Análise comparativa entre processos modernos de deposição por soldagem da liga Inconel 625 quanto a sua resistência à corrosão para aplicações na indústria de óleo e gás

Abstract

The oil and gas industry faces challenges related to corrosion problems from an environment with high salinity and impurities present in the crude oil. Metal claddings are commonly applied to prevent excessive wear generated by corrosion of exposed components, with the cladding by welding being is one of the most applied methods. Within these weld cladding processes, there are some that have not been fully explored regarding the corrosion resistance resulting from their claddings, among these processes are the PTA, TopTIG and MIG AC. The objective of this work is to evaluate the corrosion resistance of the Inconel 625 coatings deposited by the aforementioned welding processes. Through the deposition of Inconel 625, by the aforementioned processes, on ASTM A36 sheets, samples were separated into two main groups, samples for corrosion tests and samples for microstructure analysis. In the corrosion samples, the cyclic potentiodynamic polarization test was used, with a morphological analysis of the corrosion generated in the tests through the scanning electron microscope. The microstructural analysis samples were analyzed by optical microscope, for a geometric dilution analysis, and by scanning electron microscope, using backscattered electrons, secondary electrons and energy dispersive spectroscopy techniques to study the microstructure and calculate chemical dilution. Cyclic polarization results indicate that the claddings deposited by TopTIG are the most resistant to corrosion, with pitting potentials considerably above the claddings generated by the other processes. It was also possible to observe a different repassivation behavior of the TopTIG coating from the others. The surface analysis after cyclic polarization tests showed that the TopTIG claddings, despite being more resistant to corrosion, suffered from localized corrosion, while the PTA and MIG AC claddings suffered from a more generalized corrosion. In the microstructural analysis of the claddings in the as-delivered condition, we were able to observe a more destroyed microstructure for the PTA and MIG AC processes, with a greater presence of precipitated phases. The microstructure of the TopTIG cladding has a uniform appearance, containing less precipitated phases. Despite the best results of the TopTIG claddings, it was also possible to observe that it achieved chemical and geometric dilution rates far above the other processes. With the study of the Inconel 625 claddings deposited by the PTA, TopTIG and MIG AC processes, we were able to obtain some conclusions such as that due to the large heat input directed to the base material in the TopTIG process, we obtained high dilution rates, but at the same time a low presence of precipitated phases, mainly due to Inconel 625 not having absorbed as much heat. This phenomenon happens in the opposite manner for the PTA and MIG AC processes, which even with higher.