Hydrogen Concentration In Metal Research Articles

Methodology of hydrogen embrittlement study of long-term operated natural gas distribution pipeline steels caused by hydrogen transport

A methodology of experimental research on hydrogen embrittlement of pipe carbon steels due to the transportation of hydrogen or its mixture with natural gas by a long-term operated gas distribution network is presented. The importance of comparative assessments of the steel in the as-received and operated states basing on the properties that characterize plasticity, resistance to brittle fracture and hydrogen assisted cracking is accentuated. Two main methodological peculiarities are pointed out, (i) testing specimens should be cut out in the transverse direction relative to the pipe axis; (ii) strength and plasticity characteristics should be determined using flat tensile specimens with the smallest possible thickness of the working part. The determination of hydrogen concentration in metal, metallographic and fractographic analyses have been supplemented the study. The effectiveness of the proposed methodology has been illustrated by the example of the steel research after its 52-year operation.

Effect of alloying, modifying and fluxing agents on aluminum hydrogen saturation

Paper presents the laboratory research results about effect of alloying, modifying and fluxing agents, in amount corresponding to consumption standards and used at the RUSAL aluminum smelters, on hydrogen saturation of aluminum melt. In paper the comparison is made between hydrogen measurement results obtained by express analysis of liquid aluminum using an Alu Compact instrument and data of solid aluminum from specialized highly sensitive magnetic mass spectrometer AV-1. As a result of studies, it was found that the maximum of aluminum hydrogen saturation occurs when using powder refining fluxes and alloying agents containing halides of alkali and alkaline earth metals, some of which form crystalline hydrates. It was shown that powder fluxes and alloying agents with flux components contain crystallization and hygroscopic water and, when they are added to melt, increase the concentration of hydrogen in metal by 35-100%. According to the research results, technical solutions are proposed with the aim of reducing the saturation degree of aluminum melt with hydrogen. One of the most effective solutions is to use fused flux lump. The following points were proposed as technical solutions to reduce the saturation degree when alloying, refining, and modifying agents added to melt: make use of fused lump refining and cover-refining fluxes and retreat from powder fluxes; provide incoming control for fluxes and alloying agents containing fluxes; to store fluxes and alloying agents with halides of alkali and alkaline earth metals under conditions that exclude hygroscopic moisture saturation; to increase the consumption of fused refining fluxes by 1.5-2 times during preparation of aluminum-magnesium alloys.The work was performed within the framework of the state assignment for science of the Federal State Autonomous Educational Institution of Higher Education “Siberian Federal University”, project number FSRZ-2020-0013.

Analysis for Hydrogen Concentration in Titanium Alloys Using Multifrequency Eddy Current

In this article, multifrequency eddy current testing is proposed to detect hydrogen concentration in alloy titanium. The effect of hydrogen on the titanium alloy was explored across the surface layer of the material. The sample has a fixed surface area, and the samples with the same thickness and different hydrogen concentrations are analyzed. Output voltage amplitudes and dielectric loss tangent in hydrogen-filled titanium VT1-0 were studied in the range of hydrogen concentration from 0.019 to 0.290 wt.% using the instrument Micromagnetic Multiparameter Microstructure and Stress Analysis (3MA-II) at the frequency from 200 to 1000 kHz. This article proposes a method of analyzing the internal conductivity of metals by eliminating surface effects. The linear relationship between hydrogen concentration and conductivity is obtained, and the experimental results that are closer to the theory than the four-probe method and the inclusion surface are obtained. The results show that the output signal amplitudes decreased with an increase of the hydrogen concentration and frequency, and in addition, the dielectric loss tangent obtains a similar result at the hydrogen concentra- tion >0.100 wt.%. It is shown that this method can be used to evaluate the concentration of hydrogen in metal.

Role of hydrogen in operational degradation of pipeline steel

Long-term operation of oil and gas pipeline steels causes a significant worsening of their mechanical properties, especially characteristics of brittle fracture resistance. General regularities of in-service degradation of pipeline steels are analysed in the paper. Basing on these, two stages of pipeline steel degradation are distinguished: deformation aging and in-bulk steel dissipated microdamaging. Hydrogenation intensifies the damaging process due to hydrogen induced microcracking of steel and, in this way, facilitates its operational degradation. In-service damaging intensified by hydrogen can cause untypical mechanical behaviour of a metal: a) a decrease in strength and hardness is accompanied by reducing brittle fracture resistance; b) an increase in elongation simultaneously with a decrease in reduction in area. Some examples of the destructive role of hydrogen in-bulk material degradation are considered, when transported hydrocarbons serve as a source of hydrogen. It is shown that investigations of hydrogen behaviour in steels by hydrogen extraction and permeation methods provide valuable information for assessment of in-service dissipated damaging degree. In particular, a decrease of brittle fracture resistance is in a good agreement with hydrogen concentration in metal. Special attention is paid to the role of hydrogen in damaging rolled steels with texture during their operation. The main mechanism of microdamaging for textured steels is suggested to be the accumulation of hydrogen at the interface “elongated non-metallic inclusion–matrix” creating high pressure in defects with the following microdelamination along the rolling direction. This leads also to anisotropy of characteristics of brittle fracture resistance of rolled steels, which becomes more pronounced with operation time.

Specific Features of the Deformation and Fracture of Low-Alloy Steels in Hydrogen-Containing Media: Influence of Hydrogen Concentration in the Metal

We establish basic regularities of the influence of hydrogen concentration in metals on the fracture strength of low-alloy pipe steels. In particular, we determine the characteristic value of hydrogen concentration for which the mechanism of its influence on the deformation of specimens by uniaxial quasistatic tension changes, namely, below this concentration, hydrogen enhances the plasticity of the material and, above this concentration, promotes its embrittlement. For the first time, we detected an ambiguous relationship between fatigue crack-growth rate and the volume hydrogen concentration in these steels under cyclic loading in hydrogen-containing media and established its value for which the cyclic crack growth resistance of steel increases. We revealed a correlation between the intensity of hydrogenation of steels and the strength of passive film at the crack tip, which gives us an instrument for the development of efficient barriers against hydrogen penetration into the materials.

Modelling of discrete TDS-spectrum of hydrogen desorption

High concentration of hydrogen in metal leads to hydrogen embrittlement. One of the methods to evaluate the hydrogen content is the method of thermal desorption spectroscopy (TDS). As the sample is heated under vacuumization, atomic hydrogen diffuses inside the bulk and is desorbed from the surface in the molecular form. The extraction curve (measured by a mass-spectrometric analyzer) is recorded. In experiments with monotonous external heating it is observed that background hydrogen fluxes from the extractor walls and fluxes from the sample cannot be reliably distinguished. Thus, the extraction curve is doubtful. Therefore, in this case experimenters use discrete TDS-spectrum: the sample is removed from the analytical part of the device for the specified time interval, and external temperature is then increased stepwise. The paper is devoted to the mathematical modelling and simulation of experimental studies. In the corresponding boundary-value problem with nonlinear dynamic boundary conditions physical- chemical processes in the bulk and on the surface are taken into account: heating of the sample, diffusion in the bulk, hydrogen capture by defects, penetration from the bulk to the surface and desorption. The model aimed to analyze the dynamics of hydrogen concentrations without preliminary artificial sample saturation. Numerical modelling allows to choose the point on the extraction curve that corresponds to the initial quantity of the surface hydrogen, to estimate the values of the activation energies of diffusion, desorption, parameters of reversible capture and hydride phase decomposition.

Metrological Assurance of Measurement of Hydrogen Concentration in Metals – a Basis for Safety in the Oil and Gas Industry

It is demonstrated that metal properties depend strongly on both hydrogen concentration, and on its redistribution with respect to bonding energy. According to accident statistics presence of hydrogen within metal is in many cases the main reason for metal structure breakdown with occurrence of internal stresses. It is concluded that the lack of a single metrological hydrogen concentration measurement system makes it impossible to introduce extensively an effective and reliable method for production monitoring and accident prevention. Hydrogen is contained in all metals and alloys. In contrast to the majority of other alloy components, it has a very strong effect on material mechanical properties. The degree of the effect of small hydrogen concentrations on metal proper- ties may only be compared with phosphorus. The lack of necessary monitoring of hydrogen content in a metal promotes the task of measuring its concentration to a paramount category. According to statistics, in the last 30 years the reason for 62.7% of all bulk oil tanker accidents in our country was brittle failure, connected with hydrogen accumulation, and only 12.4% of accidents occurred as a result of ignition or explosions. The practice of studying operating vessels shows that their metal walls are often subject to deep pitting corrosion, as a consequence of which there is rapid local breakdown. At the boundary of an internal welded joint and wall surface, there is intergranular corrosion. Metal corrosion leads to hydrogen embrittlement for steel from which a vessel is manufactured. Hydrogen brittleness and wall delamination is one of the main reasons for the accident rate in main oil and gas pipelines. Due to a significant hydrogen concentration in raw oil and gas at sites it is necessary to prepare pipelines from special expensive grades of steel, but this only increases service life, and the problem of hydrogen brittleness is retained. The effect of hydrogen on metal properties has been studied for more than 150 years. Cases of hydrogen brittleness have been studied a great deal, and there are experimental data about a threshold hydrogen concentration with which it arises. As a rule, this is a very low concentration in the range 0.4-50 ppm. In addition, quantitative data do not fix a common standard and traceability of existing standards to a primary standard, and this leads to marked scatter of results with measurements in dif- ferent laboratories. Divergences comprise a factor from 0.2 to 2, and in the case of nanomaterials it reaches a factor of 500 (1). Contemporary measuring equipment, available on the market, differs considerably both with respect to the method for hydrogen extraction from a sample, and the recording principle. Measurements of hydrogen concentration in identical

Beyond Sieverts' law: A comprehensive microkinetic model of hydrogen permeation in dense metal membranes

There is much ongoing research on developing dense metal membranes based on palladium and its alloys for producing high purity hydrogen, e.g., for fuel cells. Such membranes are almost exclusively permeable to hydrogen in a feed gas mixture via the following steps: (s1) dissociative adsorption on the surface; (s2) sub-surface dissolution; (s3) diffusion of interstitial hydrogen atoms within the bulk metal matrix; (s4) evolution from the bulk metal to its permeate side surface; and finally, (s5) associative desorption of hydrogen. The flux is commonly described by the so-called “Sieverts' law,” which expresses the flux as a membrane permeance times the difference in square root of hydrogen pressure on the feed side and that on the permeate side. It is derived by assuming that diffusion (step s3) is controlling, and hydrogen concentration in metal is low, which strictly limits its applicability to relatively high temperatures, thick membranes, and low hydrogen pressures. We describe a comprehensive microkinetic model that includes all five steps, and is shown to be suitable for Pd over a broad range of conditions. It also describes non-ideal hydrogen solution due to phase-transition in Pd, which explains the sharp peak at intermediate temperatures in hydrogen flux observed experimentally, but not so far explained theoretically. The model includes effect of metal surface roughness, not commonly considered so far. Use of an electrical analogy and comparison of step resistances allows a reduction to a three-step (adsorption, diffusion, and desorption control) model that also adequately describes hydrogen permeation over a broad range of conditions.

The effect of hydrogen concentration on fracture of pipeline steels in presence of a notch

Abstract The comparative assessment of local fracture initiation at notches in API grade pipeline steels: X52, X70 and X100 have been done for conditions of electrochemical hydrogenating. The factor of hydrogen concentration in metal was taken into account. The relationship between hydrogen concentration in metal and work for initiation of the local fracture emanating from the notch has been derived. The existence of some critical hydrogen concentration, which causes the significant loss of local fracture resistance of material, was also shown and discussed.

The dependence of the hydrogen concentration in metals on the surface impurities

In a recent paper we have shown that there is a difference in the concentration of hydrogen set up in a metal when it is exposed to a flux of atomic hydrogen as compared to the same flux of molecular hydrogen. Whereas in the case of molecular hydrogen one reaches an equilibrium situation in which the resulting concentration is a bulk property given by Sievert's law totally independent of the condition of the surface, in the case of an atomic flux the resulting steady state concentration becomes a surface dependent property governed to a large extent by the condition of the surface and the resulting surface potentials. In this paper I extend the model to the more realistic case of energetic hydrogen atoms which are implanted into the metal and discuss the consequences. Furthermore, I compare the interaction of the plasma with metals to electrolytic hydrogen charging and point out the similarities. Also in this case, due to surface impurity layers, one obtains high concentrations of hydrogen.

Nondestructive Determination of Local Hydrogen Concentration in Metals*

Nondestructive Determination of Local Hydrogen Concentration in Metals*