Cast iron pipes were installed broadly in North American water utilities. Many of these cast iron pipes are corroded and are continuous sources of Fe(II) ions in drinking water distribution systems. Recent studies have reported that soluble or particulate iron decreases water quality in distribution systems. In this study, an array of bench scale experiments were conducted to evaluate the impact of most common water parameters (e.g., pH, PO4, Cl2, and DOM) on the oxidation rate of Fe(II) ions, and on the formation of iron suspense in synthetic water samples. This was accomplished using a 24 full factorial design approach at a 95% confidence level. This study demonstrated that a lower content of iron suspension color, turbidity, and smaller particle size would appear to be obtained in presence of a phosphate based corrosion inhibitor at a pH value of 6.5 compared to a pH value of 8.5. To investigate the impact of Fe(II) ions, phosphate, pH and reaction time, and their interaction on DBPs formation in water samples, this study was conducted following an experimental design approach. Considering all the significant (α = 0.05, p < 0.05) factors, mathematical models for HAAs and THMs prediction were developed using 80 experiments. The models’ adequacy was checked thorough the statistical and graphical diagnostics. Different sources of natural water samples collected from three main water treatment plants in Halifax, Canada, were used to validate the models. This study suggested that the models’ performance were found to be excellent under a wide range of studied variables. Consequently, the most predominant iron oxides (goethite and magnetite) were used to investigate their impact on chlorine decay and DBPs formation study. Goethite and magnetite were also used for the adsorption of DBPs precursor (DOM). The DOM adsorption data illustrated to fit well with the Langmuir adsorption isotherm, indicating monolayer coverage. Molecular weight (MW) distributions of DBPs precursor (DOM) revealed that the higher molecular weight fractions adsorbed preferentially onto goethite followed by magnetite surface. The change of MW distribution of DOM was found to be in reasonable agreement with the change of DBPs formation in iron-water systems.

No description available.

The aim of this study was to use the finite element method to model crack, corrosion, and Crack-in-Corrosion defects in a pipeline. The pipe material under investigation for this study was API 5L X60, 508 mm diameter with a wall thickness of 5.7 mm. The pipe material was evaluated using Tensile, Charpy, and J testing in order to model the defects and to establish the numerical failure criteria. Corrosion defects were modeled as flat-bottomed grooves. The collapse pressure was predicted when the deepest point in the bottom of the defect reached a critical stress. Based on this criterion, the FE corrosion failure pressure predictions were conservative compared to the experimental failure pressures, conducted by Hosseini [9], with an average error of 10.13%. For crack modeling, the failure criteria were established considering the plastic collapse limit and the fracture limit. Both the Von Mises stress in the crack ligament and the J-integral values around the crack were monitored to predict the failure pressure of the model. The crack modeling was done based on two approaches, the uniform depth profile and the semi-elliptical profile. The crack with uniform depth profile was done because the uniform shape is the logical equivalent shape for a colony of cracks. The crack with the semi-elliptical profile was done to have a less conservative results and because the experiments were done with semi-elliptical cracks. The FE crack modeling results were conservative compared to the experimental collapse pressure with an average error of 19.64% for the uniform depth profile and 5.35% for the semi-elliptical profile. In crack-in-corrosion (CIC) defect modeling, the crack was modeled with uniform depth because it was very difficult to model the semi-elliptical crack profile when the crack defect is coincident with a corrosion defect. The results were conservative compared to the experimental results with an average error of 22.18%. In general, the FE modeling provides the least conservative failure pressure prediction over the existing analytical solutions for pipe with longitudinal corrosion, crack, and CIC defects.

Reinforcing steel in concrete has been used for many years in roads, bridges and other structures to give strength and durability; concrete has only good compressive strength and reinforcing steel gives the tensile strength to the concrete to sustain both the compressive and tensile load, making concrete structures to be used in the common as well as critical areas. Reinforcing steel that was used in structures predominantly is mild steel, which is considerably cheaper than stainless steel, and more susceptible to corrosion leading to the damage of the structures and less longevity. To solve the problem with the use of mild steel in critical areas, such as bridges; stainless steel is used; which has iron as the main constituents along with the chromium as the major alloying element and various grades are manufactured varying the compositions of steel. To reduce the cost of the stainless steel, some compositions like chromium, molybdenum, nickel are varied; especially the nickel is being replaced by manganese, the cost of which is significantly less than that of nickel. The alternative grades of the reinforcing steel that were used for testing the corrosion resistance are mild steel (400), weldable mild steel (400 W) and four stainless steel 316LN, UNS 24100 (Enduramet 32), 2304, LDX 2101; among them 316LN and UNS 24100 are the austenitic steels (Valbruna) and 2304 and LDX 2101 are duplex steels (Outokumpu). The austenitic steels have no ferritic phase which is making austenitic steel more corrosion resistance than the duplex steels which have almost equal parts of the ferritic and austenitic phases. Concrete that is used commonly as the shield for the reinforcing steel providing the environment to passivate the reinforcement. Concrete has the pH of ~13.5 which is the equivalent to the pH of the pore solution. Its strength and curing time varies due to the water cement ratio and composition and also the environment in which it is placed. Good quality concrete has less permeability and fewer cracks thereby limiting the ingress of the de-icing slats to the reinforcing steel and delaying the onset of corrosion. Corrosion of the reinforcing steels was tested in concrete using both an accelerated exposure test and ASTM A 955M standard for cracked prisms to measure the corrosion rate and open circuit potential, which are quantitative measurement for corrosion. It is hoped that the results will provide a guide for the future use of the alternative grades of the reinforcing steel to be used in the concrete. Reinforcing mild steels were compared to determine if there is any advantage in using the more carefully controlled 400W welding grade, rather than the 400 grade. The service life of structures with the 400 grade of steel is well established and so the data from the 400 grade also provided a relative measure of corrosion resistance for the alternative grades of the stainless steel. Microcell corrosion of the reinforcing steel was monitored by the use of the linear polarization and the corrosion potential. The data for show that there is no significant corrosion on any of the stainless steels after 15 months of measurement, whereas both the mild steels embedded in the concrete corroded fully as confirmed by visual observation of the beams after autopsying The autopsied samples were then analysed for chloride content in the concrete adjacent to the reinforcing bars. This was accomplished by titration. The chloride content on the beams with 400 and 400W grades was found to be higher than the beams with the stainless steels, where the percentage of chloride remained almost the same. Macrocell corrosion tests were performed on the ASTM A 955M cracked prisms and showed changes in corrosion current density in agreement with the accelerated corrosion current density of the stainless steels. The only difference was observed in the corrosion potentials of the 400 and 400W steels, which were more negative in the cracked prisms than in the beams. In summary, all the stainless steels showed evident corrosion resistance both in accelerated and ASTM A 955M prisms tests and no sign of corrosion was found in the stainless steels after 400 days in beams and 200 days in prisms. The regular and weldable steels corroded in both tests in agreement with the data present in research.

This thesis discusses the results of an experimental program designed to investigate the effect of corrosion on the behaviour of shear critical reinforced concrete (RC) beams. The results of twenty RC beams (ten deep beams and ten slender beams) are described and discussed. The test variables included: corrosion level (2.5%, 5% and 7.5%) and existence of stirrups (beams without stirrups and beams with stirrups). The feasibility of repairing the corroded shear critical RC beams with CFRP laminates was also investigated. Sixteen specimens were corroded using an accelerated corrosion technique whereas four specimens acted as control un-corroded. Following the corrosion phase, all specimens were tested to failure under three point bending. Test results revealed that the corrosion does not adversely affect the behaviour of shear critical RC beams rather it improves their behaviour. It was found that corrosion changed the failure mode of the corroded beams. The control un-corroded deep beams (beams with and without stirrups) failed in shear-compression failure whereas corroded deep beams (beams with and without stirrups) failed by splitting of the compression strut. The control un-corroded slender beams (beams with and without stirrups) failed in diagonal tension failure whereas the corroded slender beams failed in anchorage failure (beams without stirrups) and flexural failure (beams with stirrups). The analysis of the results showed that corrosion changed the load transfer mechanism and the change of failure mode was associated with the mechanism. The load transfer mechanism changed from a combination of beam and arch action in the control un-corroded deep beams to pure arch action in the corroded deep beams. The load transfer mechanism changed from pure beam action in the control un-corroded slender beams to pure arch action in the corroded slender beams. Two strut and tie models are proposed: one for corroded deep beams and one for corroded slender beams. The ultimate loads of the corroded beams were predicted using these struts and tie models and compared with the experimental results. A very good correlation was found between predicted and experimental results.

No description available.

Corrosion behaviour of Al, Zn, Cu and steel samples under the conditions of constant temperature and humidity were performed in the media containing the following microorganisms. Bacillus mycoides, Aspergillus fumigatus Aspergillus niger, Cladosporium herbarum, Penicillium frequentans. The influence of metal surface morphology on the vitality of microorganisms was investigated, as well as the proceeding of microbial corrosion was under the study. The real surface area of Cu electrode was determined by means of electrochemical techniques, while the method for comparison of surface areas of other metals was proposed and this method was based on atomic force microscope measurements. It was determined that the metal nature and morphology influenced the vitality of microorganisms. The results of electrochemical impedanse spectroscopy enabledus to evaluate the corrosion behaviour of metals. The results were found to indicate the corrosion inhibition for Al, steel and Cu, however, the effect depended on the metal surface morphology and exposure time.

This thesis investigated corrosion of a reinforcing steel bar embedded in concrete and the effect of corrosion coupling on the bar/concrete interface induced by the variation of corrosion potentials with concrete depth. Two separate numerical models were used to simulate the corrosion process which included: a two-dimensional finite element model for mass transport of oxygen and chloride to the bar/concrete interface; and, a one-dimensional model for the corrosion current flow through the electrolyte induced by corrosion potential differences on the bar/concrete interface. A novel approach to corrosion modeling in reinforced concrete that had not been identified in the literature was used. This new approach, incorporated: variable solution conductivity developed from concentrations within the pore solution; anodic and cathodic areas modified to maximize corrosion current through the electrolyte; and, kinetics of corrosion set by the pore solution chemistry. Various reinforcing configurations and moisture conditions were evaluated within the simulation to obtain insight into the effect these variables have on corrosion potentials measured on the concrete surface and the corresponding corrosion currents generated on the bar/concrete interface. Variables related to bar diameter, concrete cover, and bar spacing where all shown to affect corrosion potentials and current densities on the bar/concrete interface and the concrete surface where field measurements are obtained. Moisture conditions were found to have the largest impact on corrosion potentials and current density’s on the bar/concrete interface. When relative humidity’s of 90% or higher were used, simulated corrosion potentials on the concrete surface under high chloride conditions were found to reach values identified in ASTM C876 and Alberta Transportations Deck Testing Guidelines that indicate active corrosion. However, when moisture conditions were reduced to below 90% relative humidity, simulated corrosion potentials on the concrete surface for high chloride concentrations did not achieve values that indicate a high probability of corrosion. This result suggests a secondary mechanism must be present on the bar/concrete interface that changes the chemical composition within the pore solution to shift the kinetics of corrosion to an environment that will produce the negative corrosion potentials recognized as indicating a high probability of corrosion. Therefore, a new mechanism is proposed that outlines the process necessary for the pore solution on the bar/concrete interface to transition the kinetics of corrosion to an actively corroding state at low relative humidity. This mechanism requires local acidification of the pore solution along portions of the bar where anodic processes are increased due to the presence of chloride and reduced oxygen availability. Reaching this environment requires free OH- to be consumed without replenishment from the surrounding environment by either diffusion from high pH areas or dissolution of the hardened portions of the pore structure. The proposed mechanism begins with corrosion by-products formed when Fe2+ reacts with free OH-, precipitates from the pore solution onto the pore structure as Fe(OH)2. Once precipitated, the contact area between pore solution and hardened portions of the pore structure are reduced which restricts the dissolution process for restoring OH- removed from the electrolyte. Additionally, precipitation of Fe(OH)2 reduces the flow of OH- from the surrounding high pH zones as the pore structure is restricted. Both mechanisms result in a pH gradient being formed with acidified zones created on the bar/concrete interface in the anodic regions. These acidified zones cause the kinetics of corrosion to transition from a passivated state, towards an environment similar to carbonation.

No description available.

There is an increasing interest in exploring the use of conductive polymers for protecting metals from corrosion. The corrosion resistance of steel coated with the conductive polymer polypheneylenevinylene (PPV) is studied. The corrodant used is deaerated 1% w/w NaCl(aq). / The PPV coating is deposited by a homemade spinning coater. The effect of substrate microstructure and surface treatment on PPV coating morphology is investigated. The morphology and surface roughness of the coating are measured by Atomic Force Microscopy (AFM). The PPV coating thickness and substrate surface roughness are measured by profilometer. / Open Circuit Potential (OCP), electrochemical impedance spectroscopy (EIS), linear potentiodynamic voltammetry (Tafel) and optical microscopy were used to characterize the structure and properties of the coatings. The correlation between the coating thickness, the surface treatment of the steel substrate prior to coating, and the corrosion behaviour of PPV coated steel was investigated. / Under the condition of our studies, the level of pH in the solution used for corrosion testing has the strongest effect on the corrosion behaviour of PPV coated steel.