Study on Defects of Longitudinally Welded Thin-Wall Steel Tubes Fabricated by High Frequency Induction Welding and Subsequent Tube Sinking Process

In this study different defects of longitudinally welded thin-wall steel tubes produced by high frequency induction welding and subsequent tube sinking process in order to reduce diameter of the tube were investigated. It was found that there was a lot of defect at weld zone which were resulted from roll forming and welding processes. Misalignment of the edges at the weld joint, cold weld, macroscopic cracks, big heat affected zone and also excess burr in the inside of the tube are examples of the determined defects that can cause problems in service. Optical microscope images showed a big heat affected zone and that there was significant difference in the grain size and morphologies of three zones (weld line, HAZ and base). Micro-hardness data showed an inhomogeneity in the mechanical properties of the produced tubes and it was determined that the maximum hardness is related to weld line and the minimum hardness is related to heat affected zone, and finally it was showed that this inhomogeneity in microstructure and mechanical properties can be deleted by static recrystallization heat treatment

Keywords:

Longitudinally Welded Thin-Wall Steel Tube , High-Frequency Induction Welding , Weld Defect