Demagnetization method of large-scale ferromagnetic pipe fitting and magnetic-sensitive sensor

Abstract

The invention relates to a demagnetization method of a large-scale ferromagnetic pipe fitting and a magnetic-sensitive sensor. The invention is characterized in that: for a remnant magnetic field formed at the end of the large-scale ferromagnetic pipe fitting under the action of an axial DC magnetic field, the pipe fitting is demagnetized by the DC magnetic field, wherein the direction of the DC magnetic field is opposite to that of the remnant magnetic field, the strength of the DC magnetic field is consistent with that of the detected remnant magnetic field, and then the pipe fitting is demagnetized by an alternating magnetic field with the strength gradually damped to zero; for an alternating remnant magnetic field formed in the axial direction of the large-scale ferromagnetic pipe fitting under the action of an axial alternating magnetic field with variable directions, pitches and strength, a section of pipe fitting in each pitch is demagnetized by the DC magnetic field, wherein the direction of the DC magnetic field is opposite to that of the remnant magnetic field, the strength of the DC magnetic field is consistent with that of the detected remnant magnetic field, and the pipe fitting is demagnetized by the alternating magnetic field with the strength gradually damped to zero. By adopting a complex demagnetization method, the invention solves the problem that magnetic hysteresis loops can not cover the remnant magnetic field of the pipe fitting sometimes in the conventional damped AC demagnetization method.

Description

technical field [0001] The present invention relates to a degaussing method and a magnetic sensor for large-scale ferromagnetic pipe fittings, more specifically to a degaussing method and a magnetic sensor applied to oil drill pipes, oil pipes, casings, high-pressure boiler tubes and other various ferromagnetic steel pipes. Sensor design. Background technique [0002] Large-scale ferromagnetic pipe fittings, such as oil drill pipes, oil pipes, casing pipes, high-pressure boiler pipes and other ferromagnetic steel pipes, are magnetized by DC magnetic field or alternating magnetic field in eddy current and magnetic flux leakage detection. Magnetization, but there will still be a residual magnetic field; when the pipe fittings are stacked in storage, they will also be magnetized by geomagnetism or other magnetic fields to form a residual magnetic field. A residual magnetic field above 30GS will cause the pipe fittings to absorb iron nitrate, which will affect the precision mac...

AI Technical Summary

Problems solved by technology

A residual magnetic field above 30GS will cause the pipe fittings to absorb iron nitrate, which will affect the precision machining of the threaded ends of the pipe fittings and the welding between pipe fittings; the residual magnetic field above 50GS will even cause the pipe fittings to be inaccurate during oil drilling, well construction and oil production construction. Docking, etc.

Restricted by the impedance and power of the degaussing coil, the maximum value of the degaussing intensity formed by the degaussing coil passing through the alternating current is usually smaller than the residual magnetic field Br1 at both ends of the pipe, that is, the hysteresis loop of the degaussing coil cannot surround the residual magnetism Br1 on the pipe, so conventional AC degaussing coils often cannot reliably demagnetize the axial DC residual magnetic field of pipe fittings

[0009] 2. If the residual magnetic field on the pipe is an alternating residual magnetic field, it may be because the maximum value of the degaussing intensity of the AC degaussing coil is less than Br1, and the degaussing coil cannot completely demagnetize the pipe; it may also be due to the instantaneous direction of the degaussing magnetic field and the pipe in this When the direction of point remanence is consistent, the remanence field will be strengthened

It shows that the conventional degaussing coil is also difficult to reliably demagnetize the alternating residual magnetism of the pipe fittings

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