Drill Pipe Inspection using PAUT
Drill pipe is an important component of drill string in petroleum drilling; it occupies 80%~90% of the whole drill string. The major reasons of destruction of drill pipe are: tension-compressions, strong vibrations of drill pipe during drill bit on rock, corrosion fatigues and stress damages. Body parts of pipes and thicken areas are more easily be corroded, especially the inner surface of the pipe, outer surface is uneasy to be corroded because it has frequent frictions with side walls. Early corrosion mainly embodied as etch pit during machine work, and it will receive accelerated expansion under interaction of corrosion medium and alternating stress, which lead to the stress concentration at the bottom of etch pit. After certain cycles of stress circulation, crack will appear in the etch pit.
Corrosion fatigue crack is the main failure type of drill pipe, and it may be happened in the body parts of pipes, thicken areas, weld zones, internal & external thread areas. The biggest hazard is corrosive fatigue fracture, mainly occurred in the inner upset transitional area. In so far, the drill pipe inspection is limited to conventional single channel detection method with low detection efficiency and high miss rate. Besides, the longitudinal and transverse crack of tread area is another main failure mode of drill pipe, but this is complex and distinguishing due to the reflected signal of this area. In this study, we plan to adopt the ultrasonic phased array inspection technology in the accurate detection and positioning of drill pipe crack, therefore, the inspection results will be more visual and reliable.