Entity

Time filter

Source Type


Tavares S.S.M.,Federal University of Fluminense | Pardal J.M.,Federal University of Fluminense | Souza G.C.,Federal University of Fluminense | Garcia P.S.P.,Federal University of Fluminense | And 3 more authors.
Engineering Failure Analysis | Year: 2015

Chromium molybdenum alloy steels are employed in high temperature services. Welded components in both fossil-fuel fired and nuclear power plants are some examples of critical applications. This study shows the characterization of the mechanical properties and microstructure of 9Cr-1Mo-V steel, revealing the presence of cracks and pores in the weld metal of a circumferential joint made by GMAW with metal cored wire process. Analyses by Scanning Electron Microscopy (SEM) were performed in samples obtained before and after the post weld heat treatment (PWHT). Supplementary analyses by Energy Dispersive X ray Spectroscopy (EDS) were made at diverse regions where discontinuities occurred. The cracks presented an intergranular propagation. The greater crack was localized in the root neighborhood with approximately 1.8. mm of extension in a sample with post weld heat treatment (PWHT). The fractured surfaces of Charpy specimens were also analysed by EDS-SEM. The results obtained show the cleaning process of the joint and the chemical composition of the wire and base metal can play an important role in the behavior of the weld joint in pipe service; despite the acceptable mechanical tests results, in accordance with the specifications. © 2014 Elsevier Ltd. Source


Alvarez T.R.,Federal University of Fluminense | Pavarino M.R.C.,Federal University of Fluminense | de Souza G.C.,Federal University of Fluminense | Pardal J.M.,Federal University of Fluminense | And 3 more authors.
Welding International | Year: 2016

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. © 2016 Taylor & Francis. Source


Chagas de Souza G.,Federal University of Fluminense | da Silva A.L.,Federal University of Fluminense | Tavares S.S.M.,Federal University of Fluminense | Pardal J.M.,Federal University of Fluminense | And 2 more authors.
Welding International | Year: 2016

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. © 2016 Taylor & Francis. Source


Tavares S.S.M.,Federal University of Fluminense | Pardal J.M.,Federal University of Fluminense | De Souza G.C.,Federal University of Fluminense | Fonseca M.P.C.,Federal University of Fluminense | And 3 more authors.
Studies in Applied Electromagnetics and Mechanics | Year: 2014

Duplex stainless steels are high strength and corrosion resistant alloys, whose properties are devoted to the fine microstructure composed by similar amounts of ferrite and austenite and also to the high concentrations of Cr, Mo and N in solid solution. Not for coincidence, duplex steels are extensively used in chemical and petrochemical industries. However, welding operations conditions can promote the unbalance of the ferrite/austenite proportions mainly in the welding metal, with decrease of the properties mentioned. For this reason, non destructive measurements of ferrite content, by ferritoscope, is used after welding pipes. Ferritoscope is a commercial instrument which uses the initial magnetic permeability to analyze the ferrite content in duplex and austenitic stainless steels. The inspection with ferritoscope is a procedure commonly used in building and assembly of spools of duplex and superduplex stainless steels. The objective of this work was to evaluate the amounts of phases in the welding metal for different spools welded in the field by use of ferritoscope and metallographic replica techniques. The results showed that the two techniques measured similar values of ferrite and austenite, but ferritoscope analysis can be influenced by shape and surface conditions of the welded joint. © 2014 The authors and IOS Press. Source


de Souza G.C.,Federal University of Fluminense | da Silva A.L.,Federal University of Fluminense | Tavares S.S.M.,Federal University of Fluminense | Pardal J.M.,Federal University of Fluminense | And 2 more authors.
Soldagem e Inspecao | Year: 2014

Superduplex stainless steels (SDSS) are alloys widely used in the exploration and production of oil. They are used in marine and offshore components such as heat exchangers, umbilicals, seawater injection lines and various other equipment that require 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 characterize 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 GTAW 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 critical pitting temperature at the root of the weld, though there aren’t substantial variations in the mechanical properties analyzed. © 2014 Universidade Federal de Uberlandia. All rights reserved. Source

Discover hidden collaborations