Hydrogen Environment Embrittlement Research Articles

Hydrogen environment embrittlement in nickel-base superalloy Alloy 617

Hydrogen environment embrittlement (HEE) in a nickel-base superalloy, INCONEL® Alloy 617, was scrutinized using a notch tensile test in a 99 MPa hydrogen atmosphere to determine the function of grain boundary carbides. The fracture surface ratio of the intergranular surface increased monotonically with increasing grain boundary coverage, which is defined as the ratio between the length of the grain boundary covered with carbide and the total length of the grain boundary. Strain distribution analysis clarified that more strain locally accumulated near the grain boundary covered with grain boundary carbide compared to the uncovered one. The suggested mechanism of HEE in the alloy is that a large amount of plastic strain near the grain boundary covered with grain boundary carbide triggers crack formation at the interface between the matrix and the grain boundary carbide, followed by crack growth along the grain boundary, ultimately leading to fracture.

Monitoring of environmental hydrogen embrittlement in Al-Zn-Mg-based alloys by means of dynamic hydrogen detection and digital image correlation

Monitoring of environmental hydrogen embrittlement in Al-Zn-Mg-based alloys by means of dynamic hydrogen detection and digital image correlation

Suppression of Hydrogen Embrittlement of Al-Zn-Mg Based Alloys by Means of Surface Zinc Plating

In the present study, the effect of electro zinc plating on environmental hydrogen embrittlement of 7075-T6 aluminum alloys was investigated by using a slow strain rate testing device which can detect quantitively the amount of hydrogen generated during deformation and fracture. The testing device can also detect traces of hydrogen gas as low as 5 ppb by using a semiconductor gas sensor at ambient pressure. It was revealed that the environmental hydrogen embrittlement of 7075-T6 aluminum alloys was highly suppressed by zinc-based electroplating, while not fully by anodization. The suppression of the hydrogen embrittlement by zinc plating was caused by the protection of original aluminum surfaces during plastic deformation.

µ-CT Investigation of Hydrogen-Induced Cracks and Segregation Effects in Austenitic Stainless Steel

Hydrogen can drastically degrade the mechanical properties of a variety of metallic materials. The so-called hydrogen environment embrittlement of austenitic CrNi-type steels is usually accompanied by the formation of secondary surface cracks, which can be investigated in order to assess the embrittlement process. The occurrence of hydrogen-induced cracks is often related to element segregation effects that locally impact the austenite stability. Since there is as yet a lack of investigation methods that can visualize both structures three-dimensionally, the present study investigates the imageability of hydrogen-induced cracks and element segregation structures in austenitic CrNi-steel via micro-computed tomography (CT). In order to improve the X-ray visibility of segregation structures, modified versions of the reference steel, X2CrNi18-9, that contain W and Si are designed and investigated. The investigations demonstrated that small differences in the X-ray attenuation, caused by the W or Si modifications, can be detected via CT, although segregation structures could not be imaged due to their small size scale and image noise. Hydrogen-induced cracks were characterized successfully; however, the detection of the smaller cracks is limited by the resolution capability.

Cause analysis of the cooler leakage in a stirling engine

After a stirling engine operated for 1750 h, the cooler in the engine was found leaking. The leakage led to a rapid decrease of the cycle efficiency. After dismantling, a cooling tube was found leaked by air pressure test. Through macro- and microscopic fracture morphologies, the cause of the leakage was determined as fatigue under alternating stress during operation, but the fatigue source region shows abnormal brittle fracture morphologies. By XRT and inner wall inspections, more cracks initiated from the extrusion bands on the inner wall, and F-containing lubricant was also detected there. Considering the fabrication process of the tube, the formation mechanism of the inner cracks is determined as hydrogen environment embrittlement (HEE) under the conditions of the local surface damage, deformed microstructure and pure hydrogen circumstance during bright annealing. Remedial methods are also proposed to increase the service life and service safety.

Machine learning approach for prediction of hydrogen environment embrittlement in austenitic steels

This study introduces a machine learning approach to predict the effect of alloying elements and test conditions on the hydrogen environment embrittlement (HEE) index of austenitic steels for the first time. The correlation between input features and the HEE index was analyzed with Pearson's correlation coefficient (PCC) and Maximum Information Coefficient (MIC) algorithms. The correlation analysis results identified Ni and Mo as dominant features influencing the HEE index of austenitic steels. Based on the analysis results, the performance of the four representative machine learning models as a function of the number of top-ranked features was evaluated: random forest (RF), linear regression (LR), Bayesian ridge (BR), and support vector machine (SVM). Regardless of the type and the number of top-ranking features, the RF model had the highest accuracy among various models. The machine learning-based approach is expected to be useful in designing new steels having mechanical properties required for hydrogen applications.

Ammonia mitigation and induction effects on hydrogen environment embrittlement of SCM440 low-alloy steel

The effect of ammonia (NH 3 ) contained in hydrogen (H 2 ) gas on hydrogen environment embrittlement (HEE) of SCM440 low-alloy steel was studied in association with the NH 3 concentration, loading rate, and gas pressure. NH 3 worked as both mitigator of the HEE and inducer of hydrogen embrittlement (HE) depending on the testing conditions. The mitigation of the HEE was achieved by the deactivation of the iron (Fe) surface for H 2 dissociation caused by the preferential adsorption of NH 3 on the Fe surface, which is enhanced by the increase in the NH 3 concentration and decrease in the H 2 gas pressure. NH 3 induced HE was caused due to creating hydrogen by the NH 3 decomposition. Since the NH 3 decomposition rate is low, the induction effect was observed when the loading rate was low. The effect of NH 3 was determined by the competition of the mitigation and induction effects. • NH 3 worked as both mitigator and inducer of hydrogen embrittlement. • The effects of NH 3 depended on NH 3 concentration, loading rate, and gas pressure. • NH 3 mitigated hydrogen environment embrittlement by hindering hydrogen uptake into the material. • NH 3 induced hydrogen embrittlement by creating hydrogen by its decomposition.

Predictive environmental hydrogen embrittlement on fracture toughness of commercial ferritic steels with hydrogen-modified fracture strain model

In this work, a practical numerical model with few parameters was proposed for the prediction of environmental hydrogen embrittlement. The proposed method adopts hydrogen enhanced plasticity-based mechanism in a fracture strain model to describe hydrogen embrittlement. Fracture toughness degradation of three commercial steels SA372J70, AISI4130 and X80 in high pressure hydrogen environment were investigated. Firstly, governing equations for hydrogen distribution and material damage evolution was established. Hydrogen enhanced localized flow softening effect was coupled within fracture strain dependency on stress triaxiality. Then, the numerical implementation and identification process of model parameters was described. Model parameters of the investigated steels were determined based on experiment results from literatures. Finally, with the calibrated model, fracture toughness reduction of the steels was predicted in a wide range of hydrogen pressure. The prediction results were compared with experimental results. Reasonable accuracy was reached. The proposed method is an attempt to reach balance between physical accurate prediction and engineering practicality. It is promising to provide a simplified numerical tool for the design and fit for service evaluation of hydrogen storage vessels. • Hydrogen embrittlement prediction model with few parameters was proposed. • Identification of model parameters with a few support of experiments. • Simplified Fracture toughness prediction model with acceptable accuracy.

Machine Learning Approach for Prediction of Hydrogen Environment Embrittlement in Austenitic Steels

Machine Learning Approach for Prediction of Hydrogen Environment Embrittlement in Austenitic Steels

Effect of Gas Pressure on Hydrogen Environment Embrittlement of Carbon Steel A106 in Carbon Monoxide Mixed Hydrogen Gas

Effect of Gas Pressure on Hydrogen Environment Embrittlement of Carbon Steel A106 in Carbon Monoxide Mixed Hydrogen Gas

Influence of microstructure-driven hydrogen distribution on environmental hydrogen embrittlement of an Al–Cu–Mg alloy

The hydrogen trap sites and corresponding hydrogen binding energies in an Al–Cu–Mg alloy with the different microstructures were investigated to unravel the environmental hydrogen embrittlement (HE) behavior of the alloy. The results showed that hydrogen can reside at interstitial lattices, dislocations, S′-phase, and vacancies. In the aged specimen with the highest hydrogen content, it was firstly reported that hydrogen resided at S′-phase particles with relatively high binding energy, which is a determinant factor on HE resistance of the alloy. In the cold-rolled specimen, high content of hydrogen trapped at dislocations with a reversible nature leads to intergranular hydrogen-assisted cracking. In the solution-treated specimen, hydrogen migration to the surface due to low trap density results in low hydrogen content and prevents the GBs from reaching critical hydrogen concentration. The obtained results clearly reveal that trap site density, and the nature of trap sites can determine environmental HE susceptibility of the alloy.

Role of Ultrasonic Shot Peening in Environmental Hydrogen Embrittlement Behavior of 7075-T6 Alloy

The effect of ultrasonic shot peening on the environmental hydrogen embrittlement behavior of the 7075-T6 aluminum alloy is investigated. The 7075-T6 tensile specimens were treated by ultrasonic shot peening for 50 s. Surface residual stress and the depth of residual stress under the surface were evaluated using an X-ray diffractometer. Then, the specimens were tensile tested in humid air and dry nitrogen gas by the slow strain rate technique. The results showed that the ultrasonic shot-peened specimen has a superior hydrogen embrittlement resistance. Further, the ultrasonic shot peening changes the fracture mode from an intergranular fracture mode to the transgranular one. It was suggested that ultrasonic shot-peening has two effects on hydrogen embrittlement behavior; the distribution of hydrogen inside the surface layer by introducing dislocations/vacancies as hydrogen traps and reducing the normalized amount of hydrogen trapped per unit length of the grain boundary.

Stacking Fault Energy in Relation to Hydrogen Environment Embrittlement of Metastable Austenitic Stainless CrNi-Steels

Metastable austenitic steels react to plastic deformation with a thermally and/or mechanically induced martensitic phase transformation. The martensitic transformation to α’-martensite can take place directly or indirectly via the intermediate stage of ε-martensite from the single-phase austenite. This effect is influenced by the stacking fault energy (SFE) of austenitic steels. An SFE < 20 mJ/m2 is known to promote indirect conversion, while an SFE > 20 mJ/m2 promotes the direct conversion of austenite into α’-martensite. This relationship has thus far not been considered in relation to the hydrogen environment embrittlement (HEE) of metastable austenitic CrNi steels. To gain new insights into HEE under consideration of the SFE and martensite formation of metastable CrNi steels, tensile tests were carried out in this study at room temperature in an air environment and in a hydrogen gas atmosphere with a pressure of p = 10 MPa. These tests were conducted on a conventionally produced alloy AISI 304L and a laboratory-scale modification of this alloy. In terms of metal physics, the steels under consideration differed in the value of the experimentally determined SFE. The SFE of the AISI 304L was 22.7 ± 0.8 mJ/m2 and the SFE of the 304 mod alloy was 18.7 ± 0.4 mJ/m2. The tensile specimens tested in air revealed a direct γ → α’ conversion for AISI 304L and an indirect γ → ε → α’ conversion for 304 mod. From the results it could be deduced that the indirect phase transformation is responsible for a significant increase in the content of deformation-induced α’-martensite due to a reduction of the SFE value below 20 mJ/m2 in hydrogen gas atmosphere.

Quantitative monitoring of the environmental hydrogen embrittlement of Al-Zn-Mg-based aluminum alloys via dynamic hydrogen detection and digital image correlation

In this study, a novel analytical system was developed to monitor the environmental hydrogen embrittlement of Al-Zn-Mg-based aluminum alloys dynamically and quantitatively under atmospheric air pressure. The system involves gas chromatography using a SnO2-based semiconductor hydrogen sensor, a digital image correlation step, and the use of a slow strain rate testing machine. Use of this system revealed that hydrogen atoms are generated during the plastic deformation of Al-Zn-Mg alloys caused by the chemical reaction between the water vapor in air and the alloy surface without oxide films. Digital image correlation also clarified that the generated hydrogen atoms caused numerous localized grain boundary cracks on the specimen surface, resulting in a localized grain boundary fracture. The amount of hydrogen atoms evolved from the embrittled fracture surface was 2.7 times as high as that from the surface without embrittlement.

Evaluation of hydrogen related degradation of API X42 pipeline under hydrogen/natural gas mixture conditions using small punch test

This study investigates the effect of a hydrogen/natural gas mixture on the mechanical properties of API X42 pipeline steel using small punch (SP) test. The hydrogen-assisted fracture behavior demonstrated a transition from ductile to brittle failure, similar to the temperature-assisted brittle fracture mode. The preferential sites for hydrogen-assisted crack initiation in the X42 pipeline steel were located at the ferrite/pearlite interface, where hydrogen diffusion is enhanced by localized stress/strain conditions. The feasibility of the hydrogen environment embrittlement susceptibility obtained in the SP test and the correlation to the conventional test method is also discussed.

Quantitative Monitoring of the Environmental Hydrogen Embrittlement of Al-Zn-Mg-Based Aluminum Alloys via Dynamic Hydrogen Detection and Digital Image Correlation

In this study, a novel analytical system was developed to monitor the environmental hydrogen embrittlement of Al-Zn-Mg-based aluminum alloys dynamically and quantitatively under atmospheric air pressure. The system involves gas chromatography using a SnO2-based semiconductor hydrogen sensor, a digital image correlation step, and the use of a slow strain rate testing machine. Use of this system revealed that hydrogen atoms are generated during the plastic deformation of Al-Zn-Mg alloys caused by the chemical reaction between the water vapor in air and the alloy surface without oxide films. Digital image correlation also clarified that the generated hydrogen atoms caused numerous localized grain boundary cracks on the specimen surface, resulting in a localized grain boundary fracture. The amount of hydrogen atoms associated with the grain boundary fracture was calculated to be 737 atoms/nm2.

Stress concentration affecting hydrogen-assisted crack in API X70 pipeline base and weld steel under hydrogen/natural gas mixture

A sudden change in the geometrical parameters of a material, such as bends, T-branches, and welded joints may increase the stress concentration, which in turn may enhance the diffusible hydrogen concentration. In this study, quantitative evaluations of the effect of stress concentration factors on hydrogen environmental embrittlement (HEE) will be studied based on the mechanical performance of notched tensile specimens with variations in the stress concentration factors (Kt) of the X70 pipeline base and weld metal. To highlight the role of stress concentration, the tests are performed under a 10 MPa gas mixture condition with a low partial hydrogen pressure. The maximum strengths of the notched specimens were nearly consistent across all Kt values. The degree of HEE susceptibility of the base metal increased with increasing Kt value. However, in the weld metal, prominent reductions in the RA occurred at all Kt values. The complex HEE susceptibility of the weld metal can be attributed to the synergistic action of the microstructure heterogeneity and Kt values.

Unraveling the effect of dislocations and deformation-induced boundaries on environmental hydrogen embrittlement behavior of a cold-rolled Al–Zn–Mg–Cu alloy

The effect of dislocation substructure, and deformation-induced boundaries on the hydrogen embrittlement (HE) behavior and the fracture mechanism of a 7xxx series aluminum alloy was investigated using X-ray diffraction line-profile analysis, electron backscatter diffraction, transmission electron microscopy, thermal desorption spectroscopy, and visualization of hydrogen. Hydrogen resides at interstitial lattice sites, statistically-stored dislocations (SSDs), and high-angle boundaries (HABs). SSDs are not the main trap site affecting HE behavior of the alloy. However, the HABs with the high desorption energy act as an almost irreversible trap site, which strongly absorbs hydrogen. It was firstly reported that the higher density of HABs as a strong trap site in a deformed 7xxx series aluminum alloy leads to decreasing the possibility of building up a critical hydrogen concentration required for crack initiation in a typical HAB, resulting in an excellent hydrogen embrittlement resistance.

The experiment study to assess the impact of hydrogen blended natural gas on the tensile properties and damage mechanism of X80 pipeline steel

Environmental hydrogen embrittlement has become a non-negligible problem in the hydrogen blended natural gas transportation. To qualitatively study the degradation mechanism of X80 steel used in the natural gas pipelines, the slow strain tensile experiments are carried out in this work. The nitrogen and hydrogen are adopted to simulate the hydrogen blended natural gas to explore the tensile properties of X80 steel. According to the volume proportion of hydrogen, the test atmospheres are divided into the reference atmosphere and the hydrogen-contained atmospheres of 1%, 2.2% and 5%. The tensile experiments of the smooth and notched specimens are conducted in the above gas atmospheres. Mechanical properties and fracture morphologies after stretching are further analyzed. The results show that the hydrogen blended natural gas has little effect on the tensile and yield strengths. Distinguished from the hydrogen volume proportion of 1% and 2.2%, with the increase of hydrogen proportion, the effect of hydrogen on mechanical properties of specimens increases significantly. Moreover, the deteriorated mechanical properties of notched specimens are more seriously than those of smooth specimens. This work provides the basis for safe hydrogen proportion for X80 pipeline steel when transporting hydrogen blended natural gas.

Effect of solution treatment temperature on grain boundary composition and environmental hydrogen embrittlement of an Al–Zn–Mg–Cu alloy

The effect of solution treatment temperature on hydrogen embrittlement (HE) of an Al–Zn–Mg–Cu alloy was investigated. Slow strain rate tensile tests in humid air and dry nitrogen gas were used to calculate the index of susceptibility to HE. Fracture morphology of the specimens were observed by scanning electron microscope. The grain boundary segregation of Mg, Zn and Cu was investigated using Auger electron spectroscopy for the specimens solution-treated in the temperature range 400–480 °C after fracture by a tensile test inside a vacuum chamber. The results showed that there is a strong correlation among the concentration of Mg, Zn and Cu at grain boundary, the index of susceptibility to HE and the fraction of brittle signatures in the fracture surfaces of the specimens with different solution treatment temperatures. When the segregation of the solutes kept at the minimum (at 440 °C), the HE behavior of the specimen was greatly improved.