Sub-surface Hydrogen Concentration Research Articles

Effect of tensile stress on the hydrogen permeation of MS X65 pipeline steel under sulfide films

The effect of the tensile stress on the hydrogen permeation of MS X65 pipeline with sulfide films was investigated through measuring the steady-state hydrogen permeation current (I∞), permeability (J∞L) and apparent diffusivity (Dapp) and quantitatively analysing the hydrogen-permeable resistance factor (HPRF) of single tensile stress HPRF (stress), single sulfide film HPRF (film) and the two together HPRF (stress-film). The results indicated that J∞L and sub-surface hydrogen concentration (co) greatly increase and that Dapp decreases as the elastic stress increases. When applying plastic stress, J∞L and Dapp all reduce, while co continues to increase without the film but decreases with the film. While single tensile stress can promote hydrogen permeation, with the sulfide film, the value of HPRE (stress-film) is not a simple addition of the value of the HPRE (stress) and the HPRE (film), and the interaction results in the blocking effect of hydrogen permeation. The surface morphology of the sulfide films changes caused by tensile stress should be responsible for the HPRE (stress-film) reducing as tensile stress increases but increasing with plastic tensile stress.

On the Estimation of the Diffusion Coefficient and Distribution of Hydrogen in Stainless Steel

In this work, the localisation of hydrogen in an electrochemically charged stainless steel was investigated by Scanning Kelvin Probe Force Microscopy and Glow Discharge Optical Emission Spectroscopy analysis. Both techniques indicated a high hydrogen content at less than 90 micrometres under the charged surface. Thermal Desorption Spectroscopy was used to calibrate the data from both techniques and thus to calculate the hydrogen concentration. Finally, after assuming certain hypotheses, Fick's laws were used to calculate the coefficient of diffusion and subsurface concentration of hydrogen in cathodic charging conditions.

Hydrogen permeation behavior of X70 pipeline steel simultaneously affected by tensile stress and sulfate-reducing bacteria

The hydrogen permeation behavior of submarine pipelines buried in anoxic sea mud and protected by cathodic potential is affected by both sulfate-reducing bacteria (SRB) and tensile stress. In this study, the individual and simultaneous effects of SRB and tensile stress on hydrogen permeation parameters were investigated using an electrochemical hydrogen permeation method together with mechanical tensile tests. Cathodic potentiodynamic polarization and surface morphology investigations were also conducted. Both elastic and plastic stresses were considered. Results showed that SRB enhanced the sub-surface hydrogen concentration significantly but had little influence on the diffusion coefficient. Elastic stress had a minimal effect on the hydrogen permeation behavior of X70 steel. Plastic stress reduced the diffusion coefficient and increased the sub-surface hydrogen concentration. The lattice trap produced by plastic deformation was responsible for the impact of plastic stress on hydrogen permeation. SRB and plastic stress not only enhanced the sub-surface hydrogen concentration independently, but also had synergistic effects accelerating the hydrogen accumulation on a steel surface.

Hydrogen depth profiles and microhardness of electrochemically hydrogen-charged nanostructured bainitic steels

Abstract Hydrogen depth profiles and microhardness of the electrochemically hydrogen-charged nanostructured bainitic steels (produced at two different transformation temperatures, i.e. 200 °C (NBS200) and 350 °C (NBS350)) were obtained using elastic recoil detection analysis (ERDA) technique and Vickers microhardness testing, respectively, and compared to that of mild steel. The ERDA results showed that the subsurface hydrogen concentration was higher in NBS200, followed by NBS350 and mild steel. However, the microhardness data of the hydrogen-charged steels revealed material softening in NBS200 and NBS350, whereas the mild steel exhibited material hardening effect. The microhardness along the cross-sectional depth of the steels showed that the softening effect in NBS200 was closer to the hydrogen-charged surface compared to that of NBS350. The plausible mechanisms for the softening effect in the NBS200 and NBS350, and hardening effect in mild steel have been discussed in this paper.

Hydrogen supersaturated layers in H/D plasma-loaded tungsten: A global model based on thermodynamics, kinetics and density functional theory data

In this work, we combine Density Functional Theory data with a Thermodynamic and a kinetic model to determine the total concentration of hydrogen implanted in the sub-surface of tungsten exposed to a hydrogen flux. The sub-surface hydrogen concentration is calculated given a flux of hydrogen, a temperature of implantation, and the energy of the incoming hydrogen ions as independent variables. This global model is built step by step; an equilibrium between atomic hydrogen within bulk tungsten and a molecular hydrogen gas phase is first considered, and the calculated solubility is compared with experimental results. Subsequently, a kinetic model is used to determine the chemical potential for hydrogen in the sub-surface of tungsten. Combining both these models, two regimes are established in which hydrogen is preferentially trapped at either interstitial sites or in vacancies. We deduce from our model that the existence of these two regimes is driven by the temperature of the implanted tungsten sample; above a threshold or transition temperature is the interstitial regime, below is the vacancy regime in which super-saturated layers form within tenths of angstrom below the surface. A simple analytical expression is derived for the coexistence of the two regimes depending on the implantation temperature, the incident energy and the flux of the hydrogen ions which we use to plot the corresponding phase diagram.

Effect of nickel on hydrogen permeation in ferritic/pearlitic low alloy steels

Nickel offers several beneficial effects as an alloying element to low alloy steels. However, it is, in the oil and gas industry, limited by part 2 of the ISO 15156 standard to a maximum of 1 wt% due to sulfide stress cracking resistance concerns.Hydrogen uptake, diffusion, and trapping were investigated in research-grade ferritic/pearlitic low alloy steels with Ni contents of 0, 1, 2 and 3 wt% by the electrochemical permeation method as a function of temperature and hydrogen charging conditions.Qualitatively, the effective diffusion coefficient, Deff, decreased with increasing Ni content. The sub-surface lattice hydrogen concentration, C0, decreased with increasing Ni content in all charging conditions while the trend between the sub-surface hydrogen concentration in lattice and reversible trap sites, COR, and Ni content varied with the charging conditions. Irreversible trapping, evaluated by consecutive charging transients, was not observed for any of the materials. Lastly, the possible influence of an increasing fraction of pearlite with increasing Ni content is discussed.

Comparison of hydrogen embrittlement susceptibility of three cathodic protected subsea pipeline steels from a point of view of hydrogen permeation

Revealing the hydrogen permeation behavior in steel is the foundation to analyze hydrogen induced fracture. Herein, slow strain rate tension tests were used to investigate the susceptibility of X70, X80 and X100 steel to hydrogen embrittlement induced by cathodic polarization, and the subsurface hydrogen concentration (C0) of three steels was accurately determined by two kinds of hydrogen permeation tests. Results showed that the HE index range of ductile-to-brittle transition should be determined by fracture analysis. The C0 increased in turn from X70, X80 to X100 at any given applied potential, that’s why X100 presented the highest hydrogen embrittlement susceptibility.

Investigation of hydrogen concentration and hydrogen damage on API X80 steel surface under cathodic overprotection

During the application of the API X80 grade pipeline steel in long distance gas transportation, the risk of hydrogen induced degradation for this kind of high strength material needs to be clarified from a safety point of view. Commercial X80 steel samples were hydrogen charged electrochemically at different current densities and immersion time. Hydrogen damage in the form of blisters and cracks was observed by optical microscope and scanning electron microscopy. Average hydrogen content in the sample measured by thermal desorption method and the sub-surface concentration of diffusible hydrogen detected by hydrogen permeation cell were both employed to indicate the correlation between hydrogen and surface damage. The influence of hydrogen on the mechanical properties of X80 steel was also characterized by slow strain rate tests. The results showed that the hydrogen damage can be detected on the steel surface if the hydrogen content could reach a certain threshold value during the process of rapid hydrogen uptake. It is suggested that there exists a critical hydrogen level before blisters initiate on X80 steel and that the level is 2–3 ppm, under the test conditions used in this work.

Effect of bainite in microstructure on hydrogen diffusion and trapping behavior of ferritic steel used for sour service application

Abstract

Effect of the cathodic current density on the sub-surface concentration of hydrogen in X80 pipeline steels under cathodic protection

The effect of the cathodic current density (i) on the permeation of hydrogen through API X80 pipeline steels under cathodic protection was investigated using an electrochemical permeation technique. A proper equation was presented for determining the sub-surface concentration of hydrogen (c0). With the aim to enhance the predictive capabilities of the proposed equation, actual environmental parameters such as temperature were considered. The experimental results reported herein clarified the relationship between c0 and i. It was clearly shown that the ratio of c0 to the specimen thickness (L) was proportional to √i when i was lower than its critical value (iH). On the other hand, for i values above iH, c0 was equal to the saturation hydrogen content because of reaction equilibrium. Furthermore, iH was found to be dependent on temperature (i.e., iH increased with the test temperature).

Effect of shot peening on hydrogen embrittlement of high strength steel

The effect of shot peening (SP) on hydrogen embrittlement of high strength steel was investigated by electrochemical hydrogen charging, slow strain rate tensile tests, and hydrogen permeation tests. Microstructure observation, microhardness, and X-ray diffraction residual stress studies were also conducted on the steel. The results show that the shot peening specimens exhibit a higher resistance to hydrogen embrittlement in comparison with the no shot peening (NSP) specimens under the same hydrogen-charging current density. In addition, SP treatment sharply decreases the apparent hydrogen diffusivity and increases the subsurface hydrogen concentration. These findings are attributed to the changes in microstructure and compressive residual stress in the surface layer by SP. Scanning electron microscope fractographs reveal that the fracture surface of the NSP specimen exhibits the intergranular and quasi-cleavage mixed fracture modes, whereas the SP specimen shows only the quasi-cleavage fractures under the same hydrogen charging conditions, implying that the SP treatment delays the onset of intergranular fracture.

Hydrogen permeation and embrittlement susceptibility of X80 welded joint under high-pressure coal gas environment

Hydrogen permeation and slow strain rate tests in a high-pressure hydrogen-containing coal gas, combined with microstructural analysis, were conducted on X80 base metal, weld metal, and coarse-grained heat-affected zone (CGHAZ). Variation in the calculated diffusivity from high to low was in the following sequence: CGHAZ, weld metal, and base metal. This result was contrary to those of sub-surface hydrogen concentration and hydrogen embrittlement susceptibility. Hydrogen permeation in CGHAZ decreased the cross-sectional shrinkage by 34.56%, which indicates susceptibility to hydrogen embrittlement. The co-effects of microstructure, hydrogen diffusivity, and concentration were the main factors that influenced hydrogen embrittlement susceptibility.

Diffusion of Hydrogen in the TRIP 800 Steel

The presented paper is devoted to the study of hydrogen diffusion characteristics in the C-Mn-Si TRIP 800 steel. The steel was tested in three different states: in as-received state after hot and cold rolling and subsequent heat treatment; and furthermore after 5% and 10% tensile deformation. Hydrogen diffusion characteristics were studied by means of electrochemical permeation method. Two build up transients corresponding to lower and higher charging current densities as well as a decay transient were recorded during experiment. The lowest values of hydrogen diffusion coefficient (from 1.10-7 to 3.5.10-7 cm2.s-1) were observed during the first build up transient; the value of 3.5.10-7 cm2.s-1 corresponded to 10% tensile deformation. During the 2nd build up transient corresponding to the higher charging current density, hydrogen diffusion coefficients increased markedly reflecting thus the fact that hydrogen trapping was less pronounced. For decay transients hydrogen diffusion coefficients were situated between values obtained for the 1st and 2nd build up transients. In all studied states, rather high sub-surface hydrogen concentration was observed during the 1st build up transient rising to 12.6ppm of hydrogen in as-received state. The obtained results are explained taking into account steel microstructure and hydrogen trapping.

Hydrogen Diffusion Characteristics in the TRIP 800 C-Mn-Si Steel

The presented paper is devoted to the study of hydrogen diffusion characteristics in the C-Mn-Si TRIP 800 steel. The steel was tested in three different states: in as-received state after hot and cold rolling and subsequent heat treatment; and furthermore after 5% and 10% tensile deformation. Hydrogen diffusion characteristics were studied by means of electrochemical permeation method. Two build up transients corresponding to lower and higher charging current densities as well as a decay transient were recorded during experiment. The lowest values of hydrogen diffusion coefficient (from 1 to 3.5.10-7 cm2.s-1) were observed during the first build up transient; the value of 3.5.10-7 cm2.s-1 corresponded to 10% tensile deformation. During the 2nd build up transient corresponding to the higher charging current density, hydrogen diffusion coefficients increased markedly reflecting thus the fact that hydrogen trapping was less pronounced. For decay transients hydrogen diffusion coefficients were situated between values obtained for the 1st and 2nd build up transients. In all studied states, a rather high sub-surface hydrogen concentration was observed during the 1st build up transient rising to 12.6 ppm of hydrogen in as-received state. The obtained results are explained taking into account steel microstructure and hydrogen trapping.

Modeling of Hydrogen Transport in Static and Rolling Contact

Hydrogen diffusion into steel is known to be one of the degradation material processes causing a reduction in material toughness (embrittlement) and fatigue strength, which enhances crack initiation and propagation under rolling contact loading conditions. The current work presents a finite element study of hydrogen diffusion into a metal substrate loaded by static and rolling contact. The main goal of the study is to investigate the stress effect on hydrogen transport. Initially a stress–diffusion problem for static Hertzian contact is solved and later for more complicated rolling contact conditions. Rolling contact is considered here by the moving Hertzian pressures existing around the bearing ring. Governing equations are given in dimensionless form, and a parametric study analyzing the influence of different dimensionless parameters on subsurface concentration of hydrogen is presented.

ChemInform Abstract: A Fresh Look at an Old Nano‐Technology: Catalysis

AbstractReview: 116 refs.

A fresh look at an old nano-technology: catalysis

The development of model catalyst systems for heterogeneous catalysis going beyond the metal single crystal approach, including phenomena involving the limited size of metal nanoparticles supported on oxide surfaces, as well as the electronic interaction through the oxide-metal interface, is exemplified on the basis of two case studies from the laboratory of the authors. In the first case study the reactivity of supported Pd nanoparticles is studied in comparison with Pd single crystals. The influence of carbon contaminants on the hydrogenation reaction of unsaturated hydrocarbons is discussed. Carbon contaminants are identified as a key parameter in those reactions as they control the surface and sub-surface concentration of hydrogen on and in the particles. In the second case study, scanning probe techniques are used to determine electronic and structural properties of supported Au particles as a function of the number of Au atoms in the particle. It is demonstrated how charge transfer between the support and the particle determines the shape of nanoparticles and a concept is developed that uses charge transfer control through dopants in the support to understand and design catalytically active materials.

Computational analysis of geometrical factors affecting experimental data extracted from hydrogen permeation tests: III – Comparison with experimental results from the literature

The membrane thickness is one of the major parameters affecting hydrogen diffusion during electrochemical permeation tests. In this work, we study the effects of membrane thickness by comparing experimental results from the literature with a numerical analysis by finite element method (FEM). We consider the effects of a palladium coating or an oxide layer on the diffusion through α-iron, and we also studied the effects of an oxide layer on the diffusion through martensitic steels. Our model allows us to match the experimental data and determine the initial subsurface hydrogen concentration, trap densities, and the diffusivity of the layer. However, we had to consider the effects of the mechanical polishing on hydrogen trap densities and concentrations to ensure a reasonable correlation. The balance between the effects of trapping and the oxide layer are finally discussed; while hydrogen trapping increases the effective subsurface concentration, the oxide layer decreases its value.

Hydrogen Permeation Behavior through HSLA Steels and its Implications on Hydrogen Embrittlement Susceptibility

In order to investigate the susceptibility of HSLA steels to hydrogen embrittlement (HE) when cathodic protection system was applied, a new electrochemical hydrogen permeation test method was performed to measure the hydrogen permeation current behavior through X65 steel and X80 steel in artificial seawater with different polarized potentials. Besides, slow strain rate test (SSRT) was introduced to study the effect of penetrated hydrogen atoms on the HE susceptibility of the steels. Results showed that with the decrease of the polarized potential, the sub-surface hydrogen concentration in the steels became higher and higher, and the corresponding HE susceptibility increased as well. What’s more, the X80 steel was more vulnerable to HE, and that owns to the minor grain size and M-A microstructure, which may trap more hydrogen atoms, and thus led to the HE susceptibility difference between the two steels. All these findings would be used as guidance when cathodic protection were carried out for offshore HSLA steel structures.

Modeling of Hydrogen Transport in Rolling Contact Fatigue Conditions

Current work presents Finite Elements study of hydrogen diffusion into a metal substrate loaded by rolling contact. The main goal of the presented study is to investigate stress effect on hydrogen transport in rolling contact conditions. In this work, rolling contact is defined by the Hertzian pressure, moving along the bearing ring.Although, hydrogen diffusion with respect to bearing is studied here, very similar approach can be used for other components of machinery subjected to rolling contact. Governing equations are given in the current study in dimensionless form, and parametric study, analyzing influence of different dimensionless parameters on subsurface concentration of hydrogen, is presented.