a progressive decrease followed by an increase of the hoop strain during the final stage of crack propagation until LBB failure. Hydrogen effect was clearly identified by the reduction in the number of cycles to failure comparing tests in hydrogen and in oil. Subsequent failure analysis at the end of each test revealed a typical trans-granular fatigue crack surface morphology (with fatigue striations) for tests in oil, while quasi cleavage and intergranular fracture appearance were found for hydrogen tests. (C) 2017 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.

The current international standards and codes dedicated to the design of pressure vessels do not properly ensure fitness for service of vessels used for gaseous hydrogen storage and subjected to hydrogen enhanced fatigue. In this context, the European project MATHRYCE intends to propose an easy to implement vessel design methodology based on lab-scale tests and taking into account hydrogen enhanced fatigue. In the present document the lab-scale experimental developments and results are presented. The material considered was a commercially available Q&T low alloy Cr-Mo steel from a seamless pressure vessel. Due to the high hydrogen diffusion at room temperature in such steel, all the tests were performed under hydrogen pressure to avoid outgassing. Different types of lab-scale tests were developed and used in order to identify the most promising one for a design code. The effect of mechanical parameters, such as H2 pressure, frequency and ΔK, on fatigue crack initiation and propagation was analyzed. In particular, special attention was paid on the influence of H2 on the relative parts of initiation and propagation in the fatigue life of a component. The second part of the work was dedicated to cyclic hydraulic and hydrogen pressure tests on full scale vessels. Three artificial defects with different geometries per cylinder were machined in the inner wall of each tested cylinder. They were specifically designed in order to detect fatigue crack initiation and fatigue crack propagation with a single test. The final goal of this work is to propose a methodology to derive a “hydrogen safety factor” from lab-scale tests. The proposed method is compared to the full-scale results obtained, leading to recommendations on the design of pressure components operating under cyclic hydrogen pressure.

The objective of this study was to explore an approach for measuring fatigue crack growth rates (da/dN) for Cr-Mo pressure vessel steels in high-pressure hydrogen gas over a broad cyclic stress intensity factor (ΔK) range while limiting test duration, which could serve as an alternative to the method prescribed in ASME BPVC VIII-3, Article KD-10. Fatigue crack growth rates were measured for SA-372 Grade J and 34CrMo4 steels in hydrogen gas as a function of ΔK, load-cycle frequency (f), and gas pressure. The da/dN vs. ΔK relationships measured for the Cr-Mo steels in hydrogen gas at 10 Hz indicate that capturing data at lower ΔK is valuable when these relationships serve as inputs into design-life analyses of hydrogen pressure vessels, since in this ΔK range crack growth rates in hydrogen gas approach rates in air. The da/dN vs. f data measured for the Cr-Mo steels in hydrogen gas at selected constant-ΔK levels demonstrate that crack growth rates at 10 Hz do not represent upper-bound behavior, since da/dN generally increases as f decreases. Consequently, although fatigue crack growth testing at 10 Hz can efficiently measure da/dN over a wide ΔK range, these da/dN vs. ΔK relationships at 10 Hz cannot be considered reliable inputs into design-life analyses. A possible hybrid approach to efficiently establishing the fatigue crack growth rate relationship in hydrogen gas without compromising data quality is to measure the da/dN vs. ΔK relationship at 10 Hz and then apply a correction based on the da/dN vs. f data. The reliability of such a hybrid approach depends on adequacy of the da/dN vs. f data, i.e., the data are measured at appropriate constant-ΔK levels and the data include upper-bound crack growth rates.

Along the hydrogen supply chain, metallic components, such as pressure vessels, compressors and valves, are facing high pressure hydrogen gas. The object of this paper is to address microstructural as well as mechanical aspects of fatigue crack initiation and growth at room temperature in a quenched and tempered (Q&T) low alloy steel under hydrogen pressure in the range 0.5-35 MPa. For such steel, the need to perform tests insitu under hydrogen pressure is required. The influence of hydrogen gas on the total life in terms of crack initiation and crack propagation is analyzed. The experimental techniques developed to detect crack initiation in a pressure vessel under hydrogen pressure are presented. Thanks to these technical developments the influence of hydrogen gas on the total life duration including crack initiation and crack propagation is analyzed. It is shown that the effect of hydrogen pressure on crack initiation is important. At constant load ratio, the hydrogen pressure effect on fatigue crack growth (FCG) is dependent on the loading amplitude (in terms of Delta K). These results related to cracking behavior are enriched with information on fracture surfaces appearance. The results presented have been achieved within the European project MATHRYCE [1] dedicated to Material Testing and Recommendations for Hydrogen Components under fatigue. They are part of a process necessary to give a scientific background to the development of a design methodology where hydrogen enhanced fatigue damage is taken into account. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The current international standards and codes dedicated to the design of pressure vessels do not properly ensure fitness for service of such vessel used for gaseous hydrogen storage and subjected to hydrogen enhanced fatigue. Yet, hydrogen can reduce the fatigue life in two ways: by decreasing the crack initiation period and by increasing the fatigue crack growth rate. The European project MATHRYCE aims are to propose an easy to implement vessel design methodology based on lab-scale tests and taking into account hydrogen enhanced fatigue.The study is focused on a low alloy Cr-Mo steel, exhibiting a tempered bainitic and martensitic microstructure, and classically used to store hydrogen gas up to 45 MPa. Due. to hydrogen diffusion at room temperature in such steel, tests have to be performed under hydrogen pressure to avoid outgassing.In the present work, experimental procedures have been developed to study both crack initiation and crack growth. The specimens and tests instrumentation have been specifically designed to quantitatively measure in-situ these two stages under high hydrogen pressure. We developed and tested crack gages located close to a small drilled notch. This notch simulates the presence of steel nonmetallic inclusions and other microstructural features that can affect fatigue crack initiation and propagation. The experimental results addressing the effects of the testing conditions, such as stress ratio, frequency and hydrogen pressure will be compared to the local strain and stress fields obtained by Finite Element Method and correlated to the possible hydrogen enhanced fatigue mechanisms involved.