In applications where resistance to localised corrosion is required, stainless steel alloys containing molybdenum are generally used thanks to their superior resistance to localised attack in aggressive environments. For ferritic stainless steels, vanadium additions have been found to also have a beneficial effect on the resistance to localised corrosion. In this study vanadium and molybdenum were compared directly as alloying elements in 18% chromium ferritic stainless steel as far as their effect on increasing the resistance to localised corrosion is concerned. Pitting potentials in a neutral chloride solution were used as the criterion for qualifying resistance to localised corrosion and it was shown that vanadium gave similar or slightly higher pitting potentials at addition levels of up to 4% (weight percent). It was subsequently found that the mechanism by which the molybdenum and the vanadium increase the resistance to localised corrosion, are not the same. The experimental data for the molybdenum containing alloys corresponded well with other work done in this field. The positive effect of molybdenum additions on the pitting resistance of these alloys could be explained through its effect in lowering the dissolution rate in the active dissolution region by enriching on the dissolving surface. The vanadium additions to these alloys were shown not to have an effect on the active dissolution kinetics. The effect of these two alloying elements on the initiation of metastable pits were examined, but no meaningful advantage for the vanadium containing alloys over the rest could be found. It is suggested that vanadium play a role in changing the dissolution kinetics of the salt film, which forms during the growth of a metastable pit. A delayed dissolution of salt film remnants would lead to a loss of the enriched pit solution, which would cause the metastable pit to repassivate. / Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / unrestricted

The Florida Department of Transportation (FDOT) has been using supplementary cementitious materials while constructing steel reinforced concrete marine bridge structures for over three decades. It has been found from previous studies that such additions in concrete mix makes the concrete more durable. This research was conducted to better understand the corrosion propagation stage of steel rebar embedded in high performance concrete exposed to high humidity environment. Reinforced concrete samples that were made with binary mixes, and ternary mixes were considered. None of these concretes had any admixed chloride to start with. An accelerated chloride transport method was used to drive chloride ions into the concrete so that chlorides reached and exceed the chloride threshold at the rebar surface and hence the corrosion process initiated after a short period of time (within few days to few months). Once corrosion has initiated the corrosion propagation can be studied. Electrochemical measurements such as rebar potential measurements, Linear Polarization Resistance (LPR), Electrochemical Impedance Spectroscopy (EIS), and Galvanostatic Pulse (GP) measurements were taken at regular intervals (during and after the electro-migration process) to observe the corrosion propagation in each sample. During the propagation stage, reinforcement eventually reached negative potentials values (i.e., Ecorr≤ –0.200 Vsce) for all the samples. The corrected polarization resistance (Rc) was calculated by subtracting the concrete solution resistance from the apparent polarization resistance measured. The Rc values obtained from LPR and GP measurements were converted to corrosion current (as the corroding area is unknown), and these corrosion current values measured over time were used to obtain the calculated mass loss (using Faraday’s Law). A comparison was made of the calculated corrosion current obtained using the LPR and GP tests. A comparison of mass loss was also obtained from the values measured from LPR and GP tests. From the experimental results, it was observed that the corrosion current values were largely dependent on the length of solution reservoirs. For specimens cast with single rebar as well as three rebars, the most recent corrosion current values (measurements taken between July 2018 to October 2020) in general were larger for the rebars that are embedded in specimens prepared with SL mix, followed by specimens prepared with FA, T1, and T2 mixes respectively. The range of corrosion current values (most recent) were 0.8-33.8 μA for SL samples, 0.5-22.5 μA for FA samples, 0.8-14.8 μA for T1 samples, and 0.7-10.4 μA for T2 samples respectively. It was also found that the calculated mass loss values were larger for rebars that are embedded in specimens (single rebar and three rebars) prepared with SL mix, followed by specimens prepared with FA, T1, and T2 mixes respectively. The range of calculated mass loss values were 0.07-1.13 grams for SL samples, 0.06-0.62 grams for FA samples, 0.12-0.54 grams for T1 samples, and 0.06-0.40 grams for T2 samples respectively. A variety of corrosion related parameters (Ecorr, Rs, Rc, and Icorr) and calculated theoretical mass loss values observed, were due to the changing parameters such as concrete compositions, concrete cover thickness, rebar diameter, total ampere-hour applied, and reservoir size. The specimens showed no visual signs of corrosion such as cracks or corrosion products that reached the concrete surface. The actual size of the corroding sites was unknown as the specimens were not terminated for forensic analysis. The size of the corroding sites could affect how much corrosion products are required to crack the concrete. It is speculated that the corrosion products in liquid form penetrated the pore structure but did not build up enough to cause cracks. No cracks or corrosion bleed outs were observed within the monitored propagation period of approximately 1600 days. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

As an alternative to the present toxic chromate-based coating system now in use, the Mg-rich primer technology has been designed to protect Al alloys (in particular Al 2024 T3) and developed in analogy to Zn-rich primers for steel substrate. As an expansion of this concept, metal-rich primer systems based on Mg alloy particles as pigments were studied. Five different Mg alloy pigments, AM60, AZ91B, LNR91, AM503 and AZG, were characterized by using the same epoxy-polyamide polymer as binder, a same dispersion additive and the same solvent. Different Mg alloy-rich primers were formulated by varying the Mg alloy particles and their pigment volume concentrations (PVC). The electrochemical performance of each Mg alloy-rich primer after the cyclic exposure in Prohesion chamber was investigated by electrochemical impedance Spectroscopy (EIS). The results indicated that all the Mg alloy-rich primers could provide cathodic protection for AA 2024 T3 substrates. However, the Mg alloys as pigments in metal-rich primers seemed to exhibit the different anti-corrosion protection performances, such as the barrier properties, due to the different properties of these pigments. In these investigations, multiple samples of each system were studied and statistical methods were used in analyzing the EIS data. From these results, the recommendation for improved EIS data analysis was made. CPVC studies were carried out on the Mg alloy-rich primers by using three Mg alloy pigments, AM60, AZ91B and LNR91. A modified model for predicting CPVC is proposed, and the results showed much better agreement between the CPVC values obtained from the experimental and mathematical methods. Using the data from the AM60 alloy pigment system, an estimate of experimental coarseness was done on a coating system, the first time such an estimate has been performed. By combining various surface analysis techniques, such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and confocal Raman microscopy, the oxidation products formed after exposure were identified. It was found that variation of Al content in Mg alloy could significantly affect the pH of the microenvironment in the primer films and result in the formation of various oxidation products. / Air Force Office of Scientific Research (Grant No. 49620-02-1-0398)

As an alternative to the present toxic chromate-based coating system now in use, the Mg-rich primer technology has been designed to protect A1 alloys (in particular A1 2024 T3) and developed in analogy to Zn-rich primers for steel substrate. As an expansion of this concept, metal-rich primer systems based on Mg alloy particles as pigments were studied. Five different Mg alloy pigments. AM60, A719B, LNR91, AM503 and AZG, were characterized by using the same epoxy-polyamide polymer as binder, a same dispersion additive and the same solvent. Different Mg alloy-rich primers were formulated by varying the Mg alloy particles and their pigment volume concentrations (PVC). The electrochemical performance of each Mg alloy-rich primer alter the cyclic exposure in Prohesion chamber was investigated by electrochemical impedance Spectroscopy (EIS). The results indicated that all the Mg alloy-rich primers could provide cathodic protection for AA 2024 T3 substrates. However, the Mg alloys as pigments in metal-rich primers seemed to exhibit the different anti-corrosion protection performances, such as the barrier properties, due to the different properties of these pigments. In these investigations, multiple samples of each system were studied and statistical methods were used in analyzing the EIS data. From these results. the recommendation for improved EIS data analysis was made. CPVC studies were carried out on the Mg alloy-rich primers by using three Mg alloy pigments, AM60, A2918 and LNR91. A modified model for predicting CPVC is proposed, and the results showed much better agreement between the CPVC values obtained from the experimental and mathematical methods. Using the data from the AM60 alloy pigment system, an estimate of experimental coarseness was done on a coating system, the first time such an estimate has been performed. By combining various surface analysis techniques, such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and confocal Raman microscopy, the oxidation products formed alter exposure were identified. It was found that variation of A1 content in Mg alloy could significantly affect the pH of the microenvironment in the primer films and result in the formation of various oxidation products. / Air Force Office of Scientific Research (AFOSR) (Grant No. 49620-02-1-0398)

The main objective of this work is to establish an analytical model to evaluate the rate of corrosion in a horizontal pipe downstream of an orifice under flow-accelerated corrosion (FAC). FAC is a serious issue in nuclear and fossil power plants. In this work, an experimental setup was built to observe the effect of the flow on corrosion inside a tube. The experiments confirmed that the flow inside the tube caused more corrosion. However, accurate experimental data from literature has been selected and correlated by dimensional analysis, the modelling method of repeating variables and the Buckingham Pi theorem. It was found that the Sh number and the relative distance from the orifice are the main dimensionless parameters influencing FAC downstream of an orifice. The maximum value of the FAC rate could be well-predicted for the OR of 0.25, while the location of the maximum FAC rate could be well predicted for the OR of 0.5. The maximum FAC rate occurs between 2D to 4D downstream of the orifice and increases with a decreasing OR. This work could be useful for professionals in industry and researchers in the field and could be the starting point for a new way of evaluating the FAC rate downstream of a flow’s singularity. / Dissertation (MSc)--University of Pretoria, 2017. / Mechanical and Aeronautical Engineering / MSc / Unrestricted

Technological advances are required to reduce the environmental impact of the Canadian oil sands. Oxy-direct contact steam generation (DCSG) is one such way to move toward this goal, by producing steam for oil sands operations with a higher efficiency, lower fresh water consumption, and lower CO₂ emissions than traditional once-through steam generators. For DCSG, untreated process water, which may contain a variety of inorganics, is injected directly into the combustor to produce steam. The inorganic material that may deposit in the combustor as a result of that process water was studied for two applications of DCSG in the Canadian oil sands: (1) steam assisted gravity drainage (SAGD), and (2) mining, in order to inform refractory material selection for the combustor. For SAGD, free water knockout tank discharge was used as the process water and resulting deposits in the combustor were predicted to be high in silica and sodium oxide, and enriched with sodium sulfate as the potential operating temperature of the combustor was lowered. At the lowest combustor temperature studied (1075 °C), a low viscosity molten salt phase rich in sodium sulfate was also expected to form. It is recommended that the operating temperature of the combustor be as low as possible while still remaining above the formation temperature of this potentially corrosive salt phase, thus in the range of 1200-1250 °C in the regions of the wall where solids are expected to impact it. A number of candidate refractory materials were assessed through corrosion models and corrosion tests. Aluminosilicate based refractory materials should be avoided due to their potential reaction with the sodium oxide in the slag. This can result in formation of low density solid phases such as nepheline, which can damage the refractory material through volume expansion. Of the three refractories tested, mullite zirconia yielded the worst corrosion resistance, with dissolution of the binder phase and full penetration by sodium oxide. Chromia corundum yielded the greatest resistance to penetration of the materials tested, though some dissolution of the chromia in the slag was still evident. Further investigation into high chrome refractory materials is recommended for this application. For mining applications, mature fine tailings water (MFT) combined with an oil sands processing water (OPW) was used as the process water for injection. Due to the high liquidus of the resulting inorganic deposits, co-injection of a fluxant is recommended to reduce the liquidus and viscosity of the resulting slag solution, thereby maximizing the combustor efficiency by reducing the required operating temperature. Dolomite was identified as the optimal fluxant, at a concentration of 20 wt % CaMgO₂ in the fluxed slag. This mixture was found to have a viscosity of just under 25 Pa·s at 1300 °C, making this a good operating point for the DCSG combustor, as the slag should flow freely and not cause plugging. The corrosion resistance of several candidate refractory materials was assessed through modelling and laboratory scale testing for both the fluxed and non-fluxed slag. Similar to the results for SAGD, of the refractories tested, chromia corundum offered the greatest resistance to penetration, while mullite zirconia was most deeply penetrated by sodium oxide. Again, a chromia-containing refractory is recommended for further investigation for use in the DCSG combustor. Other candidate refractories investigated in the models that warrant testing are chromia spinel and magnesium aluminate spinel. For future work, further corrosion tests at multiple durations are recommended, as well as characterization of refractory samples from CanmetENERGY’s DCSG pilot plant and quantification of the effects of slag exposure on the mechanical strength of the refractory materials.

Les alliages légers (Al, Mg) sont aujourd’hui majoritairement utilisés dans les industries aéronautique, électronique, automobile. Toutefois, la faible résistance à la corrosion et à l’abrasion de ces alliages restreint leur développement à grande échelle. Les nouveaux concepts de protection contre la corrosion des alliages légers se basent non seulement sur un effet barrière par une couche épaisse d'oxyde (PEO) ou peindre, mais surtout sur une protection active à l’aide d’inhibiteurs de corrosion spécifiques. Ces inhibiteurs de corrosion pourraient être libérés "sur demande" et génèrent un phénomène ‘d’auto guérison’. L’utilisation des méthodes d’analyse in situ and ex situ modernes spectroscopiques pourraient permettre de mettre en lumière l’évolution de systèmes aussi complexe et aider à mieux définir les facteurs régulant ces processus. / Nowadays light alloys (Al, Mg) are widely used in a number of areas such as electronics, aeronautic, automotive and construction industries. However, the low corrosion and wear resistance of these alloys hinders application of Al and Mg alloys on a larger scale. The new concepts for corrosion protection of light alloys should include not only barrier protection by a thick oxide layer (PEO) or by paint but also an active protection by specific corrosion inhibitors which can be released “on request” and ensure so-called “self-healing”. Use of in situ and ex situ spectroscopic methods could bring a new view to the evolution of such a complicated system and help to define factors controlling these processes.

Heat exchanger tubes are commonly made from stainless steel.In a heat exchanger both the process fluid and the cooling orheating media can be corrosive. It is therefore important to beable to select materials that do not suffer from corrosion.Current methods in this area, however, suffer from limitationsand shortcomings. This thesis concerns corrosion tests forgeneral corrosion, dewpoint corrosion and stress corrosioncracking, respectively. For evaluation of general corrosion ofsuperduplex stainless steels in hydrochloric acid and sulphuricacid the importance of activation was studied. The results showthat activation has a great influence on the test result.Further the results indicate that experimental differences canbe the explanation for previously reported differences incorrosion resistance of superduplex stainless steel that havebeen attributed to the alloying with Cu and W. Furthermore, asimple test loop for testing stainless steels under dew formingconditions with a formed condensate of 1 % hydrochloric acidhas been developed. In the work constant strain and constantload test result have been compared and the observationsindicate that the differences can be explained by differencesin the relaxation properties of the materials. <b>Key words:</b>corrosion testing, heat exchanger, stainlesssteel, general corrosion, immersion tests, activation, stresscorrosion cracking, constant load, u-bends, relaxation,dewpoint corrosion / NR 20140805

Underground pipelines are used in various process piping systems to transport gasses or fluids and are usually subjected to the effects of external corrosion. Corrosion can be defined as the deterioration of a material due to a reaction with its environment or the destruction of the material by means that are not mechanical (Fontana and Greene, 1967:2). External corrosion, due to the interaction between the pipe and the soil, is generally a slow process and the corrosion rate is influenced by a variety of external factors. Some of these factors include the ambient pH and salinity, the presence of moisture and bacteria, temperature, the electrical potential difference between the pipe and other structures and the implementation of preventative measures (such as cathodic protection and wrapping). Although the external corrosion of underground pipelines is generally a slow process in mild environments, pipe degradation as a result of external corrosion remains one of the prevalent reasons for the failure of underground pipelines. As with many mechanical systems that are prone to fail at one time or the other, the high costs involved with unforeseen failure necessitate some quantitative (or qualitative) indication of the condition of the pipe system. Some of the costs that can be expected as a result of unforeseen pipeline failure are, amongst others: • costs as a result of the failure of dependent systems; • costs as a result of the loss of production; • costs as a result of the loss of product (in distribution networks); • the cost of unscheduled maintenance (logistical costs); • costs as a result of damage to public property; • fines imposed by customers (in distribution networks); • costs related to pollution control, and • the loss of life The single most important parameter associated with the condition of a system is its profitable remaining life. This is the time during which a sub-system contributes to the well-being of a larger system and the organisation. Therefore, it is necessary to determine, with reasonable accuracy, the extent of the remaining life of a system so that managerial decisions (i.e. investments, cash-flow analyses, maintenance task scheduling and replacement programmes), based on this figure, can be made. Done correctly, this can directly lead to a decrease in maintenance costs and subsequently to an increase in profit. The extent of a corrosive attack on the pipeline might be highly localised or might be fairly uniform over the length of the installation. The fact of the matter is that, since the pipe is buried, it is very difficult to quantify the external damage caused by corrosion. A variety of techniques are in use to survey pipelines and detect anomalies. However, for large pipelines, most of these techniques are either inefficient or too expensive. There will always remain some uncertainty regarding the integrity of the pipeline. The work presented in this study is explained with valid generic examples and aims: 1. to provide the reader with sufficient background information so that the need for determining the integrity of a pipeline becomes apparent; 2. to indicate why a reliability-centred approach is necessary (Chapter 1); 3. to explain the basic principles of corrosion and the electrochemical nature of corrosion (Chapter 2); 4. to indicate areas, based on the basic principles of corrosion, where severe corrosion can be expected (Chapters 2 and 7); 5. to provide and elaborate on information regarding pipe surveillance techniques that are currently available (Chapter 3); 6. to establish the criteria for pipeline failure, in the form of a limit state Junction, for pipes that are subjected to near-constant internal pressures (static failure domain) as well as for pipes subjected to varying internal pressures (fatigue domain) (Chapters 5 and 6); 7. to indicate the sensitivity of the fatigue domain solution to changes in the system variables and to indicate that a significant reduction in the system variables does not necessarily reduce the solution accuracy (Chapter 6), and 8. to integrate the above-mentioned into a practical and workable guideline that can be used to determine the remaining life of an underground pipe network (Chapter 7). / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2002. / Mechanical and Aeronautical Engineering / unrestricted

Leaks in pipe networks cause significant problems for utilities and water users in terms of lost revenue and interrupted service. In many cities the leakage is as high as forty percent. A water audit is carried out to assess system-wide leakage. However, to detect leakage at the level of a pipeline, a physical measurement technique is generally employed. For large cities the distribution piping length amounts to a few thousand miles. Therefore, the physical measurements can become tedious and expensive. In this thesis it is assumed that a spatial distribution of leakage can be estimated at nodes based on a water audit bookkeeping scheme. A mathematical formulation consisting of continuity, energy (headloss), pressure-dependent demands and/or leakage, and flow direction preservation equations are utilized to distribute demand flows and leakage among pipes. The leakage is attributed to the formation of corrosion holes. Based upon the extent of corrosion, the leakage flow arriving at a particular node is apportioned among all pipes that are converging at that node. Therefore, the formulation presented in this thesis captures the two essential elements behind leakage, namely, pressure driven flow distribution and the vulnerability of pipes to corrosion. The proposed formulation allows utilities to be more proactive in identifying leakage prone districts within the water distribution system. An understanding of the pressure-dependent leakage in the system is helpful when performing a water audit and in developing strategies for leak repair programs. Restoring the full capacity of the water distribution system will greatly increase the reliability of the system, thereby benefiting local utilities and water users. / Master of Science