Metallurgical and corrosion characterization of structural materials for S-I cycle

Tensile testing involving Alloy C-22 and Nb1Zr exhibited reduced strength with increasing temperature within a range relevant to the Hlx decomposition process. A reduction in failure strain was however, noted, at 100°C possibly due to dynamic strain aging effect. Even though the ductility parameters were not influenced by the change in temperature in stress-corrosion-cracking (SCC) testing in an acidic solution the true in this alloy was reduced appreciably. Nb1Zr did not exhibit any failure stress conventional SCC pattern. The critical potentials for localized corrosion in both alloys became more active at higher temperatures. No cracking was observed with C-ring and U-bend specimens of Alloy C-22 in a similar environment at 150°C. The corrosion rate of Alloy C-22 was gradually reduced for exposure up to 28 days followed by an enhancement at a longer duration. The characterization of primary fracture surface of cylindrical specimens used in tensile and SCC testing exhibited dimpled microstructure, indicating ductile failures

Corrosion and metallurgical behavior of alloy C-22 for high-temperature applications

Austenitic Alloy C-22 has been tested for evaluation of its tensile and corrosion properties under conditions relevant to the nuclear hydrogen generation process known as the sulfur-iodine cycle. The results of tensile testing indicate that this alloy may be capable of maintaining metallurgical stability and enhanced ductility at temperatures up to 600°C. The stress-corrosion-cracking data suggest that this alloy may not undergo cracking in an acidic solution at 90°C at constant-load, the true failure stress (of) was significantly reduced under a slow-strain-rate condition using both smooth and notched specimens. The magnitude of the critical potentials determined by a polarization technique became more active with increase in temperature. The application of anodic control potential resulted in enhanced cracking tendency of Alloy C-22 showing reduced ductility, failure time and sigmaf. The corrosion rate in a similar environment at 150°C was enhanced at longer test duration showing a nonlinear weight loss versus time relationship. The fractographic evaluations of the broken specimen by scanning electron microscopy revealed dimpled microstructure indicating a ductile failure

Characterizaton of Nb75Ta for Hix decomposition process

Nb7.5Ta, a candidate refractory material for use in the HI, decomposition process, has been tested for evaluation of its tensile properties and corrosion resistance. The results of tensile testing within a temperature range of ambient to 400°C revealed a gradual drop in tensile strength with increasing temperature. However, reduced failure strain was observed at temperatures up to 300°C, suggesting the occurrence of dynamic strain aging (DSA) behavior. The characterization of the tensile specimens by transmission electron microscopy showed somewhat higher dislocation density at 300°C that could be the result of the DSA effect. Corrosion studies under a slow strain rate condition in an acidic solution exhibited enhanced cracking tendency at 90°C, suggesting a detrimental effect of higher temperature on the cracking susceptibility. No failures were observed under a constant-load condition. An application of a cathodic controlled potential to the test specimen resulted in enhanced cracking tendency in terms of failure strain. The morphology of failure, determined by a scanning electron microscope, was ductile in all tested specimens

How Virginia Can Meet Its Clean Power Plan Targets

In August 2015, the U.S. Environmental Protection Agency (EPA) finalized the Clean Power Plan (CPP), the first-ever carbon pollution standards for existing power plants. The CPP builds on progress already under way to move the country toward a cleaner electricity system, including rapidly falling prices of renewables and increased deployment of moneysaving energy efficiency measures. The plan enables states to use a wide range of options to meet their standards, such as existing clean energy policies and power plants (the focus of this analysis), other tools to cut electricity use and increase the use of renewables, and broader initiatives such as participation in a capand- trade program or use of a carbon tax.This fact sheet examines how Virginia can use its existing policies and infrastructure to meet its emission standards under the Clean Power Plan while minimizing compliance costs, ensuring reliability, and harnessing economic opportunities

Characterization of alloy C-276 as a structural material for high-temperature heat exchangers

This investigation was focused on characterizing the high-temperature tensile behavior and corrosion susceptibility of nickel-based Alloy C-276, a leading structural material for heat-exchangers in nuclear hydrogen generation. The tensile properties, evaluated at different temperatures, indicate that both the yield strength and ultimate tensile strength were gradually reduced with increasing temperature. However, the ductility parameters were not significantly influenced by the testing temperature. While no failures were observed in stress corrosion cracking (SCC) tests in an acidic solution under a constant-load, the true failure stress (sigmaf) was significantly reduced under a slow-strain-rate condition using both smooth and notched specimens. The critical potentials, determined in a similar environment by an electrochemical method, became more active at the elevated temperature. Cracking was enhanced at anodic and cathodic applied potentials, showing reduced failure strain and sigmaf. The fractographic evaluations of the primary fracture surface revealed dimpled microstructures, indicating ductile failures

Effects of metallurgical and environmental variables on the performance of alloy 718 for heat exchanger applications

Austenitic Alloy 718 was extensively investigated, evaluating its tensile properties, crack-growth-rate (CGR), impact resistance, and resistance to stress-corrosion-cracking (SCC) and localized corrosion. The tensile data enabled a development of mechanisms on dynamic strain aging (DSA) and yield strength anomaly (YSA). The magnitudes of dislocation density, activation energy and work-hardening index, related to the DSA phenomenon, were estimated using different analytical approaches. The occurrence of YSA was verified based on transmission electron microscopic evaluations. The steady state CGR followed the Paris equation, showing a linear relationship. Alloy 718 exhibited a respectable impact resistance irrespective of the testing temperature. The SCC susceptibility of this alloy was enhanced in the 90°C acidic solution, showing reduced ductility and true failure stress. The corrosion potential, measured by polarization technique, became more active with increasing temperature. The failure morphologies of all tested specimens were characterized by scanning electron microscopy

Applying the Pennsylvania Environmental Rights Amendment Meaningfully to Climate Disruption

The Pennsylvania Constitution contains a unique Environmental Rights Amendment (ERA), which recognizes an individual right to “clean air, pure water, and to the preservation of the natural, scenic, historic and esthetic values of the environment.” The ERA also includes a public trust element that makes “Pennsylvania’s public natural resources . . . the common property of all the people, including generations yet to come.” It makes the Commonwealth the “trustee of these resources,” requiring it to “conserve and maintain them for the benefit of all the people.” Recent decisions by the Pennsylvania Supreme Court (the Court) in Robinson Township v. Commonwealth and Pennsylvania Environmental Defense Foundation v. Commonwealth provide significant support for Pennsylvania regulations to address the threat of climate disruption posed by greenhouse gas (GHG) emissions to achieve net zero carbon emissions by the middle of this century. In light of the threats that climate disruption poses to Pennsylvania’s public natural resources, the text of the ERA, and the principles articulated in those recent cases, we argue that a stable climate (a climate that has not been disrupted by anthropogenic emissions of GHGs) should be considered protected by the rights recognized by the ERA, and the public trust duties it creates. We argue that these rights and duties require Pennsylvania to employ regulatory measures to reduce GHG emissions to the level warranted by the social cost of carbon and to achieve carbon neutrality (net zero emissions) by mid-century. Further, we argue that there are judicially recognizable standards to compel the Commonwealth to exercise its existing authority to limit GHG emissions. In light of existing legislative authority, the obligations imposed by the United Nations Framework Convention on Climate Change, the Paris Agreement, and the federal Clean Air Act, we make the case that this regulatory program should take the form of an economy-wide cap-and-trade program providing for the auction of allowances with a reserve price based on the social cost of carbon and additional measures to prevent leakage and a cap reaching carbon neutrality by mid-century

Stress Corrosion Cracking and Hydrogen Embrittlement of Martensitic Alloy EP-823

This investigation is focused on the evaluation of stress corrosion cracking (SCC), localized corrosion, and hydrogen embrittlement (HE) susceptibility of martensitic Alloy EP-823 in neutral and acidic solutions at ambient and elevated temperatures. While no failures were observed in smooth specimens in the neutral solution, failures were noticed in the 90°C acidic solution at constant-load (CL) leading to a threshold stress (O\u27th) of 102 ksi. The presence of a notch reduced the O\u27th value to 91 ksi in a similar environment. The ductility (%El and %RA), time-to-failure (TTF), and true failure stress (O\u27r) were gradually reduced in both environments with increasing temperature during SSR testing. The presence of a notch, however, enhanced the O\u27r value. All polarized specimens exhibited localized attack. The application of a controlled cathodic potential further reduced the ductility, TTF and O\u27r showing the characteristics of more brittle failures. Metallographic and fractographic evaluations revealed secondary cracks along the gage section, and combination of ductile and brittle failures at the primary fracture face, respectively. Il

The effect of nitrite on pitting and stress corrosion cracking of corrosion resistant alloys (CRA) under oil field conditions

The need to inject treated seawater to enhance reservoir pressure and secondary oil recovery is increasing in the oil field, so also is the reservoir souring potential caused by the activities of Sulphate Reducing Bacteria (SRB) generating H2S in the reservoir. The total cost of SRB mediated corrosion in the United States alone is estimated to be 1-2 billion US dollars per year. In the last few years, a number of potential souring mitigation and prevention tools have been studied. These include: sulphate-reduction using membranes, biocide injection and nitrate injection. Out of all the various methods used for the mitigation and prevention of reservoir souring, the use of nitrate injection in conjunction with waterflood projects is becoming more popular because of its economic benefits and least environmental impact. However, nitrate injection is still widely considered as an emergent technology because there are still many unknowns. One of the major unknowns, of great concern is the susceptibility of subsea hardware components to nitrite, which is a by-product of nitrate anti-souring treatment. Any detrimental effect can compromise the technical integrity of subsea installations. The objective of this research is to study the corrosion susceptibility of CRA (13Cr- Martensitic, 22Cr, and 25Cr super duplex stainless steel) to pitting and stress corrosion cracking in the presence of nitrite. Research hitherto, has investigated corrosion susceptibility of carbon steel to nitrite and found out that nitrite causes pitting in carbon steel. This research work built on previous studies and extensively investigated the effect of nitrite on CRA materials in terms of pitting and stress corrosion cracking. Using electrochemistry techniques in conjunction with C-ring test and slow strain rate test, with variables such as temperature, and nitrite concentration all under anaerobic conditions. Metallographic examination and further evaluation using scanning electron microscopy confirmed pitting and intergranular stress corrosion cracking of 13Cr-L80 and 25Cr due to presence of nitrite.Test data confirmed that sodium nitrite is an anodic inhibitor; it shifts the corrosion potentials to more noble potential and also shifts the anodic curve to lower current, given a net reduction in corrosion rate. A critical concentration of 400ppm is required for inhibition to be effective on 13Cr-L80 and 25Cr. However, below the critical concentration, nitrite significantly increases the corrosion rate. The experimental data generated from this research work provides very valuable information that will tremendously assist the materials selection process for subsea and subsurface hardware components and also serve as a guide in the corrosion management process in existing systems.EThOS - Electronic Theses Online ServiceYyconnect Consulting, Inc.Shell International Exploration and ProductionGBUnited Kingdo

Foundations of Session Types and Behavioural Contracts

International audienceBehavioural type systems, usually associated to concurrent or distributed computations, encompass concepts such as interfaces, communication protocols, and contracts, in addition to the traditional input/output operations. The behavioural type of a software component specifies its expected patterns of interaction using expressive type languages, so that types can be used to determine automatically whether the component interacts correctly with other components. Two related important notions of behavioural types are those of session types and behavioural contracts. This paper surveys the main accomplishments of the last twenty years within these two approaches