Hydrogen permeation behavior in pure nickel implanted with phosphorus, sulphur and their mixture

The entry and transport of hydrogen in phosphorus (P)-, sulphur (S)- and their mixture (P + S)-implanted nickel specimens with a fluence range of 1 × 10¹⁵ to 1 × 10¹⁷/cm² have been investigated using an electrochemical permeation technique and etching treatment (0.2% HF solution). From the hydrogen permeation transients obtained, the effective hydrogen concentration (C_H), apparent hydrogen diffusion coefficient (D_lag) and breakthrough time (t_lag) were estimated by using the time lag method in addition to the steady state permeation current density (P_∞). It was found that at a fluence of less than 1 × 10¹⁶/cm² almost all hydrogen permeation transients of the implanted nickel specimens were affected by the defects (vacancy, compressive stress and so on) generated during ion implantation process. At a high fluence of 1 × 10¹⁷/cm² the hydrogen permeation transient had a specific behavior because of the formation of amorphous phase for P, the structure change from fcc-structure to bcc-structure for S and both of them for the mixture (P and S). However, a synergistic effect of P and S was not observed on the hydrogen permeation transient. The behavior of these parameters depending on fluence and implanting element was discussed in terms of an amount of hydrogen entry site, the degree of defects, the properties of amorphous phase and structure and so on.     

Hydrogen embrittlement susceptibility and permeability of two ultra-high strength steels

Slow displacement rate tensile tests were carried out in a saturated H₂S solution to investigate the effect of hydrogen embrittlement on notched tensile strength (NTS) and fracture characteristics of two ultra-high strength steels (PH 13-8 Mo stainless steel and T-200 maraging steel). Hydrogen permeation properties were determined by an electrochemical permeation method. The results of permeation tests indicated that over-aged specimens showed a lower diffusivity/hydrogen flux and higher solubility than those solution-annealed. The great increase in reverted austenite (irreversible hydrogen traps) together with numerous precipitates at the expense of dislocations (reversible) in the over-aged specimen led to such a change in permeability. Ordinary tensile tests indicated that four tested specimens had roughly the same yield strength level. Hence, the hydrogen embrittlement susceptibility of the material could be related to their permeation properties. The uniform distribution of strong hydrogen traps in over-aged specimens instead of weak traps in the solution-annealed impeded the hydrogen transport toward the strained region, thus, the resistance to sulfide stress corrosion cracking was improved in over-aged specimens.     

Comparative assessment of electrochemical hydrogen absorption by pipeline steels with different strength

The assessment of ability to absorb hydrogen of three API grade pipeline steels: X52, X70 and X100 have been evaluated. The factors of cathodic hydrogen charging, time of exposure, and applied stress were taken into account. It has been shown that all steels demonstrate the sensitivity to hydrogenating in deoxygenated, near-neutral pH NS4 solution under relatively “soft” cathodic polarisation, although the efficiency of hydrogen permeation in metal is quite low and depends on time of exposure. Applied tensile stress, which equivalent to gross hoop stress in pipe wall under operating conditions, can accelerate the hydrogen absorption in several times. For studied steels the resistance to hydrogen absorption decreases with decreasing of steel strength.     

Effects of corrosion product deposit on the subsequent cathodic and anodic reactions of X-70 steel in near-neutral pH solution

The effects of corrosion product deposit on the subsequent anodic and cathodic reactions of X-70 steel in a near-neutral pH solution were investigated by localized electrochemical impedance spectroscopy (LEIS), scanning vibrating micro-electrode (SVME) and macroscopic EIS measurements as well as surface analysis technique. It is found that the deposit layer formed on the steel surface is porous, non-compact in nature. The presence of a corrosion product layer would enhance adsorption, but significantly inhibit absorption and permeation of hydrogen atoms into steel. It is due to the porous structure of the deposit that generates a spatial separation of cathodic and anodic reaction sites, resulting in an increased effective surface area for hydrogen adsorption and, simultaneously, a “blocking” effect on hydrogen absorption and permeation. The deposit enhances greatly anodic dissolution of the steel, which is attributed to the adsorption of the intermediate species and the resultant “self-catalytic” mechanism for corrosion of the steel in near-neutral pH solution. In the presence of corrosion product deposit on the pipeline steel surface, pipeline corrosion, especially pitting corrosion, is expected to be enhanced. Stress corrosion cracks could initiate from the corrosion pits that form under deposit. However, deposit does not contribute to hydrogen permeation, although the hydrogen evolution is enhanced.     

Amperometric hydrogen permeation measurement in iron using solid polymer electrolyte fuel cells

Electrolytic hydrogen permeation through iron membranes was measured simultaneously by means of a solid polymer electrolyte fuel cell (SPEFC) and standard aqueous-phase hydrogen oxidation. Two configurations of SPEFC were tested: the first included a separate anode for hydrogen oxidation and the second used the iron membrane surface itself, plated with palladium, as the anode. The results showed a limiting hydrogen permeation flux for the first configuration but not for the second, which yielded about 64% of the correct output.     

Hydrogen permeation in gamma titanium aluminides

The permeation of hydrogen in gamma titanium aluminides was studied using the Devanathan–Stachurski (DS) cell. Thin disk-shaped samples of gamma titanium aluminide with three different microstructures were appropriately prepared and cathodically charged in an aqueous 0.1 N NaOH solution. The permeation current was monitored as a function of time. Permeation parameters were calculated using the time lag criterion (non-steady state lag). Values of the apparent diffusion coefficient of hydrogen in gamma titanium aluminide varying from 1.87 × 10⁻⁷ cm²/s to 3.75 × 10⁻⁶ cm²/s were obtained. This slight variation is attributed to differences in microstructure.     

Study of the electrochemical permeation of hydrogen in iron

Hydrogen permeation through iron membranes of different thicknesses was studied by the electrochemical permeation technique. The membranes were charged with hydrogen by galvanostatic cathodic polarization in 0.1 M NaOH at 25 °C.The measured build-up and decay permeation current transient had been examined.The experimental results revealed that the diffusion apparently increases with decreasing membrane thickness. This result suggests that the hydrogen transport through membrane was mainly governed by hydrogen trapping at the trap sites present at the grain boundaries.The influence of the passive layer on the hydrogen permeation and its influence on the evaluation of diffusion and trapping characteristics were discussed.     

Hydrogen diffusion coefficients through Inconel 718 in different metallurgical conditions

We report hydrogen permeation studies through cold rolled, solutionized, and precipitation hardened Inconel 718 foils. The effective hydrogen diffusion coefficient is considerably higher (5.3–6.8 × 10⁻¹¹ cm²/s) for the solutionized Inconel 718 than for either the cold rolled (3.3–4.2 × 10⁻¹¹ cm²/s) or precipitation hardened (2.1–2.9 × 10⁻¹¹ cm²/s) specimens. Microstructural studies indicate that the reduced hydrogen diffusion coefficients in the latter specimens arise from hydrogen trapping at dislocations and precipitates that are present at much lower concentrations in the solutionized specimens. Also, repeated permeation transients provide evidence for irreversible hydrogen trapping in the cold rolled and precipitation hardened specimens, but such effects are insignificant in the solutionized specimens.     

Characterization of inclusions of X80 pipeline steel and its correlation with hydrogen-induced cracking

In this work, the microstructures of an X80 pipeline steel were characterized, and their susceptibilities to hydrogen-induced cracking (HIC) were investigated by hydrogen-charging, electrochemical hydrogen permeation and surface characterization. It is found that the microstructure of X80 pipeline steel consists of a polygonal ferrite and bainitic ferrite matrix, with martensite/austenite (M/A) constituents distributing along grain boundaries. The inclusions existing in the steel include those enriched with Si, Al oxide, Si–ferric carbide and Al–Mg–Ca–O mixture, respectively. The majority of inclusions are Si-enriched. Upon hydrogen-charging, cracks could be initiated in the steel in the absence of external stress. The cracks are primarily associated with the Si- and Al oxide-enriched inclusions. The diffusivity of hydrogen in X80 steel at room temperature is 2.0 × 10⁻¹¹ m²/s, and the estimated hydrogen trapping density in the steel is as high as 3.33 × 10²⁷ m⁻³.     

Local additional potential model for effect of strain rate on SCC of pipeline steel in an acidic soil solution

Stress corrosion cracking (SCC) behavior of X70 pipeline steel in an acidic soil solution was investigated by slow strain rate test, surface characterization, potentiodynamic polarization curve measurement and electrochemical hydrogen permeation technique. A local additional potential model (LAPM) was developed to illustrate the critical role of strain rate in SCC of the steel. According to LAPM, both density and mobility of local active spots on the steel surface, i.e., dislocation emergence point, increase linearly with strain rate. Generation of such active spots introduces an additional negative potential locally, affecting the electrochemical reaction and, consequently, the susceptibility of the steel to SCC. It is found that a maximum of the SCC susceptibility occurs at strain rate of 10⁻⁶ s⁻¹, which is associated with an enhanced hydrogen evolution due to the local additional potential (LAP) effect. When strain rate is sufficiently high to exceed 10⁻⁶ s⁻¹, the mobility of the dislocation emergence points is so fast that the reactive species in solution cannot combine with them for cathodic reaction, resulting in a decrease of the SCC susceptibility. Similarly, a maximum of hydrogen permeation current observed at the strain rate of 10⁻⁶ s⁻¹ is also attributed to the effect of strain rate on the density and mobility of dislocations in the steel. Diffusion of hydrogen atoms in a strained steel is through both body diffusion and dislocation diffusion, with the latter enhanced by an increasing strain rate. When strain rate is so high that the dislocation mobility is sufficiently fast, hydrogen atoms become incapable of catching up with the dislocations. As a result, the hydrogen diffusion is dominated by the body diffusion mode.     

Hydrogen ion reduction in the process of iron rusting

Since the acceptance of the electrochemical rusting mechanism, oxygen reduction has been considered the main cathodic process, while H⁺ reduction has been overlooked for the past four decades because oxygen can be readily renewed due to the thin layer of solution film formed during atmospheric corrosion. This study shows that measurable hydrogen can be detected at the surface opposite to the corroding side of the specimen during wet-dry cycles, and a clear correlation exists between the quantities of hydrogen permeated through iron sheet and weight loss. Results suggest the intrinsic importance of H⁺ reduction that merits further investigation.     

Hydrogen transport and embrittlement in 300 M and AerMet100 ultra high strength steels

This paper describes how hydrogen transport affects the severity of hydrogen embrittlement in 300 M and AerMet100 ultra high strength steels. Slow strain rate tests were carried out on specimens coated with electrodeposited cadmium and aluminium-based SermeTel 1140/962. Hydrogen diffusivities were measured using two-cell permeation and galvanostatic charging methods and values of 8.0 × 10⁻⁸ and 1.0 × 10⁻⁹ cm² s⁻¹ were obtained for 300 M and AerMet100, respectively. A two-dimensional diffusion model was used to predict the hydrogen distributions in the SSR specimens at the time of failure. The superior embrittlement resistance of AerMet100 was attributed to reverted austenite forming around martensite laths during tempering.     

Hydrogen induced cracking (HIC) testing of low alloy steel in sour environment: Impact of time of exposure on the extent of damage

Hydrogen induced cracking (HIC) of line pipe steel was investigated through immersion testing and hydrogen permeation measurements. At constant pH and hydrogen sulphide partial pressure (pH₂S), the extent of HIC was found to depend on exposure time until a stable level was reached. The time to reach this stable value is affected by pH and pH₂S. Results of permeation experiments confirmed that HIC is linked with the increase of hydrogen concentration in the steel. It is also shown that low severity requires longer exposures to reach equilibrium. This must be taken into account for HIC testing in mildly sour environment.     

Quantitative evaluation of detection efficiency of the hydrogen microprint technique applied to steel

The detection efficiency of a hydrogen microprint technique (HMT) applied to steel specimens was examined experimentally. Amounts of hydrogen released from the specimen surface were measured by an electrochemical hydrogen permeation method, and the amounts were also evaluated by means of HMT under the same charging conditions as employed for the permeation test. Detection efficiency of conventional HMT was found to be as low as about 1%, but nickel plating of the steel surface was found to increase this efficiency remarkably. This high efficiency by nickel plating was achieved only when the relative humidity of an experimental atmosphere was controlled to 80% or higher. The thus-modified HMT showed a detection efficiency of about 40%.     

Microstructural effects on the hydrogen permeation of an Inconel alloy 690

In the present work, hydrogen permeability tests were carried out in Inconel 690 in the as-received (AR) condition and after heat treating. The heat treatments promoted total solid solution (SA) or a microstructure full of grain boundary (gb) coverage with M₂₃C₆ carbides (A800). first and second polarization hydrogen transients were determined and used in disclosing the role of reversible and irreversible hydrogen trapping. It was found that in the SA condition, the permeation rates were the highest but they were significantly reduced in the AR condition, particularly in the A800 due to the presence of gb M₂₃C₆ carbides.     

Effect of microstructure on the sulphide stress cracking susceptibility of a high strength pipeline steel

The sulphide stress cracking (SSC) susceptibility of a newly developed high strength microalloyed steel with three different microstructures has been evaluated using the slow strain rate testing (SSRT) technique. Studies were complemented with potentiodynamic polarization curves and hydrogen permeation measurements. Material included a C–Mn steel having Ni, Cu, and Mo as main microalloying elements with three microstructures: martensitic, ferritic and ferritic + bainitic. Testing temperatures included 25, 50, 70 and 90 °C. Detailed SEM observations of the microstructure and fracture surfaces were done to identify possible degradation mechanisms. The results showed that in all cases, the corrosion rate, number of hydrogen atoms at the surface and the percentage reduction in area increased with temperature. The steel with a martensitic microstructure had the highest SSC susceptibility at all temperatures, whereas the ferritic steels were susceptible only at 25 °C, and the most likely mechanism is hydrogen embrittlement assisted by anodic dissolution.     

Hydrogen permeation in Fe-40 at.% Al alloy at different temperatures

The electrochemical permeation technique for studying transport and trapping of hydrogen in Fe-40 at.% Al alloy at temperatures of 5, 25, 45 and 65 °C was used in the paper. The influence of temperature on the effective hydrogen diffusion coefficient, hydrogen permeation rate and hydrogen solubility was determined. The activation energy of hydrogen diffusion in iron aluminide in the studied temperature range was also determined.     

Effect of residual stresses on hydrogen permeation in iron

The effect of residual stresses on electrochemical permeation in iron membrane was investigated. Four thermal and mechanical treatments were chosen to obtain different surface states in relation to the residual stresses.Residual stresses were determined by X-ray diffraction (XRD) using the Macherauch and Müller method. The results were completed by the microhardness measurements. For all iron membranes, compressive residual stresses were obtained.Electrochemical permeation experiments using a Devanathan and Stachurski cell were employed to determine the hydrogen permeation behaviour of the various iron membranes. The latter was charged with hydrogen by galvanostatic cathodic polarization in 0.1 M NaOH at 25 °C. The experimental results revealed that hydrogen permeation rate increases with increasing residual stresses introduced in iron membranes.     

Effect of post-weld heat treatment on the microstructure and hydrogen permeation of 13CrNiMo steels

The hydrogen trapping characteristics of 13CrNiMo martensitic steel weld metals, with different austenite contents resulting from different post-weld heat treatments, have been analysed. Scanning electron microscopy and X-ray diffraction have been used to study stable austenite resulting from intercritical tempering of these soft martensitic stainless steels weld metals. Austenite contents up to 25 vol.% have been obtained. Hydrogen diffusion and permeation coefficients have been obtained from an analysis of the permeation rate of hydrogen through these materials. A decrease of the hydrogen apparent diffusion coefficient is observed when the tempering temperature is increased in the range ; this decrease is attributed to changes in the martensitic matrix as well as to the increase of austenite content. The role of the austenite phase on trapping is discussed.     

Hydrogen entry into steel during atmospheric corrosion process

Hydrogen entry and permeation into iron were measured by an electrochemical method during atmospheric corrosion reaction. The hydrogen permeation was enhanced on passive films because the hydrogen adsorption increased by the hydrogen evolution mechanism which is different from that on a bear iron surface. The permeation rate during a wet and dry corrosion cycle showed a maximum in the drying process depending upon the surface pH and the corrosion potential. The pollutant such as Na₂SO₃ which decreases the pH and the corrosion potential causes an increase in the permeation rate. The mechanism of the change in the permeation rate during the wet and dry cycles is explained by the polarization diagram of the electrode covered by thin water layer.