Innovative Materials Testing Technologies (United States)

Abstract It is recognized that oxygen gas impurities can inhibit the deleterious effects of hydrogen gas on mechanical properties of steels. Most commonly, the effect of oxygen on hydrogen assisted fatigue has been studied. An increase in the measured hydrogen-assisted fracture toughness has been reported to result from oxygen gas impurities, but few efforts have been made to understand how much oxygen can be present in hydrogen gas without altering measured fracture toughness values. Routine measurements of the post-test oxygen content has revealed various instances where the measured oxygen content was unintentionally higher than expected. This paper will present some of these chance observations in which unintentionally elevated oxygen levels resulted in elevated fracture toughness measurements. Oxygen concentrations as low as 0.1 part per million have been observed to effectively inhibit hydrogen assisted fracture under certain conditions. These observations indicate the extreme importance of understanding and controlling the levels of trace oxygen impurities in hydrogen gas during fracture toughness measurements to avoid anomalously high measurements. Finally, it should be noted that these observations apply only to fracture measurements performed at laboratory test time scales (typically measured in hours); it is not currently understood whether similar trace levels of oxygen will inhibit crack growth in structures operated over operational time scales measured in months to years.

Appendix 1. Estimating allocation parameters with limited data. Appendix 2. Disequilibrium supply-and-demand dynamics. Vensim Replication model for lambda dispatch with a markup and data-supported output curves. Vensim Allocation model to reproduce study results and to extract equations for reuse. DSM-DOC for Vensim Allocation model. R code and example data files to generate Appendix 1 results. R code for general use to estimate QCT parameters in Appendix 1. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Abstract The service life of high-pressure hydrogen storage vessels at fueling stations is dictated by fatigue crack growth. Standards such as the ASME Boiler and Pressure Vessel Code (BPVC) provide a methodology for calculating the fatigue-limited design life of high-pressure hydrogen storage vessels, in which one essential input is the fatigue crack growth rate (da/dN) vs. stress-intensity factor range (ΔK) relationship measured for the material of construction in the service environment, i.e. hydrogen gas. These measurements must also be conducted at sufficiently slow cyclic loading frequency since decreasing the frequency usually results in faster crack growth rates. Generation of complete fatigue crack growth data sets according to standard test methods becomes very time consuming and expensive when these environment and frequency criteria are met. Two modifications to standard test procedures may reduce the time and associated costs related to this testing. One approach is to accelerate the rate at which ΔK changes with respect to crack extension. This can be accomplished by controlling the normalized K-gradient, C, where C = 1/K·dK/da. In addition, by using negative values of C (i.e. decreasing ΔK), multiple da/dN vs ΔK segments can be generated from a single test specimen. This paper summarizes the status of a project designed to identify the limits to which these two strategies may be employed to measure fatigue crack growth relationships for pressure vessel steels in gaseous hydrogen environments. These limits are defined as the bounds where loading history effects begin to alter the measured da/dN vs ΔK relationships.

Circumferentially notched specimens of several austenitic stainless steel alloys subjected to positive load ratio, load-controlled fatigue have been cycled to failure in high pressure hydrogen gas. The number of cycles to failure for a given applied stress amplitude varies among the alloys tested indicating that control of fatigue life in hydrogen environments may be attained through informed alloy selection. The number of cycles to initiate a crack does not vary significantly among the alloys tested, however the total life to failure varied by over an order of magnitude. This difference in life is attributed to variations of the stress and strain fields ahead of the blunt notch. These fields are influenced by the strength and strain hardening characteristics of each alloy and they dictate the driving force for fatigue crack growth while the crack is small.

Transitions in flow regimes that can occur in drinking water contact tanks may significantly affect the disinfection efficiency of the system. To demonstrate these effects, the authors investigated the internal velocity fields and flow regime of a drinking water contact tank located in Jamestown, Colo. The baffling factor (BF) of the system fluctuated annually between 0.5 and 0.6 because of a shift in flow regime caused by changes in the flow rate of the system. The authors studied the effects of the regime change from laminar to turbulent flow (or vice versa) using computational fluid dynamics (CFD) models and physical tracer studies. Several inlet modifications were then investigated using CFD to determine which alteration would be most beneficial. Key findings showed that with proper inlet modification, the BF of the system could be stabilized at 0.6 during periods of high or low flow.

The objective of this work is to enable the safe design of hydrogen pressure vessels by measuring the fatigue crack growth rates of ASME code-qualified steels in high-pressure hydrogen gas. While a design-life calculation framework has recently been established for high-pressure hydrogen vessels, a material property database does not exist to support the analysis. This study addresses such voids in the database by measuring the fatigue crack growth rates for three heats of ASME SA-372 Grade J steel in 100 MPa hydrogen gas at two different load ratios (R). Results show that fatigue crack growth rates are similar for all three steel heats and are only a mild function of R. Hydrogen accelerates the fatigue crack growth rates of the steels by at least an order of magnitude relative to crack growth rates in inert environments. Despite such dramatic effects of hydrogen on the fatigue crack growth rates, measurement of these properties enables reliable definition of the design life of steel hydrogen containment vessels.

A growing number of educators worldwide have become convinced that geotechnologies – including geographic information systems (GIS), global positioning systems (GPS), and remote sensing – are key technologies to prepare students to be tomorrow's decision makers. Grappling with local, regional, and global issues of the 21st century requires people who think spatially and who can use geotechnologies. Some educators teach geotechnologies as a discipline, emphasising skills. Other educators use geotechnologies as a tool to teach content, such as geography, history, environmental studies, Earth Science, biology, mathematics, economics and other disciplines. Issues such as traffic, population growth, urban sprawl, energy, water, crime, human health, biodiversity and sustainable agriculture are growing in complexity, exist at every scale and increasingly affect people's everyday lives. Each of these issues has a spatial component. Drivers for geotechnology education include educational content standards, constructivism, the school-to-career movement, active learning, citizenship education, authentic practice and assessment, interdisciplinary education, community connections and a sustained, increasing demand for GIS professionals. Digital Earth is an ideal framework for contextualising domains of inquiry. The Digital Earth community can have a significant impact on the growth of geotechnologies in education, and conversely, the growth of geotechnologies in education and society can foster the forward movement of Earth systems concepts.

The Remote-Field Eddy-Current Technique (RFECT) has recently been applied for detecting deeply hidden cracks and corrosion in samples simulating multi-layer aluminum aircraft structures. Experimental measurement results have shown high sensitivity of the RFECT system in these applications. For example, the system can detect a 0.03″ long fatigue crack on a fastener hole located on the bottom surface of the bottom layer. The crack is located 0.446″ below the inspection surface. The second example shows that when scanning a multiple layer aluminum sample with total thickness of 0.29″, the RFECT system can detect wall thinning as small as 1% of the total thickness.