This study investigated localized corrosion behavior of austenitic stainless steels under stressed and unstressed conditions, as well as corrosion of metallic thin films. While austenitic stainless steels are widely used in corrosive environments, they are vulnerable to pitting and stress corrosion cracking (SCC), particularly in chloride-containing environments. The corrosion resistance of austenitic stainless steels is closely tied to the alloying elements chromium, nickel, and molybdenum. Polarization curves were measured for five commercially available austenitic stainless steels of varying chromium, nickel, and molybdenum content in 3.5 wt.% and 25 wt.% NaCl solutions. The alloys were also tested in tension at slow strain rates in air and in a chloride environment under different polarization conditions to explore the relationship between the extent of pitting corrosion and SCC over a range of alloy content and environment. The influence of alloy composition on corrosion resistance was found to be consistent with the pitting resistance equivalent number (PREN) under some conditions, but there were also conditions under which the model did not hold for certain commercial alloy compositions. Monotonic loading was used to generate SCC in in 300 series stainless steels, and it was possible to control the failure mode through adjusting environmental and polarization conditions. Metallic thin film systems of thickness 10-200 nm are being investigated for use as corrosion sensors and protective coatings, however the corrosion properties of ferrous thin films have not been widely studied. The effects of film thickness and substrate conductivity were examined using potentiodynamic polarization and scanning vibrating electrode technique (SVET) on iron thin films. Thicker films undergo more corrosion than thinner films in the same environment, though the corrosion mechanism is the same. Conductive substrates encourage general corrosion, similar to that of bulk iron, while insulating substrates supported only localized corrosion.

In this research, the corrosion performance of two austenitic stainless steels, namely 316L and 254SMO, in concentrated acetic acid solutions containing bromide ions has been investigated. In this research, the influence of two different electrochemical surface treatments (electropolishing and nitric acid passivation) on the corrosion behaviour of 316L stainless steel immersed in 15.3M HAc with 18.7mM bromide ions at 900°C was examined. Also, attemptswere made to study the performance of three organic inhibitors in the same conditions. Corrosion rates are assessed both by weight loss, and linear polarisation resistance. Interfacial corrosion chemistry is further characterised by open circuit potential and potentiodynamic polarization measurements. Substrate morphology is elucidated with optical microscopy, including 3D surface profiling, and scanning electron microscopy. Also, X-ray photoelectron spectroscopy is employed to gain further insight into the quite differentcorrosion performances of 316L and 254SMO in 15.3M acetic acid with 18.7mM Br ions.It was found that 316L and 254SMO steels have good corrosion resistance and low corrosion rates in 11.9M-HAc-Br-. Increasing acid concentration to 15.3 M led to a dramatic increase in corrosion rate of 316L with clear evidence of uniform and pitting corrosion proceeding simultaneously. Notably, the step increase in OCP for 316L steel and 254SMO during immersion in 15.3M-HAc-Br- solution indicates sudden changes in corrosion activity of the steels. The step seen for the 254SMO in 15.3M-HAc-Br- is indicative of passivation which is also supported by the XPS results, as a stable passive film was observed on the surface of alloy over the immersion time. However, the step increase in the OCP observed for 316L in 15.3MHAc-Br- is not associated with a significant decrease in corrosion rate. An alternative explanation is that the step coincides with an increase in the importance of pitting due to the evolving surface structure.From the attempts which were made to improve the corrosion resistance of the 316L stainless steel in 15.3M-HAc-Br-, both electropolishing and nitric acid passivation treatments were not sufficient to give any noticeable protection from the aggressive solution. Also, no corrosion inhibition was achieved when the three organic inhibitors, BTA, TU and 2MBI were utilised.

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The master’s thesis deals with corrosion resistance of cast duplex steels. In the first part the corrosion mechanisms and their individual types are described, the second part characterizes the types of stainless steels in terms of their properties, use, structural components, and their impact on mechanical and corrosion properties of steels. Individual chapter is dedicated to duplex steels. In the experimental part the resistance of 1.4517 steel against pitting corrosion depending on the alloy contents and the PREN value was investigated. Four specimens graded according to PREN were cast. Supplemented with sample stirrer blade which was affected by corrosion during service they were subjected to corrosion test according to ASTM G48-11 standard in 6% FeCl3 solution. Cast specimens were subjected to tensile test and impact test.

No description available.

An investigation into the general and pitting corrosion rates of rolled homogeneous armor (RHA) steel in immersion and saltog environments is presented. The mechanical properties of RHA steel have been studied, but the effects of corrosion on RHA have not been analyzed. An immersion environment of 3.5% NaCl was used to induce corrosion for the total testing period of 1500 hours for four immersion samples. A Qog cyclic corrosion tester was used to simulate a saltog/humidity/drying environment for four saltog samples. The different mechanisms of corrosion (general and pitting) and their associated rates were quantified through evolved hydrogen gas measurements, profilometry, Scanning Electron Microscopy (SEM) and Optical Microscopy (OM). The primary corrosion mechanism in the immersion samples was general corrosion, while the primary corrosion mechanism in the saltog samples was pitting corrosion. The immersion samples showed no signs of pitting corrosion.

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Corrosion in underground and submerged steel pipes is a global problem. Coatings serve as an impermeable barrier or a sacrificial element to the transport of corrosive fluids. When this barrier fails, corrosion in the metal initiates. There is a critical need for sensors at the metal/coating interface as an early alert system. Current options utilize metal sensors, leading to accelerating corrosion. In this dissertation, a non-conductive sensor textile as a viable solution was investigated. For this purpose, non-woven zinc (II) oxide-polyvinylidene fluoride (ZnO-PVDF) nanocomposite fiber textiles were prepared in a range of weight fractions (1%, 3%, and 5% ZnO) and placed at the coating/steel interface. Electrochemical impedance spectroscopy (EIS) testing was performed during the immersion of the coated samples to validate the effectiveness of the sensor textile. In the second part of this dissertation, an accelerated thermal cyclic method has been applied to determine sensor's reliability in detecting corrosion under actual service condition. The results suggested that the coating is capable of detecting corrosion under harsh conditions. Moreover, the addition of ZnO decreases the error in sensor textile and improved coating's barrier property. In the next phase, experiments were conducted to detect the type of corrosion (pitting or uniform) underneath the protective coating as it has profound effect on overall performance and durability of the steel pipe. The data suggested that the pitting corrosion drew a lot of current, hence its resistance was significantly low which was tacked by the sensor accurately whereas the uniformly corroded specimens showed almost identical results which portrayed the sensor's ability to detect pitting corrosion.

No description available.

No description available.