Dissertation (Ph.D.)--Auburn University, 2009. / Abstract. Includes bibliographic references (p.111-118).

No description available.

<p>U ovom radu efikasnost odabranih derivata tiazola u inhibiciji korozije bakra u kiseloj<br />sulfatnoj sredini određena je u funkciji koncentracije inhibitora metodom merenja<br />gubitka mase, elektrohemijskom impedansnom spektroskopijom i potenciostatskom<br />polarizacijom. Polarizacionim merenjima takođe je određena zavisnost inhibitorske<br />efikasnosti od&nbsp; temperature i kinetički parametri procesa korozije bakra&nbsp; kao i&nbsp; model<br />adsorpcione izoterme prema kojem se odigrava proces adsorpcije&nbsp; inhibitora i&nbsp;odgovarajući termodinamički parametri. Merenjima kvarc kristalnom mikrovagom&nbsp;<em>in&nbsp;</em><br /><em>situ&nbsp; </em>je praćen proces elektrohemijskog rastvaranja bakra i adsorpcije ispitivanih<br />inhibitora. SEM/EDX analizom&nbsp; proučavana&nbsp; je promena morfologije bakarne povr&scaron;ine<br />usled dejstva korozione sredine i rastvora inhibitora.&nbsp; Rezultati eksperimentalnih<br />ispitivanja korelirani su&nbsp; sa teorijskim proračunima na nivou teorije funkcionala<br />gustine.</p> / <p>In this work, the efficiency of selected thiazole derivatives in&nbsp; the inhibition of corrosion of copper in the acidic sulfate solution is determined in&nbsp; the function ofthe inhibitors&nbsp; concentration by weight loss method,&nbsp; electrochemical impedance spectroscopy and potentiostatic polarization. The dependence of the inhibition efficiency of temperature and kinetic parameters of the process of corrosion ofcopper&nbsp; as well as&nbsp; adsorption isotherm model&nbsp; according to which takes place the process of adsorption of inhibitors and the corresponding thermodynamic parameters were also&nbsp; determined by polarization measurements.&nbsp; A process of electrochemical copper&nbsp; dissolution and&nbsp; adsorption of tested inhibitors is followedin situ&nbsp; by&nbsp; quartz crystal microbalance&nbsp; measurements Changes in the morphology of the copper surface due to the effects of corrosive environment and the solutions of the&nbsp; inhibitors were studied by SEM/EDX analysis.The experimental results were correlated with theoretical calculations at the density functional theory level.</p>

No description available.

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.

No description available.

The research reported in this doctoral thesis involves constructing physiochemical models that reproduce the transport behaviour of aqueous chemical species present in environments relevant to the oil and gas industry to gain an improved insight into the local electrochemistry near the electroactive surface (uniform corrosion) or inside the pit (pitting corrosion). The first part of the project involved constructing physiochemical models with one dimensional geometry with aqueous chemical species and chemical and electrochemical processes observed in oxygen (O2) containing brine environments to determine the changes in the local electrolyte composition and the potential within an initiated pit for a variety of external physical and chemical conditions. It was determined that the bottom of the pit suffers greatly from the effects of iR drop (Ohmic drop) if the pit geometry is taken to be macroscopic. The model was extended to include additional aqueous chemical species in conjunction with the chemical and electrochemical processes observed in carbon dioxide (CO2) rich environment to investigate the effects of CO2 on the local electrolyte chemistry at the bottom of the pit. It was found that the proton reduction electrochemical process on its own was incapable of supplying the high currents experimentally measured in CO2 environments via the buffering effect. The second part of the project was to investigate the influence of different experimental conditions on the polarisation behaviour of near static carbon steels in CO2 saturated brine electrolyte via multiple electrochemical measurement techniques. The key observation from this study was the presence of two distinct mass transport limited regions on the cathodic polarisation curve at natural pH (3.775). From the physiochemical model fitted to the experimental cathodic curve, the first mass transport limited region, occurring at lower cathodic potentials, was identified to be the direct reduction of carbonic acid while the second wave, occurring at slightly higher cathodic potentials, was shown to be the direct reduction of aqueous carbon dioxide. Based on the polarisation scans under forced convection, the rate of the direct reduction of carbon dioxide was determined to be under neither potential nor mass transport control. The third part of the project involved extending the existing one dimensional models to include the precipitation of salt films (iron chloride – FeCl2(s) and iron carbonate – FeCO3(s)) in O2 and CO2 saturated brine electrolyte respectively along with the capability to track their respective thickness. Furthermore, the ability of the underlying metal to undergo a change in its state from active to passive is implemented in the model via a set of rules based on the Pourbaix diagram. It was determined that the precipitation of salt films is greatly influenced by the mass transport with no or minimal thickness observed under even natural convection conditions. Furthermore the successful precipitation of salt film was determined to be a precursor step to the metal attaining passivation.

The need to inject treated seawater to enhance reservoir pressure and secondary oil recovery is increasing in the oil field, so also is the reservoir souring potential caused by the activities of Sulphate Reducing Bacteria (SRB) generating H2S in the reservoir. The total cost of SRB mediated corrosion in the United States alone is estimated to be 1-2 billion US dollars per year. In the last few years, a number of potential souring mitigation and prevention tools have been studied. These include: sulphate-reduction using membranes, biocide injection and nitrate injection. Out of all the various methods used for the mitigation and prevention of reservoir souring, the use of nitrate injection in conjunction with waterflood projects is becoming more popular because of its economic benefits and least environmental impact. However, nitrate injection is still widely considered as an emergent technology because there are still many unknowns. One of the major unknowns, of great concern is the susceptibility of subsea hardware components to nitrite, which is a by-product of nitrate anti-souring treatment. Any detrimental effect can compromise the technical integrity of subsea installations. The objective of this research is to study the corrosion susceptibility of CRA (13Cr- Martensitic, 22Cr, and 25Cr super duplex stainless steel) to pitting and stress corrosion cracking in the presence of nitrite. Research hitherto, has investigated corrosion susceptibility of carbon steel to nitrite and found out that nitrite causes pitting in carbon steel. This research work built on previous studies and extensively investigated the effect of nitrite on CRA materials in terms of pitting and stress corrosion cracking. Using electrochemistry techniques in conjunction with C-ring test and slow strain rate test, with variables such as temperature, and nitrite concentration all under anaerobic conditions. Metallographic examination and further evaluation using scanning electron microscopy confirmed pitting and intergranular stress corrosion cracking of 13Cr-L80 and 25Cr due to presence of nitrite.Test data confirmed that sodium nitrite is an anodic inhibitor; it shifts the corrosion potentials to more noble potential and also shifts the anodic curve to lower current, given a net reduction in corrosion rate. A critical concentration of 400ppm is required for inhibition to be effective on 13Cr-L80 and 25Cr. However, below the critical concentration, nitrite significantly increases the corrosion rate. The experimental data generated from this research work provides very valuable information that will tremendously assist the materials selection process for subsea and subsurface hardware components and also serve as a guide in the corrosion management process in existing systems.

In dieser Arbeit wurde die Korrosion an Kanten und Flanschen unter unterschiedlichen Klimabedingungen und räumlichen Anordnungen untersucht und modelliert. Auf Basis von Versuchsdaten konnten Simulationsmodelle zur Vorhersage der Delaminationsweite an Kanten und der Korrosionstiefe in Flanschen entwickelt werden. Mittels Stromdichte-Spannungskurven und elektrochemischer Impedanzspektroskopie wurde die Korrosionskinetik sowie die Barrierewirkung der organischen Beschichtung in das Modell überführt. Das unterschiedliche Korrosionsverhalten von vertikal und horizontal orientierten Kanten wurde durch die von Elektrolyt benetzte Fläche berücksichtigt. Darüber hinaus wurde der Einfluss verschiedener Klimaparameter in zyklischen Wechselklimatests numerisch modelliert. Durch die Kombination empirischer Simulationsparameter konnte der Zyklus eines Wechselklimatests sowohl integral, als auch differentiell unter Berücksichtigung wechselnder Testparameter modelliert werden. Zur Modellierung der Flanschkorrosion wurde ein grundlegendes Potentialmodell vorgestellt.