Browsing by Subject "corrosion"
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Item Characterization and Modeling of Transformation Induced Fatigue of Shape Memory Alloy Actuators(2011-02-22) Bertacchini, Olivier WalterThe main focus of this research is the transformation induced fatigue behavior of shape memory alloy (SMA) actuators undergoing thermally induced martensitic phase transformation. The recent development of aerospace applications employing shape memory alloys (SMAs) has expanded the need for fatigue life characterization and modeling. Lightweight, compact and with a great work output, SMAs are ideal materials for actuated structural components. However, fatigue life becomes a key factor in applications such as commercial airplanes. Therefore, it is necessary to not only perform fatigue testing but also to investigate the causes of fatigue failure. As a new class of materials, SMAs have unique characteristics and require novel test methodologies to conduct repeatable and reliable fatigue testing. For this research, two materials are being investigated: TiNiCu and Ni-rich NiTi. The experiments performed on the first selected alloy, i.e. TiNiCu SMA, explore three major parameters: the applied stress level, the amount of actuation, and the corrosive nature of the environment. Experimental results show that SMAs undergoing transformation induced fatigue exhibit a low-cycle fatigue behavior and the measurement of the accumulated plastic strain at failure is associated to a Manson-Coffin type failure criterion. Investigations conducted on the post-mortem microstructure showed evidence of a multiphysical coupling between corrosion and cyclic phase transformation, from which a novel cyclic damage mechanism is proposed and explained using the micromechanical shear lag model accounting for actuation and accumulated plastic strains. Thereafter, based upon the identified failure mechanism and considering damage accumulation through crack formation, a stress renormalization procedure is proposed in combination with the Miner?s rule to predict the reduction of number of cycles to failure due to cyclic phase transformation and corrosion. A direct method is first presented and the predictions show good agreement with experimental results. However, both corrosion and corrosion-free fatigue data are required. Therefore, a new approach is proposed: the inverse Miner?s rule, which requires corrosion fatigue data only to predict corrosion-free life. The new and attractive properties of the selected second alloy, i.e. Ni-rich NiTi SMA, have revived the motivation of the aerospace industry to design SMA actuators. One particular property is cyclic stability generated by precipitation hardening mechanism using precipitates. However, are also precipitates due to high Nickel content (60 wt.% or 55 at.%). Parameters such as processing, heat treatments, size effects, surface quality and environment are investigated. Thermomechanical response and fatigue life are discussed and the greatest impact is found to come from specimen surface quality. Finally, a detailed fractography presents the different microstructural aspects of the fatigue damage and concludes to a precipitation driven fatigue failure mechanism cause by precipitates.Item Electrochemical characterization and time-variant structural reliability assessment of post-tensioned, segmental concrete bridges(2010-07-14) Pillai Gopalakrishnan, RadhakrisIn post-tensioned (PT) bridges, prestressing steel tendons are the major load carrying components. These tendons consist of strands, ducts, and cementitious grout that fill the interstitial space between the strands and ducts. However, inspections on PT bridges have reported the presence of voids, moisture, and chlorides inside grouted ducts as the major cause of accelerated corrosion of strands. Corrosion of the strands has resulted in PT bridge failures in Europe and tendon failures in the United States. As most of the PT bridges have high importance measures and the consequences of failure are significant, it is important to maintain high levels of safety and serviceability for these bridges. To meet this goal, bridge management authorities are in dire need of tools to quantify the long-term performance of these bridges. Time-variant structural reliability models can be useful tools to quantify the long-term performance of PT bridges. This doctoral dissertation presents the following results obtained from a comprehensive experimental and analytical program on the performance of PT bridges. 1) Electrochemical characteristics of PT systems 2) Probabilistic models for tension capacity of PT strands and wires exposed to various void and environmental conditions 3) Time-variant structural reliability models (based on bending moment and stress limit states) for PT bridges 4) Time-variant strength and service reliabilities of a typical PT bridge experiencing HS20 and HL93 loading conditions and different exposure conditions for a period of 75 years The experimental program included exposure of strand specimens to wet-dry and continuous-atmospheric conditions. These strand specimens were fabricated to mimic void and/or grout-air-strand (GAS) conditions inside the tendons. It was found that the GAS interface plays a major role in strand corrosion. The GAS interfaces that are typically located in the anchorage zones of harped PT girders or vertical PT columns can cause aggressive strand corrosion. At these locations, if voids are present and the environment is relatively dry, then limited corrosion of the strands occurs. However, if the presence of high relative humidity or uncontaminated and chloride-contaminated water exists at these interfaces, then corrosion activity can be high. The strands were exposed for a period of 12, 16, and 21 months, after which the remaining tension capacity was determined. The analytical program included the development of probabilistic strand capacity models (based on the experimental data) and the structural reliability models. The timevariant tension capacity predicted using the developed probabilistic models were reasonably consistent with the tendon failures observed in PT bridges in Florida and Virginia. The strength reliability model was developed based on the moment capacity and demand at midspan. Service reliability model was developed based on the allowable and applied stresses at midspan. Using these models, the time-variant strength and service reliabilities of a typical PT bridge were determined based on a set of pre-defined constant and random parameters representing void, material, exposure, prestress, structural loading, and other conditions. The strength and service reliabilities of PT bridges exposed to aggressive environmental conditions can drop below the recommended values at relatively young ages. In addition, under similar conditions the service reliability drops at a faster rate than the strength reliability.Item High temperature oxidation and NaCl-induced accelerated corrosion of hot-dip aluminized 9Cr-1Mo and 310 stainless steel(Texas A&M University, 2005-02-17) Tsaur, Charng-ChengThe behaviors of high temperature corrosion on hot-dip aluminized on 9Cr-1Mo and 310 stainless steels when catalyzed by NaCl and cyclic heating environment were studied experimentally. The corrosion behavior and morphological development were investigated by weight gain kinetics, metallographs, depths of attack, metal losses, and X-ray analyses. The results of 310SS deposited with salt mixtures show that weight gain kinetics in simple oxidation reveals a steady-state parabolic rate law after 3 hr, while the kinetics with salt deposits display multi-stage growth rates. NaCl is the main corrosive specie in high-temperature corrosion involving mixtures of NaCl/Na2SO4 and is responsible for the formation of internal attack. Uniform internal attack is the typical morphology of NaCl-induced hot corrosion, while the extent of intergranular attack is more pronounced as the content of Na2SO4 in the mixture is increased. The thermal-cycling test results of 310SS deposited NaCl and coated 7wt%Si/93wt%Al show that the aluminized layers have good corrosion resistance during the first four cycles of testing, while degradation occurs after testing for five cycles. The reason for degradation of aluminized layers is attributed to the formation of interconnecting voids caused by aluminum inward diffusion, chloridation/oxidation cyclic reactions and the penetration of molten NaCl through the voids into the alloy substrate. The 9Cr-1Mo steels coated with 7wt%Si/93wt%Al oxidized at 750, 850, and 950?C in static air show that oxidation kinetics followed a parabolic rate law at 750 and 850 ?C. The cracks propagated through the FexAly layer due to the growth of brittle FeAl2 and Fe2Al5 at 750 and 850?C. The voids condensed in the interface of intermetallics and substrate are attributed to the Kirkendall effect. At 950?C, the fast growing aluminide layer has a different expansion coefficient than oxide scale, leading to scale cracking, oxygen penetration, and internal oxidized, evidenced by a rapid mass gain.Item Non-Destructive Evaluation of Bridge Stay Cable and External Post-Tensioning Systems(2014-10-09) McCoy, Katlyn MaeNon-destructive evaluation (NDE) of bridge stay cable and external post-tensioning (PT) systems is an essential tool to thorough bridge inspections and also eliminates any necessary repair of destructions made during evaluation. Conditions such as corrosion, steel strand and wire breakage, tendon section loss, voids in the grout, water infiltration, and other undesired grout conditions can go undetected in nontransparent stay cable and external PT ducts without proper inspection. In this research, sounding, ultrasonic tomography, infrared thermography, and ground penetrating radar are evaluated for their applicability to identify selected conditions in a mock-up specimen representative of both a stay cable system and an external PT system. A borescope is also used to collect ground truth data for comparison with the NDE results. The conditions are fabricated in the mock-up specimen to closely represent conditions in the field so that the NDE results are directly applicable to bridge construction quality control and in-service bridge inspections. Locations of corrosion, breakage, and section loss are established prior to grouting. These conditions are combined with both foam void locations and an air-filled void in the grout along the top of the duct. The sounding method was extremely applicable in accurately detecting air voids in the grout and the sounding results matched closely with the ground truth data of the air void extent collected by the use of a borescope. This research concludes that the infrared thermography and ground penetrating radar devices used did not identify any of the corrosion, section loss, or breakage locations within the specimen. However, both of these methods identified air voids and foam voids in the duct free span during both the quality control testing period and inspection testing period, although GPR did not provide accurate void depth. In addition, infrared thermography was able to identify air voids within the grout caps at each anchorage end. The ultrasonic tomograph used in this research, designed for use on concrete rather than stay cables and external PT, produced inconsistent results when used on the specimen. In future research, a different means of ultrasonic tomography testing may be applicable to identifying voids in the grout.Item Physiochemical characteristics of controlled low strength materials influencing the electrochemical performance and service life of metallic materials(Texas A&M University, 2007-04-25) Halmen, CekiControlled Low Strength Materials (CLSM) are cementitious self-compacting materials, comprised of low cement content, supplementary cementing materials, fine aggregates, and water. CLSM is typically used as an alternative to conventional compacted granular backfill in applications, such as pavement bases, erosion control, bridge abutments, retaining walls, bedding and backfilling of pipelines. This dissertation presents the findings of an extensive study carried out to determine the corrosivity of CLSM on ductile iron and galvanized steel pipelines. The study was performed in two phases and evaluated more than 40 different CLSM mixture proportions for their corrosivity. An extensive literature survey was performed on corrosion of metals in soils and corrosion of reinforcement in concrete environments to determine possible influential factors. These factors were used as explanatory variables with multiple levels to identify the statistically significant factors. Empirical models were developed for percent mass loss of metals embedded in CLSM and exposed to different environments. The first and only service life models for ductile iron and galvanized steel pipes embedded in CLSM mixtures were developed. Models indicated that properly designed CLSM mixtures can provide an equal or longer service life for completely embedded ductile iron pipes. However, the service life of galvanized pipes embedded in CLSM should not be expected to be more than the service life provided by corrosive soils.Item Prioritizing Water Pipe Replacement and Rehabilitation by Evaluating Failure Risk(2012-02-14) Lee, Sang HyunEssential to human life is water. Drinking water, in particular, is of utmost significance for all living creatures including man. An examination of the transmission process of drinking water reveals the high importance of pipe lines. The water pipe lines delivering water today encounter serious problems. Corrosion has caused deterioration in pipe lines, which contributes rust to drinking, a serious water quality problem. In addition, pipe line failures have caused social issues, such as suspension of water supply. This study developed a model to estimate the life expectancy and residual life of a pipe based on the assessment of failure risk in order to evaluate the current failure possibility and predict when the pipe will reach the point of failure. The developed model for estimation of residual life by failure risk was used to assess the failure risk of water pipes based on the general data and pipe sources of the Chang Won City water pipes. The efforts to diagnose and evaluate water pipes are limited to the assessment of current pipe conditions, which is why they can easily determine the priority of rehabilitation based on the current pipe conditions but have hard time getting information about how the pipes have deteriorated to the point of requiring rehabilitation. The objectives of this study are: (1) develop a model for estimating corrosion rates and residual thickness of water pipes, (2) assess loads and stress affecting water pipes, (3) to estimate damage risk, and (4) calculate safety factors. Results of the study could help reduce rehabilitation costs and secure water quality after renovation. Thus it would contribute to the safe and stable operation and management of pipe networks by increasing the life of water pipes.Item Removing of Formation Damage and Enhancement of Formation Productivity Using Environmentally Friendly Chemicals(2012-07-16) Mahmoud, Mohamed Ahmed Nasr EldinMatrix acidizing is used in carbonate formations to create wormholes that connect the formation to the wellbore. Hydrochloric acid, organic acids, or mixtures of these acids are typically used in matrix acidizing treatments of carbonate reservoirs. However, the use of these acids in deep wells has some major drawbacks including high and uncontrolled reaction rate and corrosion to well tubulars, especially those made of chrome-based tubulars (Cr-13 and duplex steel), and these problems become severe at high temperatures. Hydrochloric acid (HCl) and its based fluids have a major drawback in stimulating shallow (low fracture gradient) formations as they may cause face dissolution (formation surface washout) if injected at low rates. The objective of stimulation of sandstone reservoirs is to remove the damage caused to the production zone during drilling or completion operations. Many problems may occur during sandstone acidizing with Hydrochloric/Hydrofluoric acids (HCl/HF) mud acid. Among those problems: decomposition of clays in HCl acids, precipitation of fluosilicates, the presence of carbonate can cause the precipitation of calcium fluorides, silica-gel filming, colloidal silica-gel precipitation, and mixing between various stages of the treatment. To overcome problems associated with strong acids, chelating agents were introduced and used in the field. However, major concerns with most of these chemicals are their limited dissolving power and negative environmental impact. Glutamic acid diacetic acid (GLDA) a newly developed environmentally friendly chelate was examined as stand-alone stimulation fluid in deep oil and gas wells. In this study we used GLDA to stimulate carbonate cores (calcite and dolomite). GLDA was also used to stimulate and remove the damage from different sandstone cores containing different compositions of clay minerals. Carbonate cores (calcite and dolomite) of 6 and 20 in. length and 1.5 in. diameter were used in the coreflood experiments. Coreflood experiments were run at temperatures ranging from 180 to 300oF. Ethylene diamine tetra acetic acid (EDTA), hydroxyl ethylethylene diaminetriacetic acid (HEDTA), and GLDA were used to stimulate and remove the damage from different sandstone cores at high temperatures. X-ray Computed Topography (CT) scans were used to determine the effectiveness of these fluids in stimulation calcite and dolomite cores and removing the damage from sandstone cores. The sandstone cores used in this study contain from 1 to 18 wt percent illite (swellable and migratable clay mineral). GLDA was found to be highly effective in creating wormholes over a wide range of pH (1.7-13) in calcite cores. Increasing temperature enhanced the reaction rate, more calcite was dissolved, and larger wormholes were formed for different pH with smaller volumes of GLDA solutions. GLDA has a prolonged activity and leads to a decreased surface spending resulting in face dissolution and therefore acts deeper in the formation. In addition, GLDA was very effective in creating wormholes in the dolomite core as it is a good chelate for magnesium. Coreflood experiments showed that at high pH values (pH =11) GLDA, HEDTA, and EDTA were almost the same in increasing the permeability of both Berea and Bandera sandstone cores. GLDA, HEDTA, and EDTA were compatible with Bandera sandstone cores which contains 10 wt percent Illite. The weight loss from the core was highest in case of HEDTA and lowest in case of GLDA at pH 11. At low pH values (pH =4) 0.6M GLDA performed better than 0.6M HEDTA in the coreflood experiments. The permeability ratio (final/initial) for Bandera sandstone cores was 2 in the case of GLDA and 1.2 in the case of HEDTA at pH of 4 and 300oF. At high pH HEDTA was the best chelating agent to stimulate different sandstone cores, and at low pH GLDA was the best one. For Berea sandstone cores EDTA at high pH of 11 was the best in increasing the permeability of the core at 300oF. The low pH GLDA based fluid has been especially designed for high temperature oil well stimulation in carbonate and sandstone rock. Extensive studies have proved that GLDA effectively created wormholes in carbonate cores, is gentle to most types of casing including Cr-based tubular, has a high thermal stability and gives no unwanted interactions with carbonate or sandstone formations. These unique properties ensure that it can be safely used under extreme conditions for which the current technologies do not give optimal results. Furthermore, this stimulation fluid contributes to a sustainable future as it based on readily biodegradable GLDA that is made from natural and renewable raw material.