Research On Automatic Inspection System For Transverse And Longitudinal Defects Of The Oil Well Tubing

Oil well tubing is one of the most important components in the course of oil extraction. Automatic inspection of oil well tubing transverse defects and longitudinal defects is a key means to guarantee the quality of repaired oil well tubing and reduce accidents in oil extraction. The possible defects in the oil well tubing can be classified into transverse defects and longitudinal defects. Based on the local circumstance and requirements of the users, MFL testing method is adopted, which has many advantages such as rapid speed, high sensitivity and so on. According to the motional style of the oil well tubing and the inspection transducer, several possible inspection styles of the oil well tubing inspection system are deeply researched based on the theory of MFL (Magnetic Flux Leakage), and three of which are selected for the further research. In these researches, the magnetization, the signal extraction method and the structural design of probes are mainly discussed. Two magnetization methods including direct current coil magnetization and permanent magnet magnetization and two signal extraction methods including Hall sensors and inductive coils are researched in this dissertation respectively. Several inspection transducers for transverse defects and longitudinal defects have been made out, which can be used in different kinds of situation. Aiming at the loss of wall thickness of the oil well tubing because of the eccentric attrition, some preparatory researches have been taken for the wall thickness measurement with the magnetic method. Two methods are proposed, one is the method of local circumferential magnetic bridge and the other is the method of synthetically analyzing the signal of transverse and longitudinal inspection transducers, which can estimate the wall thickness of the oil well tubing precisely. These methods are validated with experiments. Synthesizing all the measures above, three styles of MFL inspection system for oil well tubing are formed. The structure, constitution and inspection flow of the inspection systems are introduced respectively. The inspection system was validated with laboratorial tests and field tests. The tests and the practical application showed that the system has specific advantages such as high-adaptation, high-efficiency, high-stability, high reliability and can meet the need of the users.