System and method for characterizing ferromagnetic material

Abstract

A system and method using magnetic sensing to non-intrusively and non-destructively characterize ferromagnetic material within infrastructure. The system includes sensors for measuring magnetic field gradients from a standoff distance adjacent to ferromagnetic material. The method includes using the system to measure magnetic fields, determining magnetic field gradients measured by a sensor array, and comparing measured and modeled or historical magnetic field gradients at the same or similar positions to identify differences caused by a phenomenon in the ferromagnetic material, and, in a particular embodiment, to recognize defects and developing defects.

What is claimed is: 
     
         1 . A method for characterizing a ferromagnetic material, comprising:
 receiving measured magnetic field data from a plurality of sensors adjacent the ferromagnetic material at a plurality of locations along the ferromagnetic material;   deriving measured magnetic field features from the measured magnetic field data; and   comparing the derived magnetic field features with modeled magnetic field features to identify occurrence of a phenomenon in the ferromagnetic material.   
     
     
         2 . The method of  claim 1 , further comprising measuring a magnetic field, using the sensors, to generate the magnetic field data. 
     
     
         3 . The method of  claim 1 , the measuring magnetic field data including obtaining measurements from a plurality of magnetometers arranged in a known pattern. 
     
     
         4 . The method of  claim 1 , the deriving magnetic field features including determining differences between measured magnetic fields for pairs of the sensors. 
     
     
         5 . The method of  claim 1 , the deriving magnetic field features including deriving magnetic field gradients between measured magnetic fields for pairs of the sensors. 
     
     
         6 . The method of  claim 1 , the magnetic field features being one or more numerics, that are derived from the measured magnetic field data, chosen from the group of numerics including: Fourier, Wavelet or any other transform, magnetic field gradients; gradient Fourier transform, wavelet transform; 2 nd  derivative matrices, Hessians, and fractal dimension. 
     
     
         7 . The method of  claim 1 , further comprising determining a nearest sensor to the ferromagnetic material based on magnetic fields measured from the plurality of sensors. 
     
     
         8 . The method of  claim 1 , further comprising characterizing the phenomenon of the ferromagnetic material to distinguish between a defect and a non-defect. 
     
     
         9 . The method of  claim 8 , the step of characterizing including applying a a pairwise comparison between the measured magnetic field features and the modeled magnetic field features to characterize a type of phenomenon. 
     
     
         10 . The method of  claim 9 , the step of applying utilizing a pairwise statistical comparison plot. 
     
     
         11 . The method of  claim 8 , the step of characterizing including determining a signature from the measured magnetic field features associated with a non-defect of the ferromagnetic material. 
     
     
         12 . The method of  claim 11 , the step of characterizing further including determining a magnetization direction and a magnetization amplitude based on the signature of the non-defect. 
     
     
         13 . The method of  claim 12 , the step of characterizing further including using the magnetization amplitude of the non-defect to scale the measured magnetic field data derived features to identify a phenomenon as a defect. 
     
     
         14 . The method of  claim 12 , further comprising determining modeled magnetic field features is based on the magnetization direction and the magnetization amplitude in the ferromagnetic material. 
     
     
         15 . The method of  claim 14 , the step of determining modeled magnetic field gradients being based on at least one physics model. 
     
     
         16 . The method of  claim 14 , determining modeled magnetic field gradients being based on prior measurements of the ferromagnetic material. 
     
     
         17 . The method of  claim 1 , the step of characterizing the phenomenon incorporating data from non-magnetic sensors with the measured magnetic field data. 
     
     
         18 . The method of  claim 17 , said data from non-magnetic sensors including location information corresponding to scan positions. 
     
     
         19 . A system for characterizing a ferromagnetic material, comprising:
 memory capable of storing magnetic field data from at least one sensor configured to measure magnetic field data at a plurality of scan positions along the ferromagnetic material, and software including machine readable instructions,   a processor coupled with the memory, the processor configured to, in response to execution of the software, perform the steps of:
 derive magnetic field feature data from the magnetic field data at the plurality of scan positions, and 
 compare the measured magnetic field feature data with modeled magnetic field feature data to identify a phenomenon in the ferromagnetic material. 
   
     
     
         20 . The system of  claim 19 , further comprising the at least one sensor, the at least one sensor being hardwired to the memory. 
     
     
         21 . The system of  claim 19 , the at least one sensor selected from the group consisting of a one-axis magnetometer, a two-axis magnetometer, or a three-axis magnetometer. 
     
     
         22 . The system of  claim 19 , the at least one sensor being a plurality of sensors arranged in a one-, two-, or three-dimensional array positionable at a standoff distance from the ferromagnetic material. 
     
     
         23 . The system of  claim 19 , the plurality of sensors having adjustable positions to adjust spacing distances therebetween. 
     
     
         24 . The system of  claim 19 , the ferromagnetic material comprising a pipe and the phenomenon comprising a welded junction connecting a first segment of the pipe to a second segment of the pipe. 
     
     
         25 . The system of  claim 24 , the welded junction between the first segment and the second segment producing a magnetic flux leakage, the processor further configured to determine magnetization direction and magnetization amplitude of the first segment and the second segment in response to the magnetic flux leakage. 
     
     
         26 . The system of  claim 19 , the step of comparing including comparing a likelihood based on the magnetic field feature to a threshold, the phenomenon being a known non-defect if the likelihood is below the threshold, the pheonomenon being a defect if the likelihood is above the threshold. 
     
     
         27 . The system of  claim 19 , the memory further storing a pairwise statistical plot, the processor further configured to characterize the phenomenon based on the pairwise statistical plot.