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The deleterious effect of hydrogen on steel is a long-standing problem. Embrittlement in the presence of hydrogen is, in part, a consequence of the fast diffusion of hydrogen in ferritic steels. Because of the identical chemical properties but large differences in mass between hydrogen isotopes, interaction of hydrogen isotopes with steel structures are of interest as a tool to study the role of diffusion in hydrogen embrittlement under all-else-equal conditions. In this paper, we present tensile and fatigue data for steel samples measured in air, in hydrogen, and in deuterium. Tensile measurements show deuterium causes a loss of ductility comparable to the loss due to hydrogen. In fatigue, a large pressure effect on deuterium-assisted fatigue crack growth was observed, an effect which is not exhibited in uniaxial tensile measurements. With sufficient pressure to show an enhanced fatigue crack growth effect, the fatigue crack growth rate is well-predicted assuming a scaling of the diffusion coefficient by 1 / 2 . These results suggest surface adsorption kinetics play a large role in hydrogen-assisted fatigue crack growth at low pressure. At higher pressures, hydrogen-assisted fatigue crack growth is primarily affected by the kinetics of diffusion of hydrogen within the steel lattice.

Strain-life testing of a 4130 pressure vessel steel was conducted in hydrogen gas through the careful adaptation of an existing hydrogen-gas mechanical-testing apparatus. The strain-life mechanical results reveal that hydrogen has a significant effect on the strain-life, and impacts both the elastic and plastic responses of the material. Microscopy analysis shows a distinct difference in the microstructural development of the material after cyclic loading in air compared to after loading in hydrogen gas. These experimental results will inform coupled damage and deformation modeling.

This work aims to create finite element models to simulate the three ISO 11114-4 test methods applicable to hydrogen gas cylinders, coupled with calibrated constitutive models, to predict the deformation response of each. Experimental measurements are used to calibrate a monotonic constitutive model and a constitutive model of cyclic deformation. Six finite element solid models are discussed: monotonic tensile test of dog bone-shaped specimens, strain-controlled fatigue test of dog bone-shaped specimens, ISO test Method A, ISO test Method B, and ISO Method C (from ISO 11114-4), and a gas cylinder. Each finite element solid model is paired with the appropriate constitutive model based upon loading conditions. The modeling results are then combined with a new damage parameter in an attempt to compare each of the test methods to the others, as well as to in-service conditions. It is shown that the proposed damage parameter may be used to correlate all test methods considered (except for ISO Method A, a burst-disc test) as well as in-service conditions. The calibrated damage parameter may be coupled with any geometry, loading condition, and boundary condition modeled within a finite element package to predict the onset of critical damage in the material for which the coupled constitutive model is calibrated to. Parametric modelling study results provide estimated cycles to the onset of crack extension for DOT 3AA cylinders having varying sizes of internal thumbnail-shaped cracks. This work provides the baseline for measurements and models in air, with similar work in hydrogen to follow.

The economical and efficient transportation of hydrogen gas is necessary for it to become a widespread source of energy. One way to improve the economics is to lower the cost of building hydrogen gas pipelines. The recent modification to the ASME B31.12 Code for Hydrogen Piping and Pipelines begins to lower the cost of building pipelines for hydrogen service by allowing the use of high-strength steel that will provide the same margin of safety with thinner pipe walls. Less steel directly impacts the cost of materials and welding. A means of improving efficiency would be to increase the hydrogen gas pressure to augment the volume of products transmitted through the pipeline. The recent B31.12 code modification characterized dozens of fatigue crack growth test results conducted in hydrogen gas pressurized up to 21 MPa with an upper boundary of fatigue crack growth rate (FCGR), defined as a function where all measured FCGRs fall below this boundary. In this study, different pipe geometries, strengths, and pressures with established design protocols were evaluated to determine if the code would require further modifications should linepipes be designed for higher hydrogen gas pressures, up to 34 MPa. It was shown through a numerical exercise that the code could be minimally modified and safety margins would be adequate for those pressures for steels up to and including API-5 L Grade X70.

A comprehensive testing program to determine the fatigue crack growth rate (FCGR) of pipeline steels in pressurized hydrogen gas was completed. Four steels were selected, two X52 and two X70 alloys. Other variables included hydrogen gas pressures of 5.5 MPa and 34 MPa, a load ratio, R, of 0.5, and cyclic loading frequencies of 1 Hz, 0.1 Hz, and 0.01 Hz. Of particular interest was whether the X70 materials would exhibit higher FCGRs than the X52 materials. The American Petroleum Institute steel designations are based on specified minimum yield strength (SMYS), and monotonic tensile tests have historically shown that loss of ductility correlates with an increase in yield strength when tested in a hydrogen environment. The X70 materials performed within the experimental spread of the X52 materials in FCGR, except for the vintage X52 material at low (5.5 MPa) pressure in hydrogen gas. This program was developed in order to provide a modification to the ASME B31.12 code that is based upon fatigue, the primary failure mechanism in pipelines. The code modification is a three-part Paris law fit of the upper bound of measurements of FCGR of pipeline steels in pressurized hydrogen gas. Fatigue crack growth data up to 21 MPa (3000 psi) are used for the upper bound. This paper describes, in detail, the testing that formed the basis for the code modification.

Hydrogen will likely play a key role in a future clean energy economy. However, fundamental understanding of the deleterious effects of hydrogen on the fatigue and fracture properties of pipeline steels is lacking. Furthermore, engineering tools for design and lifetime prediction of pipeline steels in gaseous hydrogen are yet to be developed and implemented into national codes. A constitutive model that couples deformation and hydrogen-diffusion, supporting a phenomenological predictive model for fatigue crack growth, is presented for pipeline steels in high-pressure gaseous hydrogen. The semi-empirical model is predicated upon the hypothesis that one of two mechanisms dominates the fatigue crack growth response, depending upon the applied load and the material’s hydrogen concentration. The model correlates test results well, and illustrates how the deformation mechanisms contribute to fatigue crack propagation in pipeline steels in environments similar to those found in-service.

This work proposes a phenomenological fatigue crack propagation (FCP) model for API-5L X100 pipeline steel exposed to high-pressure gaseous hydrogen. The semi-empirical model is predicated upon the hypothesis that one of two mechanisms dominate the fatigue crack growth (FCG) response depending upon the crack extension per cycle ( da / dN ) and the material hydrogen concentration. For da / dN between approximately 1 × 10 −5 mm/cycle and 3 × 10 −4 mm/cycle, fatigue crack growth in hydrogen is markedly increased over that in laboratory air, resulting in a Paris exponent over two and a half times that of air and producing a predominately intergranular crack propagation surface. Fatigue crack growth in hydrogen at da/dN above approximately 3 × 10 −4 mm/cycle result in FCP rates over an order of magnitude higher than that of lab air. The Paris exponent in this regime approaches that of lab air and the crack morphology is predominately transgranular. Increasing the hydrogen test pressure from 1.7 MPa to 20.7 MPa increases the FCG rate by as much as two, depending upon the stress intensity factor. It is proposed that the FCG response in hydrogen at da / dN −4 mm/cycle is primarily affected by the hydrogen concentration within the fatigue process zone, resulting in a hydrogen-dominated mechanism, and that the FCG response in hydrogen at da / dN >3 × 10 −4 mm/cycle results from fatigue-dominated mechanisms. The proposed model predicts fatigue crack propagation as a function of applied Δ K and hydrogen pressure. Results of fatigue crack growth tests in gaseous hydrogen as well as fracture morphology are presented in support of the proposed model. The model correlates well with test results and elucidates how the proposed mechanisms contribute to fatigue crack propagation in pipeline steel in environments similar to those found in service.

Hydrogen is known to have a deleterious effect on most engineering alloys. It has been shown repeatedly that the strength of steels is inversely related to the ductility of the material in hydrogen gas. However, the fatigue properties with respect to strength are not as well documented or understood. Here, we present the results of tests of the fatigue crack growth rate (FCGR) on API X70 from two sources. The two materials were tested in air, 5.5 and 34 MPa pressurized hydrogen gas, and at both 1 and 0.1 Hz. At these hydrogen pressures, the FCGR increases above that of air for all values of the stress intensity factor range (ΔK) greater than ~7 MPa · m1/2. The effect of hydrogen is particularly sensitive at values of ΔK below ~15 MPa · m1/2. That is, for values of ΔK between 7 and 15 MPa · m1/2, the FCGR rapidly increases from approximately that found in air to as much as two orders of magnitude above that in air. Above 15 MPa · m1/2, the FCGR remains approximately one to two orders of magnitude higher than that of air.

A high pressure, electron-beam directed-vapor deposition process has been used to deposit partially stabilized zirconia containing 7% mass yttria at deposition pressures of 7.5–23 Pa. Anisotropic, ultra-small-angle X-ray scattering (USAXS) was then used to determine the surface area, shape and orientation of pores within the coatings. The total surface area of the ellipsoidal shaped pores was found to increase with deposition pressure. However, the through-thickness thermal conductivity measurements reveal the existence of a minimum thermal conductivity in coatings deposited at an intermediate pressure. Observations of the anisotropic X-ray scattering intensity at this intermediate pressure indicated greater proportions of both feather-like (oblate) pores with their major dimension at about 60° to the plane of the coating and fine columnar (prolate) pores oriented perpendicular to the coating plane. Since these oblate pore orientations are most efficient at impeding conductive thermal transport through the coating, it is believed that the change in preferred pore orientations with pressure is responsible for the higher thermal resistance of coatings grown in the intermediate pressure regime.

We demonstrate the rapid growth of grains in nonpassivated, sputtered Al-1 at. pct Si interconnects during 200 Hz thermal cycling induced by alternating current. Mean grain diameters were observed by use of automated electron backscatter diffraction (EBSD) to increase by more than 70 pct after an accumulated cycling time of less than 6 minutes over a temperature range of 200 °C, which corresponded to a total strain range of 4 × 10−3. Plasticity in growing grains primarily took the form of topography formation at the free surface and grain rotation, while consumed grains tended to retain relatively high dislocation content. Grain growth was characterized by means of pairwise comparisons in EBSD pattern quality across moving boundaries. Out of 92 cases where a grain was observed to grow into its neighbor, 61 cases indicated that the growing grain had a higher average pattern quality factor than that of the consumed grain, at the 95 pct confidence level. The results are consistent with a strain-induced boundary migration mechanism, wherein stored plastic strain energy differences from grain to grain drive growth, some of which was observed after only 10 seconds of cycling.

Experiments studying cardiovascular geometries require a working fluid that matches the high index of refraction of glass and silicone, has a low viscosity, and is safe and inexpensive. A good candidate working fluid is diethyl phthalate (DEP), diluted with ethanol. Measurements were made of index of refraction and viscosity of varied dilutions at a range of temperatures, and empirical models are proposed. Material compatibility tests showed that only specific formulations of ABS, acrylic, vinyl and PVC are compatible. A silicone elastomer additionally tested negative for change in compliance with DEP exposure.

A tribometer at the National Institute of Standards and Technology in Boulder, Colorado is used to measure the coefficient of friction and the wear rate for various specimens in a controlled atmosphere of oxygen or non-corrosive gas. The wide range of demonstrated operating temperature of 80 to 1030 K is presently unavailable in any commercial apparatus. The machine uses ball-on-flat or ring-on-flat specimen geometries for comparison of conforming and non-conforming contacts. The tribometer can be loaded to produce a hertzian contact stress in excess of 12 GPa (1.7×10 6 Ibf in −2 ) and surface velocities from 0.06 m s −1 to 4.0 m s −1 . A range of environmental conditions this wide is unusual, especially the temperature range. The apparatus is described and some test results are compared with known values.

AISI 440C martensitic stainless steel is the material of choice for the high pressure oxygen turbopump (HPOTP) of the space shuttle main engine (SSME). Tests have been done over a range of sliding speeds from 0.5 to 2.0 m s−1, initial hertzian stresses from 0.915 to 3.66 GPa, and bulk temperatures from −184 °C (liquid oxygen temperature) to 760 °C, which cover the variations thought to exist in the HPOTP. Data are presented in the form of contour wear maps to allow a more direct view of the interdependencies of the major tribological variables than can be obtained with wear data presented vs. a single variable. Wear maps are used as a tool to aid in the determination of regions dominated by a given wear mode. Parametric combinations that result in transitions between wear modes are more easily detected with the use of wear maps. Wear maps can simplify design by identifying combinations of speed, load, and bulk temperature that need to be avoided, because of undesirable wear modes.

Unlubricated sliding friction and wear of 440C steels in an oxygen environment have been studied under a variety of load, speed, and temperature ranging from approximately -185 to 675 deg C. A specially designed test apparatus with a ball-on-flat geometry has been used for this purpose. The observed dependencies of the initial coefficient of friction, the average dynamic coefficient of friction, and the wear rate on load, speed, and test temperatures have been examined from the standpoint of existing theories of friction and wear. High contact temperatures are generated during the sliding friction, causing rapid oxidation and localized surface melting. A combination of fatigue, delamination, and loss of hardness due to tempering of the martensitic structure is responsible for the high wear rate observed and the coefficient of friction.