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A simple screening technique of hydrogen embrittlement (HE) of steels for hydrogen energy facilities using an in-situ small-punch (SP) test method under external hydrogen condition has been established. Using this method, we investigated the HE behaviors of API X70 steel welds under test conditions mimicking pipeline operating environments. The HE sensitivity at each region of the base metal, heat-affected zone, and weld metal of the steel weld was examined qualitatively and quantitatively and compared to one another. Under 8 MPa H2 gas, the welds showed pronounced HE: the HE behaviors induced were similar across all tested regions. This shows that the in-situ SP test is effective for screening HE susceptibility of pipeline steel welds in high-pressure hydrogen environments.

Hydrogen uptake, tensile, and fatigue properties of a precipitation-hardened martensitic stainless steel with a newly developed coating (alumina/aluminum/Fe–Al) were presented. The developed coating had an excellent resistance to hydrogen entry in 100-MPa hydrogen gas at 270 °C. Measurements of bulk and local hydrogen by thermal desorption analysis and secondary-ion mass spectrometry (SIMS) suggested that the excellent resistance was attributed to the reduction in permeation areas by interfacial hydrogen trapping between the aluminum and Fe–Al layers. Tensile tests of a smooth, round-bar specimen, and fatigue tests of a circumferentially notched specimen after exposure to 100-MPa hydrogen gas at 270 °C were performed in air at room temperature (RT). These properties of the coated specimens were not degraded by hydrogen exposure, whereas those of the noncoated specimens were significantly degraded. Hydrogen-pressure cycle tests of coated, tubular specimens with an inner notch in 95-MPa hydrogen gas at 85 °C also demonstrated that the fatigue life was improved by the coating.

Three stainless steels - ASTM 304, 316 and 316L - used in hydrogen utilization equipment are under investigation at conditions of tension-compression, rotating-bending and fretting fatigue. Fatigue tests are carried out with hydrogen charged and uncharged specimens. Hydrogen charging includes cathodic type of charging and exposure to high pressure hydrogen gas. The experiments under rotating bending and tension-compression fatigue are conducted under different frequencies in three different laboratories: at The University of Chemical Technology and Metallurgy, Sofia, Bulgaria; at Sandia National Laboratory, California and The University of Tufts, Medford, Massachusetts, USA; The HYDROGENIUS Institute at Kyushu University, Japan. The fretting fatigue tests are presented by The HYDROGENIUS Institute at Kyushu University, Japan. The obtained results are presented in Wohler curves complemented by plots "Short fatigue crack length-Number of cycles" and "Tangential force coefficient-Stress amplitude". The found fatigue characteristics are analyzed and compared at different loading conditions, showing the best performance of Steel 316L.

Banded ferrite–pearlite X65 pipeline steel was tested in high pressure hydrogen gas to evaluate the effects of oriented pearlite on hydrogen assisted fatigue crack growth. Test specimens were oriented in the steel pipe such that cracks propagated either parallel or perpendicular to the banded pearlite. The ferrite–pearlite microstructure exhibited orientation dependent behavior in which fatigue crack growth rates were significantly lower for cracks oriented perpendicular to the banded pearlite compared to cracks oriented parallel to the bands. The reduction of hydrogen assisted fatigue crack growth across the banded pearlite is attributed to a combination of crack-tip branching and impeded hydrogen diffusion across the banded pearlite.

In Japan, with regards to the widespread commercialization of 70 MPa-class hydrogen refueling stations and fuel cell vehicles, two national projects have been promoted on both the infrastructure and the automobile sides. These projects have been promoted to establish the criteria for determining hydrogen compatibility of materials and to expand the usable materials for high-pressure hydrogen environment. For these projects, establishing test methods to evaluate the hydrogen compatibility of materials is one of the most important tasks. This paper describes the status of common standardization of testing methods. Two projects share a common database for the testing results, which is currently put to practical use.

Traditional high pressure mechanical compressors account for over half of the car station’s cost, have insufficient reliability and are not feasible for a large-scale fuel cell market. An alternative technology, employing a two-stage, hybrid system based on electrochemical and metal hydride compression technologies, represents an excellent alternative to conventional compressors. The high-pressure stage, operating at 100-875 bar, is based on a metal hydride thermal system. A techno-economic analysis of the metal hydride system is presented and discussed. A model of the metal hydride system was developed, integrating a lumped parameter mass and energy balance model with an economic model. A novel metal hydride heat exchanger configuration is also presented, based on mini-channel heat transfer systems, allowing for effective high-pressure compression. Several metal hydrides were analyzed and screened, demonstrating that one selected material, namely (Ti0.97Zr0.03)1.1Cr1.6Mn0.4, is likely the best candidate material to be employed for high-pressure compressors under the specific conditions. System efficiency and costs were assessed based on the properties of currently available materials at industrial levels. Results show that the system can reach pressures on the order of 875 bar with thermal power provided at approximately 150 °C. The system cost is comparable with the current mechanical compressors and can be reduced in several ways as discussed in the paper.

Japan began constructing and upgrading HRS (Hydrogen Refueling Stations) for its FCV (Fuel Cell Vehicle) demonstration program in 2002, as shown in Fig. 1. In 2013, Japanese energy providers started constructing commercial HRS for refueling FCV with 70 MPa hydrogen, and almost 100 HRS are now in service. Maintaining the reliability of refueling equipment is essential for safe, stable operation of commercial HRS. However, as a result of experience with commercial HRS operation during the past few years, Japanese energy providers have recognized that maintenance for small leaks from cone and thread mechanical joints involves a significant loss of resources.

The paper presents the hydrogen-entry, tensile, and fatigue properties of a precipitation-hardened martensitic stainless steel, JIS-SUS630, with a newly developed coating, whose thickness ranges from 10 to 20 μm. The newly developed coating consists of alumina, aluminum, and ferroaluminum, and has an excellent resistance to hydrogen entry in 100-MPa hydrogen gas at 270°C. The hydrogen entry in the coated specimen occurred under a diffusion-controlled process and the effective hydrogen diffusivity was approximately one thousandth of that of the base steel. Although the hydrogen diffusivity of JIS-SUS630 was two orders of magnitude larger than that of JIS-SUS304, the effective hydrogen diffusivity of the coated JIS-SUS630 was nearly equal to that of the coated SUS304. In our previous study with secondary-mass ion spectroscopy (SIMS), the coating’s excellent resistance to hydrogen entry was attributed to interfacial hydrogen trapping between the aluminum and ferroaluminum layers. The experimental result obtained in this study suggested that the excellent resistance to hydrogen entry demonstrated by the developed coating can be attributed to the reduction in the permeation area induced by the interfacial trapping of hydrogen. The tensile tests of a smooth, round-bar specimen and fatigue tests of a circumferentially notched specimen with exposure to 100-MPa hydrogen gas at 270°C were performed in air at room temperature (RT). The test results showed that the tensile and fatigue properties of the coated specimens were not degraded by hydrogen exposure, whereas those for the non-coated specimens were significantly degraded. Hydrogen-pressure cycle tests of the coated, tubular specimens with an inner notch were also carried out with 95-MPa hydrogen gas at 85°C, demonstrating that the fatigue life of the tubular specimen was improved by the developed coating.

Tension-compression fatigue tests using smooth specimens of low carbon steel JIS-SM490B were carried out in air and hydrogen gas environment under the pressure of 0.7 and 115 MPa at room temperature. In 0.7 MPa hydrogen gas, fatigue life curve was nearly equivalent to that in air. On the other hand, in 115 MPa hydrogen gas, fatigue life was significantly degraded in the relatively short fatigue life regime (e.g. Nf < 105). To clarify the effect of hydrogen environment on fracture process, fracture surfaces of these specimens were observed. In general, fatigue fracture process of steels with low or moderate strength is macroscopically divided into 3 stages. In the first stage (stage I), fatigue cracks initiate in some crystalline grains. In the second stage (stage II), the cracks propagate stably on a cycle-by-cycle basis. In the final stage (stage III), a tilted fracture surface, shear-lip, is formed by ductile tearing. In SM490B steel, this general fracture process was confirmed in air and 0.7 MPa hydrogen gas. In contrast, in 115 MPa hydrogen gas, there was no tilted portion in the stage III region, and the fracture surface was totally flat. Observation with scanning electron microscope revealed that dimples were formed by ductile tearing in the tilted fracture region in air and 0.7 MPa hydrogen gas. On the other hand, only a quasi-cleavage fracture surface existed in the final fracture region in 115 MPa hydrogen gas. To understand the cause of this peculiar fracture morphology, we conducted elasto-plastic fracture toughness tests in each environment, and investigated the fracture morphology. As a result of fracture toughness tests, crack growth rate in air and 0.7 MPa hydrogen gas was approximately equal to each other, and both the fracture surfaces were covered by dimples. This fracture morphology was in accordance with that of stage III morphology in fatigue specimen tested in air and 0.7 MPa hydrogen gas. However, in 115 MPa hydrogen gas, the crack growth was significantly accelerated, and the whole fracture surface was covered by quasi-cleavage. In this paper, firstly, the similarity of fracture surface between two test methods, i.e. fatigue test and fracture toughness test, is investigated. And then, the formation mechanism of the flat fracture surface is discussed by paying attention to the crack-growth acceleration in high-pressure hydrogen gas.

Evaluations of mechanical properties under high pressure hydrogen gas environments are difficult because special testing equipment which can obtain data under high pressure hydrogen gas is necessary and the cost of installing those machines is very high. Therefore, a method for predicting mechanical properties under high pressure hydrogen gas without special equipment was investigated in this study. A JIS SCM435 steel, of which the typical chemical composition is Fe-0.35%C-0.2%Si-0.75%Mn-1.1%Cr-0.2%Mo, was used. Material with the size of 22mm in square and 200mm in length was heat-treated by quenching in oil and tempering, followed by water cooling. The material microstructure was tempered martensite, and the tensile strength of the steel was about 1000MPa. The fatigue property was evaluated in cathodic hydrogen charging service and high pressure hydrogen gas service. The fatigue property obtained by the cathodic charging method was almost the same as the property under the high pressure hydrogen gas condition. The reason is conjectured to be that the hydrogen fugacity on the specimen surface and the surface state of the specimen under those test services was substantially the same.

In order to ensure the safety of carbon fiber reinforced tanks for 35 and 70 MPa fuel cell vehicles, it is necessary to clarify the fatigue crack growth behavior of A6061-T6 aluminum alloy for the tank liner. In this study, the fatigue crack growth tests were carried out under the conditions of test frequencies f = 0.001-10 Hz in 90 MPa (≒70 MPa×125 %) hydrogen gas, 90 MPa nitrogen gas, air and deionized water at room temperature. The fatigue crack growth rates in hydrogen and nitrogen gas at f = 1-10 Hz were lower than those in air and deionized water. However, the fatigue crack growth rates in hydrogen and nitrogen gas at f = 0.001-0.1 Hz were nearly the same as those in air and deionized water. It was found from those results that the fatigue crack growth rate was not accelerated in 90 MPa hydrogen gas. The results of fatigue crack growth tests in this study were applied to the failure analysis of 35 MPa hydrogen tanks. In JARI (Japan Automotive Research Institute), using 35 MPa hydrogen tanks, the pressure cycling tests were conducted at -40, 25 and 85°C by water or PEPF (Perfluoroalkylpolyether) under 125 % filling pressure. The tanks fractured by LBB (Leak Before Break). Increasing in the test temperature increased in the number of cycles to LBB failure. Such a behavior was predicted by the fatigue crack growth properties of A6061-T6 obtained in this study.

The dependences of low-cycle durability of 11 corrosion-resistant steels of the main grades on gaseous hydrogen pressure within the range of 0.1…35 MPa at 293 K have been obtained. Homogeneous austenitic steels as well as the steels with intermetallide strengthening possess the highest service ability in hydrogen. Ni–Al–Ti steels treated for maximum heat resistance have the durability in hydrogen which is proportional to the content of Ti/Al and Ti, and is also determined by the treatment conditions. Transition materials and steels with unstable austenite form a group of steels with medium sensitivity to hydrogen. The group of metals that are catasrophic embrittled in hydrogen includes high-strength martensitic-ageing and ferritic steels.

We have established correlations between the effect of hydrogen under a pressure of 35 MPa on the low-cycle fatigue of 15 corrosion-resistant steels, on the one hand, and their initial mechanical characteristics and the parameter of austenite stability A γ on the other. Materials with A γ

The standard 2.25Cr–1Mo steel, has been used for most of the hydroprocessing reactors built during the 30 years up to the end of the 1990’s. Under service conditions, the steel, and in particular its weldments, may experience degradation by “hydrogen attack”, or high-temperature hydrogen attack (HTHA), which is responsible for several failures and even casualties occurring in the history of the industry. The selection of the structural steels is still based on the empirical Nelson curves which, among other limitations, do not provide information on the behaviour of weldments. This causes uncertainties in the definition of the safety boundaries for operation of pressurized components in the petrochemical industry. The results of the present study confirm that weldments are a weak point of the pressurized components and suggest that the HAZ, and in particular the ICHAZ, is the most sensitive metallurgical zone to hydrogen attack.

Bending fatigue samples were plasma cut and water jet cut from sheets of 304 stainless. Samples were exposed to high pressure hydrogen (138 MPa at 300C for three weeks) or 1 atm hydrogen at room temperature for one week, or were unexposed. Preliminary results from bending fatigue testing show a decrease in fatigue life for hydrogen supersaturated samples. The present investigation shows SEM fractographic imaging from fatigue samples for each of the hydrogen exposure populations. Samples that were not exposed to hydrogen preliminarily appear to show fatigue striations on fractographic images. The ongoing research seeks to discern a difference in failure surfaces between hydrogen-exposed and unexposed samples.

Type 316/316L austenitic stainless steels are considered the benchmark for resistance to hydrogen embrittlement in gaseous hydrogen environments. Type 316/316L alloys are used extensively in handling systems for gaseous hydrogen, which has created engineering basis for its use. This material class, however, is relatively expensive compared to other structural metals including other austenitic stainless steels, thus the hydrogen fuel cell community seeks lower-cost alternatives. Nickel content is an important driver of cost and hydrogen-embrittlement resistance; the cost of austenitic stainless steels is largely determined by nickel content, while high nickel content generally improves resistance to hydrogen embrittlement. These circumstances create the perception that less-expensive grades of austenitic stainless steels are not appropriate for hydrogen service. While other grades of austenitic stainless steels are generally more susceptible to hydrogen embrittlement, in many cases the hydrogen-affected properties are superior to the properties of materials that are considered acceptable, such as aluminum alloys and A-286 austenitic stainless steel. In this paper, the properties of a variety of austenitic stainless steels are compared with the aim of promoting the consideration of a wider range of austenitic stainless steels to reduce cost and reduce weight of high-pressure components for hydrogen service.Copyright © 2014 by ASME

For the low alloyed fine grained ferritic structural steel 15 MnNi 6 3 in a first step J-integral tests were performed at room temperature in argon, pure high pressure hydrogen gas as well as with admixtures of oxygen (10 vpm, 150 vpm) in the single specimen technique. The JR-curve received for pure hydrogen environment is essentially lower than the curve for argon. The JR-curve for hydrogen with 10 vpm oxygen is shifted towards the one for pure hydrogen whereas the admixture of 150 vpm oxygen results in a JR-curve near the argon curve. The JIc-value for 10 vpm oxygen admixture is approximately twice the one for pure hydrogen, for 150 vpm oxygen admixture about three times that for pure hydrogen. For the specimen fractured in argon a dimpled fracture surface, for the one tested in pure hydrogen a flat quasi-cleavage fracture was observed. With increasing oxygen admixture the portion of ductile fracture grows.

There have been limited studies of the fracture of unhydrided cold worked Zircaloy-2 in a gaseous hydrogen atmosphere. It was found that subcritical fracture occurred at low temperatures, but not at temperatures above 80 C. Recently, notched tensile tests of recrystallized Zircaloy-4 in high pressure H{sub 2} gas showed a {approximately} 50% drop in room temperature reduction in area relative to samples tested in air but there was little or no effect of the H{sub 2} atmosphere on reduction in area at 100 C and 200 C. The present work investigated the subcritical cracking of Zircaloy-2 in high pressure H{sub 2} gas at a temperature of 325 C. Fracture was observed at crack propagation rates that were several orders of magnitude faster than DHC. A new mechanism of fracture that occurred by fracture of a rapidly forming crack tip hydride layer was suggested.

This report summarizes the research and development accomplishments during FY12 for the tritium effects on materials program. The tritium effects on materials program is designed to measure the long-term effects of tritium and its radioactive decay product, helium-3, on the structural properties of forged stainless steels which are used as the materials of construction for tritium reservoirs. The FY12 RD (2) Developed an Experimental Plan for Measuring Cracking Thresholds of Tritium-Charged-and-Aged Steels in High Pressure Hydrogen Gas; (3) Calculated Sample Tritium Contents For Laboratory Inventory Requirements and Environmental Release Estimates; (4) Published report on “Cracking Thresholds and Fracture Toughness Properties of Tritium-Charged-and-Aged Stainless Steels”; and, (5) Published report on “The Effects of Hydrogen, Tritium, and Heat Treatment on the Deformation and Fracture Toughness Properties of Stainless Steels”. These accomplishments are highlighted here and references given to additional reports for more detailed information.

High pressure gaseous hydrogen (HPGH2) storage offers the simplest solution in terms of infrastructure requirements and has become the most popular and highly developed method. HPGH2 storage vessel is the key equipment for HPGH2 storage system. China issued the first national standard on HPGH2 storage vessel named “stationary flat steel ribbon wound vessels for storage of high pressure hydrogen” in 2011. Some crucial technical points are involved in this standard, such as material selection, design method for the shell’s thickness, mehod for determining the winding parameters and detection techniques for the attaching quality between the flat steel ribbon layers. In this paper, a brief introduction is given to the aforementioned technical points.

Hydrogen environment embrittlement (HEE) of stainless steels in the environment of high pressure and low temperature hydrogen gas was evaluated using a very simple mechanical properties testing procedure. In the method, the high-pressure hydrogen environment is produced just inside the hole in the specimen. In this work, the effects of HEE on fatigue properties for austenitic stainless steels SUS304L and SUS316L were evaluated at 298 and 190 K. The effects of HEE on the tensile properties of higher strength stainless steels, such as strain-hardened 316, SUS630, and other alloys, SUH660 and Alloy 718 were also examined. The less effect of HEE on fatigue properties of SUS316L and tensile properties of strain-hardened 316 were observed compared with SUS304L and other steels at room temperature and 190 K.

The LE-7 engine which will be used as the first stage main engine for the H-II rocket has been under development in Japan. This engine has a lot of welded joints, but various troubles have occurred at those joints. Therefore, tensile properties of Inconel-718 test specimens with a welded joint were investigated at various temperatures in high pressure hydrogen and helium environments in order to study fundamental characteristics of the welded joints. And by using those results, the relation between tensile properties and micro-structures was examined. It was found of the welded joint that the ductility was less than that of the parent metal and that the deterioration of ductility was due to the dendrite structure of Ni3Nb phase.

Threshold stress intensity factors were measured in high-pressure hydrogen gas for a variety of low alloy ferritic steels using both constant crack opening displacement and rising crack opening displacement procedures. The sustained load cracking procedures are generally consistent with those in ASME Article KD-10 of Section VIII Division 3 of the Boiler and Pressure Vessel Code, which was recently published to guide design of high-pressure hydrogen vessels. Three definitions of threshold were established for the two test methods: K{sub THi}* is the maximum applied stress intensity factor for which no crack extension was observed under constant displacement; K{sub THa} is the stress intensity factor at the arrest position for a crack that extended under constant displacement; and K{sub JH} is the stress intensity factor at the onset of crack extension under rising displacement. The apparent crack initiation threshold under constant displacement, K{sub THi}*, and the crack arrest threshold, K{sub THa}, were both found to be non-conservative due to the hydrogen exposure and crack-tip deformation histories associated with typical procedures for sustained-load cracking tests under constant displacement. In contrast, K{sub JH}, which is measured under concurrent rising displacement and hydrogen gas exposure, provides a more conservative hydrogen-assisted fracture threshold that ismore » relevant to structural components in which sub-critical crack extension is driven by internal hydrogen gas pressure.« less

CERT-Versuche mit niedriglegierten Vergutungsstahlen im Festigkeitsbereich 700–1200 N/mm2 wurden mit elektropolierter und geschliffener Oberflache bei Abzugsgeschwindigkeiten von 1 bis 227 · 10−7s−1 in Stickstoff und Wasserstoff (100 bar) bei 20°C sowohl einsinnig bis zum Bruch als auch mit Sagezahncharakteristik durchgefuhrt. Bei einsinniger Belastung wurde die hochste H-Schadigung bei e = 2,2 · 10−5s−1 gefunden. Ein Einflus der Legierungsbestandteile Mn, Cr, Ni, Mo war nicht feststellbar, wohl aber ein Effekt de Konzentration nichtmetallischer Einschlusse. Wahrend lastgesteuerte Schwellversuche keine ausreichende Differenzierung erlaubten, wurden H-Effekte bei Wechselbelastungen mit oberer Last, definiert durch σmax = σ(F=0), klar erkennbar. Der Einflus der Belastungsamplitude ist gering. Eine deutliche Abnahme der relativen Standzeit in Wasserstoff wurde erst bei Festigkeiten oberhalb 1000 N/mm2 beobachtet. Vergleichbare Resultate lieferten dehnungsgesteuerte Schwellversuche. Investigations on hydrogen embrittlement of high strength low alloy steels in high pressure hydrogen under static and dynamic loading CERT experiments with high strength low alloy steels with ultimate tensile strengths in the range 700-1200 N/mm2 were performed with electropolished and ground surfaces with elongation rates of 1 to 277 · 10−7s−1 in nitrogen and hydrogen (100 bar) at 20°C under conditions of unidirectional straining as well as cyclic loading with saw tooth characteristics. Under unidirectional straining the highest hydrogen effect was observed at e = 2,2 · 10−5s−1. While no influence was detectable of the alloy elements Mn, Cr, Ni and Mo, the concentration of nonmetallic inclusions proved to be very important. Cyclic loading with load steering gave no sufficient discrimination of H effects. However, cyclic loading with a maximum load defined by σmax = σ(F=0), yielded good results. The effect of the loading amplitude is poor. A significant decrease of the time to failure in hydrogen is observed only at ultimate tensile strengths above 1000 N/mm2. Comparable results were obtained from cyclic loading experiments steered by elongation.

The effect of high-pressure hydrogen and temperature on crack growth was studied in wedge-opening-load (WOL) samples of a low-carbon steel. At temperatures above 280 ‡C, a hydrogen pressure of 3 ksi gave an increasing amount of acceleration in crack growth. These conditions approached but were below that needed to give hydrogen attack (HA) in the surrounding matrix. The value ofda/dt increases exponentially with temperature, andQ is roughly equal to that for grain boundary diffusion. The growth is absent atK1 = 0 but varies little withK1 above 15 MPa√m. The value ofda/dt increases steadily with hydrogen pressure in the range of 3 to 21 MPa.