Seam welded tube production technology has developed to a point where seam-welded tube quality reaches very closely to seamless tube combining advanced welding technology and drawing technique. Improvements have been gained over the years to minimize welding effects and smoothened both outer and inner diameter of the tube from welding material excess. Unfortunately, micro defects and metallurgical changes caused by welding are still present in the product that might influence its performance when it is used for sub surface safety valve control lines and also chemical injection lines.
High alloyed nickel based material UNS N08825 is selected in this study where similar dimensions and chemical composition were chosen in the observation by using electrochemical potentio-dynamic polarization in chloride solution, and scanning electron microscope (SEM), glow discharge optical emission spectrometry (GD-OES) for the surface analysis. The result of this investigation shows that the seam welded tubes have the same level of hardness with seamless tubes. Nevertheless, the weld defects along the fusion line could be the cause of diminishing corrosion resistance of the tube. Chromium nitride precipitates and lack of fusion have been observed in the outer tube surface of the Alloy 825 seam welded tubes which could not be detected by non-destructive testing (NDT) methods.
This study signifies that seamless tubing is a better option as SSSV control line to maintain well integrity than seam welded tube.