Magnetic testing is performed to verify the magnetic interference of downhole components located near sensitive magnetometer sensors found in directional modules of Measurement While Drilling and wireline tools.
Sensitive magnetometer sensors are used in downhole directional modules to reference the earth's magnetic field and determine well bore placement. The magnetometer must be free of magnetic interference from nearby components within the tool assembly. National K Works performs magnetic interference testing for customers mostly on welded assemblies since natively non-magnetic material can become magnetic during welding. The welded components are weld joined components, hard facing and weld cladding.
During testing the sensor is stationary and the specimen travels past the sensor in a spiral pattern at a designated pitch and speed. The sensor's location is tailored to the end application, such as the outer diameter surface, center of the bore or displaced within the bore and close to the bore surface.
Another form of magnetic testing is verifying the electromagnetic induction trigger point of "drop" style tools. The trigger is calibrated to sense the transition from ferrous drill pipe to non-magnetic drill collars while free falling downhole and then commence data logging. In this application, the drill pipe and drill collar size are established per the application because mass and distance are variables to the sensor's sensitivity. Then mock pieces are created that represent the drill pipe and non-magnetic drill collar and used to test the tool's ability to detect the transition.