Tenacidade ao impacto e resistência a fadiga de aço API 5L X70 modificado ao Nb

O transporte de gás e derivados de petróleo é realizado pelo uso de tubulações, denominadas de oleodutos ou gasodutos, que necessitam de elevados níveis de resistência mecânica e corrosão, aliadas a uma boa tenacidade à fratura e resistência à fadiga. A adição de elementos de liga nesses aços, Ti, V e Nb entre outros, é realizada para o atendimento destes níveis de resistência após o processamento termomecânico das chapas para fabricação destes dutos, utilizando-se a norma API 5L do American Petroleum Institute, API, para a classificação destes aços. A adição de elementos de liga em associação com o processamento termomecânico visa o refino de grão da microestrutura austenítica, o qual é transferido para a estrutura ferrítica resultante. O Brasil é o detentor das maiores reservas mundiais de nióbio, que tem sido apresentado como refinador da microestrutura mais eficiente que outros elementos, como o V e Ti. Neste trabalho dois aços, denominados Normal e Alto Nb foram estudados. A norma API propõe que a soma das concentrações de Nióbio, Vanádio e Titânio devem ser menores que 0,15% no aço. As concentrações no aço contendo mais alto Nb é de 0,107%, contra 0,082% do aço de composição normal, ou seja, ambos atendem o valor especificado pela norma API. Entretanto, os aços são destinados ao uso em dutovias pela PETROBRÁS que impõe limites nos elementos microligantes para os aços aplicados em dutovias. Deste modo estudos foram desenvolvidos para verificar se os parâmetros de resistência à tração, ductilidade, tenacidade ao impacto e resistência à propagação de trinca por fadiga, estariam em acordo com a norma API 5L grau X70 e com os resultados que outros pesquisadores têm encontrado para aços dessa classe. Ainda, como para a formação de uma dutovia os tubos são unidos uns aos outros por processo de soldagem (circunferencial), o estudo de fadiga foi estendido para as regiões da solda e zona termicamente afetada (ZTA). Como conclusão final observa-se que o aço API 5L X70 com Nb modificado, produzido conforme processo desenvolvido pela ArcelorMittal - Tubarão, apresenta os parâmetros de resistência e ductilidade em tração, resistência ao impacto e resistência a propagação de trinca em fadiga (PTF) similar aos aços API 5L X70 com teores de Nb = 0,06 % peso e aqueles da literatura com teores de Nb+Ti+V < 0,15% peso. O metal base, metal de solda e zona termicamente afetada apresentaram curvas da/dN x ΔK similares, com os parâmetros do material C e m, da equação de Paris, respectivamente na faixa de 3,3 - 4,2 e 1.3x10-10 - 5.0x10-10 [(mm/ciclo)/(MPa.m1/2)m].

Estudio de la susceptibilidad a la corrosión bajo esfuerzos de uniones en tuberías de acero API 5L, X70 obtenidas por soldadura SMAW y MMA.

Tesis (Maestría en Ciencias de la Ingeniería Mecánica con Especialidad en Materiales) UANL, 2013.

Aumento da velocidade de soldagem para processo de arco submerso em juntas de um tubo de aço API X70

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Avaliação da tenacidade à fratura na região de transição dúctil-frágil dos aços API 5L X70 e X80 utilizando a metodologia da curva mestra

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Avaliação da integridade estrutural em um tubo de aço API 5L X70 através da propagação de trincas por fadiga

Pós-graduação em Engenharia Mecânica - FEG

Avaliação da tenacidade CHARPY-V de um tubo de aço API 5L X70 soldado com arco submerso

This research project focused primarily on assessing the impact toughness of the weld and the base material of a steel pipe API 5L X70 submerged arc welded, used to conduct remote oil and gas (linepipes). The analysis followed strictly the Specification for Line Pipe - API 5L Standard, regarding the removal of the specimens of regions-of-proof-long section of the pipe, at 90o and 180o from the welded joint, and mechanical properties of toughness and Charpy-V, both the joint welded as the base material. Specimens of steel tube supplied by Tenaris Confab-SA were sized for tensile and Charpy-V, according to ASTM E 8M and ASTM E23, respectively. The result obtained showed that the API X70 steel tube has high Charpy-V toughness, near to each other at both 90o and 180o from the welded joint of the tube, and both higher than the weld metal. Microstructural and microhardness analysis complemented the present study

Determinação experimental da tenacidade à fratura em baixas temperaturas de tubos de aço API 5L X70

Because of the great metallurgical advances, the welded tubes by HF / ERW (High Frequency / Electrical Resistance Welding) have played a more active role in the oil and gas, gradually replacing tubes produced by other processes (UOE, SAW, and others) to deep water applications, in high and extremely low temperatures, highpressure conditions and in highly corrosive environments. However, studies have revealed that defects in the welded joints are in one of main causes of failures in pipelines. Associated with damage external and the stringent requirements of this sector, the welded joints become particularly critical for his toughness and the determination of this particular property is fundamental. This study aims to evaluate the toughness of the HF / ERW pipes in HSLA steel API X70 class, used in pipelines transport systems of gas and oil from data obtained with CTOD tests (Crack Tip Opening Displacement). The main objectives of this project are: mechanical and microstructural characterization of steels API X70 manufactured in Brazil; and evaluation of the toughness of weld process by HF / ERW steel API X70 national. After having the tests done, mechanical, chemical and metallurgical, we have the conclusion that those pipe are in agreement to API 5L 42ª edition for X70MO and the toughness behaves like the expected

Investigação experimental da tenacidade em tubos de aço API 5L X70 soldados pelo processo HF/ERW

Studies about structural integrity are very important when it desires to prevent disasters associated with flaws inherent in materials used in structural components. The welded joints in steel pipes used to conduction and distribution of oil and gas correspond to the regions most susceptible to flaw. Aiming to contribute to this research line, the present study was designed to assess experimentally the structural integrity of welded joints in steel pipes API 5L X70 used in pipeline systems. This assessment is given from tests of CTOD, whose aim is simulate in laboratory the real behaviour of crack from of his propagation on the welded joint obtained by high frequency electric resistance welding. In this case, the analyses are performed from specimens SE(B) obtained directly of steel pipe API 5L X70. The proposed methodology involves tests of CTOD at lower temperature, in order to assess the toughness of material in critical operation conditions. From performance of CTOD tests, was possible assess the toughness of welded joints in terms of quantity through CTOD parameter and in terms of quality from behaviour of curve load versus CMOD. In this study, also, sought to compare CTOD’s results obtained through rules ASTM E1820 (2008) and BS 7448 (1991). Although the two standards cited previously have adopted different parameters to calculated the value of CTOD, concluded that the values of CTOD tend to converge for a common value

Estudo do comportamento em fadiga de uma chapa de aço microligado, grau API 5L X70

In engineering, for correct designing the structural components required for cyclical stresses, it is necessary to determine a limit of resistance to fatigue, which is the maximum amplitude of the applied tension under which the fatigue failure does not occurs after a certain number cycles. The marine environment is hostile, not only by the high pressure, corrosion, but also by low temperatures. Petrol Production units, composed of the risers (pipelines connecting the oil well to the ship), are dimensioned to remain installed for periods of 20 up to 30 years, and must therefore be prepared to support various efforts, such as tidal, wind currents and everything that is related. This paper focuses on a study on the fatigue behavior of microalloyed steel, API 5L Grade X70, used to transport oil and gas by pipelines. For analysis, we obtained the curves S-N (stress vs. number of cycles) using laboratory data collected from cylindrical longitudinal and transverse specimens used in axial fatigue test in accordance with ASTM E466. The tensile tests and microhardness were performed to characterize the mechanical properties of the samples, and it was found that the values meet the specifications of the standard API 5L. To characterize microstructurally the material, it was also made a metallographic analysis of the steel under study, and the origin of the fatigue crack was investigated with the support of a scanning electron microscope (SEM).

Avaliação da influência da taxa de resfriamento posterior ao tratamento térmico nas propriedades mecânicas do aço API 5L X70

In this work a study about the mechanical properties of the API 5L X70 steel, with or without heat treating, has been made, with the intetion of assess the influence of cooling after the austenitization heat treating by air cooling (normalizing) and a rapid cooling with oil (tempering). This steel is known by high strength and ductility values and it is commonly used in the manufacture of oil pipes. The growing energy demand encouraged the study and manufacture of this material. Although this microalloyed dispense subsequent heat treatings, it was proven that its implementation is very advantageous for this type of application, improving hardness and plastic stability. It was also assessed that the faster the cooling rate is, the better will be these properties

Estudo do comportamento em fadiga de um tubo de aço microligado, grau API 5L X70

This work focuses on a study on the fatigue behavior of a microalloyed steel API 5L X70, used in pipes lines to transport oil and gas. These types of steels have excellent mechanical resistance values and ductility and therefore increased their study driven by increased demand for oil and especially natural gas, which consequently raises the need to build new pipelines to transport these products. The oil extraction units, composed of the risers (pipelines connecting the oil well to the ship), are dimensioned to remain installed for periods of 20 to 30 years in the marine environment, a hostile environment for high pressure, corrosion, low temperatures and the stresses caused by the movement of water and tides. For analysis, the S-N (stress versus number of cycles) curves were obtained from data collected from bodies-of-proof cylindrical longitudinal, transverse and that one removed from the weld area of the pipe, tested in accordance with ASTM E466. Tensile tests were performed for characterizing the mechanical properties of the samples and welded joints, concluded that the values meet the specifications of the standard API 5L. To characterize microstructural material, also metallographic analysis was made of regions of the base metal and the HAZ. The results of fatigue tests demonstrated a higher life for the specimens removed from the longitudinal direction the pipe, followed by those in the transverse direction and, finally, the welded joint. The origins of the fatigue cracks were determined by scanning electron microscopy (SEM)

Características do aço API X70 utilizado em tubos de transporte de petróleo e gás

Having in mind that petroleum's history presents a huge growth, the exploration and production areas have been receiving lots of investments, in order to attend the increasing demand for gas and petroleum. Looking through that scenario, new technologies have been evolving in favor of discovering new natural petroleum deposits and act with effectiveness in truly deep waters without giving up the worldwide best operational security practices. The use of rigid pipes in marine installations have been rising quickly and, thanks to this reality, the many storage and pipe launching forms became study objects and are getting improved. The analysis of steel API X70 characteristics, proving that they are suitable for use in pipes developed to transport gas and petroleum is the theme of this presentation. A tensile test was conducted to determine the base metal's mechanical properties, draining's tension, traction's resistance, elasticity's modulus and maximum tension. An aspect that is concerning too is the metallographic analysis, in order to determine the studied iron's microstructure. Results of analyzes showed that the steel has high resistance, with good capacity for deformation and well defined yield point, concluding suitable for the application in question

Estudo do efeito Bauschinger em tubos de aço API 5l x70 aplicados no transporte de petróleo e gás

Despite the growing concern in seeking more sustainable energy sources, oil demand is likely to grow in coming years. To keep up with this growth, the oil industry has increasingly invested in innovation and efficiency. Knowing that, new technologies have been developed to explore deeper waters, without giving up the best practices in worldwide operational safety. The use of rigid pipelines in deepwater offshore facilities is increasing quickly and because of this, the ways of storing and launching pipe have been studied and perfected. In this paper the Bauschinger effect on API 5L X70 steel was analyzed proving that there was a reduction in yield strength when an effort was applied in a previous direction, then an effort was then applied in the opposite direction. To observe this phenomenon, the tensile test was conducted to determine the mechanical properties of the base metal, such as yield stress, tensile strength, elasticity and maximum tensile, so then compare it with the results obtained in the Bauschinger Effect Test. The analysis results showed that the steel had high resistance, with good plastic deformation capacity without failing, well-defined yield point, showing itself appropriate for the operation of oil and gas pipes

Características do aço API X70 utilizado em tubos de transporte de petróleo e gás

Having in mind that petroleum's history presents a huge growth, the exploration and production areas have been receiving lots of investments, in order to attend the increasing demand for gas and petroleum. Looking through that scenario, new technologies have been evolving in favor of discovering new natural petroleum deposits and act with effectiveness in truly deep waters without giving up the worldwide best operational security practices. The use of rigid pipes in marine installations have been rising quickly and, thanks to this reality, the many storage and pipe launching forms became study objects and are getting improved. The analysis of steel API X70 characteristics, proving that they are suitable for use in pipes developed to transport gas and petroleum is the theme of this presentation. A tensile test was conducted to determine the base metal's mechanical properties, draining's tension, traction's resistance, elasticity's modulus and maximum tension. An aspect that is concerning too is the metallographic analysis, in order to determine the studied iron's microstructure. Results of analyzes showed that the steel has high resistance, with good capacity for deformation and well defined yield point, concluding suitable for the application in question

Estudo do efeito Bauschinger em tubos de aço API 5l x70 aplicados no transporte de petróleo e gás

Despite the growing concern in seeking more sustainable energy sources, oil demand is likely to grow in coming years. To keep up with this growth, the oil industry has increasingly invested in innovation and efficiency. Knowing that, new technologies have been developed to explore deeper waters, without giving up the best practices in worldwide operational safety. The use of rigid pipelines in deepwater offshore facilities is increasing quickly and because of this, the ways of storing and launching pipe have been studied and perfected. In this paper the Bauschinger effect on API 5L X70 steel was analyzed proving that there was a reduction in yield strength when an effort was applied in a previous direction, then an effort was then applied in the opposite direction. To observe this phenomenon, the tensile test was conducted to determine the mechanical properties of the base metal, such as yield stress, tensile strength, elasticity and maximum tensile, so then compare it with the results obtained in the Bauschinger Effect Test. The analysis results showed that the steel had high resistance, with good plastic deformation capacity without failing, well-defined yield point, showing itself appropriate for the operation of oil and gas pipes