Fault detection for pipelines

Abstract

The invention concerns structural integrity assessment apparatus for determining stress concentration zones in a structure, such as a pipeline. The apparatus allows particularly to detect defects in buried pipelines using magnetometric surveying where anomalies in the magnetic field around the pipelines are detected. The appar-atus has a plurality of triaxial magnetic field sensors, each sensor being arranged to measure magnetic field components in a plurality of directions. A support is provided to maintain said sensors in a predetermined relative spacing and orientation. The support is moveable relative to a structure under assessment in use and may be portable. Three or more magnetic field sensors are provided which may be arranged in a linear, two-dimensional or three-dimensional array. The ap-paratus may include position determining means, such as a global positioning system (GPS), so that stress concentration zones can be located on the structure.

What is claimed is: 
     
         1 . A structural integrity assessment instrument for determining stress concentration zones in a structure, the instrument comprising:
 at least three magnetometers, each of the three magnetometers arranged to measure magnetic field components in a plurality of directions;   a support arranged to maintain the three magnetometers in a linear array and moveable relative to a structure under assessment;   a satellite positioning system mounted on the support;   a memory device; and   a processor for controlling or coordinating the operation of the instrument;   wherein the processor records magnetometer and satellite positioning data to the memory device in real-time by coordinating concurrent readings for the magnetic field from the magnetometers with position data from the satellite positioning system and time stamping a memory entry of all those readings.   
     
     
         2 . The structural integrity assessment instrument of  claim 1 , further comprising a correction factor that is determined by the processor based on one of a known or estimated depth of the structure and/or the magnetic permeability of a medium between the structure and the at least three magnetometers. 
     
     
         3 . The structural integrity assessment instrument of  claim 1 , wherein the instrument further comprises an inclinometer that provides a real-time indication of the angular orientation of the at least three magnetometers relative to one or more of the X, Y and/or Z axes. 
     
     
         4 . The structural integrity assessment instrument of  claim 4 , wherein the instantaneous angle of the at least three magnetometers is determined by the inclinometer, and the instantaneous angle of the at least three magnetometers is also time stamped and recorded in the memory entry. 
     
     
         5 . The structural integrity assessment instrument of  claim 1 , the at least three magnetometers comprising a centrally mounted magnetometer on the support, and an equal number of further magnetometers disposed on each side of the centrally mounted magnetometer. 
     
     
         6 . The structural integrity assessment instrument of  claim 1 , further comprising one or more multi-channel analog to digital converters that digitize the output of the at least three magnetometers prior to being recorded in the memory entry. 
     
     
         7 . The structural integrity assessment instrument of  claim 6 , wherein each channel of the one or more analog to digital converters is assigned to a reading of the magnetic field in a different direction. 
     
     
         8 . The structural integrity assessment instrument of  claim 1 , wherein the instrument identifies the centre of any peaks or local maxima in an absolute gradient and/or resultant fields along a length of the structure above a threshold value. 
     
     
         9 . The structural integrity assessment instrument of  claim 8 , wherein the instrument determines whether there is a maximum in magnitude of the gradient on either side of a location of an identified local peak magnetic field. 
     
     
         10 . The structural integrity assessment instrument of  claim 1 , wherein the controller records readings at a frequency of greater than 1 Hz. and preferably greater than 10 or 20 Hz. [page 5, lines 20-21] 
     
     
         11 . The structural integrity assessment instrument of  claim 1 , wherein the controller records readings at a frequency of greater than 10 Hz. 
     
     
         12 . The structural integrity assessment instrument of  claim 1 , wherein the controller records readings at a frequency of greater than 20 Hz. 
     
     
         13 . The structural integrity assessment instrument of  claim 1 , wherein the controller records readings at a frequency between 20 HZ and 50 Hz. 
     
     
         14 . The structural integrity assessment instrument of  claim 1 , wherein the memory device is a removable memory device. 
     
     
         15 . The structural integrity assessment instrument of  claim 1 , wherein the controller is arranged to record an RMS error of each measurement.