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For a hydrogenation heat exchanger operating under severe working conditions such as high temperature, high pressure and a hydrogen environment, perforation accidents caused by NH4Cl corrosion occur frequently. However, few reports on the effect of hydrogen on the corrosion behavior of metal materials in NH4Cl aqueous solution have been published. In this paper, X-ray photoelectron spectroscopy (XPS), electrochemical dynamic potential polarization, electrochemical impedance spectroscopy (EIS), Mott–Schottky (M-S) curves and scanning electron microscopy (SEM) were used to study the effect of electrochemical hydrogen charging (EHC) on the corrosion behavior of 321 stainless steel in an NH4Cl solution environment. The results show that: (1) hydrogen can change the structure and chemical composition of 321 stainless steel passive film and promote the conversion of metal oxide to hydroxide. At the same time, it can reduce the stability of the passive film. (2) Hydrogen can increase the thermodynamic and kinetic tendency of corrosion reaction and cooperate with Cl− to promote the occurrence of pitting corrosion. [ABSTRACT FROM AUTHOR]

Electrolytic hydrogen charging experiments on cold-deformed and well-annealed (annealing at 700 °C for 2 h) pure titanium samples were carried out, respectively. Positron annihilation spectroscopy and X-ray diffraction were used to characterize all experimental samples to explore the formation of vacancy defects and the storage form of hydrogen in pure titanium after charging. Results showed that hydrides formed in well-annealed samples after electrolytic hydrogen charging, but a new phase in the cold-deformed samples was not observed. The annealed samples formed vacancy-type defects in the process of electrolytic hydrogen charging, and the excess hydrogen atoms were easily trapped by vacancies to form a hydrogen vacancy complex (HmVn). The defects formed in the cold-deformed hindered the diffusion of hydrogen atoms and inhibited the formation of vacancies. Compared with the well-annealed electrolytic hydrogen charging samples, the S parameters of the deformed electrolytic hydrogen charging samples hardly changed. The coincidence Doppler broadening spectrum results showed that wide peaks related to hydrogen vacancy complexes were found in electrolytic hydrogen charging samples. The formation of hydride in titanium affected the positron annihilation environment in the low-momentum region. The hydride-related peak was observed only in the electrolytic hydrogen-charged samples after being well annealed. [ABSTRACT FROM AUTHOR]

For a hydrogenation heat exchanger operating under severe working conditions such as high temperature, high pressure and a hydrogen environment, perforation accidents caused by NH4Cl corrosion occur frequently. However, few reports on the effect of hydrogen on the corrosion behavior of metal materials in NH4Cl aqueous solution have been published. In this paper, X-ray photoelectron spectroscopy (XPS), electrochemical dynamic potential polarization, electrochemical impedance spectroscopy (EIS), Mott–Schottky (M-S) curves and scanning electron microscopy (SEM) were used to study the effect of electrochemical hydrogen charging (EHC) on the corrosion behavior of 321 stainless steel in an NH4Cl solution environment. The results show that: (1) hydrogen can change the structure and chemical composition of 321 stainless steel passive film and promote the conversion of metal oxide to hydroxide. At the same time, it can reduce the stability of the passive film. (2) Hydrogen can increase the thermodynamic and kinetic tendency of corrosion reaction and cooperate with Cl− to promote the occurrence of pitting corrosion.

Electrolytic hydrogen charging experiments on cold-deformed and well-annealed (annealing at 700 °C for 2 h) pure titanium samples were carried out, respectively. Positron annihilation spectroscopy and X-ray diffraction were used to characterize all experimental samples to explore the formation of vacancy defects and the storage form of hydrogen in pure titanium after charging. Results showed that hydrides formed in well-annealed samples after electrolytic hydrogen charging, but a new phase in the cold-deformed samples was not observed. The annealed samples formed vacancy-type defects in the process of electrolytic hydrogen charging, and the excess hydrogen atoms were easily trapped by vacancies to form a hydrogen vacancy complex (HmVn). The defects formed in the cold-deformed hindered the diffusion of hydrogen atoms and inhibited the formation of vacancies. Compared with the well-annealed electrolytic hydrogen charging samples, the S parameters of the deformed electrolytic hydrogen charging samples hardly changed. The coincidence Doppler broadening spectrum results showed that wide peaks related to hydrogen vacancy complexes were found in electrolytic hydrogen charging samples. The formation of hydride in titanium affected the positron annihilation environment in the low-momentum region. The hydride-related peak was observed only in the electrolytic hydrogen-charged samples after being well annealed.

Copyright of Rare Metal Materials & Engineering is the property of Northwest Institute for Nonferrous Metal Research and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Rare Metal Materials & Engineering is the property of Northwest Institute for Nonferrous Metal Research and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

By using electrolytic hydrogen charging, differences in hydrogen pick-up, trapping, hydrogen-induced cold cracking (HICC) and blistering were investigated for an X70 steel for a range of processing and microstructural conditions: as-rolled strip (banded ferrite-pearlite, BFP); transfer bar (ferrite-granular bainite, FGB); normalised and annealed transfer bar (equiaxed ferrite-pearlite, EFP); and a simulated grain coarsened heat affected zone (GCHAZ) (bainitic ferrite, BF). The microstructure was found to have a profound effect on the response to electrolytic hydrogen charging, with the BFP structure being the most susceptible to HICC and the development of surface blisters. In contrast, the simulated GCHAZ structure did not show any blistering for the maximum charging time of 24 h. These trends are consistent with the ratios of residual to total hydrogen content obtained for the same charging conditions (charging time; electrolyte, current density and sample geometry). The ratio decreased in the order BFP (46%), EFP (34%), FGB (33%), and BF (14%), reflecting the relative capacities of the different microstructures for strong trapping of hydrogen and the related susceptibility to HICC. [ABSTRACT FROM AUTHOR]

Hydrogen-induced cold cracking and blistering in hydrogen-charged X70 steel was found to be highly dependent on microstructure, with the banded ferrite-pearlite microstructure of hot rolled strip showing a higher susceptibility than other microstructures produced by different thermal-mechanical routes. Although crack initiation was particularly sensitive to microstructure, crack growth occurred largely parallel to the rolling plane, at least at a macroscopic level, for all of the microstructures investigated. The crack plane was associated with structural anisotropy arising from processing by rolling and was not found to be related to a preferred grain orientation. At a microstructural level, crack propagation was mostly transgranular and occurred dominantly along slip planes of the ferrite grains. Cracks were initiated at strong traps in the microstructure when the hydrogen and local stress concentrations reached critical levels for hydrogen-induced fracture. The main initiation sites were coarse inclusions, mainly oxides, and ferrite-pearlite interfaces. [ABSTRACT FROM AUTHOR]

• The fracture mode of specimen after EHC changed from ductile fracture to brittle fracture. • The hydrogen cracks are preferentially appeared at grain boundaries, inclusions and interface. • The transformation and growth of α' martensite reduce the plasticity of the material. AISI 321 stainless steel is widely used in hydrogenation refining pipes and hydrogen storage vessel and so on owing to its excellent performance of creep stress resistance and high-temperature resistance. In this study, slow strain rate tensile tests (SSRT) were conducted under the condition of electrolytic hydrogen charging (EHC). The hydrogen embrittlement mechanism of AISI 321 stainless steel was analyzed in detail by means of scanning electron microscopy(SEM), X-ray diffraction spectrometer (XRD) and transmission electron microscope (TEM). The results show that hydrogen can change the fracture mode of tensile specimens from ductile fracture to brittle fracture mode. The main reason is that dislocations slide carrying hydrogen continuously in the material under the action of slow strain rate stress, resulting hydrogen cracks are preferentially produced at austenite grain boundaries, inclusions and the interface between δ ferrite and austenite. Additionally, it is easy to induce the transformation and growth of α' martensite in the process of hydrogen charging and reduce the plasticity of the material. [ABSTRACT FROM AUTHOR]

The influence of the aluminium content in the B2 FeAl alloys on the absorption of electrolytically generated hydrogen was determined. It has been found that the amount of absorbed hydrogen increases when the alloy composition approaches the stoichiometric composition. Changes in alloy microhardness, caused by cathodic hydrogen charging, were studied. An increase in hardness of B2 FeAl alloys was observed after hydrogen absorption. [Copyright &y& Elsevier]