Steel In Hydrogen Gas Research Articles

Application of line pipe and hot induction bends in hydrogen gas

For the upcoming hydrogen economy, transport pipelines for hydrogen gas and gas mixtures of hydrogen and natural gas are one of the important components. For the application of steel in hydrogen gas it is necessary to handle the risk of hydrogen embrittlement by adapting the right knowledge. Compared to existing hydrogen pipelines, which are safely running since decades, higher gas pressures and steel strength levels are in discussion. For a safe operation and limited resource consumption it is necessary to clarify the product requirements. The semi-finished products medium and large line pipes and bends are regarded over the production chain: pre-material, hot rolled strip, welded pipes, and induction bent pipes. The interaction of hydrogen with steel is investigated since decades. For hydrogen gas, the surface reaction with steel is considerably reduced compared to other corrosion reactions i.e. with sour gas. This results in a much lower amount of introduced hydrogen atoms within the material. Results of lab trials of different materials after storage in pressured hydrogen gas will be shown to clarify this point. Furthermore, results of tests of applicability of commonly used flow coats in hydrogen atmosphere are shown. For a possible failure scenario of a hydrogen transport line the investigations must be focused on local effects of hydrogen enrichment in conjunction with mechanical loads. There are different laboratory tests possible to evaluate these material reactions. They are shown and discussed in the view of the following aspects: product qualification, further product and specification development and suitable approval tests.

Peculiar temperature dependence of hydrogen-enhanced fatigue crack growth of low-carbon steel in gaseous hydrogen

The peculiar temperature dependence of hydrogen-enhanced fatigue crack growth (HEFCG) of low-carbon steel in hydrogen gas was successfully interpreted in terms of ‘trap-site occupancy’ of hydrogen. HEFCG decreased with increasing temperature in hydrogen gas at 0.7 MPa and 298 to 423 K due to lower occupancy of trap sites at higher temperatures. In hydrogen gas at 90 MPa, HEFCG was insensitive to the temperature because most of the trap sites were occupied by hydrogen, regardless of the temperature. Trap sites with a binding energy of 47 kJ/mol, corresponding approximately to the dislocation core, dominated the temperature dependence of HEFCG.

Fatigue crack growth modelling for pipeline carbon steels under gaseous hydrogen conditions

A corrosion-crack correlation model is proposed for the hydrogen embrittlement (HE) influenced fatigue crack growth modelling of pipeline carbon steels under gaseous hydrogen conditions. The model is developed primarily based on the correlation of environment-affected zone (EAZ) and plastic zone. In the model, fatigue crack growth rate is predicted by Forman equation to take into account the influence from fracture toughness. The critical frequency and the “transition” stress intensity factor (SIF) are derived based on stress-driven hydrogen diffusion and Hydrogen-Enhanced De-cohesion (HEDE) hypothesis, which provides reasonable explanation on the frequency dependence of fatigue crack growth for pipeline carbon steels in hydrogen gas. Furthermore, an approximation formula involving threshold the SIF range and the stress ratio is established to describe the phenomenon of crack growth rate plateau. In addition, a formula is proposed to estimate the equilibrium fracture toughness according to the equilibrium between crack growth and hydrogen delivery rates. A series of experimental data from different grades of carbon pipeline steels (including high-strength grades such as X70 and X80) are utilized for demonstrate the validity of the proposed formulae and model effectiveness. The comparison between model predictions and experimental data shows that the proposed model is capable of capturing the essence of pipeline carbon steels’ fatigue crack growth process under gaseous hydrogen conditions.

環状切欠きを有する低合金鋼およびオーステナイト系ステンレス鋼丸棒の水素ガス中における疲労寿命特性

環状切欠きを有する低合金鋼およびオーステナイト系ステンレス鋼丸棒の水素ガス中における疲労寿命特性

Slow strain rate tensile and fatigue properties of Cr–Mo and carbon steels in a 115 MPa hydrogen gas atmosphere

Slow strain rate tensile (SSRT) tests were performed using smooth specimens of two types of steels, the Cr–Mo steel, JIS-SCM435, which has a tempered, martensitic microstructure, and the carbon steel, JIS-SM490B, which has a ferrite/pearlite microstructure. The tests were carried out in nitrogen gas and hydrogen gas, under a pressure of 115 MPa at three different temperatures: 233 K, room temperature and 393 K. In nitrogen gas, these steels exhibited the so-called cup-and-cone fracture at every temperature. In contrast, surface cracking led to a marked reduction in ductility in both steels in hydrogen gas. Nonetheless, even in hydrogen gas, JIS-SCM435 exhibited some reduction of area after the stress-displacement curve reached the tensile strength (TS), whereas JIS-SM490B demonstrated little, if any, necking in hydrogen gas. In addition, tension-compression fatigue testing at room temperature revealed that these steels show no noticeable degradation in fatigue strengths in hydrogen gas, especially in the relatively long-life regime. Considering that there was little or no hydrogen-induced degradation in either the TS or the fatigue strength in JIS-SCM435, it is suggested that the JIS-SCM435 is eligible for safety factor-based fatigue limit design for hydrogen service under pressures up to 115 MPa.

A quantitative description on fracture toughness of steels in hydrogen gas

Fracture toughness or critical stress intensity factor of many steels can be reduced by hydrogen gas. In this paper, a simple quantitative model to predict the fracture toughness of steels in gaseous hydrogen is proposed. This model is based on the assumption that fracture of a cracked body occurs when the maximum principal stress ahead of the crack tip reaches the critical cohesive stress for crack initiation. The critical stress is inversely proportional to the accumulated hydrogen concentration. The notion is that the crack will initiate at the elastic-plastic boundary ahead of the crack tip when hydrogen concentration reaches a maximum value after a long-term hydrogen diffusion assisted by the hydrostatic stress. The model describes the dependence of fracture toughness on hydrogen pressure, temperature and yield strength of steels. It can be used to quantitatively predict fracture toughness of steels in hydrogen gas, particularly in high pressure. Some experimental data reported in literature were used to validate the model, and a good agreement was obtained.

Elucidating the variables affecting accelerated fatigue crack growth of steels in hydrogen gas with low oxygen concentrations

The objective of this study was to quantify the effects of mechanical and environmental variables on oxygen-modified accelerated fatigue crack growth of steels in hydrogen gas. Experimental results show that in hydrogen gas containing up to 1000v.p.p.m. oxygen fatigue crack growth rates for X52 line pipe steel are initially coincident with those measured in air or inert gas, but these rates abruptly accelerate above a critical ΔK level that depends on the oxygen concentration. In addition to the bulk gas oxygen concentration, the onset of hydrogen-accelerated crack growth is affected by the load cycle frequency and load ratio R. Hydrogen-accelerated fatigue crack growth is actuated when threshold levels of both the inert environment crack growth rate and Kmax are exceeded. The inert environment crack growth rate dictates the creation of new crack tip surface area, which in turn determines the extent of crack tip oxygen coverage and associated hydrogen uptake, while Kmax governs the activation of hydrogen-assisted fracture modes through its relationship to the crack tip stress field. The relationship between the inert environment crack growth rate and crack tip hydrogen uptake is established through the development of an analytical model, which is formulated based on the assumption that oxygen coverage can be quantified from the balance between the rates of new crack tip surface creation and diffusion-limited oxygen transport through the crack channel to this surface. Provided Kmax exceeds the threshold value for stress-driven hydrogen embrittlement activation, this model shows that stimulation of hydrogen-accelerated crack growth depends on the interplay between the inert environment crack growth increment per cycle, load cycle frequency, R ratio and bulk gas oxygen concentration.

Small fatigue crack growth characteristics and fracture surface morphology of low carbon steel in hydrogen gas

Owing to energy conservation and environmental concerns, hydrogen has been suggested as a next-generation energy source. However, hydrogen known to seep into a metal, degrade its strength, and accelerate fatigue crack growth rates. We have investigated the effects of hydrogen gas on the small fatigue crack growth characteristics of low carbon steel JIS S10C by conducting bending fatigue tests on a specimen with a small blind hole and placed in a low-pressure hydrogen environment. The fatigue crack growth rate in hydrogen was higher than that in nitrogen. The fracture surface of the specimen in hydrogen showed intergranular facets in the low- growth-rate range and a quasi-cleavage fracture surface with brittle striations in the high-growth-rate range. The specimen only showed a ductile fracture surface for nitrogen. The small-fatigue-crack growth rate for nitrogen is given by \({dl/dN\propto \Delta \varepsilon_{p}^{n}l}\), where l, N, and \({\Delta \varepsilon_{p}}\) represent the crack length, number of repetitions, and plastic strain range, respectively. This equation was also satisfied for hydrogen, but only over a short strain range from \({\Delta \varepsilon_t = 0.25}\) to 0.37 % in which the fracture surface exhibited intergranular facets and a ductile morphology, but no quasi-cleavage fracture. The exponent n of the equation was 1.22 in nitrogen and 0.66 in hydrogen environment. The small-fatigue-crack growth law can be used for safe material designs in hydrogen environments.

Effects of Mechanical and Environmental Factors on the Notch Tensile Strength of 1,300MPa Class SCM435 High-Strength Steel in Hydrogen Gas

There are several factors that affect the strength of high-strength steel SCM435 as a sharp notched specimen in a hydrogen gas environment. In this paper, tensile tests were carried out in several hydrogen and helium gas environments. The examined factors were the gas pressure, the gas temperature, the cross-head speed and the notch root radius. The results of the tensile tests in the hydrogen gas environments showed a decrease in the tensile strengths for any given environmental factor. This was not observed in the helium gas environments. Additionally, by investigating the area of intergranular fracture, it was found that the tensile strength had a reciprocal relationship with the area of the intergranular fracture regardless of several environmental factors.

水素ガス中におけるフェライト・パーライト鋼の疲労き裂進展特性に及ぼす水素圧力と試験周波数の影響

水素ガス中におけるフェライト・パーライト鋼の疲労き裂進展特性に及ぼす水素圧力と試験周波数の影響

A23 水素ガス中におけるステンレス鋼のフレッティング疲労強度低下機構(A2 材料力学(水素II))

A23 水素ガス中におけるステンレス鋼のフレッティング疲労強度低下機構(A2 材料力学(水素II))

Hydrogen-assisted cracking studies of 4340 steel by using the optical method of caustics

The optical method of caustics is used to measure the effect of hydrogen on the localized deformation within the fracture process zone (PZ). In particular, the role of the PZ in hydrogen-assisted cracking (HAC) of 4340 steel in hydrogen gas at 1 atm is examined. No change in the caustic diameter was detected prior to crack initiation but an “anomalous” enlargement of the caustic diameter as a function of crack growth was observed as a result of crack tunneling. The “center” of the caustic follows the position of the internal crack front, thus providing a simple means to monitor the growth of internal cracks. It is demonstrated that the technique provides a sensitive means for detecting HAC initiation (the smallest crack depth change detected is 35 μm) and insight into the three-dimensional character of the PZ.

Hydrogen degradation of 21-6-9 and medium carbon steel by disc pressure test

This paper reports the method of disc pressure test and the results for 21-6-9 stainless steel and medium carbon steel in hydrogen gas with different pressures and time of storage. The results show the hydrogen induced degradation of these two kinds of steel. An attempt was made to establish an index which uses variation of area of deformed disc to determine the degradation of ductility in a hydrogen environment.

Corrosion fatigue of high-strength steel in low-pressure hydrogen gas

AbstractFatigue tests on 835M30 steel in hydrogen gas at atmospheric pressure have confirmed that two distinct forms of corrosion fatigue crack growth can occur. The dominant mechanism of corrosion fatigue is governed by whether the cyclic stress intensity level is above or below the threshold stress intensity value for hydrogen-induced crack growth under static load, and by the stress ratio and cyclic frequency employed during testing. It has been shown that existing mechanistic models are unable to account quantitatively for the observed corrosion fatigue behaviour at stress intensity levels below the static load threshold. However, a model designated the ‘Process Competition Model’ can be used for quantitative predictions of corrosion fatigue behaviour at stress intensity levels above the static load threshold. An extended version of the model is also described in which the effects of cyclic waveform are incorporated. The translation of crack propagation rates to cyclic lifetimes is discussed and the e...