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Hydrogen embrittlement (HE) is a major concern when steel pipelines are used for hydrogen transportation and storage. The weldments of steel pipelines are of particular concern because they are reported to have higher HE susceptibility compare to the base metal. In this work, targeted heat treatments were used to manipulate the microstructure in a pipeline steel weldment to examine the effects of different microstructural features on HE susceptibility. Complementary analyses of the microstructure, mechanical testing, and fracture surface identified inclusions and ferrite morphology as the most dominant microstructural features that affect the susceptibility to HE. Specimens with different microstructures but sharing similar Ti-rich inclusions exhibited significant reductions in elongation to failure after hydrogen charging and showed brittle fracture surfaces decorated with multiple 'fish-eye' features. In addition, co-existence of bainitic microstructure with Ti-rich inclusions resulted in the highest susceptibility to HE. • Heat-treated and as-received WM specimens showed the highest HE susceptibility. • Inclusion and ferrite morphology are dominant features affecting HE susceptibility. • LB microstructure exhibited higher HE susceptibility than PF or AF microstructures. • High stress level/dislocation density in LB correlated to high HE susceptibility. • Ti-rich inclusions dominate HE susceptibility over other microstructural features. [ABSTRACT FROM AUTHOR]

An investigation was performed to identify the cause of failure for a pipeline component that included a welded block valve and reducer. The component was provided with limited details about its manufacturing and operational history. Along with examining the background information for the piece, a series of tests were performed including nondestructive examination, visual examination, metallography, microhardness and scanning electron microscopy. Once the tests were concluded and the results were examined, a cause for failure was established as the evidence pointed to hydrogen-induced cracking. [ABSTRACT FROM AUTHOR]

Hydrogen‐induced cracking (HIC) in high‐strength 45CrNiMoVA steel is investigated using smooth and notched cylindrical specimens by performing uniaxial tensile tests. Specimens with different notch geometries are used to analyze the interacting effects of the stress concentration factor and HIC micromechanism. The results show that hydrogen charging reduces the elongation at fracture and the ultimate tensile strength of smooth tensile specimens. The microscopic fracture mode changes from ductile dimples with some quasicleavage fracture without hydrogen to a mixture of brittle quasicleavage and intergranular cracking with hydrogen. For notched specimens with a lower notch root radius, significant stress concentration occurs at the notch root, which enriches hydrogen in these highly stressed regions. This causes a lower notch tensile strength and greater susceptibility to hydrogen embrittlement. Microfracture observations show that the area fraction of the intergranular cracking surface increases gradually, and the brittle zone moves farther away from the notch root upon decreasing the notch root radius, causing the embrittlement index to remain high. These results will help determine the applicability of existing steel for hydrogen service and also provide guidance for developing new high‐strength martensitic steels that can resist hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

Hydrogen‐induced cracking (HIC) presents a significant concern in industries, such as oil and gas, petrochemicals, and aerospace, where high‐strength steel is prevalently used. This phenomenon compromises the structural integrity of steel pipelines and equipment. Accurate detection and monitoring of HIC are crucial for the safety and reliability of these assets. While traditional defect detection methods are usually costly and easily affected by human physiological state, deep learning approaches offer both time and financial benefits along with high accuracy. This study focuses on employing deep learning to segment HIC in steel, utilizing the robust and state‐of‐the‐art YOLOv8‐seg architecture for defect identification and segmentation. The process involves acquiring two‐dimensional B‐scan images through a scanning acoustic microscopy (SAM) system, followed by employing the YOLOv8‐seg architecture to address the segmentation task within these images. The experimental results demonstrate the effectiveness of the YOLOv8‐seg model, achieving a mean average precision (mAP) score greater than ˜0.95. Notably, this research pioneers the development of a framework for reconstructing HIC within steel based on B‐scan image segmentation results, offering researchers and professionals a comprehensive understanding of internal defects in steel blocks. This work underscores the potential of YOLOv8‐seg architecture for accurate detection and segmentation of HIC in steel, providing a valuable tool for inspection and maintenance activities. [ABSTRACT FROM AUTHOR]

Alloy 625 plays a crucial role in high-pressure hydrogen environments typical of hydrogen refuelling stations, where cyclic temperature and loading conditions prevail. In this study, we reveal that hydrogen-induced ductility loss of nickel-based alloy 625 significant difference which change from 11.9% at slow strain rate to 20.1% at conventional strain rate. The difference can be attributed to a change in deformation mode: from dislocation slipping under slow strain rate to twinning under conventional strain rate. Specifically, hydrogen-refined deformation twins and the promotion of twin bundles under conventional strain rates diminish the twin-induced plasticity effect of the alloy. This shift in deformation mode also alters the hydrogen embrittlement mechanism across the two strain rates. These findings provide valuable insights for hydrogen embrittlement-resistant designing and evaluating hydrogen compatibility for alloy 625. [Display omitted] • The nickel-based alloy 625 has more significant hydrogen-induced ductility loss at 5 × 10−3 s−1 than that at 5 × 10−6 s−1. • The deformation mode change from dislocation slipping at 5 × 10−6 s−1 to twinning at 5 × 10−3 s−1. • Hydrogen weakens the TWIP effect of the alloy because of hydrogen refining DTs. • Hydrogen will promote the formation of deformation twin bundles, resulting in cracking along DTs. • A new mechanism of hydrogen-induced cracking along DTs in nickel-based alloys was proposed. [ABSTRACT FROM AUTHOR]

Abstract Hydrogen‐induced cracking (HIC) presents a significant concern in industries, such as oil and gas, petrochemicals, and aerospace, where high‐strength steel is prevalently used. This phenomenon compromises the structural integrity of steel pipelines and equipment. Accurate detection and monitoring of HIC are crucial for the safety and reliability of these assets. While traditional defect detection methods are usually costly and easily affected by human physiological state, deep learning approaches offer both time and financial benefits along with high accuracy. This study focuses on employing deep learning to segment HIC in steel, utilizing the robust and state‐of‐the‐art YOLOv8‐seg architecture for defect identification and segmentation. The process involves acquiring two‐dimensional B‐scan images through a scanning acoustic microscopy (SAM) system, followed by employing the YOLOv8‐seg architecture to address the segmentation task within these images. The experimental results demonstrate the effectiveness of the YOLOv8‐seg model, achieving a mean average precision (mAP) score greater than ˜0.95. Notably, this research pioneers the development of a framework for reconstructing HIC within steel based on B‐scan image segmentation results, offering researchers and professionals a comprehensive understanding of internal defects in steel blocks. This work underscores the potential of YOLOv8‐seg architecture for accurate detection and segmentation of HIC in steel, providing a valuable tool for inspection and maintenance activities.

X80 pipeline steel has played a vital role in oil and gas transportation in recent years. However, hydrogen-related issues frequently lead to pipeline failures during service, resulting in significant losses of properties and lives. Three heat treatment processes (furnace cooling (FC), air cooling (AC), and water cooling (WC)) were carried out to investigate the effect of different microstructures on hydrogen-induced cracking (HIC) susceptibility of X80 pipeline steel. The WC sample demonstrated the highest hydrogen embrittlement index, registering at 21.9%, while the AC and FC samples exhibited progressively lower values of 15.45% and 10.98%, respectively. Under equivalent hydrogen charging durations, crack dimensions with a maximum length exceeding 30 μm in the WC sample generally exceed those in the FC sample and AC sample. The variation is attributed to the difference in microstructures of the samples, predominantly lath bainite (LB) in water-cooled samples, granular bainite (GB) in air-cooled samples, and ferrite/pearlite (F/P) in FC samples. The research results demonstrate that the sensitivity of lath bainite (LB) to HIC is significantly higher than that of pearlite, ferrite, and granular bainite (GB). The presence of a large amount of martensite/austenite (M/A) constituents within bainite results in a multitude of hydrogen trap sites. HIC cracks in bainite generally propagate along the profiles of M/A constituents, showing both intergranular and transgranular cracking modes. [ABSTRACT FROM AUTHOR]

In the oil and gas industry, the selection of tubing and casing materials is required to follow international standard ISO 15156. However, it does not provide guidance on selecting stainless steel materials for H2S-containing wells above 232 °C, which raises uncertainty about the suitability of 13Cr steel. This work focuses on investigating the mechanical degradation and failure mechanisms of 13Cr stainless steel exposed to high-temperature conditions and proposed a creep constitutive model. Then, the corrosion and cracking mechanisms of 13Cr stainless steel at temperatures ranging from 150 °C to 350 °C were elucidated. Results show that 13Cr stainless steel meets the current material selection criteria (GB/T34907-2017) for mechanical properties and creep resistance. In the range of 150–250 °C, the localized corrosion is dominant, and stress-oriented hydrogen-induced cracking occurs at 150 °C. As the temperature increases from 250 °C to 350 °C, although the maximum value of uniform corrosion rate is as high as 0.2960 mm/a, the cracking does not happen. Therefore, with the implementation of suitable protective measures, 13Cr stainless steel can be utilized in wells that the temperatures ranging from 250 °C to 350 °C and H2S partial pressures up to 0.17 MPa. This aligns with the global carbon-neutral agenda.

At present, Zn–Al alloys suffer from rapid intergranular corrosion in hot seawater. However, little attention has been paid to the effect of hydrogen evolution coupled with anodic dissolution on Zn–Al alloys. In this work, Zn–Al binary alloys with different Al contents (0.05 wt.%, 0.15 wt.% and 0.25 wt.%) and pure Zn in seawater at 80 °C were investigated by electrochemical measurements, scanning electron microscopy and x-ray diffraction. Result showed that Al homogenously dissolved in Zn–Al alloy when the Al content reached 0.25 wt.%, and Al segregation or precipitation at grain boundaries was not observed. The addition of Al negatively shifted the working potential of Zn–Al alloy and promoted continuous hydrogen production. Potentiodynamic polarization curves showed that Al addition accelerated the hydrogen evolution reaction rate of Zn–Al alloy. After 30 days of anodic polarization at 0.4 mA/cm2, severe intergranular cracking was found on the surface and cross section of Zn–Al alloy, and only pitting corrosion was found on pure Zn. The cracks propagated along the oxide inclusion and grain boundaries of Zn–Al binary alloy, which conformed to the characteristics of hydrogen-induced cracking (HIC). The present study suggests that Al addition could enhance the embrittlement of Zn–Al alloy and reduce the cohesive bond energy among atoms at grain boundary. HIC primarily causes the intergranular corrosion of Zn–Al binary alloy in hot seawater. [ABSTRACT FROM AUTHOR]

In order to study the influence of hydrogen environment on the initiation and propagation of fatigue cracks in duplex stainless steel and establish the correlation mechanism between the fatigue strain microstructure evolution and hydrogen induced cracking in hydrogen environment，slow strain rate tensile and fatigue crack growth rate tests were carried out on 2205 duplex stainless steel specimens in 5 MPa hydrogen and 5 MPa nitrogen environments.Results showed that the hydrogen embrittlement sensitivity of 2205 duplex stainless steel was not high in the process of slow strain rate tensile in hydrogen environment，while it was significant during the fatigue process.The fatigue crack growth rate of 2205 duplex stainless steel in a hydrogen environment of 5 MPa was 18 times higher than that in a nitrogen environment.Hydrogen could promote local plastic deformation around the fatigue crack tip of 2205 duplex stainless steel and further led to hydrogen-induced cracking.In the process of fatigue deformation of 2205 duplex stainless steel in a hydrogen environment，different phase structures had different hydrogen-induced cracking mechanisms.The ferrite phase was easy to form a river-like pattern fracture morphology (cleavage fracture)，while the austenite phase fracture appearance mostly presented the characteristics of parallel slip bands.Austenite phase hindered cracks during the cleavage and cracking process of the ferrite phase.

The purpose of this work is to study the effect of charging conditions on hydrogen damage. The effects of electrochemical hydrogen charging current density and time on hydrogen-induced blistering (HIB), cracking behavior, and mechanical properties of Q690 steel are studied by electrochemical hydrogen charging, microstructure observation, and slow strain rate tensile (SSRT) tests. The results show that HIB and internal cracks occur when the Q690 steel is charged at different current densities. The charging conditions have a significant effect on the HIB characteristics of the material and the morphology, number, size, and location of internal cracks. The geometrical parameters of blisters on the surface of Q690 steel are quantitatively evaluated, and deeper cracks are found at higher hydrogen concentrations. At high hydrogen charging current density (50 mA/cm2), due to the accumulation of a large number of hydrogen atoms and the precipitation of hydrogen, the active sites on Q690 steel surface increase dramatically, leading to the initiation of a large number of blisters. At this time, high current density is responsible for the initiation of blisters. The relationship between hydrogen charging current density and mechanical properties of Q690 steel is studied, and the change in the fracture morphology is observed. The Q690 steel was damaged and failed due to an internal crack caused by excessive hydrogen pressure. On the other hand, electrochemical hydrogen charging leads to the degradation of mechanical properties and the transition from ductile fracture to brittle fracture. [ABSTRACT FROM AUTHOR]

Water-based lubrication faces the common challenge of component lifetime extension which is impaired by tribocorrosion due to material surface depassivation. However, such mechanisms in a pH-neutral and low-halide electrolyte require additional understanding. A ball-on-flat configuration study of hard-phase materials in a low amplitude–high frequency sliding contact against martensitic chromium steel with contact pressures around 200 MPa is presented. Under lubrication by purified water, tungsten carbide-based metal matrix composite (MMC) with NiCr binder and silicon nitride-based ceramic (SiAlON) against DIN/EN 1.4108 steel yielded coefficients of friction above unity. Wear scar enlargement led to fretting-like conditions with adhesion becoming the fundamental wear mechanism. A tribocorrosion-induced depletion of tungsten carbide and nickel was determined for MMC. SiAlON materials suffered extreme wear under the formation of abrasive SiO2, while heat-treated DIN/EN 1.4125 steel showed lower friction and wear, but also showed signs of hydrogen embrittlement. Results from accompanying single-material corrosion experiments could not satisfactorily explain the phenomena. Including galvanic interaction and the influence of contact geometry, a new tribocorrosion model for fretting conditions is proposed. It describes an expanding anodic belt located at the inner-most crevice position of an otherwise cathodically polarized material. Low conductivity of the electrolyte is seen as a key player in this process, while the galvanic situation between two materials in contact was shown to invert when water was substituted by a wet organic phase. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) technology is a non-destructive testing (NDT) technique that is able to monitor the process of hydrogen-induced cracking (HIC). AE uses piezoelectric sensors to convert the elastic waves generated from the growth of HIC into electric signals. Most piezoelectric sensors have resonance and thus are effective for a certain frequency range, and they will fundamentally affect the monitoring results. In this study, two commonly used AE sensors (Nano30 and VS150-RIC) were used for monitoring HIC processes using the electrochemical hydrogen-charging method under laboratory conditions. Obtained signals were analyzed and compared on three aspects, i.e., in signal acquisition, signal discrimination, and source location to demonstrate the influences of the two types of AE sensors. A basic reference for the selection of sensors for HIC monitoring is provided according to different test purposes and monitoring environments. Results show that signal characteristics from different mechanisms can be identified more clearly by Nano30, which is conducive to signal classification. VS150-RIC can identify HIC signals better and provide source locations more accurately. It can also acquire low-energy signals better, which is more suitable for monitoring over a long distance. [ABSTRACT FROM AUTHOR]

Mechanism of Hydrogen-induced defects and cracking in Ti and Ti–Mo alloy was systematically analyzed from the perspective of microstructure. Results show that more hydrogen atoms can be dissolved in Ti–Mo alloy due to the existence of β phase, and the precipitation amount of hydride is reduced under the same hydrogen charging conditions. The analysis of positron annihilation results show that the solid solution of Mo element reduces the hydrogen induced defect concentration in the alloy and inhibit the combination of hydrogen and defects. At the same time, Mo atom can affect the electronic structure of Titanium hydrides, and then reduce the bonding between titanium atoms and hydrogen atoms, thereby reducing the formation of brittle titanium hydride. The reduction of hydride and hydrogen induced defect concentration significantly decrease the hardening rate of Ti–Mo alloy, thereby effectively reducing the hydrogen embrittlement sensitivity of titanium and inhibiting its hydrogen absorption cracking tendency. • The formation of β phase in Ti–Mo alloy improves the solubility of hydrogen, thereby reducing the precipitation of hydride. • The solid solution of Mo can affect the electronic structure of titanium hydride and weaken the bonding between Ti–H. • The solid solution of Mo can reduce the concentration of hydrogen-induced defects in Ti–Mo alloy. • Reducing the concentration of hydride and hydrogen induced defect can inhibit hydrogen absorption cracking tendency. [ABSTRACT FROM AUTHOR]

Nowadays, an increasing number of oil and gas transmission pipes are constructed with high-strength low alloy steels (HSLA; nonetheless, many of these pipelines suffer from different types of hydrogen damage, including hydrogen-induced cracking (HIC). Many studies are being done to investigate the role of key metallurgical and processing factors to limit the negative effects of HIC in HSLA steel pipes.

• Develop a phase field method for assessing the threshold conditions to initiate hydrogen-induced cracks on dented pipelines. • Define the influences of dent depth, initial hydrogen concentration and internal pressure on crack initiation. • Determine the threshold values of dent depth and internal pressure to initiate cracks under hydrogen impact. An accurate determination of the threshold conditions to initiate cracks on aged hydrogen pipelines is paramount for ensuring energy transport safety. In this work, a finite element-based phase field method was developed to assess the crack initiation on dented pipelines while considering the hydrogen (H) impact. Theoretical and multi-physics numerical formulas were derived for prediction of the elastic-plastic fracture behavior of H-contained steel. A critical phase field parameter, ϕ =0.69, is defined for predicting crack initiation at the dent on pipelines. The presence of H within the steel decreases the threshold dent depth for initiating H-induced cracks. When the initial H concentration increases from 0 to 0.5 wppm, the maximum dent depth for crack initiation reduces from 17.5 mm to 10.7 mm. The maximum dent depth required for crack initiation reduces from 17.5 mm to 7.8 mm when an internal pressure of 8 MPa is applied on the steel pipe. The site with the maximum phase field parameter changes during indentation, implying that the location initiating cracks depends on the dent dimension. The existing criteria in ASME B31.12 standard are not applicable for predicting H-induced crack initiation on dented pipelines. This study proposes a new method to predict hydrogen-induced cracking on aged pipelines when transporting hydrogen. [Display omitted] [ABSTRACT FROM AUTHOR]

This study explores the hydrogen trapping capability and hydrogen embrittlement (HE) of a second-generation single crystal (SX) superalloy. Embrittlement susceptibility is greater as the duration of hydrogen charging is extended. The presence of hydrogen induces cleavage, micro-crack formation and denser slip traces. Moreover, hydrogen facilitates the formation of nano-voids and the activation of high-density dislocations, leading to denser slip bands which serve as initiation sites for micro-cracks. In addition, the desorption activation energy of hydrogen trapped at dislocations and soluble in the γ matrix is 33.7 kJ/mol, and hydrogen trapped at the γ/γ′ interface and vacancies is 42.4 kJ/mol. First-principles calculations have indicated that hydrogen reduces the binding strength at the γ/γ′ interface, which promotes the propagation of micro-cracks. • Hydrogen facilitates the initiation of more micro-cracks along slip bands in Ni-based SX superalloy. • The desorption activation energy of hydrogen trapped at the γ/γ' interface and vacancies is 42.4 kJ/mol. • Hydrogen reduces the bonding strength of Ni-Ni bond and particularly Ni-Al bond at the γ/γ' interface. • HE failure in SX superalloy is due to nano-voids, γ/γ' interface decohesion, and stress concentration around cracks. [ABSTRACT FROM AUTHOR]

The cracking behaviors of VCoNi medium-entropy alloys with and without short-range order (SRO) structures under different durations of hydrogen charging were investigated. The findings demonstrate that the presence of short-range order in the VCoNi alloy effectively traps hydrogen within the grain interior, thereby mitigating hydrogen segregation at grain boundaries. Consequently, the SRO structure within the VCoNi alloy prolongs the incubation period for hydrogen-induced grain boundary cracking and results in a higher density of grain interior cracks after 12 h of hydrogen charging, indicating that SRO impedes the diffusion of hydrogen into the alloy's interior compared to the alloy lacking SRO. Grain boundary cracking is a consequence of stress concentration and hydrogen segregation at grain boundaries. The initiation of cracks within grains is primarily ascribed to the generation of nanovoids at the intersection of intersecting slip bands. • Aging treatment can promote the generation of SRO in VCoNi alloy. • SRO can directly capture hydrogen confirmed by secondary ion mass spectrometry directly. • SRO reduces hydrogen segregation and delays cracking at grain boundaries. • Hydrogen-induced grain interior crack initiation and propagation mechanism is elucidated. [ABSTRACT FROM AUTHOR]

Quenching and partitioning (Q&P) steels are extensively used in the automotive industry due to their exceptional strength and ductility. However, the impact of hydrogen embrittlement (HE) poses a huge challenge to the safe service of Q&P steels, highlighting the necessity to investigate the hydrogen-induced cracking mechanisms. This study investigates the hydrogen-induced failure mechanisms in Q&P steels through experiments and finite element simulations, focusing on microstructure, local stress heterogeneity, hydrogen distribution characteristics, and hydrogen-induced cracking. The results reveal that hydrogen cracking nucleation in Q&P steel is primarily due to the further accumulation of hydrogen in local high-stress martensitic/austenitic regions. [Display omitted] • Hydrogen-induced cracks in Q&P steel are mainly nucleated in M(M/A). • During the stretching process, the hard M(M/A) region tends to produce many local high stress regions. • In the stress-free state, hydrogen is mainly adsorbed in M(M/A). • The hydrogen will accumulate further in the high-stress regions in M(M/A), thus inducing hydrogen cracking. [ABSTRACT FROM AUTHOR]

• Assessment of hydrogen-induced crack propagation along the grain boundaries orientated to {0 0 1} planes. • Influence of hydrogen on loading at low strain rate test. • Evaluation of the chemical composition of two different pearlitic steels related to hydrogen embrittlement. Understanding hydrogen embrittlement (HE) in pearlitic steels is crucial for manufacturing tensile reinforcements used in pipes for the oil and gas industry. This study aimed to elucidate the susceptibility of pearlitic steels to HE, focusing on microstructural influences. Two types of steel (Fe-0.3 %C and Fe-0.7 %C wt.) used in the tensile armor of flexible ducts, differing in chemical compositions and thermomechanical treatments, were analyzed, both exhibiting HE in a hydrogen-rich environment. Samples were investigated using microstructural examination, mechanical testing at low strain rates, and crystallographic texture analysis via Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD), and X-ray Diffraction (XRD). Slow strain rate tests (SSRT) at 1.0 × 10–⁶ s–1 were conducted in air and in a 3.5 % NaCl solution with cathodic protection. Sample A showed a decrease in yield strength from 810 MPa in air to 687 MPa after hydrogen charging, with total elongation reduced from 11.15 % to 7.38 %. Sample B, with higher carbon content, showed the highest YS and UTS overall, with YS slightly increased from 1216 MPa in air to 1246 MPa after hydrogen charging. UTS increased from 1311 MPa in air to 1336 MPa after hydrogen charging, while elongation significantly dropped from 8.52 % in air to 2.82 % after hydrogen charging. Fracture surfaces were analyzed by SEM, revealing that cracks propagated through ferrite-cementite interfaces and preferential intergranular pathways. The Hollomon model illustrated reduced plasticity due to hydrogen interaction, highlighting embrittlement risks. EBSD analysis revealed that cracks caused by HE propagates more easily along the {0 0 1} planes due to their lower planar atomic density. Taylor factor analysis indicated that {1 1 1} grains harden under load, preventing crack propagation and causing the crack to change direction at {1 1 0} and {1 1 1} grain interfaces. The kernel misorientation map showed that regions of high plastic deformation deflect the crack path, emphasizing the influence of crystallographic orientation on crack propagation dynamics. [ABSTRACT FROM AUTHOR]

The influence of hydrogen saturation of steel specimens on the results of their standardized testing for resistance to hydrogen cracking has been carried out. The simulation took into account the hydrogen skin effect observed when metal samples being charged with hydrogen in various electrolyte solutions. The classical decohesion model of hydrogen embrittlement HEDE was used. It was shown that, despite the microscopic skin depth, the effect led to a dual fracture pattern, when the specimen’s cross-sectional view exhibited both a hydrogen brittleness area and a normal destruction one. The comparison of calculated results with experimental ones showed the strong influence of the hydrogen skin layer on the results of standardized metal testing. This skin effect plays a significant role in the destruction propagation over a metal sample and should be taken into account when conducting industrial tests, simulations and experimental studies.

The purpose of this work is to study the effect of charging conditions on hydrogen damage. The effects of electrochemical hydrogen charging current density and time on hydrogen-induced blistering (HIB), cracking behavior, and mechanical properties of Q690 steel are studied by electrochemical hydrogen charging, microstructure observation, and slow strain rate tensile (SSRT) tests. The results show that HIB and internal cracks occur when the Q690 steel is charged at different current densities. The charging conditions have a significant effect on the HIB characteristics of the material and the morphology, number, size, and location of internal cracks. The geometrical parameters of blisters on the surface of Q690 steel are quantitatively evaluated, and deeper cracks are found at higher hydrogen concentrations. At high hydrogen charging current density (50 mA/cm2), due to the accumulation of a large number of hydrogen atoms and the precipitation of hydrogen, the active sites on Q690 steel surface increase dramatically, leading to the initiation of a large number of blisters. At this time, high current density is responsible for the initiation of blisters. The relationship between hydrogen charging current density and mechanical properties of Q690 steel is studied, and the change in the fracture morphology is observed. The Q690 steel was damaged and failed due to an internal crack caused by excessive hydrogen pressure. On the other hand, electrochemical hydrogen charging leads to the degradation of mechanical properties and the transition from ductile fracture to brittle fracture.

[Display omitted] • The dendritic zone, the elemental diffusion layer and the decarburization layer of the bimetallic clad pipe together constitute the heat affected zone. • The microcracks that initiated at the compound interface after hydrogen charging extend towards the alloy 825 side. • The Cr carbide and TiN become hydrogen-rich sites after hydrogen charging. • Crack extension is mainly related to hydrogen enrichment at dendritic grain boundaries and crack tips. This study investigated the mechanical properties and fracture characteristics of an alloy 825/L360 bimetallic clad pipe after it was subjected to hydrogen charging. The results indicated that the elongation loss of the pipe increased from 12.3% to 50.0% with increasing hydrogen charging time. In addition, results obtained from hydrogen microprinting and scanning Kelvin probe force microscopy indicated that the hydrogen distribution characteristics of the aforementioned material influenced the hydrogen fracture failure mechanism of the clad pipe. Specifically, carbides and TiN initiated hydrogen cracking, and crack extension occurred through brittle cracking at grain boundaries, which was caused by the interaction of hydrogen with dislocation slip bands within the dendritic zone. [ABSTRACT FROM AUTHOR]

• HIC API 5L X65 steel was investigated. • Stress relieving was carried out at different temperatures. • HIC resistance of was investigated in NACE solution A. • HIC susceptibility and inclusion relationship was investigated. • Improved HIC resisatnce was linked with the reduction in residual stresses. This study investigates the hydrogen-induced cracking (HIC) of a thermomechanical controlled processed (TMCP) API 5L X65 steel pipe fabricated using the JCOE forming process. Despite passing HIC testing as a plate, the final pipe exhibited unexpected failure, highlighting the critical influence of pipe fabrication on material performance. In this study, failed pipes were subjected to heat treatment, and HIC testing following NACE TM 0284 standard, SEM, and EDX examinations. The effect of heat treatment on the grain size, residual stress and susceptibility to HIC was investigated. The findings revealed that welding played a detrimental role, as all the HIC failures occurred at the welded area (0° orientation) due to welding-induced stresses and potential microstructural changes. It is believed that the welding process imposed reversible hydrogen traps in the HIC resistance plate ultimately reducing the HIC resistance. The heat treatment proved an effective method for relieving the applied micro-residual stresses that resulted in enhanced HIC resistance of the material. [ABSTRACT FROM AUTHOR]

Nowadays, an increasing number of oil and gas transmission pipes are constructed with high-strength low alloy steels (HSLA; nonetheless, many of these pipelines suffer from different types of hydrogen damage, including hydrogen-induced cracking (HIC). Many studies are being done to investigate the role of key metallurgical and processing factors to limit the negative effects of HIC in HSLA steel pipes. The thermomechanical control process (TMCP) is a microstructural control technique that avoids the conventional heat treatment after hot rolling and attempts to obtain the desired mechanical properties during the forming process. Recent research has shown that TMCP provides high HIC resistance without adding high amounts of alloying elements or applying expensive heat treatments. However, there is an incipient knowledge on predicting HIC behavior, both in susceptibility and kinetics, in HSLA steel pipe when it is exposed to hydrogen charging service conditions. This paper presents a review of the current developments of HSLA and TMCP of pipeline steels, as well as the phenomenological and empirical models proposed to predict the kinetics of HIC as a function of key parameters such as heat treatments and microstructures, especially nature and spatial distribution of non-metallic inclusions and the hydrogen permeation rate and the mechanical and fracture mechanics properties. [ABSTRACT FROM AUTHOR]

The mechanical properties and microstructural evolution of high-strength bainitic steel before and after hydrogen charging were investigated by nanoindentation creep tests and multiscale morphology observations. The results showed that hydrogen charging led to higher local nanoindentation hardness and lower stress exponent of the steel. The elongation of the material decreased, and the susceptibility to hydrogen embrittlement increased after charging. SEM observation showed that the presence of hydrogen changes the material's fracture characteristics from ductile to a mixture of ductile and transgranular cleavage fracture. TEM and SADP analysis indicated that the energetically favorable and stress-promoted hydrogen induced the enhanced dislocation activity in the lath, and the hydrogen might accumulate at the interface between the harder M-A and the softer substrate, as well as at GB. The influence of hydrogen on material properties is caused by the interaction of hydrogen-induced local hardening and hydrogen-induced cracking. [ABSTRACT FROM AUTHOR]

One of the most critical problems related to welding is the occurrence of Hydrogen-Induced Cracking (HIC), and despite all the efforts made to mitigate this defect, it remains present in the modern welding industry. Although the Gapped Bead-on-Plate (G-BOP) test is one of the most practical methods for assessing susceptibility to HIC, the use of a thick plate as the base metal (BM) restricts its application. Considering that many materials, such as the High-Strength-Low-Alloy (HSLA) steels, are difficult to find commercially in the required thickness, and also the fundamental need to appropriately represent the relationship between BM and electrode, da Silva, Fals and Trevisan developed a modified G-BOP test that uses a thinner sheet as the BM. Thus, the present paper aims to evaluate the ability of the Finite Element Method (FEM) to represent the thermomechanical aspects of the G-BOP test and to analyze its modified version using a numerical-experimental approach. In addition to consolidating the modified G-BOP test, the results corroborate the FEM as an important ally in HIC studies. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) technology is a non-destructive testing (NDT) technique that is able to monitor the process of hydrogen-induced cracking (HIC). AE uses piezoelectric sensors to convert the elastic waves generated from the growth of HIC into electric signals. Most piezoelectric sensors have resonance and thus are effective for a certain frequency range, and they will fundamentally affect the monitoring results. In this study, two commonly used AE sensors (Nano30 and VS150-RIC) were used for monitoring HIC processes using the electrochemical hydrogen-charging method under laboratory conditions. Obtained signals were analyzed and compared on three aspects, i.e., in signal acquisition, signal discrimination, and source location to demonstrate the influences of the two types of AE sensors. A basic reference for the selection of sensors for HIC monitoring is provided according to different test purposes and monitoring environments. Results show that signal characteristics from different mechanisms can be identified more clearly by Nano30, which is conducive to signal classification. VS150-RIC can identify HIC signals better and provide source locations more accurately. It can also acquire low-energy signals better, which is more suitable for monitoring over a long distance.

The results of studies on the effect of nonmetallic inclusions and the metal structure formed after using different modes of thermomechanical treatment and subsequent cooling, as well as different heat treatment modes, exerted on the resistance of rolled products and electric-welded pipes obtained by welding by using high frequency currents (HFC welding) with respect to cracking in the environment of hydrogen sulfide (HIC) are presented. It is established that the presence of nonmetallic inclusions of extended morphology exerts a decisive effect on the corrosion damage in H2S-containing media, whereas the metal structure (type, dispersion, homogeneity) plays a secondary role, with the exception of the formation of increased hardness structures in the metal due to segregation processes. It is shown that plastic deformation in a cold state significantly reduces the resistance of the metal with respect to hydrogen-induced cracking. [ABSTRACT FROM AUTHOR]

• A novel multiscale simulation strategy linked hydrogen diffusion to the cracking. • Micro-structure dependent non-uniform lattice hydrogen diffusion was examined. • Internal shearing and necking modes induced different failure mechanisms was determined. • The risk of hydrogen-induced failure at different stages of void evolution was evaluated. Leveraging on a recently developed multiscale simulation method, we propose a pioneering strategy for the multiscale analysis of hydrogen-induced cracking in reactor pressure vessels that considers micro-voids, their influences on hydrogen diffusion as well as the operating pressure of the vessel. In the finite element analysis, the nodal lattice hydrogen concentration and displacements are exchanged bi-directionally between the macroscale and microscale within a monolithic solution procedure. During the analysis, the voids are shown to cause non-uniform lattice hydrogen diffusion and the trapping effect, resulting in inter-void hydrogen accumulation, is demonstrated. Based on the hydrogen concentration on the void surfaces, the void hydrogen pressure was calculated for the hydrogen-induced cracking analysis. It was found that both internal shearing and necking failure modes exhibited micro-structure dependence. The internal shearing mode caused oriented through-wall propagation of cracks in the vessel pressure while the internal necking mode promoted void nucleation in the reactor pressure vessel. As a result, during the early stages of void evolution, the oriented internal shearing of the dispersed small voids showed a high possibility to induce through-wall failure of the reactor pressure vessel. [Display omitted] [ABSTRACT FROM AUTHOR]

• Modifying microstructure influences hydrogen diffusion and cracking of steels. • HIC susceptibility of steels is dependent on their diffusion characteristics. • Phase composition was seen to play the most significant role in influencing HIC. • Low local misorientaions in steels facilitates the elimination of HIC. This work examines the effect of stress-relief (SR) and quenching and tempering (QT) heat treatments on the hydrogen-induced cracking (HIC) susceptibility of pipeline steels. Two trials of a similar X65 pipeline steel were used in this study. They had distinct differences in microstructural characteristics, which significantly affected their cracking behaviour. The SR treatment reduced local misorientations, without significantly altering the microstructural appearance of the steels. Hence, this treatment resulted in a hydrogen permeation transient and cracking response similar to the as-received steels. However, the QT treatments significantly modified the microstructure of the steels, with some treatments resulting in equiaxed polygonal ferrite grains and lower local misorientations, depending on the quenchant used. These microstructural changes contributed to increasing hydrogen diffusion and permeation through the steels, as well as alleviating or eliminating HIC after hydrogen charging. Comparing the permeation transients and diffusion characteristics of the steels without cracks to those with significant cracking, a dependence of HIC susceptibility on the diffusion and trapping behavior within the steels was observed. [ABSTRACT FROM AUTHOR]

We investigated the effect of nanosized NbC precipitates on hydrogen-induced cracking (HIC) of high-strength low-alloy steel by conducting slow-strain-rate tensile tests (SSRT) and performing continuous hydrogen charging and fracture analysis. The results reveal that the HIC resistance of Nb-bearing steel is obviously superior to that of Nb-free steel, with the fractured Nb-bearing steel in the SSRT exhibiting a smaller ratio of elongation reduction (Iδ). However, as the hydrogen traps induced by NbC precipitates approach hydrogen saturation, the effect of the precipitates on the HIC resistance attenuate. We speculate that the highly dispersed nanosized NbC precipitates act as irreversible hydrogen traps that hinder the accumulation of hydrogen at potential crack nucleation sites. In addition, much like Nb-free steel, the Nb-bearing steel exhibits both H-solution strengthening and the resistance to HIC. [ABSTRACT FROM AUTHOR]

This work evaluates the effect of hydrogen on the mechanical integrity of a weld in a martensitic base metal. Different regions in the heat-affected zone (HAZ) are reproduced to investigate the interaction of the local microstructure with hydrogen. The hardness strongly depends on the distance from the welding joint due to the different phases present. The HAZ contains zones of acicular ferrite, coarse martensite and tempered martensite. Additionally, the entire weld is subjected to a constant load while being simultaneously electrochemically charged with hydrogen. During this test, a crack initiates in the filler, showing the highest hydrogen solubility as demonstrated by thermal desorption spectroscopy, while propagation occurs along the microstructure of the HAZ with the highest hardness level. [ABSTRACT FROM AUTHOR]

We investigate the corrosion-electrochemical properties of 17G1SU steel in chloride-acetate solutions for different concentrations of hydrogen sulfide. It is shown that, if this concentration increases, then the corrosion potential of steel shifts to the side of more negative values and the corrosion rate increases almost linearly. The presence of hydrogen sulfide does not affect the values of Tafel constants of the cathodic and anodic reactions. It is shown that the rate of cathodic reactions may become higher as a result of the direct reduction of hydrogen from H2S molecules. For hydrogen-sulfide concentrations > 1500 mg/dm3, the rate of cathodic processes decreases due to the complications of diffusion, which may be caused by the adsorption of hydrogen-sulfide molecules and a decrease in the rate of catalytic recombination of adsorbed hydrogen atoms. Hydrogen-induced cracking of stress-free steel is revealed for hydrogen-sulfide concentrations ≥ 500 mg/dm3. [ABSTRACT FROM AUTHOR]

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Hydrogen diffusivity and trapping have been studied in two advanced high strength steel grades and model samples using electrochemical permeation test. Microstructures of CP1000 and DP1000 steels consist of ferrite, martensite and a small fraction of retained austenite. In addition, bainite is present in CP1000. Model phases with predominance of a particular phase have been prepared by specific heat treatment. DP1000 has shown the lowest diffusivity among all materials, while ferritic model sample has shown the highest. Differences in hydrogen diffusion coefficient values are linked to trapping microstructural characteristics and grain size. [ABSTRACT FROM AUTHOR]

In the present work, the critical crack nucleation size and the hydrogen trapping capability of inclusion were discussed with a numerical simulation considering the factors of inclusion/matrix heterojunction. The results showed that the inclusion composition had a significant effect on hydrogen capacity and its critical nucleation size of hydrogen-induced cracking (HIC). The MnS inclusions exhibited a larger critical size tolerance of HIC nucleation (approximately 2.5 μm), but for some typical oxide inclusions, it ranged between 0.1 and 0.4 μm. In addition, two sheets of steel containing different composition, morphology, and distribution of inclusions were studied by the standard-based test and thermal desorption spectroscopy (TDS) to evaluate the HIC susceptibility and hydrogen trapping behaviour. The results complementarily demonstrated that when controlling the non-metallic inclusions into the proper size and compound with MnS into the sphere, the HIC resistance of steel could be efficiently improved. • Values of critical size triggering HIC of some typical inclusions are determined. • Oxides with big shear modules exhibit the lower critical size. • Compounding effect of MnS can enlarge the critical size of oxides. • Finely dispersed inclusions can relieve the local H-pressure and optimize HIC. [ABSTRACT FROM AUTHOR]

The estimation of failure probability is challenging in hydrogen embrittlement in steel pipelines due to the complexity of the synergistic effect of multiple factors. The present study proposed a hybrid methodology to estimate the failure probability of steel pipelines due to hydrogen embrittlement. The methodology integrates the fault tree analysis with a fuzzy comprehensive evaluation. Fault tree analysis captures the logical relationships between influencing indicators to develop a new assessment model of hydrogen embrittlement in steel pipelines. An improved fuzzy fault tree analysis method was proposed to process aleatoric and epistemic uncertainties to estimate the probability of each basic event due to the difficulty in obtaining the actual probabilities. The failure probability of blended hydrogen natural gas pipelines was estimated by considering the correlation of events. A case study demonstrated the applicability of the proposed method. Maintenance measures can be implemented according to the evaluation results to ensure pipeline safety. [Display omitted] • An indicator system regarding hydrogen embrittlement in steel pipelines is developed. • An improved fuzzy fault tree analysis method is proposed. • Failure probability of natural gas pipeline due to hydrogen embrittlement is assessed. [ABSTRACT FROM AUTHOR]

In 2021, cracks formed in an onshore buried X80 natural gas pipeline with a diameter of 1219 mm. The present study investigated the cause of this failure through environmental and operational assessment, metallurgical evaluation, mechanical testing, material testing, stress analysis, and hydrogen embrittlement (HE) sensitivity testing. The results indicated that the failure was primarily attributable to hydrogen-induced cracking (HIC). The main factors contributing to this failure were identified as excessive material hardness and strength, which resulted in a high sensitivity to HE, even within the normal cathodic protection range. In addition, the mechanical damage that occurred during the construction process resulted in the destruction of the coating, causing stress concentration on the pipe body and further facilitating HIC. • This may be the first hydrogen-related failure in a long-distance X80 pipeline. • The pipeline's excessive strength and hardness led to its failure due to hydrogen embrittlement. • Mechanical gouges led to coating damage, stress concentration, and hydrogen accumulation. • The hardness and strength of the pipeline, and the quality of construction should be strictly controlled. • Regular inspections and prompt repairs or replacements are recommended for pipeline hardness and coating conditions. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement (HE) and hydrogen-induced cracking (HIC) behaviour of a X65 steel pipeline weldment were investigated using slow strain rate tensile (SSRT) testing of specimens that were specifically extracted from different zones of the weldment (i.e., weld metal (WM), heat-affected zone (HAZ), and base metal (BM)). The WM was found to be the most susceptible zone to HE and HIC, while BM the least. Analysis of microstructure, fracture surface, secondary crack formation, and mechanical behaviour revealed that the high HE susceptibility of WM is correlated to microstructural features including Ti-rich inclusions, martensite/austenite (M/A) constituents, and prior austenite grain boundaries (PAGBs). • Susceptibility of a pipeline steel weldment to HE and HIC was assessed and discussed. • Specimens from each zone of the weldment were hydrogen charged for SSRT test. • The weld metal was found to be the most susceptible zone to HE and HIC. • HE susceptibility of the weld metal is correlated to several microstructural features. • HIC was found to initiate from Ti-rich inclusions, M/A constituents, and PAGBs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The HE indexes of tensile properties of BM are more sensitive than that of the WJ. • The FAC coupling with HE shrinks from the outside to the inside in the FAD. • The reduction trend of safety factors with HE for crack depth differs from pressure. • The impact fracture morphology with HE for WJ presents brittle characteristics. Currently, no systematic approach exists for the safety assessment method of hydrogen transmission low-strength pipeline, it is necessary to study the effect of hydrogen embrittlement (HE) on the method of failure assessment diagram (FAD) for the defective pipe. The hydrogen charging experiments of tensile and Charpy impact specimens for the L245 pipe steel were carried out with charging time of 0, 30, 90, and 120 h, and then the tensile and Charpy impact tests were immediately conducted. The HE indexes of tensile and Charpy impact properties were presented to quantitatively analyze the effect of HE under tensile and impact deformation processes. Subsequently, the FAD method coupled with the effect of HE was investigated to analyze the difference in the safety assessment method between hydrogen and non-hydrogen environments. Finally, the fracture morphology of tensile and Charpy impact specimens was observed to analyze the responses of microscopic fracture modes between hydrogen and non-hydrogen environments. The results show that the effect of HE on the tensile properties of the base material is more sensitive than that of the weld joint. The FAC with the effect of HE for safety assessment of defective pipes shrinks by reducing the safe zone. The decrease ratio of safety factors affected by HE presents an increasing tendency as the increase of crack depth while showing a decreasing tendency as the increase of internal pressure. [ABSTRACT FROM AUTHOR]

In sheets of low-alloy pipe steels with high purity by harmful impurities and non-metallic inclusions, the nucleation and propagation sites of hydrogen-induced cracking (HIC) are extended segregation bands of increased hardness in the axial zone, with sections consisting of high-carbon structures. The use of intensive cooling after controlled rolling from the austenitic region to the bainitic transformation temperatures and a decrease in the concentration of liquor carbon and manganese in steel helps to increase the sheet resistance to HIC due to reducing central segregation heterogeneity. [ABSTRACT FROM AUTHOR]

Experimental studies of the distribution of hydrogen in metal samples after a standardized saturation procedure in a neutral solution are described. It is shown that the hydrogen concentrates in a thin surface layer which plays the role of a shield for the further propagation of hydrogen. We refer to this phenomenon as a skin effect in the hydrogen saturation since the internal regions of the metal are not saturated by hydrogen. A review of similar experimental results for other standardized methods for saturation of metals with hydrogen (cathodic polarization, saturation in gaseous hydrogen) is provided, and the universal nature of the skin effect for metals is shown. The analysis of mechanisms of the skin effect is carried out by methods of continuum mechanics based on a bi-continual model of a solid. The problem of saturating a metal sample with hydrogen without external load is posed. It is shown that the model taking into account the mutual influence of hydrogen and mechanical stresses allows one to obtain solutions describing the highly non-uniform distribution of hydrogen at standardized saturation. [ABSTRACT FROM AUTHOR]

The susceptibility of age-hardened nickel-based Alloy 718 to hydrogen embrittlement was studied by the controlled electrochemical charging combined with slow strain-rate tensile tests (SSRT) and advanced characterization techniques. We proposed some novel ideas of explaining hydrogen embrittlement mechanisms of the studied material in regard to two cracking morphologies: transgranular and intergranular cracking. It is for the first time to report that electrochemical charging alone could cause slip lines, surface and subsurface cracks on nickel-based superalloys. The formation of pre-damages was discussed by calculating the hydrogen concentration gradient and the internal stress generated during cathodic charging. Pre-damages were proved to result in transgranular cracks and lead to the evident reduction of mechanical properties. In addition, the STRONG (Slip Transfer Resistance of Neighbouring Grains) model was used to analyze the dependence of hydrogen-assisted intergranular cracking on the microscopic incompatibility of the grain boundaries. The results show that in the presence of hydrogen, grain boundaries with a lower dislocation slip transmission are more prone to cracking during loading and vice versa. Image 1 [ABSTRACT FROM AUTHOR]

The effects of the prior austenite grain sizes in hydrogen embrittlement of Co-containing 18Ni 300 maraging steel were studied employing Slow Strain Rate Testing (SSRT) in 0.6 M NaCl electrolyte under simultaneuos cathodic polarization. The material was susceptible to hydrogen embrittlement in all investigated conditions. In addition, the examination of the fractured surface revealed that the presence of hydrogen in steel promotes the formation of quasi-cleavage regions and hydrogen-induced cracks along the grain boundaries. However, the refining of the prior austenite grain allowed an improvement in the HE resistance. Moreover, EBSD analysis showed that intergranular cracks propagated along to grain boundaries orientated to {001} planes parallel to normal direction, whereas they were deflected on {101} and {111} crystallographic planes. • The control of the prior austenite grain leads to the improvement of the HE resistance. • Intergranular cracks propagated along the grain boundaries orientated to {001} planes. • The cracks were deflected on grain boundaries {110} and {111} crystallographic planes. [ABSTRACT FROM AUTHOR]