Miguel Luiz Ribeiro Ferreira

Study of deleterious phase precipitation under continuous cooling of superduplex stainless steel UNS S32750

Abstract Duplex and superduplex stainless steels have high strength and high corrosion resistance with a crescent demand in chemical and petrochemical industries. The best mechanical properties of this family of steels are obtained with approximately equal parts of ferrite and austenite. Grain refinement increases the toughness and resistance to environmentally assisted cracking. The precipitation of tertiary phases, such as σ, χ and secondary austenite, decreases the mechanical and corrosion resistance properties. The σ phase is the most dangerous of these deleterious phases and the one that precipitates in higher amounts. The majority of research works on deleterious phases in duplex and superduplex steels evaluate the kinetics of precipitation in specimens isothermally treated. In the present work, the precipitation of deleterious phases during continuous cooling from 1100°C was evaluated by optical and scanning electron microcopies, hardness measurements and electrochemical corrosion tests. Two superduplex stainless steel steels UNS S32750 with similar composition but quite different grain sizes were analysed in order to evaluate the influence of this microstructural feature.

Estimativa da produtividade em soldagem pelo Método de Monte Carlo

The aim of this article is to analyze the feasibility of using Monte Carlo method to estimate productivity in industrial pipes welding of carbon steel based on small samples. The study was carried out through an analysis of a reference sample containing productivity data of 160 welded joints by SMAW process in REDUC (Duque de Caxias Refinery), using ControlTub 5.3 software. From these data was taken at random samples with, respectively, 10, 15 and 20 elements and were performed simulations by Monte Carlo method. Comparing the results of the sample with 160 elements and the data generated by simulation is observed that good results can be obtained by using Monte Carlo method in estimating productivity of industrial welding. On the other hand in Brazilian construction industry the value of productivity average is normally used as a productivity indicator and is based on historical data from other projects collected and measured only after project completion, which is a limitation. This article presents a tool for evaluation of the implementation in real time, enabling adjustments in estimates and monitoring productivity during the project. Similarly, in biddings, budgets and schedule estimations, the use of this tool could enable the adoption of other estimative different from of the average productivity, which is commonly used and as an alternative are suggested three criteria: optimistic, average and pessimistic productivity.

Comparación de la estimación de la productividad del proceso de soldadura eléctrica por los métodos de simulación de Monte Carlo e Hipercubo Latino

The ability of Monte Carlo simulation and Latin Hypercube Sampling methods in estimating the productivity of the Shielded Metal Arc Welding (SMAW) applied in works of industrial piping assembly based on small samples is evaluated. The study was conducted by analyzing a sample collected from assembly operations done at refinery Duque de Caxias, Rio de Janeiro in Brazil. The ControlTub 5.3 software was used for data acquisition and MathWorks in the simulation step. For data analysis the results were compared using the proposed simulation methods. Then the similarities and differences between the methods to estimate the process productivity in analysis were evaluated. The results demonstrated the feasibility of applying the methods of Monte Carlo Simulation and Latin Hypercube Sampling in estimating productivity considering a welding process of industrial pipes.

Mechanical properties and corrosion resistance evaluation of superduplex stainless steel UNS S32760 repaired by GTAW process

Abstract Superduplex stainless steels (SDSSs) are alloys widely used in the exploration and production of oil. They are used in marine and offshore components such as heat exchangers, umbilicals, sea water injection lines and various other equipment that requires high corrosion resistance with elevated mechanical strength values. These characteristics are due to its fine two-phase microstructure composed of similar proportions of austenite and ferrite and the alloying elements of Cr, Ni, Mo, N and W. However, during welding, and also in the stages of fabrication and pipe assembly, the presence of defects may occur that requires the need for repair procedures to be carried out on the welded joint. This study aims to characterise the microstructure, mechanical properties, nitrogen content and critical pitting temperature (CPT) of a SDSS pipe, UNS S32760, in certain regions of a welded joint, where the gas tungsten arc welding process was performed, with the completion of two sequential repair procedures. The results show that there is a decrease in the value of the CPT at the root of the weld, though there are not substantial variations in the mechanical properties analysed.

Influence of interpass temperature on the properties of duplex stainless steel during welding by submerged arc welding process

Abstract Duplex stainless steels are materials that present high corrosion resistance with high values of mechanical strength, therefore motivating their use in various components in the offshore industry. However, there are major challenges in the welding of these materials in terms of the productivity and quality of the joint produced, considering its extensive use for components of small thickness, such as umbilicals, to those of large thickness, such as salt water injection pipelines. In relation to pipes of small thickness, the gas tungsten arc welding process is successfully used. In thick-walled pipes, the automatic process of submerged arc welding (SAW) has been recently implemented in lines of pre-assembled piping, and this has considerably increased the productivity of the joints produced, though, a great deal of time is required to perform a new weld pass, due to the fact that the maximum interpass temperature needs to be lower than 150 °C. This work presents the results of characterization and the evaluation of corrosion resistance of a welded joint corresponding to DSS UNS S31803, with a wall thickness of 21.4 mm, welded by the gas metal arc welding process in the root and SAW process in the filling and cap passes, employing an interpass temperature between 150 and 290 °C. The results of the characterization of the mechanical properties, chemical composition and corrosion resistance in different regions of the welded joint were compared with those obtained for the base metal of the pipe, as well as with the minimum values required by the project standards. Therefore, this study has made an evaluation of the influence of the interpass temperature in the properties of the joints produced, motivated by a possible increase in productivity in pipe welding.

Análise da resistência à corrosão por pite em soldas de reparo pelo processo TIG em aço inoxidável superduplex UNS S32750

Atualmente, os acos inoxidaveis superduplex (AISD) estao sendo muito empregados no Brasil em setores industriais tais como petroquimico, energetico, naval e plataformas offshore, tendo vasta aplicacao em vasos de pressao em processos criticos, trocadores de calor, reatores, tubulacoes, umbilicais, digestores, bombas e naqueles componentes onde a produtividade continua e essencial e o custo nao e a maior limitacao. No entanto, durante processos de fabricacao e montagem, assim como na vida em servico destes componentes de processo pode existir a necessidade eventual de efetuar soldagens de reparo. Deste modo, o presente trabalho, visa avaliar a microestrutura e os valores de resistencia a corrosao por pites na zona termicamente afetada (ZTA) e metal de solda do AISD UNS S32750 durante a simulacao de um processo de reparo mediante a utilizacao do processo de soldagem TIG (GTAW). Os resultados obtidos permitem estabelecer diretrizes para a realizacao de procedimentos de soldagem de reparo em AISD.

Influência da temperatura interpasse nas propriedades do aço inoxidável duplex durante a soldagem pelo processo a arco submerso

Duplex stainless steels (DSS) are materials that present high corrosion resistance with high values of mechanical strength, therefore motivating their use in various components in the offshore industry. However, there are major challenges in the welding of these materials in terms of the productivity and quality of the joint produced, considering its extensive use for components of small thickness, such as umbilicals, to those of large thickness, such as salt water injection pipe lines. In relation to pipes of small thickness, the gas tungsten arc welding process (GTAW) is successfully used. In thick-walled pipes the automatic process of submerged arc welding (SAW) has been recently implemented in lines of pre-assembled piping, and this has considerably increased the productivity of the joints produced. Though, a great deal of time is required to perform a new weld pass, due to the fact that the maximum interpass temperature needs to be lower than 150°C. This work presents the results of characterization and the evaluation of corrosion resistance of a welded joint corresponding to DSS UNS S31803, with a wall thickness of 21.4 mm, welded by the gas metal arc welding process (GMAW), in the root, and submerged arc welding process (SAW), in the filling and cap passes, employing an interpass temperature between 150 and 290oC. The results of the characterization of the mechanical properties, chemical composition and corrosion resistance in different regions of the welded joint were compared with those obtained for the base metal of the pipe, as well as, with the minimum values required by the project standards. Therefore, this study has made an evaluation of the influence of the interpass temperature in the properties of the joints produced, motivated by a possible increase of productivity in pipe welding.