Coatings are often used as a means of protecting aluminum alloy and steel structures in industry. The assessment of corrosion under these coatings can be challenging. Corrosion sensing coatings can exhibit properties that allow undercoating corrosion to be identified before it can be seen with the naked eye. This would be very advantageous and could potentially result in tremendous savings in time and money when structures undergo routine maintenance. Our work involved the study of corrosion sensing coatings with incorporated fluorescent indicators that can be used to sense the undercoating corrosion on metal substrates. The fluorescent indicator in the coated-aluminum system was a negative indicator, i.e. the indicator in the coating was initially fluorescent and subsequently non-fluorescent due to the reduced pH at the anodic sites of corrosion. The fluorescent indicator in coated-steel system was positive, in the sense that the coating changed from non-fluorescent to fluorescent over the cathodic areas due to increased pH. The corrosion sensing coating was composed of commercial epoxy-polyamide and the indicator: 7-amino-4-methylcoumarin (7-AMC) for the coated-aluminum alloy system and 7-diethylamino-4-methylcoumarin (7-DMC) for the coated-steel system. The feasibility of using 7-AMC for sensing early undercoating corrosion was demonstrated by using fluorescent observations, Electrochemical Impedance Spectroscopy (EIS), Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) tests. EIS results estimated that with continuous immersion the undercoating corrosion occurred within 24 hours after immersion in the salt solution. When corrosion occurred, the corrosion was invisible under natural light. However, small spots appeared in the fluorescent image, changing from initially fluorescent to non-fluorescent where the anodic sites were identified by SEM and EDS. In other words, the fluorescent indicator could sense the early undercoating corrosion, although blistering can be a competing mechanism associated with corrosion under some conditions. The sensitivity of the 7-AMC corrosion detection system was tested by applying anodic current to the metal and measuring the charge at which fluorescence quenching was detected. The critical charge for a detectable pit under the coating was approximately 2x10⁻⁵ C, which implied a critical radius of a single corrosion spot or set of spots of approximately 10 [mu]m. The fluorescent properties of 7-AMC, its effect on the protectiveness, its sensitivity to pH and its concentration in the coating are explored as well. Fourier transform spectroscopy (FTIR) was used to characterize the structure of the coating with and without 7-AMC. The results suggested that there is no structure change occurring after adding 7-AMC into the coating. Fluorescence behavior, electrochemical behavior, microscopic evidence, and visual observations of coated steel specimens with 7-DMC are compared based on exposure to saltwater conditions. Some of the challenges associated with the use of these types of coatings will be presented. This includes the interference from the increased production of ferrous and ferric ions. All of this information is aimed at the development of corrosion sensing coatings that can reveal undercoating corrosion before it is visible to the naked eye. / text

Corrosion of embedded reinforcement is the leading form of deterioration affecting the integrity of reinforced and prestressed concrete bridge members around the world. If undetected, corrosion can limit the service life of the bridge and lead to expensive repairs. The research team at the University of Texas at Austin has developed a new class of passive wireless corrosion sensors. The noncontact (NC) sensor platform provides an economical and nondestructive means for detecting corrosion initiation within concrete. The sensor is powered through the inductive coupling to an external mobile reader that can be handheld or mounted on a vehicle. It is envisioned that the four-dollar sensor will be embedded in concrete during construction and interrogated sporadically over the service life of the structure. The sensor output can be used to detect corrosion initiation within concrete and is expected to enhance the quality information collected during qualitative routine bridge inspections. The NC sensor prototype consists of a resonant circuit that is inductively coupled to a sacrificial transducer. Corrosion of the sacrificial element alters the measured sensor response and is used to detect corrosion within concrete. Electrochemical evaluations were conducted to ensure that the sacrificial element exhibited identical response as the reinforcement steel. In addition, the results of extensive experimental parametric studies were used in conjunction with circuit and electromagnetic finite element models to optimize the NC sensor design. Long-term exposure tests were used to evaluate the reliability of the passive noncontact sensors. Sensors were embedded in reinforced concrete specimens and successfully detected the onset of corrosion in the adjacent reinforcement. Unlike the traditional corrosion evaluation methods, such as half-cell potentials, the sensors output was insensitive to environmental variations. / text

Ships and vessel conditions demand regular assessment to maintain their safety. In the traditional environment, their assessment was conducted using surveys and complex and time-consuming operations. But now, with the emergence of Industry 4.0 where intelligence and smart devices serve the imagery, drone-based, and many other alternative methods for inspection, the subject is obtaining considerable interest. The concept is highly effective with low cost and less disruption delivering a safer inspection approach. This study has examined Industry 4.0 technology as a quality inspection technique of a ship/vessel, examined drone-based ship inspection techniques for quality inspection of the ship/vessel without human involvement, to analyse robotic underwater surveillance methods for quality inspection of the ship/vessel, and to identify vision-based corrosion detection techniques for quality inspection of the ship/vessel. In the finding, it was revealed ship inspection through Industry 4.0 technology and other techniques can help the marine industries rely more on automated systems to gather the information that is required to be capable of authenticating process and product conformance also they can reduce human error, risks and uncover useful insights from the gathered vessel/ship data.

Corrosion of reinforcement in reinforced concrete is a huge problem. Corrosion of reinforcement has a great effect on the service life of reinforced concrete structures. The subject of this work is to verify the inhibitors properties and their efficiency using physical and electrochemical methods. The aim of this work is the design of formwork panels with corrosion protection. The formwork panels are on different material basis. Corrosion protection is ensured by the use of migration corrosion inhibitors.

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The first part of this doctorate dissertation examines the factors influencing the occurrence and costs of pinhole leak corrosion as well as the household decisions for corrosion prevention and plumbing material selection. Three mail surveys of households were used to elicit the experiences with leaks as well as the optimal corrosion prevention and material choices. Probability modeling (i.e. MNL) and linear regression analysis were used to analyze survey responses. Pinhole leak occurrences were found associated with pipe type installed, property age, pipe failure history, and dwelling distance from a water treatment plant. The number and location of pinhole leaks in the dwelling and the pipe type are associated with the financial costs of pinhole leaks. The corrosion prevention choices as well as the plumbing materials depended on the risk of corrosion and cost associated with each option. Previous experiences with pinhole leak impacted the decision for household choices. Faster responses to pinhole leak outbreaks by utility managers and policymakers in terms of advising homeowners on the best ways of responding to leaks would assist homeowners in reducing costs of pinhole leak repairs and associated damages. The second part of this document deals with the debt financing issues. Debt financing decisions are made simultaneously by lenders and borrowers. Since lenders are unable to observe directly the firms’ investment decisions, the banks offer contracts based up on firms’ observable characteristics (i.e. wealth and size) and the prevailing market conditions. When deciding on the financing decisions, firms also take into account the changes in macroeconomic variables in order to lower the cost of borrowing. As a result, the goal for this article is to examine empirically the hypothesis of the effect of the debt determinant as well as the macroeconomic variables on the debt maturity structure. A reduced form of the simultaneous financing decisions model is estimated by employing several OLS estimation methods. The empirical findings offer strong support for firms with few growth options, large, and of low quality having more long-term debt in their capital structure. There was, however, no clear support for the impact of macroeconomic variables on debt maturity as some variables were not statistically significant. / Ph. D.

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