Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2005. / Includes bibliographical references (leaves 65-67).

Thesis (M.Sc. in Applied Science(Metallurgical Engineering))--University of Pretoria, 2008. / Abstract in English. Includes bibliographical references (leaves 67-69).

Made available in DSpace on 2014-10-09T12:47:17Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:54Z (GMT). No. of bitstreams: 1 07965.pdf: 13989863 bytes, checksum: 2913793c77d98e847907fe76fc84fe02 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:47:17Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:54Z (GMT). No. of bitstreams: 1 07965.pdf: 13989863 bytes, checksum: 2913793c77d98e847907fe76fc84fe02 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Submitted by Pedro Silva Filho (pfsilva@ipen.br) on 2017-11-16T17:59:00Z No. of bitstreams: 0 / Made available in DSpace on 2017-11-16T17:59:00Z (GMT). No. of bitstreams: 0 / Neste trabalho foram realizados experimentos de soldagem circunferencial em tubos de aço inoxidável super duplex UNS S32750, com diâmetros de 19,05 mm e 48,20 mm. Foram executadas soldas utilizando-se diversos parâmetros de soldagem num equipamento MIG com controle CMT&reg Cold Metal Transfer. Os cordões de solda foram avaliados por inspeção visual e dimensional, além dos ensaios de tração e microdureza Vickers, bem como a análise microestrutural em conjunto com análise de precipitação de fases, a qual foi realizada em acordo com a prática A da norma ASTM A923, e ensaio de corrosão conforme a prática A da norma ASTM G48 em conjunto com a norma ASTM A923. Os resultados indicaram que a soldagem do tubo com diâmetro de 19,05 mm apresentou cordão de solda com dimensões inaceitáveis conforme norma, tendo sido esta condição atribuída a utilização de um elevado diâmetro do arame para as condições (parâmetros) usadas de soldagem. A soldagem do tubo com diâmetro de 48,20 mm apresentou falta de penetração nas condições empregadas, quando soldado pelo processo CMT&reg convencional. No caso da utilização do CMT&reg combinado com arco pulsado, em condições que geraram maior aporte de calor durante a soldagem, assim obteve-se penetração total da junta e acabamento superficial adequado. Os resultados indicaram que a soldagem utilizando o processo CMT&reg combinado com arco pulsado, nas condições (parâmetros) empregados geraram bom acabamento superficial, aliado propriedades mecânicas compatíveis, atendendo exigências de normas, bem como uma microestrutura balanceada e alta resistência à corrosão. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Stainless steel (SS) has emerged as an alternative corrosion-resistant reinforcement in concrete instead of the commonly used carbon steel (CS). The biggest advantage of SS is that it takes more time for corrosion to initiate than for CS. An additional benefit from the use of SS in concrete may be derived from the period after the corrosion started until the concrete structure reaches a limit state. This period is called corrosion propagation stage (CPS) and it has been hardly studied in SS reinforced structures. The duration of this period could be related, among other factors, to the morphology of corrosion of stainless steel in concrete. In some instances, the corrosion detection methods for CS have been used on SS reinforced structures to estimate the corrosion condition. However, there is uncertainty if these methods can detect corrosion in SS reinforced structures properly. This investigation was organized in two parts: literature review and experimental work. The literature review indicated among other findings that the duration of the CPS of SS’s embedded in concrete may be estimated to be in the order of several decades. High-grade SS’s would have a longer duration of the CPS. The review also indicated that even localized corrosion of SS reinforcement may induce concrete cracking. The literature also suggested that the corrosion detection on SS reinforced concrete may require a combination of conventional methods (half-cell potential) and advanced electrochemical techniques such as Electrochemical Impedance Spectroscopy, Electrochemical noise, etc. The experimental work focused on further determining whether corrosion of SS in concrete can be detected by methods traditionally used for CS reinforcement, and to what extent localization of corrosion of SS compares with that of CS in concrete. The experiments consisted in accelerated corrosion testing of controlled anodic regions along concrete beams, for which tests were designed and initiated. Martensitic UNS S41000 SS bars were partially embedded in chloride contaminated concrete (5.84% by weight of cement) to cause active corrosion. AISI 1018 CS was also used for comparison purposes. Traditional half-cell potential measurements on the reinforced concrete specimens were evaluated in comparison to that of advanced electrochemical impedance spectroscopy. Additional concrete resistivity monitoring gave an indication of the degree of the pore structure formation. The traditional half-cell potential measurements on AISI 1018 CS reinforced concrete specimens appeared to be suitable to estimate the corrosion state of the reinforcement. However, there was uncertainty on the interpretation of the half-cell potential results and thus the corrosion state of UNS S41000 SS reinforced concrete specimens. Low-dispersion corrosion rates values were found over large areas on SS and CS bars in concrete, but that SS embedded in concrete also seemed to develop instances of corrosion rate peaks. Among other findings, the duration of CPS of CS in concrete was estimated to be in the interval [6-59] years. Assuming that the CPS had been reached, SS specimens in concrete appeared to have a much longer duration of CPS than CS, with an interval [57-253] years. However, this assumption is likely not valid and more work is required to assess the CPS of SS reinforced concrete.

Zinc-nickel ?-phase silicate and copper-nickel silicate corrosion resistant coatings have been prepared via electrochemical methods to improve currently available corrosion resistant materials in the oil and gas industry. A layered silicate, montmorillonite, has been incorporated into the coatings for increased corrosion protection. For the zinc nickel silicate coatings, optimal plating conditions were determined to be a working pH range of 9.3 -9.5 with a borate based electrolyte solution, resulting in more uniform deposits and better corrosion protection of the basis metal as compared to acidic conditions. Quality, strongly adhering deposits were obtained quickly with strong, even overall coverage of the metal substrate. The corrosion current of the zinc-nickel-silicate coating is Icorr = 3.33E-6 for a borate based bath as compared to a zinc-nickel bath without silicate incorporation (Icorr = 3.52E-5). Step potential and direct potential methods were examined, showing a morphological advantage to step potential deposition. The effect of borate addition was examined in relation to zinc, nickel and zinc-nickel alloy deposition. Borate was found to affect the onset of hydrogen evolution and was examined for absorption onto the electrode surface. For copper-nickel silicate coatings, optimal conditions were determined to be a citrate based electrolytic bath, with pH = 6. The solutions were stable over time and strong adhering, compact particle deposits were obtained. The corrosion current of the copper-nickel-silicate coatings is Icorr = 3.86E-6 (copper-nickel coatings without silicate, Icorr = 1.78E-4). The large decrease in the corrosion current as the silicate is incorporated into the coating demonstrates the increase in corrosion resistance of the coatings with the incorporation of silicates.

No description available.

The corrosion resistance of two commercially available SiC filter materials coated with Mg-doped Al₂ TiO₅ and (Ca _0.6.6' Mg_0.52) Zr₄P₆O₂₄ (CMZP) was investigated in high-temperature high pressure (HTHP) alkali-steam environments. Coated specimen properties, including cold and hot compressive strengths, bulk density, apparent porosity, permeability, and weight change, detected after exposure to 92% air-S% steam 10 ppm Na at 8OO°C and 1.8 MPs for 500 h were compared with those of uncoated specimens. Procedures for applying homogeneous coatings of Mg-doped Al₂ TiO₅ and CMZP to porous SiC filters were established and coating of the materials was successfully accomplished. Efforts to stabilize the Al₂ TiO₅ coating composition at elevated temperature were successful. Coatings show promise for providing improved corrosion resistance of the materials in pressurized fluidized bed combustion (PFBC) environments as evidenced by higher compressive strengths exhibited by coated SiC specimens than by uncoated SiC specimens following HTHP alkali-steam exposure. / Master of Science

The corrosion resistance of chemically modified β-eucryptite (Li_0.41Mg_0.035AlP_0.52Si_0.480₄) having low expansion anisotropy and a near zero coefficient of thennal expansion was evaluated. Samples were exposed to aqueous hydrochloride acid at temperatures up to 100°C and environments containing sodium sulfate up to l000°C. The corrosion resistance was characterized by dilatometry, scanning electron microscopy, X-ray diffraction, energy dispersive x-ray analysis, weight variations, and mechanical properties variations. The results show that modified β-eucryptite is more severely corroded than commercial lithium-alumina-silicate glass-ceramics when exposed to these environments. Aqueous HCI removes AIP04 from modified β-eucryptite leaving a very porous structure. Molten salt corrodes modified β-eucryptite by penetration of sodium and sulfur which form an alkali melt under the surface. The modulus of rupture and the Young's modulus are reduced by both types of corrosion. / Master of Science