steel API 5L X70

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Role of texture in hydrogeninduced cracking of steel API 5L X70 under various  paths

Role of texture in hydrogeninduced cracking of steel API 5L X70 under various paths

Crystallographic texture analyses are considered as a new approach to improve the HIC resistance. Grain orientations, grain boundaries distribution and microstructure in pipeline steels depend on several manufacturing processes, such as the rolling conditions, cooling rate and start and finish rolling temperatures. However, it is a very challenging task to create an ideal texture and microstructure that have the highest resistant against HIC. Shukla et al. [17 ] have shown that the intensity of α { }//RD and γ { }//ND fibers increased with the decrease in finish rolling temperature (FRT). Venegas et al. [18] discovered a strong correlation between texture and mitigation of HIC in pipeline steel. The same authors also showed that {111} and {211} dominant textures decrease HIC susceptibility. It is reported that grain boundaries having planes of similar Miller indices are crack-resistant [19]. Also, Arafin et al. [20] documented that grain boundaries having the {100} grain orientation with <100> rotation axis are prone to cracking. Szpunar et al. [21,22] also papered the importance of grain boundary distributions ahead of the crack tip. They explained that low-angle boundaries (LABs) and coincidence site lattices (CSLs) are resistant to crack propagation through the formation of better lattice compliance in adjacent grains, whereas high-angle boundaries (HABs) with high stored energy provoke crack propagation.
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Study of texture and  evaluation of steel API 5L X70 under various  cycles art hfgabreu

Study of texture and evaluation of steel API 5L X70 under various cycles art hfgabreu

Water quenching following hot rolling produced a material that was essentially composed of low-carbon lath martensite and small amounts of retained austenite. The martensite laths were detected at several microns (Fig. 2d). The laths were normally separated by low-angle grain boundaries (LAGBs) and were highly distorted. Water quenching generates a large number of dislocations in the grain interiors, and dislocations become trapped at the sub- boundaries. Piled-up dislocations at the sub-boundaries change the sub-boundaries into LAGBs with higher stored energy. As a result, the hardness was increased significantly to 34875 HV. Moreover, a notably small amount of retained austenite was observed between the martensite laths. Thus, the carbon content at the grains decreases, and thus, the tetragonality of the lath martensite declines. The crystal structure of the lath martensite with carbon content below 0.2% is essentially body-centred cubic (bcc). Speich et al. [17] has reported that in low-carbon steel (c o 0.2%), carbon diffusion in martensite during quenching is sufficient to form segregation of dislocations and lath boundaries. This carbon motion is attributed to the only slightly destroyed bcc structure. In other words, tetragonality distortion induced by solute atoms at octahedral sites could be ignored in the bcc lattice. E. Anelli and D. Colleluor [18] declared that for linepipes of X65 and X70 grades, the tempering temperatures should be greater than 600 1C to produce the best toughness levels suitable for satisfying the specifications requirements, especially after strain aging. At temperatures above 600 1C, the lath structure is partially recovered, dislocation annihilation can take place, and moderate dislocation density can result. In addition, re-crystallisation of ferrite begins in certain areas. New strain-free re-crystallised austenite grains can develop at aging temperatures of approxi- mately 640 1C. The AC1 temperature for the steel is approximately
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Estudo do comportamento em fadiga de um tubo de aço microligado, grau API 5L X70

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).
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Avaliação da tenacidade à fratura de aço API 5L X70 utilizado na fabricação de dutos...

Avaliação da tenacidade à fratura de aço API 5L X70 utilizado na fabricação de dutos...

A primeira vez que se utilizou aços microligados para construção em 1950 de um duto entre Michigan a Wisconsin, nos Estados Unidos. O aço X52 foi produzido pela Great Lakes Steel (MORRISON, 2008) – a primeira empresa a produzir comercialmente um aço microligado ao nióbio. O teor de carbono, baixo para a época, era da ordem de 0,16%. Hoje, aços modernos de resistência elevada contêm usualmente um quarto desse teor. A figura 9 mostra cronologicamente a evolução dos desenvolvimentos de vários graus de aços. Atualmente, o grau de alta resistência mais produzido comercialmente é os X70 e, rapidamente, o grau X80 vem ganhando espaço nos novos projetos. O aumento de resistência permite diminuição da espessura e conseqüente diminuição da quantidade de aço e da quantidade de soldas. Os custos do aço representam aproximadamente metade do custo de um duto e, portanto, a redução de espessura representa uma economia considerável no projeto.
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Hydrogen Cracking in an API 5L X70 Steel Welded with Cellulosic Electrodes of Different Levels of Mechanical Resistance

Hydrogen Cracking in an API 5L X70 Steel Welded with Cellulosic Electrodes of Different Levels of Mechanical Resistance

Resumo: Aços classificados segundo a norma do American Petroleum Institute (API) enfrentam o problema de trincamento a frio decorrente da soldagem. Neste trabalho foi estudado, por meio do ensaio de implante, o efeito da resistência mecânica do metal de solda sobre a susceptibilidade de um aço API-5L-X70 ao trincamento pelo hidrogênio. As soldas foram realizadas com dispositivo de soldagem por gravidade, usando-se dois eletrodos celulósicos, AWS-E6010 e AWS-E8010. O hidrogênio difusível dos eletrodos foi determinado por cromatografia gasosa. Como resultado do ensaio de implante, observou-se uma tendência maior à fissuração quando foi utilizado o eletrodo AWS-E6010. Isso pode ser relacionado à menor resistência mecânica apresentada pela solda resultante do mesmo e ao fato de o eletrodo ser menos ligado. Assim, o metal de solda pode ter se transformado a temperaturas mais elevadas, o que levou a uma maior migração do hidrogênio para a ZTA. Observou-se, ainda, que mesmo as soldas que não falharam no ensaio apresentaram trincas. Isso pode ser devido às condições de resfriamento do cordão que levaram ao aparecimento ilhas com estruturas frágeis e susceptíveis ao trincamento. Para as menores cargas usadas (0,8.σ e ), contudo, estas trincas
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Effect of  orientations on the hydrogeninduced cracking resistance improvement of API 5L X70 pipeline steel under various  processing art hfgabreu effect

Effect of orientations on the hydrogeninduced cracking resistance improvement of API 5L X70 pipeline steel under various processing art hfgabreu effect

Grains oriented in preferred crystallographic orientation that develop during manufacturing process can influence both the mechanical properties and the HIC resistance. The texture of a rolled sheet is represented by a combination of crystallographic plane and direction {hkl}<uvw>, which means that {hkl} are the planes parallel to the rolling plane and the <uvw> are the direc- tions parallel to the rolling direction which is shown in Fig. 1 [10]. Venegas et al. [11,12] studied influence of texture on HIC sus- ceptibility in API X46 steel. They showed that the preferred grain oriented with plane {111} parallel to normal direction ({111}//ND) produced via warm rolling bellow recrystallisation temperature increased the HIC resistance. Ghosh et al. [13] reported that the cleavage {001}//ND grains generated during rolling at high tem- perature by rescrystallisation of austenite grains followed by ferrite transformation, provide an easy crack path and reduce significantly both the mechanical properties and the HIC resistance. Verdeja et al. [14] documented that the crystallographic textures associated with {110}//ND and {332}//ND reduce the sensitivity to HIC in ferritic- pearlitic steels, while {001}//ND and {112}//ND textures have the opposite effect. Recently, Mohtadi-Bonab et al. [15–17] reported that there is no preferred direction for hydrogen crack propa- gation, and that crack can propagate along various orientations. However, different factors such as grain orientation, grain bound- ary distributions, special coincidence site lattice (CSL) boundaries, and distribution of recrystallised grains play significant roles in HIC resistance by providing good lattice fit with low stored energy ahead of the crack tip [18,19]. It is worth mentioning that the
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Caracterização microestrutural e mecânica em juntas soldadas por arco submerso em chapas de aço microligado API 5l x70 utilizadas em minerodutos

Caracterização microestrutural e mecânica em juntas soldadas por arco submerso em chapas de aço microligado API 5l x70 utilizadas em minerodutos

The present work investigates the possible changes that occur in the mechanical properties and microstructure of welded joints through the process of submerged arc in steel plates High Strength Low Alloy (HSLA) type API 5L X70, used in pipelines. These are usually constructed starting from calendered plates and welded through submerged arc process, forming 600 mm diameter pipes, with 12 m long. To reproduce faithfully the pipes manufacturing processes, for further characterization of test bodies were produced, welding plate supplied by USIMINAS, through the submerged arc welding, and withdrawing samples to perform the characterization of the regions of the weld metal (WM), the heat affected zone (HAZ) and the base metal (BM). Conventional tensile and Charpy V-Notch were performed to determine mechanical and impact properties of the tested materials, as well as macrograph tests and Optical microscopy (OM) and weld metal (WM), the heat affected zone (HAZ) and the base metal (BM). The metallographic examination showed banded microstructure consisting of polygonal ferrite, pearlite and bainite with small grain size. The results showed increased strength and hardness influenced by the presence of acicular ferrite. The fractography analysis after impact tests revealed ductile-brittle behavior. Impact tests were performed at temperatures of 0°C and -20°C, which exhibited significant toughness decrease, that is 260J to 202J for the BM, 106J to 81J for HAZ and 25J to 19J to the WM, while the Vickers hardness testing (HV10) was increased from the fusion zone to the base metal (194HV for WM, 202 HV for HAZ and 218 HV for BM).
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REPOSITORIO INSTITUCIONAL DA UFOP: Efeito da espessura na tenacidade à fratura e no crescimento de trinca por fadiga em um aço do tipo API 5L-X70.

REPOSITORIO INSTITUCIONAL DA UFOP: Efeito da espessura na tenacidade à fratura e no crescimento de trinca por fadiga em um aço do tipo API 5L-X70.

As a result of the discovery of large oil reserves in Brazilian territory and the expansion of several mining companies, the main challenge is transport raw material until the industrial centers and the pipeline transport becomes more viable, among others ways of transporting. To attend this demand, must be used the pipelines of bigger strength steels with the goal to increase the diameter and decrease the walls of the tube, without the necessity of reduction of the pressures of operation, however it reduces the weight and the costs of installing these structures. In the present research, the aim focused on the evaluation of the influence in the thickness of the specimen related to fracture toughness (J integral) and fatigue crack growth (da /dN x ΔK) of a type of steel API5L-X70. It was compared to the results of test specimens of the type SEN(B) with the thickness of 7,5mm and 15,0mm and a constant width of 30,0mm. The steel presented a microstructure with banding of pearlite and polygonal ferrite and central segregation originated from chemical and mechanical forming process. The effect of the thickness revealed as a crack divider composite. Thus, in the fracture toughness tests occurred the delamination phenomenon, increasing the crack growth resistance of the thicker specimen. Moreover, in the fatigue test, the thicker specimen has a bigger number of alternate layers of pearlite and ferrite, which developed resistance to crack growth.
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Avaliação da tenacidade à fratura na região de transição dúctil-frágil dos aços API 5L X70 e X80 utilizando a metodologia da curva mestra

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

Materials used in oil pipelines are highly susceptible to structural changes when exposed to a hostile environment and at low temperature. For better understanding the behavior of the fracture toughness in the API 5L X70 and X80 steels, both known as high strength and low alloy (HSLA) micro alloys steels, the fracture toughness assessment checking the master curve concept of the conventional ASDM E1921 05 standard was proposed. Dhis methodology uses the universal dependence temperature concept of fracture toughness in brittle to ductile transition region, so called master curve. Dhe methodology suggests that it may be applicable in CCC ferritic steels, including hardened martensitic ferritic steels. In this work the samples were submitted to heat treatments, in order to change their microstructures and mechanical properties. Charpy impact test, tensile test, fracture toughness and hardness measurements were applied. Dhe samples were tested at various temperatures on the transition region to allow the master curve analysis application and the Weibull statistics by using the ASDM E1921 standard. Analysis in optical microscope and scanning electron microscope were done in order to assess the fracture surface changes and their microstructures. Both results of the API 5L X70 and 80X steels tested showed a wide range of data with relevant characteristics and scattering. According to a 100 MPa√m toughness, the API X80 steel showed better performance and reliability than the API X70 steel. Both steels showed brittle fracture with cleavage mechanisms and a ferrite bainite microstructure predominant.
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ESTUDO DA SOLDADURA EM CARGA DE UMA TUBAGEM API 5L

ESTUDO DA SOLDADURA EM CARGA DE UMA TUBAGEM API 5L

Regarding the need to perform repair operations and connections to existent pipelines, a major advantage arise from welding the fittings without decommission the lines. To accomplish this, it was needed to weld a fitting made of carbon steel to the outside pipeline wall which remains in service. Those fitting welds have to be made in such a way so that tightness between both has to be assured till the maximum working pressure. This thesis approaches the operational problems that arise from in-service welding operations, giving the correct support to minimize a dangerous potential operation. It focus on the major concerns of in-service welding which are: burnthrough and cold cracking, either breaching the pipeline at some point, which could result in total installation collapse with lost of lives. To minimize these events, thermal analyses were made to verify the heat flow conditions, like pre-heat and interpass temperatures, heat input validations, joint geometries and weld deposition sequence. Additionally it was showed that the API 5L X70 material is suitable for in-service welding, regarding Cold Hydrogen cracking. Finally, welding procedures were produced aiming to overcome such welding problems. In recent years, several approaches have been developed in Engineering, both academic and experimental, which lead to manual or computerized applications. Nevertheless, this theses showed that, on future works, thermal flow studies should be done by FEM (Finite Elements Methods) for several fittings geometries and fluid flows.
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Estudo da influência de variáveis de laminação em uma linha de tiras a quente convencional nas propriedades mecânicas de um aço alto nióbio da classe API 5L X70

Estudo da influência de variáveis de laminação em uma linha de tiras a quente convencional nas propriedades mecânicas de um aço alto nióbio da classe API 5L X70

This study has screened the influence of two thermomechanical processing variables over the microstructure and the mechanical properties of API 5L X70-PSL2 coils with chemical composition typical of a HTP steel, manufactured by Usiminas Ipatinga’s Hot- Rolling Strip Mill. It has been verified that, for the processing conditions employed, there were not relevant changes on the resulting microstructure, which was constituted by a very fine polygonal ferrite added to a lower volumetric fraction of second phase, constituted by degenerated pearlite (between 5 to 10%) and other carbides. The average each sample FGS measured from 3.9 to 5.3 µm. Mechanical parameters (YS and UTS) and elongation stayed well above the minimum limits required for ERW pipe fabrication for the specified steel grade. Maximum encountered hardness, of 223 HV 10
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REPOSITORIO INSTITUCIONAL DA UFOP: Avaliação comportamental de aços API 5L X52 e API 5L X70, soldados pelo processo de eletrodo revestido, utilizados em tubulações.

REPOSITORIO INSTITUCIONAL DA UFOP: Avaliação comportamental de aços API 5L X52 e API 5L X70, soldados pelo processo de eletrodo revestido, utilizados em tubulações.

Steels used in the manufacture of pipes are being continually developed with the objective of raising the strength of the same, keeping adequate toughness and good weldability. This makes it possible to employ steel with smaller thickness, which reduces the weight per length of pipe and also allows increased allowable working pressure for tubes of equal thickness. This study evaluated the behavioral characteristics of steel pipes API 5L X52 and X70 grades, welded by the electric arc process with coated electrodes. After cutting of pipes in cross section, were welded with V-groove samples using AWS E6010 electrode for root pass and electrode AWS E7018 for filling and finishing passes. The welded joints were characterized chemical, mechanical and metallographically. The tensile and bending tests indicated poor performance of welds due to the poor quality of the electrodes, probably due to inappropriate storage system. Assays were performed hardness / microhardness in the weld region. The specimens were tested and analyzed macro, using scanning electron microscopy, microfractografically.
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Avaliação da integridade estrutural em um tubo de aço API 5L X70 através da propagação de trincas por fadiga

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

In deep water offshore extraction and transport of oil and gas, the pipelines are undergo high stresses. It has to withstand high static and dynamic loads arising from external and internal fluid pressure, its own weight and sea currents that can lead to catastrophic failures. The fatigue behavior of the employed pipe in the offshore pipeline systems has been studied with aid of fatigue crack growth tests, in order to obtain experimental data for definition of safer periodic maintenance inspections. The objective of this work was to assess the fatigue crack propagation behavior in the base metal 90° and 180° from the welded joint of offshore pipeline API 5L X- 70 grade steel commonly employed in the transport of oil and gas. In addition, the fatigue test was carried out in the weld metal of a longitudinal welded joint obtained by SAW (Submerged Arc Welding) process. The fatigue crack propagation tests were performed in accordance with ASTM E647 from compact tension specimens C(T). The crack growth rates curves (da/dN) as a function of ∆K and the Paris law constants were obtained under constant load amplitude conditions at the stress ratio level of 0,1. For each specific region of base metal (90° and 180°) two specimens were taken across the thickness, one close to the outside diameter and other nearby to the inner diameter. Likewise, two samples were taken from weld metal, one specimen for a root weld and one for a reinforcement weld. From the a vs. N curves it could be inferred that the base metal specimens taken from location 90° tended to have lower fatigue crack growth resistance than the base metal taken from location 180°. Overall, the achieved outcomes from da/dN vs. ΔK curves indicated that the fatigue crack growth rate for the base metal taken from location 90° was higher than base metal taken from location 180°, which in turn was higher than the weld metal. From the correlation between microstructure and fatigue crack growth rate, it was verified that the fatigue crack growth rate for a microstructure consisting predominantly of acicular ferrite was lower than a microstructure composed primarily of ferrite- pearlite.
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Determinação experimental da tenacidade à fratura em baixas temperaturas de tubos de aço API 5L X70

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, high- pressure 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.
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Resistência à propagação dúctil de trincas em aço API 5L X70 com teor de nióbio ...

Resistência à propagação dúctil de trincas em aço API 5L X70 com teor de nióbio ...

High performance applications such as pipelines used to transport oil products require materials with an exceptional combination of mechanical properties, such as high mechanical strength, toughness and fatigue resistance. The API 5L X70 steel with enhanced niobium as an option to the production of this type of HSLA steel. Arcelor Mittal, Tubarão/Brazil has great interest in producing API 5L X70/X80 steels, without V and with Nb content above the recommended by Petrobras. Thus, the main objective of this thesis is the study of the mechanical strength and fracture toughness of API 5L X70 steel with Nb content of 0.06% Nb and 0.09% by weight processed as HSM Arcelor Mittal Tubarão process. To meet this goal, microstructural characterization following the ASTM E3, tensile tests following the ASTM E8M and Elastic Plastic Fracture toughness testing, according to ASTM E1820, were carried out. Specimens were taken from the base material region, weld bead and heat affected zone. From the results obtained it was observed that the controlled hot rolling process from ArcelorMittal, produced very similar microstructures for both compositions, as a consequence similar mechanical resistance and both met the criteria specified by the API Standard 5L X70, PSL2 level. The produced girth welds presented hardness values slightly higher than those from the base metal (overmatch), and resulted in very similar microstructures. The fracture toughness tests were able to provide valid JR curves that are representative results of resistance to ductile crack propagation for this pipe thickness. Both steels presented resistance to ductile crack propagation, and that the MB of the NNB steel showed superior resistance to the ANb steel. MS showed the lowest J-R curves, while MB and ZTA presented similar behavior. These differences were attributed to microstructural composition of each region.
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Estudo do comportamento em fadiga de uma chapa de aço microligado, grau API 5L X70

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

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

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

Due to increased in the demand for conduction pipes in the market, there has been a necessity to increase the welding speed in the internal phase, which has an average discrepancy of 10 inches / min when compared to the external phase. It happens because the process works with three wires in the internal step method following the submerged arc welding, while the external one uses four wires. As a consequence the internal step was increased to four wires in order to equalize the speed of these steps. There are need to define what the top speed limit is. Therefore this study is applied to conduction pipes, according to API 5L grade X70 and, at first, a sample was drawn from Macrographic solder to assess the alignment between the weld and the inside and the outside overlap between the weld. This was followed by the analyses of the inside portion of weld, the hardness test method for Vickers and impact test Charpy method, obtaining the curves of transition. With the help of graphic ǻ t 8 / 5 speed limits were set to apply to welding in WPS (Welding Procedure Specification). It is possible to achieve more reliability in the decision about variable welding speed that will include the WPS and the least amount of sampling through the limits and minimum and maximum hardness. Thus the practice was satisfactory and the results showed that the speed range meets the safety limits of values of the mechanical properties required by the standard API 5L.
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A Comparative Investigation of the Corrosion Resistance and HIC Suceptibility of API 5L X65 and API 5L X80 Steels

A Comparative Investigation of the Corrosion Resistance and HIC Suceptibility of API 5L X65 and API 5L X80 Steels

The shapes both of the EIS diagrams and of the polarization curves were similar in the deaerated and in the H 2 S saturated solution indicating similar corrosion mechanisms. The monitoring of the corrosion behavior as a function of immersion time in the sour medium, which was performed during 24 h (Figure 8), showed that, regardless the steel, the OCP remained very stable throughout the test period, indicating that there were no changes in the corrosion mechanism and that the surface modifications resulting from the corrosive process did not alter the interfacial electrochemical processes. Moreover, throughout the period, the OCP of the API 5L X65 steel was more noble. The results of the EIS tests (Figures 9 and 10) showed increased impedance with immersion time, indicating improved corrosion resistance. As reported by different authors for steels immersed in sour medium 28,30,40
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Efeitos da Taxa de Resfriamento na Soldagem do Aço API 5L-X80.

Efeitos da Taxa de Resfriamento na Soldagem do Aço API 5L-X80.

As duas menores temperaturas estudadas podem causar trincas nas juntas devido a suas altas taxas de resfriamento. A temperatura mínima recomendada de pré-aquecimento para soldar o API 5L-X80 com baixo risco de causar defeitos é de 100 °C [1] . Porém, pode-se afirmar que pela alta tenacidade do X80 e com o uso de consumíveis de baixo hidrogênio, é possível realizar a solda com menores temperaturas de pré-aquecimento e de interpasse, sem risco de trincas [1] . Além disto, processos de soldagem usando robôs permitem realizar cordões de soldas com menores áreas de ZAC (Zona Afetada pelo Calor) e é possível obter microestrutura refinada (ou bainíticas) quando comparado ao processo manual de soldagem por eletrodo revestido [2] .
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