Helical Welding of ASTM A-1018 Steel Tubes Produced in Field and its Correlation with Mechanical and Microstructural Characteristics of Welded Joints

Abstract

A problem commonly found in the production of tubes is related to transportation due its large dimensions. This fact, makes field welding a complex and often costly operation. An alternative fabrication process for pipes is the process of forming tubes with helical welds. This work proposes to study the microstructural characteristics and perform a mechanical evaluation of these welds performed in field of ASTM A1018 steel tubes. In order to reach the aim, two steel tubes manufactured from sheets with a thickness of 12.5 mm and a nominal diameter of 1200 mm were welded by the process of submerged arc welding through the equipment adapted for field welding. Subsequently, samples were taken to perform characterization by microanalysis. Chemical composition, bending and hardness tests were also conducted. The main difference between the samples was the increase of the acicular ferrite and reduction of the primary ferrite of the grain boundary with the decrease of the thermal contribution in the microstructures formed in the molten zone as in the ZTA as presented. Also, changes in the geometry of the weld beads were observed. Finally, it was identified that the main parameter that influences the microstructural changes presented is the welding current.

Key-words:
Helical tubes; Submerged arc welding; Microstructural and mechanical characterization