Premium connection downhole tubing corrosion

Macro- and micro-corrosion morphology analyses and material testing of corroded premium connection downhole tubing with couplings of 2 7/8-in by 6.4-lb/ft P110 tubing have been discussed. Corrosion was limited to the internal surface throughout the length of the coupling, and featured axial groove morphology. Corrosion perforation was observed at the field pin and it was also observed that corrosion from the field pin end to 28 mm away was most severe. Scanning electron microscopy of the corrosion perforation and pits on the internal surface of the tubing indicated corroded penetration, CO₂ corrosion, and belt erosion-corrosion morphology. Micro-corrosion morphology and corrosion product analysis recognized that corrosion products were carbonate and chloride. The cause of the premium connection corrosion was the V form notch at the subsidiary shoulder, causing an abrupt geometric change and leading to fluid turbulence and erosion-corrosion.