Safety pipe loop and method for strain monitoring of mountainous pipelines

A method for strain monitoring of mountainous pipelines, comprising:

• determining a correction factor of each of a plurality of magnetic test detectors;
• assembling the plurality of magnetic test detectors each of which is provided with the corresponding correction factor, so as to obtain a safety pipe loop for strain monitoring of mountainous pipelines;
• wherein the correction factor is determined by operations including:
• making a flat test piece using a same material as a monitored pipeline;
• clamping the flat test piece on a clamp of a tensile testing machine;
• fixing the magnetic test detector directly above a measurement line of the flat test piece, a magnetic field test direction of the magnetic test detector being consistent with a loading direction of the flat test piece;
• turning on the tensile testing machine to perform a cyclic loading process to stretch the flat test piece;
• obtaining values of a normal magnetic induction intensity of a surface of the flat test piece within a range of elastic deformation of the flat test piece during the cyclic loading process;
• determining a change curve of change values of the normal magnetic induction intensity by processing the values of the normal magnetic induction intensity of the surface of the flat test piece;
• obtaining an actual strain curve of the flat test piece during the cyclic loading process from an upper computer corresponding to the tensile testing machine;
• and
• determining a value of the correction factor by comparing the change curve with the actual strain curve;
• wherein the safety pipe loop for strain monitoring of mountainous pipelines includes the plurality of magnetic test detectors and a protective shell for protecting the plurality of magnetic test detectors, a count of the plurality of magnetic test detectors is set to 4n, n is an integer number greater than or equal to 1, an angle between any two adjacent detectors of the plurality of magnetic test detectors is 180°/2n, at least two of the plurality of magnetic test detectors are connected in parallel through a data transmission line and output data through a data transmission interface, an outer layer of the protective shell includes non-magnetic hard alloy, and an inner layer of the protective shell includes non-metallic materials;
• installing the safety pipe loop on the monitored pipeline;
• installing a supporting device of the safety pipe loop, the supporting device including a data collector;
• for each of the plurality of magnetic test detectors of the safety pipe loop, converting, based on the correction factor of the magnetic test detector, the change value into a local longitudinal strain value of a monitoring location on the monitored pipeline corresponding to the magnetic test detector, the change value being obtained based on normal magnetic induction intensity values of a surface of the monitored pipeline, the normal magnetic induction intensity values being collected by the data collector from the safety pipe loop, the change value is converted into the local longitudinal strain value based on:
• EεL=fy·ΔBy,
• wherein E is an elastic modulus of a material of the monitored pipeline, a unit of which is MPa;
• εL is the local longitudinal strain value, a unit of which is με;
• fy is the correction factor, which is dimensionless;
• and ΔBy is the change value, a unit of which is nT;
• determining an overall axial strain value of a section of the monitored pipeline based on the local longitudinal strain values of the plurality of magnetic test detectors, wherein the overall axial strain value is determined based on:
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• wherein εa is the overall axial strain value, a unit of which is με;
• a count of the plurality of magnetic test detectors in the safety pipe loop is 4n;
• εLi is the local longitudinal strain value of the ith magnetic test detector of the plurality of magnetic test detectors, a unit of which is με;
• y is a Poisson coefficient of the monitored pipeline, which is dimensionless;
• εhp is a hoop strain of the monitored pipeline, a unit of which is με;
• P is an operating pressure of the monitored pipeline, a unit of which is MPa;
• D is a diameter of the monitored pipeline, a unit of which is mm;
• and δ is a wall thickness of the monitored pipeline, a unit of which is mm;
• determining an axial strain warning threshold of the monitored pipeline;
• comparing the axial strain warning threshold with the overall axial strain value;
• and
• determining a monitoring strategy based on a signal characteristic of the plurality of magnetic test detectors and the comparison result.