Les aciers inoxydables lean duplex, à faible teneur en nickel et sans molybdène, représentent une alternative économique pour les usines de dessalement et l’industrie pétrolière. Celles-ci ont la particularité d’être exposées à des milieux très agressifs dont la présence de chlorure, de sulfure d’hydrogène, de hautes températures ou encore d’acides peut provoquer des phénomènes de fissuration sous contrainte.Cette étude est divisée en deux parties, la première se consacre aux milieux purement chlorurés et la seconde aux milieux contenant du sulfure d’hydrogène. Dans les deux parties, la compréhension des phénomènes liés à la fissuration sous contrainte des lean duplex est effectuée sur la nuance S32304, puis est comparée aux comportements des nuances S32202 et S32101. L’influence des milieux bouillants sur la résistance à la fissuration des aciers inoxydables, les mécanismes de dépassivation et de dissolution sélective des lean duplex, les différents modes de fissuration en présence de sulfure d’hydrogène ou encore l’amorçage de la corrosion sous contrainte assistée par le sulfure d’hydrogène sont abordés dans ce rapport. / Lean duplex stainless steels, with low content of nickel and without molybdenum, represent an economic alternative for desalting plants and petroleum industry. For these uses, steel have the particularity to be exposed to very aggressive environments inducing phenomenon of Stress Corrosion Cracking as chlorides, hydrogen sulphur, high temperatures or acids.This study is divided in two parts dedicated to two different environments. The first part is devoted to chloride middles and the second to hydrogen sulphur middles. In both parts, the understanding of phenomenon linked to the stress corrosion cracking of lean duplex is studied on the grade steel S32304, then is compared to the behaviour of grade steels S32202 and S32101. The topics treated in this report are notably the influence of boiling environments on the cracking resistance of stainless steels, the mechanism of unpassivation and selective dissolution of lean duplex, the different modes of cracking in presence of hydrogen sulphur, and the initiation of stress corrosion cracking assisted by hydrogen sulphur

This thesis deals with corrosion problems of underwater turbines in marine environment. The effect of a tensile stress on the uniform corrosion rate of a metal bar is studied, and an analytical model predicting the time of service of a bar under a tensile load in a corrosive environment is proposed. Stress corrosion relationships are provided for different type of alloys, and different types of relationships. Dolinskii's and Gutman's models are studied and extended to a general order polynomial, along with a Least Square and Spline Interpolation of the experimental data. In a second part, the effect of the passive film, delaying the initiation of the corrosion process, is studied. Finally, an algorithm predicting the time of service of a cracked bar is provided, using the stress corrosion assumption, along with a validation using experimental data. / by Yohann Miglis. / Thesis (M.S.C.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2012. Mode of access: World Wide Web.

Kam Tat-ting. / Thesis (M.Phil.)--Chinese University of Hong Kong. / Bibliography: leaves 111-113.

This research evaluated corrosion and scale deposition in steel and copper pipe sections from apartment complexes located in Rhode Island (RI), Massachusetts (MA), and Maryland (MD). Piping samples from these locations had corroded at an accelerated rate and consisted of HVAC piping, and domestic copper pipes. Pipes were analyzed by scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS) to quantify the elemental composition of the samples. The water chemistry of each system was compared to the elemental data to determine correlations. Particular elements from the EDS analysis in comparison to the water quality parameters, Langelier Saturation Index, and Larson Skold indices exhibited inverse and direct correlations. The deposition of corrosion product and scales occurred in all systems that had implemented corrosion control in the form of pH adjustment and inhibitors to prevent infrastructure degradation. Although measures were taken to prevent corrosion, the current practices were not effective at the current dosing rate showing that the municipalities could consider other options such phosphate blend inhibitors and lime as effective corrosion control mechanisms.

Although many organic compounds are known to inhibit corrosion, in most cases it remains unknown how they specifically interact with a surface and how they decrease the corrosion rate. This lack of mechanistic knowledge currently makes the design and choice of new active compounds a case of trial and error. Understanding these organic molecule-metal surface interactions could lead to the design of new corrosion inhibitors for the oil and gas industry. In this project it is intended to move the understanding of corrosion inhibition and other surface phenomena from empirical observation towards a mechanistic understanding. Using a combination of surface sensitive techniques such as vibrational sum frequency generation and X-ray photoelectron spectroscopy, and theoretical modelling through the preparation of model complexes of relevant corrosion inhibitors. Two families of corrosion inhibitors have been studied and are presented here. For nitrogen based corrosion inhibitors a combination of theoretical calculations and experimental analysis of vibrational modes of model compounds have proved to be a good method to assist in understanding of surface phenomena. For phosphorus based corrosion inhibitors an extensive study of model compounds has been done. In addition to this, different phosphonic acids and phosphate esters have been studied on a Fe (110) and steel surfaces in ultra high vacuum and in more realistic conditions using near ambient pressures in order to investigate if changes in the environmental conditions lead to a different behaviour. These have been compared to the study of PAE 136, a commercial corrosion inhibitor composed by a mixture of phosphate esters used in the extraction of oil, proving that one of the selected model compounds has a better inhibitive activity in both an ideal and a more realistic system. The results presented in this thesis demonstrate that every corrosion inhibitor needs to be tested in the conditions in which it is going to be used as it is not possible to predict if a given active compound is going to have the same behaviour for different environments.

This study combined research available through literature with extensive experimental studies and substantial physical modelling to estimate the remaining ultimate life of large offshore reinforced concrete structures. Although much research has focussed on concrete degradation due to chloride ingress, corrosion of permanently submerged concrete is regarded as negligible due to the long-assumed apparent worst case of tidal or splash zone exposure. Around 350 specimens were tested with a further 200 exposed for further testing by future research groups. Specimens ranged in size from standard cubes to various beam lengths up to 1.5 metres, allowing for material and structural properties to be assessed. My original contribution to knowledge in the sector enhances the fundamental understanding of corrosion in subsea concrete, challenging the generally held belief of negligible corrosion. Results and modelling provides an improved ability to ultimately estimate the longevity of fully submerged offshore reinforced concrete. Throughout this thesis, the results from experimental works, carried out as a direct result of the lack of data or information in literature, are reported, assessed and then utilised to provide updated ultimate life estimations. With the current offshore concrete structures currently coming to the end of their service life, and the likelihood of further offshore development using concrete for the renewables sector, understanding the long-term degradation is vital in determining the most effective decommissioning and derogation options. The research carried out directly provides detailed information of the likely time-to-failure, allowing for an informed decision to be made on operational and decommissioning plans. Experimental work was carried out over four main phases; corrosion initiation due to bulk diffusion of chlorides (Phase I), corrosion propagation in low oxygen environments (Phase II), corrosion in statically and dynamically cracked sections (Phase III) and structural response of heavily corroded individual and lapped bar sections (Phase IV). Phase I work shows a marked difference between submerged exposures to seawater as opposed to NaCl solution, the unsuitability for accelerated testing with seawater and the likelihood of rapid initiation in offshore structures. Further experimental works through Phases II and III found that although exposed to low oxygen concentrations, reinforcement corrosion continued at significant rates. A variation between anode sizes on the reinforcement is noted, but critically the cross sectional area of the steel was still reduced, albeit in fewer locations. Corrosive products were visibly different, with fewer expansive products, if any, present. Additionally, this study further highlights the importance of cracking on corrosion, currently ignored by recent model codes, such as the fib Model Code 2010, up to 0.2mm crack width. A linear relationship was found between crack width and corrosion rates, with cracking above 0.1mm considered significant. The loss of cross sectional area due to propagation was determined for the given environment, and consequently further studies were initiated in an attempt to determine the relationship between this corrosion propagation and the reduced serviceability or ultimate life of concrete beams. Serviceability, defined by beam stiffness, was reduced due to bond loss along reinforcement. Most importantly, however, results prove that the loss of cross sectional area to be the critical influence on loss of ultimate life. Initial estimates on the remaining ultimate life of the large offshore structures support early rough work that the structures would last centuries. This thesis, however, has shown this is due to the ability of concrete structures with such large volumes of steel to continue to ultimately withstand loading at high corrosion percentages and not due to negligible corrosion, or long initiation periods, commonly suggested in submerged, low oxygen environments.

This research was conducted to better understand the corrosion propagation stage on dry-cast reinforced concrete pipes (DCRCPs) while exposed to high moisture conditions and chlorides. Corrosion initiation and propagation were studied in instrumented specimens obtained from segments of dry-cast reinforced concrete pipes. All specimens were subjected to accelerated chloride transport by the application of an electric field. Corrosion of the steel wire mesh initiated after a few days to a few months rather than several years. The specimens were then transferred to high moisture environments (immersed in water, high humidity and/or covered with wet sand) during the corrosion propagation stage. Reinforcement potentials, linear polarization resistance (LPR) and Electrochemical Impedance Spectroscopy (EIS) measurements were carried out periodically. During the propagation stage in different exposures, reinforcement eventually reached negative potentials values (< –-0.55 Vsce), which suggest mass transfer limitations. These specimens showed no visual signs of corrosion such as cracks or corrosion products except the ones exposed to high humidity and laboratory environments; where some corrosion products have reached the concrete surface. Moreover, the apparent corrosion rate values obtained suggest high corrosion rates. No crack appearance on specimens exposed to other conditions could be explained by the porosity of the specimens; the corrosion products moved into saturated pores. It is speculated that although there might be mass transfer limitations present, the current demanded by the anode is being balanced by a larger cathode area due to macrocell effects since the high moisture conditions likely reduced the concrete resistivity and increased the throwing power. The corrected polarization resistance (Rc) was calculated by subtracting the solution resistance from the apparent polarization resistance measured. The Rc values measured over time were used to obtain the calculated mass loss (using Faraday’s Law). Most specimens were forensically analyzed and the measured mass loss compared to the calculated mass loss. The forensic examination includes the measurement of the actual corroding areas. The measured corroding areas were used to obtain corrosion current density (icorr) values. A comparison was made of the calculated corrosion current densities obtained using the linear polarization resistance method (LPR) and the extrapolation method from cyclic polarization tests. It was evident that most of the specimens’ corrosion rates were significantly high. The corrosion products filled the wet-pores inside the concrete and provide an explanation for no cracks or corrosion bleed outs being visually observed on the specimens. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

Corrosion can take place as chloride ions accumulate above a critical concentration (CT) at the surface of a reinforcing bar inside concrete in marine service. The initiation of corrosion can be delayed by polarizing the steel cathodically, which is known to increase the value of CT. That effect is the basis of the cathodic prevention (CPrev) method to control corrosion of reinforcing steel in concrete. However, concrete cracks are a common occurrence and at cracks, the buildup of chloride ions is accelerated to the extent that CPrev may be less effective. The findings from an ongoing investigation to determine the effectiveness of cathodic prevention on cracked concrete exposed to a marine environment are presented. Experiments were conducted on reinforced concrete blocks with controlled-width cracks placed along the length of a central reinforcing steel bar. A ponding area on top of each specimen allowed for cyclic exposure to a 5% NaCl solution to imitate a marine environment. Crack widths ranging from 0.01 inch to 0.04 inch and polarization levels ranging from -330 mV to -540 mV were used. The onset of corrosion as a function of time of exposure was determined by measurements of the cathodic current demand needed to reach each target polarization level. The ranking of time to onset of corrosion was used as an indicator to determine how much cathodic prevention is necessary to effectively extend the life of cracked concrete. Results to date suggest that a minimum cathodic polarization level in the range of -540 mV would be needed.

The demand for hydrogen as a clean energy carrier has increased greatly. The Cu-Cl cycle is a promising thermochemical cycle that is currently being developed to be the large-scale method of hydrogen production. The lifetime of materials for the pipes transporting molten CuCl is an important parameter for an economic design of a commercial thermochemical Cu-Cl hydrogen plant. This research is an examination of candidate materials following an immersion test in molten CuCl at 500 °C for 100 h. Two alloys, Ni based super-alloy (Inconel 625) and super austenitic stainless steel (AL6XN) were selected as the base metal. There were two types of coating applied to improve the corrosion resistance of the base metals during molten CuCl exposure. A metallic of Diamalloy 4006 and two ceramic of yttria stabilized zirconia and alumina coatings were applied to the base metal using thermal spray methods. An immersion apparatus was designed and constructed to perform an immersion test that has a condition similar to those in a hydrogen plant. After the immersion test, the materials were evaluated using an electrochemical method in combination with ex-situ surface analysis. The surface condition including elemental composition, film structure and resistivity of the materials were examined and compared. The majority of the coatings were damaged and fell off. Cracks were found in the original coated specimens indicating the sample geometry may have affected the integrity of the sprayed coating. When the coating cracked, it provided a pathway for the molten CuCl to go under the coating and react with the surface underneath the coating. Copper deposits and iron chloride that were found on the sample surfaces suggest that there were corrosion reactions that involved the metal dissolution and reduction of copper during immersion test. The results also suggest that Inconel 625 performed better than stainless steel AL6XN. Both Diamalloy 4006 and YSZ (ZrO2 18TiO2 10Y2O3) coatings seemed to provide better protection to the underlying base metal than alumina (Al2O3 3TiO2) coating. / UOIT

The recovery boiler in a pulp and paper mill plays a dual role of recovering pulping chemicals and generating steam for either chemical processes or producing electricity. The efficiency of producing steam in the recovery boiler is limited by the first melting temperature of ash deposits that accumulate on the superheater tubes. Above the first melting temperature, the molten salt reacts with the protective oxide film that develops and dissolves it. The most protective oxide is determined by evaluating how little it dissolves and how its solubility changes in the molten salt. Solubility tests were done on several protective oxides in a known salt composition from a recovery boiler that burns hardwood derived fuel. ICP-OES was used to measure concentration of dissolved metal in the exposure tests while EDS and XRD were used to verify chemical compositions in exposure tests. NiO was found to be the least soluble oxide while Cr₂O₃ and Al₂O₃ had similar solubility with Fe₂O₃ being less soluble than Cr₂O₃ but more soluble than NiO. Exposure tests with pure metals and selected alloys indicated that even though Fe₂O₃ has little solubility, it is not a protective oxide and causes severe corrosion in stainless steels. The change in performance of iron based alloys was due to the development of a negative solubility gradient for Fe₂O₃ where Fe₂O₃ precipitated out of solution and created a continuous leaching of oxide. Manganese was found to be beneficial in stainless steels but its role is still unknown. Nickel based alloys were found to be least corroded due to nickel's low solubility and because it did not form a negative solubility gradient.