Corrosion Analysis of G105-Coated Drill-Pipe Washout and Electroless Plating Ni-P as Drill-Pipe Protection in Freshwater Mud

G105 (API SPEC 5D group 3)-coated drill pipes suffer from washout after drilling for 70,000 m to 80,000 m. The microstructure, micromorphology, and corrosion products near the washout were analyzed by metallurgical microscopy, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). Electroless plating Ni-P as drill pipe protection in freshwater mud was studied. Results showed the metallographic microstructure of the material was typical tempered sorbite. No fatigue crack was observed. Drill-pipe washout was caused mainly by the inclusion of manganese sulfide (MnS) in steel because of the excess S and by damaged coating, both of which induced pit nucleation and promoted the pitting corrosion process. Electroless plating was cystiform in structure on the surface, and phosphorus content was 13.23%, which was high phosphorus and corrosion-resistant plating. Maximum corrosion rate of electroless plating was a quarter of the minimum of the corrosion rate of G105. Organic coating was damage...