Mestrado em Engenharia Mecânica

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Agora exibindo 1 - 11 de 11

Análise comparativa de aços ARBL usados na fabricação de tubos flexíveis para produção de petróleo no mar, em formações com baixo teor de H2S : um estudo de FPH utilizando solução de tiossulfato de sódio
(Universidade Federal do Espírito Santo, 2006-06-02) Girelli, Rosental Alves; Scandian, Cherlio; Macêdo, Marcelo Camargo Severo de; 1º membro da banca
This document is an experimental study of the Stress Corrosion Cracking (SCC) and Hydrogen Embrittlement (HE) behavior of a Brazilian high-strength low-alloy steel, in media with low content of H2S. It is intended to begin a qualification process of the material, which is already used in flexible pipes for petroleum production operations at the sea in situations where there is no H2S presence, to also act in cases where low concentration of this gas exists. A heat treatment is proposed for the resistance improvement of the material in these environments. The base for experimental results comparison was another material, a French one, which is already qualified and used in flexible pipes for sour oil (with H2S) production. Hence, three materials were tested: the original Brazilian one, without heat treatment (it is used in flexible pipes, in situations without H2S), the same material with the heat treatment suggested for the property improvement and possible use in low H2S environments and the French one (qualified material used in flexible pipes for oil production operations, in situations where the presence of H2S is a reality). The SCC Slow Strain Rate and Constant Strain techniques were used as the experimental tests and the media was an aqueous solution of NaCl with micro addictions of sodium thiosulfate (Na2S2O3), indicated to simulate corrosive environments with low concentration of H2S. Damage parameters (energy), embrittlement measurements, tensile properties and also fracture features of the specimens were evaluated at the comparative analysis of the materials.
Avaliação da resistência à corrosão localizada de cladding de aço inoxidável duplex UNS S39209 em aço carbono pela técnica eletroquímica de reativação potenciodinâmica de ciclo duplo (DL-EPR)
(Universidade Federal do Espírito Santo, 2018-08-30) Lima, Gustavo Fernandes Negris; Luz, Temístocles de Sousa; Macêdo, Marcelo Camargo Severo de; Ponzio, Eduardo Ariel; Cotta, Rômulo Almeida
The study of welding coating deposition technology is necessary because it is widely used in industries, combining good mechanical characteristics and high resistance to corrosion at low cost, both with regard to the manufacturing process (cladding) and the process of recovery, through over thickness.In this work the results obtained by DL-EPR techniques were evaluated in terms of the susceptibility to localized corrosion of duplex stainless steel cladding UNS 39209. The relationship between welding energy, dilution and sensitization was also sought.DL-EPR assays wereperformed in a 33% H2SO4solution + 0.5% HCl by volume, and a scan rate of 1.5 mV / s, in order to quantify the level of sensitization after the TIG welding thermal cycle fed with cold wire.With the results obtained, it was concluded that the increase ofthe dilution rate of the coating and the welding energy, increase the degree of sensitization and, consequently, increase the susceptibility to localized corrosion. This fact can also be observed in the proportion of ferrite-austenite and in the formationof phases such as secondary austenite and chromium nitrides
Avaliação da resistência à corrosão localizada de cladding de aço inoxidável duplex uns S39209 em aço carbono por meio de espectroscopia de impedância eletroquímica
(Universidade Federal do Espírito Santo, 2018-08-31) Sperandio, Bruno Filipe da Penha; Luz, Temístocles de Sousa; Macêdo, Marcelo Camargo Severo de; Ponzio, Eduardo Ariel; Cotta, Rômulo Almeida da
In this work electrochemical impedance spectroscopy tests were performed on the open circuit potential in samples of duplex steel UNS S39209 deposited by TIG welding on ASTM A36 steel sheets. A solution of 33% H2SO4+ 0.5% HCL with perturbations in the order of ± 10mV was used varying the frequency of 100Khz to 10mhz and 10 points per decade varying in potential. In order to evaluate the corrosion resistance of the duplex steel, relate to the ferrite / austenite volumetric fraction and compare with the results found by the DL-EPR technique.To reach the results an area adjustment was performed using the ferrite / austenite volumetric fraction. It was verified that the sample with lower dilution and austenite fraction presented higher resistance to corrosion than the others, consistent with the sensitization data. A tendency was observed for increasing the dilution and penetration of the addition metal with increasing welding energy. Deposition welding has proved to be an efficient option to increase the corrosion resistance of a material
Avaliação do efeito do fluxo e da concentração de ácido acético na corrosão por CO2 dos aços carbono SAE 1020 e 1045
(Universidade Federal do Espírito Santo, 2015-03-31) Monfardini, Warlen Alves; Macêdo, Marcelo Camargo Severo de; Martins, Marcio Ferreira; Rodrigues, Cezar Henrique Manzini
The CO2corrosion is a big concern in many industries, in particular in the oil and gas exploration field. In this industry, the CO2is in gaseous form and it is hydrated forming H2CO3(carbonic acid). This acid is a weak acid and it can decrease the pH value and increase the corrosion rate. Another factor that has been studied is the presence of acetic acid (HAc) which is present in small concentration (a few mM). Considering the relevance of concentration of acetic acid, presence of CO2and mass transport, this work aim evaluate the flow effect and acid acetic concentration on the CO2corrosion of low carbon steels (SAE 1020 and 1045). Were performed the potentiodynamic polarization by a RDE geometry in solution with 3 % NaCl, saturated by CO2(1 atm), andsmall concentration of HAc (0, 300, 1000, 2000 ppm). Through the polarization curves was possible to observe a significant influence of the flow and concentration of HAc on the corrosion parameters like Ecorr, Icorr, Ilim, ba, bcand Ru. This behavior evidence a complex interaction between anodic and cathodic reactions on the corrosion process in presence of HAc. After each testing, the superficial surface wasobserved by optical microscopy and scanning electron microscopy (SEM). Was observed pitting attack in practically all conditions
Efeito da temperatura de tratamento térmico na corrosão localizada do aço inoxidável duplex UNS S31803 avaliado por espectroscopia de impedância eletroquímica
(Universidade Federal do Espírito Santo, 2015-09-18) Helker, Paulo Victor Toso; Macêdo, Marcelo Camargo Severo de; Cotta, Rômulo Almeida; Ponzio, Eduardo Ariel
This study evaluated the comparative results obtained from the DL-EPR techniques and electrochemical impedance spectroscopy, in terms of behavior susceptibility to localized corrosion of UNS S31803 duplex stainless steel. Also sought the relationship between the heat treatment, microstructure and sensitization. For these samples were heat treated at the temperatures 645 ° C, 820 ° C and 960 ° C for 12 hours besides the sample under the condition "as received". These treatments resulted in the precipitation of sigma phase. DL-EPR tests were conducted in a 2 M H2SO4 solution + 0.5M NaCl + 0.01 M KSCN in order to quantify the degree of sensitization after heat treatment, and testing electrochemical impedance spectroscopy in the same solution, however the open circuit potential (OCP) and the potential of +350 mVsce where the samples are passive, in order to verify that the results were consistent with those obtained with DL-EPR. The samples suffered a considerable change in the proportion of ferrite-austenite due to heat treatment. Thus, the EIS results were evaluated with caution, in order to consider that effectively attacked areas experienced great variation, which should be appropriately compensated before evaluating the results
Efeito da velocidade de resfriamento após tratamento térmico em alta temperatura na resistência à corrosão localizada do aço UNS S31803
(Universidade Federal do Espírito Santo, 2014-02-25) Garcia, Davi Pereira; Macêdo, Marcelo Camargo Severo de; Pardal, Juan Manuel; Tavares, Sérgio Souto Maior
Duplex Stainless Steel have both phases ferrite and austenite in his microstructure in almost equal proportions, allowing it to have great strength corrosion and mechanical resistance , being extremely used in petrochemical and chemical industries. When exposed to high temperatures they are subject to microstructural changes making his properties to be modified. In this work localized corrosion resistance of the duplex stainless steel UNS S31803 heat treated by high temperature(1300◦C) for 30 minutes followed by different cooling rates is studied.Somesamples were solution treated at 1000◦C for 1 hour and fast cooled after the high temperaturetreatment.A wide range of microstructures,with differents morphologies and phase proportions, were obtained by this way, also this microstructural changes during cooling process have promoted the precipitation of deleteriusphases such as nitrides and sigma, making the corrosion strength to be altered.The intergranular corrosion resistance wasmeasured with DL-EPR technique,and pitting corrosion was made using potentiodynamic polarization both according to the standard ASTM.Besides these tests were made microhardness analysis,optical microscopy andscanning electron microscopy of the samples.
Efeito do tempo de exposição nas temperaturas de 645°C e 820°C na corrosão localizada do aço inoxidável duplex UNS S31803 avaliado por espectroscopia de impedância eletroquímica
(Universidade Federal do Espírito Santo, 2015-09-18) Faria, Eduardo Sarcinelli; Macêdo, Marcelo Camargo Severo de; Cotta, Rômulo Almeida; Ponzio, Eduardo Ariel
In the present work were evaluated theelectrochemicalimpedance techniqueto detect the corrosion susceptibility of the UNS S31803 duplex stainless steel. This material was studied in the ‘as received’ condition (RC) and after heat treatment at temperatures of 645ºC and 820ºC, for times ranging from 4 hours, 8 hours and 12 hours. These treatments lead to precipitation, especially the sigma phase and also, chromium carbide and chromium nitrides. The study was performed using Double-loop Electrochemical Potenciokinect Reactivation (DL-EPR) method and Electrochemical Impedance Spectroscopy (EIS) in theOpen Circuit Potential (OCP) and just after film formation in a 2M H2SO4+ 0,5M NaCl + 0,01M KSCN solution. On the DL-EPR test it was found the presence of reactivation peaks in samples of 645ºC and 820ºC due to material sensitization. On the EIS test, were found inconsistent values for the charge transfer resistance (Rct) and a high value for Constant Phase Element (CPE) for the sample treated at 645ºC which indicates that there is more ion transport in these samples thanin the material treated at 820ºC. Values of inductance (L) and intermediate adsorption strength (Rads) were higher for the treated samples than for the ‘as received’ condition, leading to a misleadingthat the sample treated at 820ºC has a better corrosion resistance than the RC specimen. Due to this behavior, a correction was proposed in the area subject to corrosion so that the values are more plausible with the actual context
Estudo da corrosão de aços-carbono e patinável durante 39 meses de exposição em ambiente marinho-industrial
(Universidade Federal do Espírito Santo, 2007-12-15) Leite, Leandro Alberto Silva; Queiroz, Rogério Silveira de; Macêdo, Marcelo Camargo Severo de; Bozzi, Antônio César
Following the results presented by OLIVEIRA (2002), in which the corrosive process analysis was carried out after 4 months exposition, the corrosion pattern for longer periods of exposition under similar geo-environmental conditions is investigated by this present work. ASTM A36 and ASTM A242 steel samples were exposed during 39 months in two industrial marine sites located in the southern shore of Espírito Santo State. Meteorological conditions were monitored and SO2 concentration was tested during the exposition period. Mössbauer s spectroscopy was used to characterize the corrosion outcomes. The samples from both sites presented similar composition, with emphasis to α-FeOOH. Smaller fractions of γ- FeOOH, Fe3O4, γ-Fe2O3 and α-Fe2O3 were also observed, being the latter originated from the particulates precipitated from the surrounding environment. Corrosion rates and thickness losses were determined through mass loss essays. The ASTM A36 steel sample showed steeper curves as function of time and always superior to those found for the weathering steel in both sites, especially for the area with higher SO2 concentration. ASTM A242 steel presented specific results for each site. In the less aggressive site, it showed a more stable corrosion process with good formation of protective rust layer and mass loss of around 2% in mass, whilst at the other site it presented similar pattern as the ASTM A36 steel, although less intense. Finally it was determined the industrial applicability of the ASTM A242 steel at regions with lower concentration of sulfates
Estudo de corrosão em tubulações de Gás de Coqueria
(Universidade Federal do Espírito Santo, 2004-12-17) Vieira, Wander Pacheco; Macêdo, Marcelo Camargo Severo de; Scandian, Chérlio; Miranda, Luiz Roberto Martins de
Within an integrated steelworks process, several types of gases are produced. From an energy volume standpoint, the most important among them are those resulting from the production of coke and hot metal, namely, Coke Oven Gas (COG) and Blast Furnace Gas (BFG), respectively. If they are not properly treated, these gases may display intense corrosive features due to the presence of humidity and corrosive agents. As a result, the steel piping used for carrying these gases can fail because of clogging and perforation, as it happens in the case of COG. As part of an experiment, six test specimens were immersed in a condensate for up to six months. They were made of ASTM 283-C steel and were inside sealing pots within the COG piping. The corrosion rate and the loss of thickness were determined by bulk loss chemical tests. The characterization of the corrosion product’s composition was undertaken through tests such as X-ray diffractometry, infrared spectrophotometry, fluorescence spectrometry, Mössbauer spectroscopy as well as optical and scanning electronic microscopy.
Estudo do Efeito da Temperatura e do Tempo de Tratamento Térmico na Corrosão Localizada do Aço Inoxidável Duplex uns S31803
(Universidade Federal do Espírito Santo, 2014-11-28) Silva, Christiano Honorato Pereira e; Pardal, Juan Manuel; Tavares, Sérgio Souto Maior; Ponzio, Eduardo Ariel; Macêdo, Marcelo Camargo Severo de
This study aims to evaluate the influence of time of exposure to certain temperatures on the mechanical properties and resistance to localized corrosion of duplex stainless steel UNS S31803. The tested specimens were obtained from ribbons of stainless steel, and treated at temperatures of 475ºC, 570°C, 645°C, 820° C, 914°C and 960°C. For each temperature, samples were heat treated at different times of 4, 8 and 12 hours respectively. Samples provided "as received" were also evaluated.Testing double loop electrochemical potentiokinetic reactivation (DL-EPR) were performed and Testing the hardness and metallographic analysis, which allowed us to evaluate the proportion of microconstituents varied over time and according to the treatment temperature were performed. Furthermore, only the samples exposed for 12 hours at each temperature,were evaluated by X-ray diffraction.The experimental results showed that secondary phases arise at different treatment temperatures and have direct influence on increasing the hardness of steel. For resistance to localized corrosion, only samples undergoing treatment at temperatures of 645, 820 and 914 °C showed a peak of reactivation.
Influência do efeito da temperatura de preaquecimento, do tipo de corrente e do gás de proteção na soldagem de chapas finas de aço inoxidável duplex uns s31803
(Universidade Federal do Espírito Santo, 2016-09-29) Santos, Rodrigo Soares dos; Luz, Temístocles de Sousa; Macêdo, Marcelo Camargo Severo de; Pardal, Juan Manuel; Liskevych, Olga
The necessity of materials that combine high corrosion resistance and good mechanical properties make the duplex stainless steel UNS S31803 widely used in corrosion environments, such as petrochemical industry, marine and others. Their weldability necessary for mounting and repairing equipment, still have many technological difficulties, such as precipitation of deleterious phases and alteration of ferrite/austenite balance. It becomes more complex when is difficult to control the heat flux. This work has the purpose to evaluate samples of duplex stainless steel UNS S31803 of thinness, subjected to GTAW weld process without filler metal with preheating in order to enable better control of the fusion zone. Experiments were conducted varying current (convectional and pulsed) and temperature of the preheating stage. Test of double loop electrochemical potentiodynamic reactivation was also performed in order to study the corrosion resistance in this region. The balance of ferrite/austenite was accounted and the microstructural characterization was evaluated by optical microscopy and scanning electron microscopy (MEV). It was concluded that changing the types of current, the shielding gas and the temperature of preheating influenced the microstructural balance and corrosion resistant.

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