High-pressure Gas Environment Research Articles

Hydrogen-modified dislocation structures in a cyclically deformed ferritic-pearlitic low carbon steel

The fatigue-crack growth rate of a ferritic-pearlitic low carbon steel was faster when the tests were conducted in high-pressure H2 gas environments than in air. The predominant fracture feature changed from ductile fatigue striations with some “quasi-cleavage-like” regions when the test was conducted in air to mixed “quasi-cleavage” and “flat” facets when tested in a H2 gas environment. The microstructure beneath the fracture surfaces produced in air was sub-grains, and over a distance of 15 μm from the fracture surface, the dimensions of the sub-grains increased. With hydrogen, dense dislocation bands and refined dislocation cells existed beneath the “quasi-cleavage” and “flat” fracture surfaces. The cell size increased with distance from the fracture surface. The decrease in the dimensions of the key microstructural features as the fracture surface is approached is attributed to the propagation of the crack through an already deformed matrix. The differences in evolved dislocation structure are explained in terms of the hydrogen-enhanced localized plasticity mechanism, and the hydrogen-modified dislocation structure establishes the local conditions that promote the fracture mode transition from ductile fatigue striations to a mixture of “quasi-cleavage” and “flat” features, which directly leads to enhanced fatigue-crack growth.

Development of four-point bending fatigue test method using continuously hydrogen-charging pipe specimen

To evaluate hydrogen embrittlement, the following two types of testing method are available: (i) testing in high-pressure hydrogen gas environment and (ii) testing in ambient air using hydrogen precharged specimen. Testing in high-pressure hydrogen gas environment is technically difficult and expensive because high-pressure gas equipments, such as high-pressure vessel and pipe, have to be installed in the laboratory. On the other hand, in the case of precharging method, outgassing of hydrogen from the specimen occurs during the test. Therefore, hydrogen embrittlement can hardly be evaluated properly, especially, in long-term testing such as high cycle fatigue test at low frequency. In this study, to effectively evaluate the hydrogen embrittlement in fatigue, an experimental method, which was the four-point bending fatigue test system with a mechanism of internal circulation of hydrogen-charging solution in a pipe specimen, was developed. By using this method, the fatigue crack growth properties in the presence of hydrogen were investigated at frequencies of 0.05 Hz and 1 Hz.

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.

Analysis of geological materials containing uranium using laser-induced breakdown spectroscopy

Laser induced breakdown spectroscopy (LIBS) is a rapid atomic emission spectroscopy technique that can be configured for a variety of applications including space, forensics, and industry. LIBS can also be configured for stand-off distances or in-situ, under vacuum, high pressure, atmospheric or different gas environments, and with different resolving-power spectrometers. The detection of uranium in a complex geological matrix under different measurement schemes is explored in this paper. Although many investigations have been completed in an attempt to detect and quantify uranium in different matrices at in-situ and standoff distances, this work detects and quantifies uranium in a complex matrix under Martian and ambient air conditions. Investigation of uranium detection using a low resolving-power LIBS system at stand-off distances (1.6m) is also reported. The results are compared to an in-situ LIBS system with medium resolving power and under ambient air conditions. Uranium has many thousands of emission lines in the 200–800nm spectral region. In the presence of other matrix elements and at lower concentrations, the limit of detection of uranium is significantly reduced. The two measurement methods (low and high resolving-power spectrometers) are compared for limit of detection (LOD). Of the twenty-one potential diagnostic uranium emission lines, seven (409, 424, 434, 435, 436, 591, and 682nm) have been used to determine the LOD for pitchblende in a dunite matrix using the ChemCam test bed LIBS system. The LOD values determined for uranium transitions in air are 409.013nm (24,700ppm), 424.167nm (23,780ppm), 434.169nm (24,390ppm), 435.574nm (35,880ppm), 436.205nm (19,340ppm), 591.539nm (47,310ppm), and 682.692nm (18,580ppm). The corresponding LOD values determined for uranium transitions in 7Torr CO2 are 424.167nm (25,760ppm), 434.169nm (40,800ppm), 436.205nm (32,050ppm), 591.539nm (15,340ppm), and 682.692nm (29,080ppm). The LOD values determine for uranium emission lines using the medium resolving power (10,000λ/Δλ) LIBS system for the dunite matrix in air are 409.013nm (6120ppm), 424.167nm (5356ppm), 434.169nm (5693ppm), 435.574nm (6329ppm), 436.205nm (2142ppm), and 682.692nm (10,741ppm). The corresponding LOD values determined for uranium transitions in a SiO2 matrix are 409.013nm (272ppm), 424.167nm (268ppm), 434.169nm (402ppm), 435.574nm (1067ppm), 436.205nm (482ppm), and 682.692nm (720ppm). The impact of spectral resolution, atmospheric conditions, matrix elements, and measurement distances on LOD is discussed. The measurements will assist one in selecting the proper system components based upon the application and the required analytical performance.

SCM435 鋼陰極水素チャージ試験片の SSRT による水素脆性評価

Evaluation test of high-pressure hydrogen gas should be carried out more simplified. As an alternative approach in high-pressure hydrogen gas test, to simulate the hydrogen gas environment SSRT was performed with cathodically charged. Specimen was used a low-alloy steel, SCM435 with the tensile strength of 1000 MPa. The tensile properties was evaluated with cathodic charging with 3%NaCl solution and the current density of 50～600A/m2 . Values of RRA obtained by the tests at cathode current density of 400A/m2 are equivalent to those in the 35MPa hydrogen gas. In addition, an amount of diffusible hydrogen equivalent to that in high-pressure hydrogen gas was obtained by increasing the current density. Therefore, this approach is able to simulate the SSRT conducted in high-pressure hydrogen gas environment.

クロムモリブデン鋼を高圧水素ガス環境中で使用するための強度設計指針の提案

クロムモリブデン鋼を高圧水素ガス環境中で使用するための強度設計指針の提案

A setup for Ba-ion extraction from high pressure Xe gas for double-beta decay studies with EXO

An experimental setup is being developed to extract Ba ions from a high-pressure Xe gas environment. It aims to transport Ba ions from 10bar Xe to vacuum conditions. The setup utilizes a converging–diverging nozzle in combination with a radio-frequency (RF) funnel to move Ba ions into vacuum through the pressure drop of several orders of magnitude. This technique is intended for use in a future multi-ton detector investigating double-beta decay in 136Xe. Efficient extraction and detection of Ba ions, the decay product of 136Xe, would allow for a background-free measurement of the 136Xe double-beta decay.

Comparison of hydrogen embrittlement in three pipeline steels in high pressure gaseous hydrogen environments

The tensile properties of X52, X65, and X100 pipeline steels have been measured in a high-pressure (13.8MPa) hydrogen gas environment. Significant decreases in elongation at failure and reduction of area were observed when testing in hydrogen as compared with air, and those changes were accompanied by noticeable changes in fracture morphology. In addition to baseline characterization of the effects of strength and microstructure on the X52, X65, and X100 alloys, the influence of strain rate and hydrogen gas pressure was studied for only the X100 alloy.

Temperature measurements in a decaying laser-induced plasma in air at elevated pressures

This article discusses two measurement techniques for temperature determination of laser-induced plasmas in a gas at pressures relevant for combustion engines. Plasmas induced by laser breakdown in air at initial pressures ranging from 0.3 MPa to 2.5 MPa are investigated using optical spectroscopy. Results for 0.8 MPa, 1.2 MPa and 1.6 MPa are reported here. Due to the elevated pressure, a significant contribution from continuum radiation is apparent. The first temperature measurement technique relies on the interpretation of the continuum emission. The second technique is based on the line emissions from different elements and ionization stages in the plasma and is implemented with the multi-element Saha–Boltzmann plot method. The methodology may be applicable for temperature measurements under various conditions, e.g., for plasmas in high pressure gas environments such as in industrial applications of laser-induced breakdown spectroscopy or for plasma sources for illumination purposes. We investigate optimizations of laser-induced spark ignition. The energy released in the laser-induced plasma is determined based on temperature measurements.

Thermal stability of gas phase magnesium nanoparticles

In this work we present a unique transmission electron microscopy study of the thermal stability of gas phase synthesized Mg nanoparticles, which have attracted strong interest as high capacity hydrogen storage materials. Indeed, Mg nanoparticles with a MgO shell (∼3 nm thick) annealed at 300 °C show evaporation, void formation, and void growth in the Mg core both in vacuum and under a high pressure gas environment. This is mainly due to the outward diffusion and evaporation of Mg with the simultaneously inward diffusion of vacancies leading to void growth (Kirkendall effect). The rate of Mg evaporation and void formation depends on the annealing conditions. In vacuum, and at T=300 °C, the complete evaporation of the Mg core takes place (within a few hours) for sizes ∼15–20 nm. Void formation and growth has been observed for particles with sizes ∼20–50 nm, while stable Mg nanoparticles were observed for sizes >50 nm. Furthermore, even at relative low temperature annealing (as low as 60 °C), void formation and growth occurs in 15–20 nm sized Mg nanoparticles, indicating that voiding will be even more dominant for nanoparticles smaller than 10 nm. Our findings confirm that Mg evaporation and void formation in nanoparticles with sizes less than 50 nm present formidable barriers for their applicability in hydrogen storage, but also could inspire future research directions to overcome these obstacles.

256 高圧ガス中における遠心圧縮機羽根車の固有振動数(流体構造連成振動のメカニズムと計測制御,OS-22 流体関連振動・音響メカニズムと計測制御,総合テーマ「伝統を,未来へ!」)

To predict natural frequencies of high-pressure centrifugal compressor impellers accurately, we measured the natural frequencies of an impeller vibrating in a high-pressure gas environment. In order to clarify the effect of gaseous species, we used four different gasses as the surrounding gas. It is known that natural frequencies of pump impellers in water decrease compared with their natural frequencies in air due to the added mass effect. However, in our experiments in a high-pressure gas environment, the natural frequencies of the impeller not only decreased but also increased compared with those conducting under atmospheric condition.

Pulsed Power Technology for Pollution Control

Recently, the pulsed power technology led us to generate discharge plasma in high-pressure gas, liquid and solid environment. The discharge plasmas have a lot of functions such as an intense electric field, a large current flow, a chemically active radical formation, a shockwave generation, and an ultraviolet irradiation. Using the functions, the pollution control technologies, including exhaust gases treatment, ozone generation, water treatment, and material destruction or separation, were developed in laboratory. In the paper, the NO removal by ns pulsed discharge plasma and the aggregate recycling by the discharge inside of concrete would be introduced.

552 高圧ガス中における円板の固有振動数 : 軸方向隙間とガス種の影響

To predict natural frequencies of high-pressure centrifugal compressor impellers accurately, we measured the natural frequencies of an equivalent disc vibrating in a high-pressure gas environment. It is known that natural frequencies of pump impellers in water decrease compared with their natural frequencies in air due to the add mass effect. However, in our experiments in a high-pressure gas environment, the natural frequencies of the disc not only decreased but also increased compared with those operating under atmospheric condition. In order to clarify the effect of axial gap length and gaseous species, we set three ways of the axial gap length of our test apparatus and used four different gasses as the surrounding gas.

Estimate of Hydrogen Density at Starting Point for Crevice Corrosion and Cracking of Cold Rolled Type 304 Stainless Steel

AbstractIn the past work of authors, a cold rolled type304 stainless steel pipe with shot peening was prepared. A crevice was created between the outside of the pipe and an O-ring, and the pipe was applied stress by press fitting another part. Cracking from a crevice corrosion pit was observed in a chloride environment, and it was presumed to be Hydrogen Embrittlement-Stress Corrosion Cracking（HE-SCC）. Provided that the crack is caused by HE-SCC､it is thought that hydrogen is generated by corrosion reaction and the SUS304 pipe absorbs it more than its critical level. Generally, the hydrogen distribution in the steel is analyzed in the condition that the hydrogen concentration of the environment is constant as the high-pressure hydrogen gas environment etc. In the case of HE-SCC described above, however, the hydrogen concentration is presumed to change with pitting growth, and there is no example of analysis in such condition. In this work, cyclic corrosion tests were conducted using the samples with no press-fitting part. The hydrogen density at the initiation point of crevice corrosion and cracking was estimated by following technique. First, the amount of hydrogen diffused from the corrosion pit was measured using Thermal Desorption Spectroscopy（TDS ）, and the number of pits was measured. Then, the average hydrogen quantity in a pit was derived. On the other hand, it is thought that hydrogen is generated by the hydrolysis of a metallic salt and the cathode reaction of the hydrogen ion in the pit. Therefore, the amount of the hydrogen is proportional to the quantity of corrosion amount. Then, assuming that pitting corrosion takes the form of half sphere shape and grows with time, the simulation model was made that the hydrogen absorbed and diffused from the pit surface with the development of corrosion. The profile of the hydrogen density in SUS304 from pit initiation till crack initiation was calculated based on this model. The calculated profile of the hydrogen density was compared with the amount of hydrogen measured by cyclic corrosion test. As a result, the hydrogen concentration at the crack starting point was derived 0.3ppm. At this density level, He-SCC can occur in high strength SUS304.

Evaporation of a Binary Component Miscible Fuel Droplet on a Hot Surface in High Pressure Gaseous Environments

Evaporation of a Binary Component Miscible Fuel Droplet on a Hot Surface in High Pressure Gaseous Environments

THERMOELASTICITY: The use of thermoelastic stress analysis to identify defects in polymeric materials

The work described here emerged from an EPSRC-funded programme investigating the thermomechanical ageing of selected engineering plastics used in the offshore oil & gas industry. The polymers investigated are PEEK and PEK, materials of the polyaryletherketone family. The latest infrared array thermoelastic camera, coupled with an innovative five-times magnification zoom lens, was used to identify and quantify sub-surface defects in the materials, which had been aged in high pressure gas environments at elevated temperatures. The results were subsequently verified using a scanning electron microscope. The work demonstrates that Thermoelastic Stress Analysis (TSA) is a powerful technique, capable of identifying defects of less than 100 microns in size. The observed defects arise from so-called 'explosive decompression' (ED) damage; here absorbed pressurised gas can cause swelling, blistering and fracturing of non-metallic materials when the external pressure is rapidly reduced. ED is a significant industry issue for sealing elastomers, meaning that thermoplastics receive relatively little research attention.

Surface processing of CdTe crystals by an excimer laser and its application in fabricating nuclear radiation detectors

Excimer laser based surface processing of CdTe crystals is investigated in two different ways, namely laser ablation and laser enhanced impurity doping, for their applications in fabrication of nuclear radiation detectors. Micro-pattering on CdTe surface is performed by irradiating the laser through a shadow mask placed on the CdTe in a high vacuum condition. On the other hand, single pulse laser irradiation on the thin In-layer evaporated CdTe surface at a high-pressure argon gas environment produced an In-doped n-type thin surface layer. Finally, a strip type CdTe nuclear imaging detector was constructed by utilizing these two distinct features of excimer laser. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Monitoring chemical reactions at a liquid–solid interface: Water on CuIn(S,Se)2 thin film solar cell absorbers

The chemical and electronic structure of the interface between liquid water and a CuIn(S,Se)2 thin film surface was studied with synchrotron-based, high energy-resolution soft x-ray emission spectroscopy (XES). By probing the local environment around the sulfur atoms, an x-ray-induced sulfate formation at the CuIn(S,Se)2 surface can be monitored, correlated with a substantial enhancement of sodium impurity atoms from the CuIn(S,Se)2 film and its glass substrate. The results demonstrate that, with XES, an experimental probe is available to in situ study chemical reactions at liquid–solid interfaces or at surfaces in a high-pressure gas environment in a chemically sensitive and atom-specific way.

Ultrafast Reaction Dynamics in Different Environments

We review recent work done on the femtosecond time-resolved investigation of the influence of solvation on elementary molecular and reaction dynamics of solvated molecules. Using the photo dissociation reaction of I2 and NaI molecules as models, the solvation effect is studied for varying environments. By adding inert gases (He, Ar, N2) at pressures ranging from 0 to 3000 bar, the dynamics is studied starting from isolated molecules, going steadily to solvent-like conditions. Clearly different reaction behaviour can be found when comparing I2 and NaI. While I2 molecules predissociate due to the collisions with the surrounding gas particles and afterwards recombine due to the caging effect, NaI is stabilized in its adiabatic potential well formed by the first excited electronic state and the ionic ground state. I2 is also embedded in a solid matrix, formed by a crystalline porosil. For I2 in both cases the recombination dynamics is studied by varying the probe wavelength. The experimental data are discussed using a theoretical model. For I2 in a high pressure gas environment, geminate primary and secondary recombination can be detected; in the porosils also nongeminate processes contribute on a very short time scale.

High power laser welding in hyperbaric gas and water environments

A hyperbaric laser welding facility has been constructed and the feasibility of high power CO2 and Nd:YAG laser welding in both high pressure gas and water environments, to simulated water depths of 500 m, has been established. From initial trials on welding through water at atmospheric pressure, it was found that the different absorption characteristics of water to 10.6 μm (CO2 laser) and 1.06 μm (Nd:YAG laser) radiation proved crucial. The Nd:YAG laser was totally unsuitable as the beam was largely diffused in the water, whereas the CO2 beam was readily absorbed and, using high speed video equipment, was found to form a high irradiance channel and a dry region around the weld area. Welding under a high pressure gas environment produced a highly energized plume which prevented keyhole welding at pressures over 1 × 106 Pa. An investigation carried out into the efficacy of a gas jet delivery system to alleviate the extent of the plume showed that argon blown horizontally across the weld was the optimum configuration, extending the welding range up to 5 × 106 Pa. A limited investigation into high pressure underwater welding showed porosity to be a problem although sound welds were produced at pressures up to 2 × 106 Pa.