Today's welding technology has been developed which enables to minimize the negative effects of the welding. Further processes on the longitudinally seam welded tubing like sink or plug drawing will improve the geometry of the tube in both outer and inner diameter to smoothen the weld bead and increase the wall thickness and outer diameter tolerances of the tube. Annealing process on the entire welded tubing eliminates residual stress from welding and cold forming. However, the weld defects are difficult to be entirely removed by these processes and therefore the seam welded tubes carry more risks of failure to be used as sub surface safety valve (SSSV) control lines and chemical injection lines.
The selected seam welded tubes and seamless tubes of Superduplex 2507 (UNS S32750) stainless steels in similar dimensions and of similar chemical compositions have been studied by using CPT determination with ASTM G150 method, scanning electron microscope (SEM) for microstructure and surface analysis. This study shows that seam welded tubes have similar hardness compared to the seamless tubes. However the weld defects, such as undercut, micro-cracks and oxides along the fusion line, could be responsible for the reduced corrosion properties of the tube.
This study signifies that the seamless tubing is a better option as SSSV control line to maintain well integrity than seam welded tube.