Operationalization of Topology of Sustainable Management to Estimate Qualitatively Different Regions in State Space

To apply the framework of Topology of Sustainable Management (TSM) by Heitzig et al. (2016) to dynamical models, we connect it to viability theory (VT) via a variant definition of the former. This enables us to use the Saint-Pierre algorithm to estimate the main partition of TSM, improving the operationalization of TSM. Furthermore, we present an extension of the algorithm to compute implicitly defined capture basins, a notion from VT that is more elaborated in the article, as these come up in TSM. We use a low- complexity model coupling environmental and socio-economic dynamics to demonstrate the applicability of this approach. Two common problems of estimations in VT are critical for this example: (i) an unbounded state space and (ii) highly varying time scales. We solve both by introducing appropriate coordinate transformations. These solutions are applicable for general systems, too

Couplage analyse thermogravimétrique et émission acoustique pour l'étude de la corrosion haute température

National audienceAfin d'améliorer les connaissances du comportement à haute température des matériaux, le couplage de plusieurs techniques d'analyse physique in situ est une voie prometteuse. Dans ce but, des thermobalances ont été équipées d'un appareil spécifi que de mesure des signaux acoustiques émis par les échantillons dont la variation de masse est continûment mesurée sous diverses atmosphères représentatives de conditions industrielles. Les corrosions de surface à haute température sont à l'origine d'émission d'ondes acoustiques générées lors de la croissance ou de la fi ssuration de couches formées. Des mesures simultanées in situ des variations de masse et des signaux acoustiques apportent donc des informations sur ces mécanismes de corrosion haute température. L'application de cette méthodologie aux mécanismes d'oxydation, réduction ou attaque par les atmosphères carbonées (cokage) est présentée dans ce document. Une perspective de ces études est de pouvoir établir des référentiels pour une éventuelle utilisation de l'émission acoustique pour l'étude de la corrosion des équipements fonctionnant à haute température. // In order to improve the knowledge on the high temperature behaviour of materials, the coupling of in situ physical analysis is a promising way. For this purpose, thermobalances have been equipped with specific devices to measure the acoustic signals emitted by samples for which the mass variation is continuously recorded under simulated industrial atmospheres. The high temperature corrosion of materials surfaces generates acoustic emission signals associated to the growth or the cracking of the formed layers. In situ simultaneous measurements of the mass variation and the acoustic signals give information on the high temperature corrosion mechanisms involved. In this document, this methodology has been applied to the study of oxidation, reduction or attacks under carbon-rich atmosphere (coke deposition). These studies could lead to reference data for a possible application of acoustic emission for the corrosion monitoring of high temperature equipments

O2 contamination in SSC / HIC test environments. Impact on test results and discussion on acceptable limits for high H 2 S content

International audienceIt is a well admitted fact that oxygen contamination shall be avoided during H 2 S cracking tests of low alloy steels. In the 2016 revisions of NACE TM0177 and NACE TM0284 documents, quantitative limits of O 2 contamination were included with thresholds at 10 and 50 ppb of dissolved oxygen depending on the considered mechanical properties of the tested grade. However, the scientific basis of these values are not well established and there is still a lack of experimental data to illustrate the potential impacts of an oxygen pollution. In addition, while the revised test methods explicitly address initial contamination of the test solution before H 2 S introduction, they do not consider a continuous oxygen supply during testing. Yet, continuous contamination is extremely difficult to be completely eliminated. In order to better understand the impact of O 2 contamination on H 2 S cracking, a 3-years Joint Industrial Project was launched at the end of 2015. The objectives were to evaluate if O 2 contamination can affect H 2 S cracking test results. A range of steel grades covering different types of O&G applications for High H 2 S content were used. SSC (uniaxial tensile tests as well as 4 point-bend) and HIC tests were conducted, with well controlled and continuous O 2 contamination. Three levels of O 2 partial pressures in the gas feed corresponding to 300 ppb, 50 ppb and less than 10 ppb dissolved O 2 were used. In parallel to the standard qualification tests, hydrogen permeation and weight-loss corrosion experiments were performed with the same test matrix, covering all regions of the SSC severity diagram. This paper aims at sharing the main results of this project for high H 2 S content

Prediction of the flexible pipe annulus pH at high CO2 content and high temperature

International audiencePrevious works have shown that the typical ratio between the volume of electrolyte and the exposed steel surface observed in the annulus of flexible pipelines leads to a specific corrosive environment whose pH deviate from the classical thermodynamic models. In this case, due to the supersaturation in iron ions in the annulus, the commercial models even with their most recent updates cannot precisely predict the measured pH. Due to these specificities, tests are necessary to overcome these limitations and to improve with a better accuracy the pH considered in the design of the flexible pipes. Nowadays, with the development of the Brazilian oil and gas pre-salt basins, a high CO2 partial pressure associated with high temperature are observed in the flexible pipe annulus. Due to the lack of experimental data concerning the pH evolution under these conditions, tests were carried out with a continuous pH monitoring at CO2 partial pressure and temperature up to, respectively, 70 bara and 84 °C. The test results presented in this article show an amplitude between the experimental data and the predicted pH values of at least +0.4 pH units which confirms the conservatism of the thermodynamic models at saturation. In all the tests, the pH reached a maximum value after the first days of immersion followed by a decrease and fast stabilization after this event. An impact of the temperature was verified on the pH behavior in these tests. Keywords Flexible pipes; annulus pH; high pressure; high temperature

Acoustic emission monitoring of wet H2S cracking of linepipe steels: Application to hydrogen-induced cracking and stress-oriented hydrogen-induced cracking

cited By 9International audienceAcoustic emission (AE) was used for monitoring steel cracking during exposure to wet hydrogen sulfide (H2S) environments. A method for filtering AE data related to hydrogen-induced cracking (HIC) was presented and applied for several case studies. In a series of tests on unstressed sweet service steels, evolution of AE indicated three successive HIC phases. An initial incubation period corresponded to hydrogen entry in the steel, during which no cracking occurred. Then two cracking phases were detected. The first was associated with decohesion of weak steel interphases. The second was identified as crack propagation under high internal hydrogen pressure. Crack propagation decreased and eventually ceased over time. Analysis of AE data was then used to evaluate the extent of HIC after sour exposure. Correlation was found when appropriate data filtering was applied. AE analysis was also applied to sour service steels under an applied load. The first steel exhibited HIC AE signals. Its fracture surface was typical of a stress-oriented hydrogen-induced cracking (SOHIC) mode of failure, in good agreement with AE results. For the second steel, which also failed during the test, no AE related to HIC was detected. Fracture surface was typical of sulfide stress cracking (SSC), also in good agreement with AE findings. © 2011, NACE International

Contribution of acoustic emission to the understanding of sulfide stress cracking of low alloy steels

cited By 17International audienceThe acoustic emission technique was applied to standard tests devoted to evaluate sulfide stress cracking susceptibility of steels for oil and gas industry. The mapping of the density of AE signals vs. their location on the specimen gauge length as a function of time allowed early detection of cracking, and gave meaningful information on incubation times and propagation rates. Sulfide stress cracking initiation was correlated with the presence of critical surface defects. A mechanism involving plastic strain and/or metal dissolution was proposed to account for crack propagation. © 2011 Elsevier Ltd

Exploring the limits of the self consistent Born approximation for inelastic electronic transport

The non equilibrium Green function formalism is today the standard computational method for describing elastic transport in molecular devices. This can be extended to include inelastic scattering by the so called self-consistent Born approximation (SCBA), where the interaction of the electrons with the vibrations of the molecule is assumed to be weak and it is treated perturbatively. The validity of such an assumption and therefore of the SCBA is difficult to establish with certainty. In this work we explore the limitations of the SCBA by using a simple tight-binding model with the electron-phonon coupling strength $\rm{\alpha}$ chosen as a free parameter. As model devices we consider Au mono-atomic chains and a $\rm{H_2}$ molecule sandwiched between Pt electrodes. In both cases our self-consistent calculations demonstrate a breakdown of the SCBA for large $\rm{\alpha}$ and we identify a weak and strong coupling regime. For weak coupling our SCBA results compare closely with those obtained with exact scattering theory. However in the strong coupling regime large deviations are found. In particular we demonstrate that there is a critical coupling strength, characteristic of the materials system, beyond which multiple self-consistent solutions can be found depending on the initial conditions in the simulation. We attribute these features to the breakdown of the perturbative expansion leading to the SCBA.Comment: 12 pages, 16 figures, 1 Tabl

Reversible catastrophic oxidation of a 38Fe-34Ni-25Cr alloy induced by sodium sulphate at low oxygen potential atmospheres

International audienceThe chromia-forming nickel-based alloy Haynes (R) HR-120 was oxidised with and without Na2SO4 deposit in a CO/H-2/CO2 (45/45/10%vol.) simulated process atmosphere at 900 degrees C for 96 h. During the first hours of oxidation, samples covered by sodium sulphate exhibit higher oxidation rate than non-covered ones. However, after 24 h both sulphate-covered and uncovered specimens follow the same linear kinetics. In this very low oxygen partial pressure environment (10(-18) atm), the presence of Na2SO4 promotes the growth of localized iron-rich oxide nodules leading to the observed accelerated oxidation. The development of these nodules is discussed to be the result of the chromia dissolution induced by a basic fluxing mechanism. As soon as the salt is evaporated, slower kinetics are observed and the nodules disappear. In these specific conditions, the oxidation could be considered as a self-healing process

Thermogravimetric experiments coupled with acoustic emission analysis dedicated to high-temperature corrosion studies on metallic alloys

International audienceHigh temperature corrosion of metallic alloys in industrial equipments, such as refinery and petrochemical equipments concerns several phenomena: oxidation, carburization... These phenomena can create stresses in the materials, the relaxation of which mostly produces transient elastic waves. Several methods enable the recording and analyzing of these transient elastic waves. Piezoelectric sensors fixed directly on the sample can record elastic waves with a low decrease in energy and frequency at ambient temperature. In case of high temperature environments, a waveguide can also be used to transmit waves from sample to sensors. For this purpose, alumina or platinum are mainly used as waveguide materials because these materials conserve the waveform. The goal of this study is to assign the elastic waves to the corrosion phenomena. This data base will then be useful for the monitoring of industrial equipment using acoustic emission methods. For this purpose, thermogravimetric analysis (TGA) has been coupled with acoustic emission (AE) devices. Simultaneous measurements of the mass variation and of the acoustic signals emitted during the corrosion of samples of the Zirconium based alloy Zircaloy 4 at high temperatures in the range of 400 °C to 900 °C can provide complementary information to increase the level of understanding of high temperature corrosion mechanisms. Our work focuses on a specific waveguide (WG) conception and on the transmission of elastic waves (acoustic signals) through the waveguide at high temperature. Results on experiments concerning the corrosion of zirconium alloy plates under oxygen atmosphere are presented

Corrosion and hydrogen permeation of low alloy steel in H2S-containing environments : the effect of test buffer solution chemistry

International audienceH 2 S-containing (sour) service environments present a considerable risk of hydrogen induced cracking (HIC) and sulfide stress cracking (SSC) to steel line pipe, pressure vessel and tubular components during upstream oil and gas production, through the ability of H 2 S to corrode and promote hydrogen entry into the material bulk via a cathodic reaction process. Materials selection for sour service is made via standard test methods such as NACE TM0284 and NACE TM0177. A commonly used test solution (NACE TM0177 solution A) comprises sodium chloride (5.0%) + acetic acid (0.5%), to work in a range between pH 2.8-4.0. When pH stability is essential over long testing periods, solutions that are buffered by acetic acid with sodium acetate are proposed. NACE TM0177 solution B (5.0% NaCl + 0.4% sodium acetate + 2.5% acetic acid) presents an initial pH of 3.4-3.6, specified not to exceed pH 4.0 over the testing duration. Newer, alternative solutions from the high-strength line pipe (HLP) research committee from the Iron and Steel Institute of Japan (ISIJ) propose higher acetic acid/acetate concentrations for enhanced buffering capacity. This may offer practical testing advantages, although material corrosion rates and hydrogen uptake are possibly affected. In this conference proceeding, we report on the corrosion and hydrogen uptake performance of a sour-grade X65 steel exposed to NACE Solutions A and B, and an HLP solution (at the same pH as NACE B solution, i.e. pH 3.5) under continuous H 2 S purging (0.1 MPa, T = 24°C) over 720 hours. Electrochemical methods measure electrochemical impedance at the entry face of, and hydrogen permeation across, the X65 membrane. Overall, the differences we note are linked to the different weak acid/conjugate base concentration. Keywords Hydrogen permeation, acetic acid, hydrogen sulfide, X65 steel