The European Hydrogen Backbone initiative plans to develop a large hydrogen transport grid, mainly from repurposing of existing Natural Gas infrastructures The mechanical integrity of such infrastructure still relies on a better and quantified knowledge of the effect of hydrogen on the steel properties. This paper discusses the hydrogen embrittlement mechanisms of ferrite-pearlite low alloy pipeline steel (L485MB steel) subjected to monotonic tensile loading in a pressurised hydrogen environment. Although the main mechanisms involved are now well described in the literature, uncertainties remain regarding their respective quantified implications, in particular concerning the effect of hydrogen on enhanced or reduced local plastic activity. Thus, tensile tests on smooth specimens were performed at room temperature up to 30 MPa H2 gas with initial strain rates of 10-6 s-1 and 10-4s-1. The results under hydrogen display a strong plastic localisation at the macroscale in very active shear bands oriented at 45 degrees of the tensile axis. Such hydrogen induced localisation leads to a transition from diffuse necking under air to localised necking under hydrogen pressure. Although softening was not observed at a macroscopic level on tensile curves, this strain localisation is attributed to a softening effect of hydrogen. This assumption is supported by dislocation density measurements. Moreover, the observation of the gage length of the smooth specimen shows that during tensile testing under hydrogen, microcracks formed in mode 1 in pearlite bands and served as initiation sites for shear bands. Based on these observations, a complete failure scenario is proposed.

A key point for the development of a renewable energy economy at a large scale is the possibility to use the current natural gas network and storage capacity to transport and store hydrogen. This study is dedicated to evaluate the integrity of materials used for underground aquifer storage regarding hydrogen embrittlement in a gaseous environment saturated with water vapour and containing few amounts of H2S. In this environment, the water vapour content in the gas stored may reach saturation at bottom well pressure and temperature. It is known that the presence of impurities in the gas, such as H2O, can promote or inhibit hydrogen embrittlement phenomenon, depending on the nature of the steel. This work investigates mechanical properties of a tempered martensite N80-Q steel, and a ferrite-perlite L360-NB C-Mn steel issued from a completion and a collect tube respectively. The testing environments are NG, NG + H2S, NG + 25%H2 and NG + 25%H2 + H2S saturated in water vapour at 8.5 MPa and room temperature. These environmental conditions aim at replicating the storage service conditions. Fracture toughness and fatigue crack growth properties are assessed. So far, the mechanical behaviour of such steels under hydrogen gas pressure saturated with water vapour and low amount of H2S has poorly been addressed. Regarding toughness properties, the two steels present different behaviour: for the L360 NB crack has not propagated for any testing environments, while cracks propagated in all the tests for the N80 Q. Despite this difference, for the two steels, the toughness does not seem to be affected by hydrogen as the results obtained in NG + 25%H2 + H2O and NG + H2O are similar. Based on the literature C-Mn steels toughness is affected by the presence of dry hydrogen. Hence, the results presented here show that H2O inhibits hydrogen embrittlement as far as toughness is concerned. The L360NB, however, presented a slight decrease in toughness properties with the combination of NG + 25%H2 + H2S + H2O. FCG (fatigue crack growth) results, on the opposite, clearly highlight the influence of hydrogen on the mechanical behaviour of the two steels. The FCG rates are faster from a factor five (resp. 10) in NG + 25%H2 + H2O compared to NG + H2O for the N80 Q (resp. L360). In this article, toughness and FGC results on the two steels are discussed in terms of microstructure and mechanical loading modes, aiming to quantify and better understand the influence of H2O and H2S on the sensitivity of low alloy steels to hydrogen embrittlement.

Laser Powder Bed Fusion is not power efficient at processing copper-chromium-zirconium alloy due to the high reflectivity of the powder at the laser standard wavelength (1070 nm). A way to reduce the optical reflectivity is to modify the powder surface. This work aims to study the impact of reduction and oxidation pre-treatments on the surface chemistry of the particles, and to understand their consequences on the powder properties. X-ray photoelectron spectroscopy analyses show that, starting from a 2???3 nm thick native Cu2O layer, a wet atmo-sphere leads to the formation of a 54 nm thick Cu2O layer, whereas a reduction under hydrogen leads to pure copper. Under argon, the Cu2O thickness slightly increases up to 3???4 nm. The oxidation and the reduction treatments improve the flowability, respectively, by 46% and 26%. The reduction increases the reflectivity by 2%, whereas the oxidation reduces it by 26%.

Sous atmosphère d’hydrogène gazeux, les alliages métalliques présentent une chute de ductilité, une baisse de ténacité ou une accélération de la vitesse de propagation des fissures de fatigue. Mais comment caractériser la fragilisation par l’hydrogène de ces matériaux ?

CuCrZr is a precipitation hardening alloy, used for its good electrical and thermal properties combined to high mechanical properties. Using additive manufacturing technologies, and more specifically the laser powder bed fusion (L-PBF) process, allows designing highly complex parts such as compact and efficient CuCrZr heat exchangers. Additional understanding of the specific CuCrZr metallurgy during this manufacturing process is still needed to fully take advantages of these possibilities. This work aimed (i) to clarify the impact of the L-PBF process and post-fabrication heat treatments on the microstructure of L-PBF CuCrZr alloy, (ii) to determine the corresponding mechanical and electrical properties and (iii) to quantify the contributions of the different nano scale strengthening mechanisms (nano-precipitation, dislocations, solid solution, grain size refinement) depending on the different heat treatments. The microstructures of the CuCrZr samples are carefully analyzed at different scales thanks to scanning electron and transmission electron microscopy, highlighting the effect of the different heat treatments. In all heat-treated samples, Cr nano-precipitates are uniformly dispersed in the Cu matrix; few Zr nano-precipitates are observed either at grain boundaries, next to Cr nano-precipitates, or inside the Cu matrix. Moreover, the mean grain size, dislocation density, mean radius and volume fraction of the Chromium nano-precipitates are measured. These data are introduced in the identified hardening mechanisms to estimate the yield strengths (YS) of the different analyzed CuCrZr microstructures. The results are compared to the experimental values, including those of a reference wrought heat-treated CuCrZr, and discussed. A good correlation is found between calculated and experimental values. For the first time, the main hardening mechanisms of L-PBF CuCrZr are quantified and the interest of the "L-PBF + Direct Age Hardening (DAH)" process route to get a high amount of Cr nano-precipitates is confirmed. The DAH applied to L-PBF materials provides high mechanical properties (184 HV1 hardness, YS = 527 MPa, UTS = 585 MPa) while keeping a good elongation (14%) and electrical conductivity (42 MS.m(-1)). These results are due to a combination between (i) a high Cr nano-precipitates density, leading to a high precipitation hardening, and (ii) a high dislocation density associated to the presence of remaining solidification cells.

The present document is part of a larger literature survey of this WP, aiming to establish the current status of gas utilisation technologies in order to determine the impact of hydrogen (H2) admixture on natural gas (NG) appliances. This part focuses on the non-combustion related aspects of injecting hydrogen in the gas distribution networks within buildings, including hydrogen embrittlement of metallic materials, chemical compatibility and leakage issues. In the particular conditions of adding natural gas and hydrogen (NG / H2) mixture into a gas distribution network, hydrogen is likely to reduce the mechanical properties of metallic components. This is known as hydrogen embrittlement (HE) (Birnbaum, 1979). This type of damage takes place once a critical level of stress / strain and hydrogen content coexist in a susceptible microstructure. Currently, four mechanisms were identified and will be discussed in detail. The way those mechanisms act, independently or together, is strongly dependent on the material, the hydrogen charging procedure and the mechanical loading type. The main metallic materials used in gas appliances and gas distribution networks are: carbon steels, stainless steels, copper, brass and aluminium alloys (Thibaut, 2020). The presented results showed that low alloy steels are the most susceptible materials to hydrogen embrittlement followed by stainless steels, aluminium, copper and brass alloys. However, the relative pressures of the operating conditions of gas distribution network in buildings, are low i.e. between 30 to 50 mbar. At those low hydrogen partial pressures, it is assumed that a gas mixture composed of NG and up to 50% H2 should not be problematic in terms of HE for any of the metallic materials used in gas distribution network, unless high mechanical stress / strain and high stress concentrations are applied. The chemical compatibility of hydrogen with other materials, and specifically polyethylene (PE) which is a reference material for the gas industry, is also discussed. PE was found to have no corrosion issues and no deterioration or ageing was observed after long term testing in hydrogen gas. The last non-combustion concern related to the introduction of hydrogen in natural gas distribution network is the propensity of hydrogen toward leakage. Indeed, the physical properties of hydrogen are different from other gases such as methane or propane, and it was observed that hydrogen leaks 2.5 times quicker than methane. This bibliographical report on material deterioration, chemical compatibility and leakage concerns coming with the introduction of NG / H2 mixture in the gas distribution network sets the basis for the upcoming experimental work where the tightness of gas distribution network components will be investigated (Task 3.2.3 WP3). In addition, tightness of typical components that connect end-user appliances to the local distribution line shall be evaluated as well.

The purpose of the present work is to study the effect of the hydrogen content in a H-2-NG (Natural Gas) blend on the mechanical behavior of a C-Mn low alloy steel L485-MB (NF EN ISO 3183) under monotonic loading. Different testing conditions were explored for the blend: 2% H-2-NG, 25% H-2-NG, 100% H-2 and 100% NG at a total pressure of 8.5 MPa using two slow strain rates: 10(-4) s(-1) and 10(-6) s(-1). Tests in the blend were compared to those under pure hydrogen at the same partial pressures. Furthermore, two surface roughnesses have been explored, one corresponding to a mirror polish, the other as lathed. The embrittlement has been assessed by necking measurements and fracture analysis for the whole testing conditions. The results show a drop of ductility with the increase of partial pressure of hydrogen in NG. Besides, no significant effect of hydrogen were observed on flow stress. In addition, the L485-MB pipeline steel presents a shear type fracture mode in high partial pressure of hydrogen, whereas a cup and cone type fracture were observed in air, NG and low partial pressure of hydrogen in NG (0.2 MPa H-2).

The implementation of mechanical tests within controlled aggressive environments remains essential for the study of stress corrosion cracking (SCC), corrosion fatigue (CF), and hydrogen embrittlement (HE) phenomena insofar as the constant evolution of materials requires requalifying and reevaluating their sensitivity for each new grade and more generally for each new material/environment system.

Solubility and diffusion of hydrogen are two determining factors to understand its damaging mechanisms. However, the adsorption and desorption stages and the integration of the trapping phenomena are fundamental processes to be taken into account in H-metallic material interaction studies in order to better understand/model hydrogen embrittlement (HE) phenomena. This chapter aims to establish the current situation regarding the knowledge of these processes. The following chapters will focus more on the HE mechanisms, on presenting industrial case studies and on establishing a picture of the characterization techniques for the quantities developed here.

The European Union is intending to reduce their carbon emissions by up to 80–95% by 2050. This will imply the increase of electricity coming from variable renewable energy sources. Producing hydrogen from this electricity is one way to facilitate the integration of such intermittent sources. Currently, there is no consensus in the world on the allowed amount of hydrogen in the natural gas with the aim to use the natural gas existing transportation grid to transport such mixture. The object of the present study is to provide additional experimental data concerning the effect of the hydrogen content in a N2/H2 mixture on the toughness of an API X70 steel dedicated to gas transport. The toughness has been measured in terms of Crack Tip Opening Displacement under a total pressure of 85 bar. The mechanical results are compared to existing results. It is confirmed that 1% H2 induces a significant decrease of the material toughness. Moreover, the content of O2 impurity in the N2/H2 mixture has been considered and its effect on HE mitigation has been quantified for an O2 content ranging between 10 vol. ppm and 100 vol. ppm. Finally, several approaches to take into account the effect of H2 in the NG/H2 blend on the design or on the service life of gas pipelines will be discussed.

Hydrogen embrittlement is a subject of great scientific curiosity since it has detrimental effects in many industrial sectors. As an example, the website “Hydrogen tools” identifies the incidents or accidents related to the presence of hydrogen and tries to give an explanation of each problem and the measures that should be taken to avoid it. The causes may be related to equipment failure, human error, inappropriate maintenance, unsupervised procedures, unsuitable materials, etc. This highlights the need to better understand the degradation mechanisms involved with regards to the loading conditions (environment, temperature, pressure, materials, etc.), in order to establish the strategies required to avoid these problems. The aim of this chapter is to present, in a non-exhaustive way, industrial examples of the consequences of hydrogen embrittlement in metals. The sensitivity to HE may affect the size of the components, the material selection or the security measures implemented near the devices. Furthermore, in order to facilitate the development of hydrogen-related infrastructure, it is necessary to improve the design codes and standards to take into account the presence of this element in a better way. Some ongoing developments around the world on this subject will also be presented here.

For several years, Inconel 718 made by Laser Beam Melting (LBM) has been used for components of the Ariane propulsion systems manufactured by ArianeGroup. In the aerospace field, many components of space engines are used under hydrogen environment. The risk of hydrogen embrittlement (HE) can be therefore a first order problem. Consequently, to improve the HE sensitivity of LBM Inconel 718, a systematic approach needs to be developed to characterize the microstructure at different scales and its interaction with hydrogen. This study addresses the impact of gaseous hydrogen on the material mechanical behavior under fatigue loadings. In a first step, the low cycle fatigue behavior under 300 bar of hydrogen gas has been evaluated with specimen loaded at a constant load ratio of R=0.1 and a frequency of 0.5 Hz. A reduction in the cycle number of fracture is shown. This reduction of fatigue life is a consequence of the impact of hydrogen damage processes. The impact of hydrogen is evaluated at the stages of crack initiation, crack propagation. These results are discussed in relation with the hydrogen embrittlement mechanisms and particularly in terms of hydrogen / plasticity interactions. To achieve this, the fracture surface morphology was first examined using scanning electron microscopy and second samples near the fracture surface were extracted using Focused-Ion Beam machining from regions containing striation. The main result observed is a reduction of the size of dislocation organization in relation with a decrease of the striation distance.

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.

In the aerospace field, some components of rocket engines are solicited under "hydrogen atmosphere". Under these conditions, the risk of hydrogen embrittlement of these components may be significant. We focused this work on the influence of hydrogen on mechanical behaviors of a nickel-based alloy obtained by Laser Beam Melting. For that, we characterized the microstructure of this material at different scales, and then, we performed several fatigue tests under a hydrogen pressure at room temperature. The obtained results show a reduction of the number of cycles to failure in the presence of hydrogen. This situation is discussed in regard of the interaction between hydrogen and plasticity.

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.

X4CrNiMo 16.5.1 steel (commercial name APX4) is a low carbon martensitic stainless steel known for its remarkable mechanical characteristics and its good resistance to corrosion. The use of APX4 in the manufacture of high pressure gas vessels requires a thorough understanding of its resistance to Hydrogen Embrittlement (HE) as the gas can contain traces of hydrogen, and martensitic steels, and their welds, are generally very sensitive to HE.This paper deals with the first part of this study, involving the characterization of the microstructure and the mechanical properties of each zone of the electron beam weld (melted zone and four different heat affected zones), and the investigation of their embrittlement in a hydrogen environment. For this purpose, tensile tests were performed in hydrogen gas at various pressures on both the base metal and the welded samples.In situ tensile tests with picture correlation analysis have been planned for the subsequent part of our study. These experiments will enable us to track the strain in the different zones and examine the effect of hydrogen on their mechanical behavior.These results, combined with permeation tests, should lead to a complete model for predicting hydrogen location inside the vessel as a function of time and local properties, as well as the associated embrittlement.