API 5L X80 steels are widely used in welded pipes in the petroleum industry. However, microstructural changes in the heat affected zone are a concern when welding such pipes due to the potential formation of regions with low toughness. Despite all the research concerning mechanical properties of welded joints, the acceptance criteria for the qualification of welding procedures are still limited. Welded joints do not always guarantee the safe operation of industrial equipment, because the current Standards adopted are not able to evaluate the properties at some critical regions of the welded joint. This work studied the characteristics of a girth welded joint and showed evidences of low toughness at 0.5 mm from the fusion line due to the micro-phases necklacing the prior austenite grain boundaries. As this feature is not considered by the current Standards for approval of welding procedures, this work proposes an alternative approach to improve the safety of welded structures.

RESUMO O presente trabalho apresenta os resultados de um programa de pesquisa cujo objetivo principal é o desenvolvimento de consumíveis adequados para a soldagem de componentes de ancoragem fabricados em aços de alta resistência. Após avaliação de diferentes composições químicas, com base no balanço de Mn e Ni é feita uma análise detalhada das propriedades mecânicas e microestruturais da composição química que propiciou os melhores resultados para permitir uma conclusão decisiva. Foram soldadas juntas pelo processo eletrodo revestido utilizando consumíveis de 4,0 mm de diâmetro, com preaquecimento de 200 ºC, corrente contínua, posição plana e energia de soldagem nominal de 1,5 kJ / mm. Após a soldagem, foram realizados ensaios mecânicos (tensão, impacto Charpy-V, dureza) e metalográficos por microscopia ótica, microscopia eletrônica de varredura e EBSD em amostras removidas integralmente do metal de solda, tanto na condição de como soldado quanto após tratamento térmico pós-soldagem (TTPS) realizado a 600 ºC. Os resultados mostram que os metais de solda obtiveram propriedades mecânicas satisfatórias após o TTPS, sendo adequados para aplicação em componentes de ancoragem de acordo com a especificação IACS W22. Além disso, observou-se que a tenacidade ao impacto experimentou uma melhoria com o aumento do tempo de TTPS, o que é crucial para componentes com maiores espessuras.

ABSTRACT The present work show the results of an extensive working program whose the main goal is the development of consumables suitable for welding of mooring components manufactured in high strength steels. After an exhaustive evaluation of different chemical compositions, based on a balance of Mn and Ni, a detailed analysis of the mechanical and microstructural properties is done for the heat which proposed the best results in order to allow a decisive conclusion. Welded joints were produced by using 4,0 mm diameter covered electrodes, with preheat of 200 ºC, direct current, flat position and nominal heat input of 1.5 kJ/mm. After welding, mechanical tests (tension, impact Charpy-V, hardness) and metallographic examination (optical microscopy and scanning electron microscopy, electron back scattering diffraction) were performed in specimens removed integrally from the weld metal both in the as welded condition and post weld heat treatment at 600 º C. The results show that the weld metals obtained satisfactory mechanical properties after PWHT, being adequate for application on high strength steel mooring components with several grades according to the IACS W22 specification. In addition, it was noted that impact Charpy-V results were improved with increasing the time of PWHT, which is crucial for larger components.

Abstract In the present paper, an adjustment of the heat inputs corresponding to the cooling times of interest “t12/8” and “t8/5” in the HAZ of the GMAW of a duplex stainless steel 2205, of 10 mm thickness, using finite element simulation is made. For simulation, a welding modeling methodology previously developed was used, and it was enriched with the incorporation of a correction factor of the heat transferred to the finite elements by which the heat source passes. The methodology, using a code in APDL language, was initially validated through the comparison with experimental results of thermal cycles. In the paper is also demonstrated that the results of the relation of the heat input and cooling time variables are more accurate when using the Rykalin 2D theoretical model with the average properties of the steel in the range from room to solid temperature, than those obtained when the properties are replaced at room temperature.

Resumen En el presente artículo se realiza un ajuste de los calores de entrada que se corresponden con los tiempos de enfriamiento “t12/8” y “t 8/5” de interés, en la ZAT de la soldadura GMAW de una chapa de acero inoxidable dúplex 2205, de 10 mm de espesor, empleando la simulación por elementos finitos. Para la modelación de la soldadura se empleó una metodología desarrollada previamente, la cual se enriqueció con la incorporación de un factor de corrección del calor aportado, a los elementos finitos por los que pasa la fuente de calor. La metodología, implementada a través de un código en lenguaje APDL, fue validada inicialmente a través de la comparación con resultados de ciclos térmicos experimentales. En el trabajo además se demuestra que, cuando se utiliza el modelo teórico de Rykalin 2D, son más precisos los resultados que relacionan las variables calor de entrada - tiempo de enfriamiento, empleando las propiedades promedio del acero en el rango de temperatura desde la ambiente hasta la de sólido, que los que se obtienen cuando se sustituyen las propiedades a temperatura ambiente.

AbstractThe main goal this work is to evaluate the occurrence of the constituents and microphases observed in as-received API X80 pipe through the microstructures transformed from rich-carbon remaining austenite obtained via heat treatments. These heat treatments comprised austenitization at 1000 °C for 30 minutes, followed by annealing at 700 °C, 623 °C, 542 °C and 462 °C for 15, 60 and 300 minutes and then cooling in water or still air. The effects of the increase in annealing parameters were: 1) the increase of microhardness values of the MA constituents and martensite islands, 2) the grain size of both ferritic phase and the martensite islands were increased, 3) the rise in the mean free path of ferrite and 4) the microstrains of samples were decreased. The cooling rates influenced significantly the transformation of carbon-rich remaining austenite to hard constituents and several microphases. After annealing at 700 °C during 60 min followed by quenching, the morphology of the MA constituents and its microhardness values were compatible for both heat-treated and as-received conditions.