WO2020088765A1

WO2020088765A1 - Magnetic flux leakage testing device and associated method for identifying and differentiating defects in metallic plates

Info

Publication number: WO2020088765A1
Application number: PCT/EP2018/079901
Authority: WO
Inventors: Matthias Janssen; Stefan HABERLA; Axel DEHRMANN
Original assignee: NOV Downhole Eurasia Ltd
Current assignee: NOV Downhole Eurasia Ltd
Priority date: 2018-10-31
Filing date: 2018-10-31
Publication date: 2020-05-07
Anticipated expiration: 2021-04-30

Abstract

A testing device for detecting a defect in a tank plate, such a plate extending through a thickness from an upper proximal surface to a lower distal surface, the device comprising:a first testing unit configured to detect a defect in a proximal surface of a plate; a second testing unit configured to detect a defect through a thickness from a proximal surface to a distal surface of a plate;and wherein the device is configured to use data output from the first testing unit together with data output from the second testing unit so as to identify and differentiate between a defect in a proximal surface of a plate and a defect in a distal surface of that plate. Methods and testing units for use with, and in, such devices are also presented.

Description

MAGNETIC FLUX LEAKAGE TESTING DEVICE AND ASSOCIATED METHOD FOR IDENTIFYING AND DIFFERENTIATING DEFECTS IN METALLIC PLATES

FIELD

The present disclosure relates to devices and methods for the detection of defects, more specifically the accurate detection of corrosion in oil and gas tank plates, such as floor plates.

BACKGROUND

Oil and gas tanks are frequently exposed to damp and challenging environments and, as such, are therefore susceptible to defects such as corrosion. Severe corrosion can make a tank unsuitable for use and thus reduce the service life of the tank. Defects which are not detected may also pose a health and safety risk, as it can reduce the integrity of the tank. The risks associated with defects such as corrosion can be better mitigated if the defects are efficiently and accurately detected at an early stage.

In order to reduce corrosion, tanks are often coated - for example with a plastic material - in an attempt to reduce the exposure of the metal tank surface to the environment. However, coatings are not 100% effective so coated tanks may still suffer from corrosion. While coatings can help to reduce corrosion, they also make it difficult to detect corrosion when it occurs as the corrosion may be located under the coating and thus may not be visible.

A tank will typically rest on its floor, or bottom, plate. As such, this plate will be in contact with the ground and it may not be possible to visually inspect the external surface of the plate. This makes it more difficult to determine whether corrosion identified under a coating is present on the internal surface, external surface, or both surfaces of a tank floor plate.

SUMMARY

The presently-described devices and methods may identify defects located under coatings. As such, defects which are not visible to the human eye may be accurately identified for treatment. According to the present disclosure is a testing device for detecting a defect in a tank plate, for example a tank bottom plate or floor plate.

The plate tested by the device may be defined extending through a thickness from an upper proximal surface to a lower distal surface.

The tank may be for use in the oil and gas industry. As such, in an example, the plates of the tank may be of an industry-standard size for use in the production and/or transport of oil and gas.

The testing device may comprise a first testing unit configured to detect a defect in a proximal surface of a plate. The first testing unit may be configured to detect a defect only in the proximal surface of the plate. The testing device may comprise a second testing unit configured to detect a defect in the plate - for example through a thickness from a proximal surface to a distal surface of a plate. Data output from the first testing unit and second testing unit may be used to identify and differentiate between a defect in the proximal surface of the plate and a defect in the distal surface of the plate. The device may be configured to use data output from the first testing unit together with data output from the second testing unit so as to identify and differentiate between a defect in a proximal surface of a plate and a defect in a distal surface of that plate.

The testing device may be configured to determine that a defect is present on a proximal surface of the plate when: a defect in the proximal surface is detected by the first testing unit; and a defect in the plate is detected by the second testing unit. The testing device may be configured to determine that a defect is present on a distal surface of the plate when: a defect in the proximal surface of the plate is not detected by the first testing unit; and a defect in the plate is detected by the second testing unit.

The device may comprise a first testing unit configured to detect a defect in a proximal surface of a plate.

The first testing unit may comprise: a first magnetic field generating module configured to provide or generate a first magnetic field. The first magnetic field may penetrate the proximal surface of the plate. The first magnetic field may be for penetrating a proximal surface of a plate. The first magnetic field may have a first penetration depth or extent.

The first magnetic field generating module may be configured to generate a first magnetic field for penetrating only partially through a thickness of a plate.

The first testing unit may also comprise a first sensor module configured to monitor the generated first magnetic field such that changes in that first magnetic field caused by a defect in a proximal surface of a plate can be detected.

The first testing unit may also comprise an output configured to output data relating to the first magnetic field (i.e. the monitored first magnetic field).

The device may further comprise a second testing unit configured to detect a defect in the plate (for example in the proximal surface and a distal surface of the plate). The second testing unit may be configured to detect a defect through a thickness from a proximal surface to a distal surface of a plate.

The second testing unit may comprise a second magnetic field generating module configured to generate a second magnetic field. The second magnetic field may penetrate the plate to the distal surface of the plate. The second magnetic field may be for penetrating through a thickness of a plate from a proximal surface to a distal surface. The second magnetic field may have a second penetration depth or extent; the second penetration depth or extent may be larger than the first penetration depth or extent.

The second testing may further comprise a second sensor module configured to monitor the generated second magnetic field such that changes in that generated second magnetic field caused by a defect in a plate (for example the proximal and/or distal surface of the plate) can be detected.

The second testing unit may further comprise an output configured to output data relating to the second magnetic field (i.e. the monitored second magnetic field). The testing device may further comprise: a carriage configured to support the first and second testing units and arranged to move the first and second testing units over a plate.

The data output from the outputs of the first and second testing units may be used or usable to identify and differentiate between a defect in the proximal surface of a plate and the distal surface of a plate.

A testing device as disclosed herein may comprise a first testing unit configured to detect a defect in a proximal surface of a tank floor plate and a second testing unit configured to detect a defect in the proximal surface of the plate and configured to detect a defect in the distal surface of the tank floor plate, such that the results from the two testing unit can be combined to identify and differentiate between a defect in the proximal (top) surface of the plate and a defect in the distal (bottom) surface of the plate. The testing device may combine and/or cross reference defect detection results from two testing units to determine the location of a detected defect.

There are described devices for the detection of defects. The defects may be corrosion. Although the majority of the present disclosure discusses the detection of corrosion, it is to be understood that the present embodiments and methods may apply equally to the characterisation of any defect, corrosion being only one such example. As such, any statement made herein relating to defects are to be understood to apply equally to other forms of defect.

The devices and methods described herein provide improved feedback to the user in terms of the location and/or size of the detected defect. As such, the accuracy and reliability of said testing devices are improved and tank maintenance can be improved.

According to the disclosure, a testing device may be configured to identify whether detected defects are located on the proximate (e.g. top) or distal (e.g. bottom) of a floor plate of a tank. Said testing device may therefore allow defects to be more accurately located and thus treated.

Examples according to the disclosure provide an economical and robust method for differentiating between defects on the upper and lower surfaces of a plate. The disclosure may provide a low-complexity solution which may ensure that errors are minimised, implementation is simplified and reliability is increased. Examples according to the disclosure may be readily implemented in place of current testing systems, with minimal disruption.

The testing device may be configured to identify and differentiate between a defect in the proximal surface of the plate and the distal surface of the plate. The testing device may be configured to provide an output identifying and differentiating between a defect in the proximal surface of the plate and the distal surface of the plate. The testing device may comprise an output configured to output data identifying and differentiating between a defect in the proximal surface of the plate and the distal surface of the plate. The output may comprise a laptop, screen or any type of physical data port described herein (e.g. Ethernet or USB).

The testing device may be a tank testing device and may be for detecting corrosion. The testing device may be for detecting, or configured to detect, corrosion in the floor plate of a tank. The testing device may be a tank (e.g. oil and gas storage tank) testing device. Such tanks are typically made of a ferromagnetic material.

The testing device may be configured to test an area of a tank floor plate located substantially under the testing device. The testing device may be configured to move, or be moved, over the upper surface of the tank floor plate in order to test the whole floor plate.

The surface of the plate referred to herein as the proximal surface may be the surface of the plate on which the testing device is located or supported - typically the upper surface of the tank floor plate. The surface of the plate referred to herein as the distal surface may be the other surface of the tank floor plate - typically the bottom surface - which is furthest from the testing device.

The testing device, first testing unit and second testing unit may be configured such that an area of a plate to be tested is located below the testing device (and hence below the first and/or second testing units). The first and second testing units may be configured such that proximity to the plate is required to detect defects. As such, where it is stated herein that the first or second testing unit may detect defects, it is to be understood that any defects being detected may be located in a portion of the plate located adjacent, e.g. under, the testing device/testing unit(s).

The testing device may comprise a first testing unit. The first testing unit may be configured to detect a defect in a proximal surface of the plate. The first testing unit may be configured to only detect a defect in a proximal surface of the plate. As such, the first testing unit may be configured such that it is unable to detect a defect in a distal surface of the plate.

The first testing unit may be detachable such that it can be connected and disconnected from the testing device (both mechanically and electrically). For example, the first testing unit may be releasably connectable to the carriage. The first testing unit may comprise a body for supporting the first magnetic field generating module and the first sensor module. The body may be configured to be connected and disconnected from the carriage and the components carried thereon, both mechanically and electrically.

The first testing unit may comprise a first magnetic field generating module. The first magnetic field generating module may be configured to generate or provide a first magnetic field. The first magnetic field may reach or penetrate the proximal surface of the plate (but, for example, not the distal surface of the plate). The first magnetic field may penetrate the proximal surface of the plate.

The first magnetic field may penetrate the proximal surface of the plate only - i.e. the first magnetic field may be arranged to penetrate the proximal surface, but not the distal surface of the plate. The first magnetic field may not penetrate or reach the distal surface of the plate.

The first magnetic field generating module may be configured to generate a magnetic field with a strength and size so as to penetrate the proximal surface of the plate but not the distal surface of the plate.

The first magnetic field generating module may be configured to generate a magnetic field which extends up to 20mm, up to 15mm or up to 10mm from the magnetic field generating module. The first magnetic field generating module may be configured to generate a magnetic field which penetrates up to 10mm, up to 5mm or up to 2mm into the proximal surface of a tank floor plate being tested.

The first magnetic field generating module may comprise a permanent magnet arranged to generate or provide the first magnetic field.

The first magnetic field generating module may comprise an electromagnet configured to generate a steady or oscillating magnetic field.

The first testing unit may comprise an inductive sensor, e.g. an inductive proximity sensor or switch. The first magnetic generating module may form a part of the inductive sensor. The first magnetic field generating module may be configured for use in an inductive proximity sensor.

The first magnetic field generating module may comprise a coil and an oscillator configured to produce an oscillating magnetic field.

The first testing unit may comprise a first sensor module. The first sensor module may be configured to monitor - which may be interpreted to include detecting, using or measuring - the first magnetic field. The first sensor may monitor the first magnetic field such that changes in the first magnetic field can be detected. These changes may be caused by defects such as corrosion.

The changes detected by the first sensor module may be changes in the magnetic flux of the magnetic field, or the oscillation frequency or amplitude of the magnetic field. Monitoring changes in the first magnetic field may include monitoring eddy currents resultant from the oscillation of the magnetic field, or any phenomena directly linked to characteristics of the magnetic field. Equivalent comments apply to the second sensor module and second magnetic field, mutatis mutandis.

The first sensor module may be arranged in the first magnetic field. The first sensor module may be arranged adjacent the proximal surface of the plate during use. The first sensor module may be arranged perpendicularly to the plate. The first sensor module may be configured such that its output is dependent on the magnetic field which it monitors.

The first sensor module may comprise a Hall Effect sensor arranged to monitor the generated first magnetic field.

The first sensor module may be a Hall Effect sensor. The first sensor module may comprise a Hall Effect sensor and supporting circuitry.

A testing unit comprising a Hall Effect sensor (e.g. and permanent magnet) may be configured to detect small scale defects. Small scale defects may be considered to be those with a diameter of approximately, or less than, 3mm.

When the first sensor comprises a Hall Effect sensor, monitoring the first magnetic field may comprise monitoring for changes in the magnetic flux sensed by the Hall Effect sensor. Changes in the first magnetic field caused by defects may cause a change in the magnetic flux of the first magnetic field.

Testing units comprising a Hall Effect sensor and permanent magnet may be configured for use with thin coatings. Thin coatings may be coatings which have a thickness of less than 3mm.

The first sensor module may comprise an inductive sensor, an eddy current sensor, a device configured to use magnetic flux leakage methods, or any other sensor suitable for detecting changes in a magnetic field.

The first testing unit may comprise an inductive sensor, e.g. an inductive proximity sensor or switch. The first sensor module may form part of the inductive sensor. The first sensor module may comprise a coil and associated circuitry. The circuitry may be configured to monitor (e.g. measure) voltage or current induced in the coil.

The first testing unit may comprise an inductive proximity sensor comprising a coil and oscillator that creates an electromagnetic field. The presence of a metallic object in the oscillating magnetic field may cause a dampening of the oscillation amplitude. The presence of defects in the metallic object may affect the change imposed on the induced magnetic field by the metallic object - for example, the presence of a corroded object in the oscillating magnetic field may dampen the oscillation amplitude less than a non-corroded object. Accordingly, the measured current/voltage oscillation amplitude might be greater when in the presence of corroded plate than when in the presence of plate which is not corroded. As such, the testing unit may be able to identify areas of corrosion or other defects.

A testing unit comprising an inductive sensor may be configured to detect larger-scale defects. Large scale defects may be considered to be defects with a diameter of greater than 10mm.

When the first testing unit comprises an inductive proximity sensor, monitoring the first magnetic field may comprise monitoring the amplitude of a(n) (oscillating) voltage or current induced in a coil by the first magnetic field.

Testing units comprising an inductive sensor comprising a coil and excitation oscillator may be configured for use with thick coatings. Thick coatings may be coatings which have a thickness of greater than 2mm, 4mm, 6mm, 8mm or 10mm. Thick coatings may be coatings which have a thickness of up to 12mm.

Changes in the first magnetic field may be caused by a defect in the proximal surface of the plate. Changes in the first magnetic field may be caused by a defect in the proximal half of the plate. Changes in the first magnetic field may be caused by small scale or large scale defects in the proximal surface of the plate.

Corroded, or otherwise defective, sections of the floor plate may have different magnetic and electrical conductive properties compared to sections of the plate which are not corroded or otherwise defective. These properties may affect the first magnetic field when the defects are located inside the first magnetic field.

The first (and second) magnetic fields may be largely unaffected by the presence of a coating. As such, changes in a magnetic field caused by defects may be largely unaffected by the presence or absence of a coating. This may be the case provided the magnetic field is sufficiently large to penetrate the coating. The first testing unit may comprise an output arranged to output data relating to the first magnetic field. Thus, the first testing unit may be configured to output data relating to the first magnetic field. Data“relating” to the second (or first) magnetic field may include data indicative of the presence or absence of, strength of, or changes in any property of the corresponding magnetic field.

The output data may be processed or unprocessed. The output may constantly output data which fluctuates when the monitored magnetic field changes, may only output data when the magnetic field changes or may only output data when defects are detected.

The output may be an analogue or digital output. The output data may be a voltage or current. The output data may be an oscillating voltage or current.

The first sensor module and/or first testing unit may be configured to output a voltage or current, the value of which is dependent on the monitored first magnetic field. Accordingly, fluctuations in the output voltage/current may correspond to fluctuations in the first magnetic field which may correspond to a defect in the proximal surface of the plate.

The first sensor module may comprise supporting circuitry. Each inductive sensor or Hall Effect sensor of the first sensor module may comprise supporting circuitry. The output signals from the first sensor module (and/or each inductive sensor or Hall Effect sensor) may be subject to the supporting circuitry.

The supporting circuitry may be configured to have a self-zeroing or auto-zeroing functionality. The supporting circuitry may comprise an auto-zero amplifier. The auto- zero functionality may act to reduce the effects of offset, drift and noise.

The supporting circuitry may comprise an analogue-to-digital converter and a microcontroller. The microcontroller may constitute the processor of the first/second testing unit or device. The supporting circuitry may comprise an Ethernet interface. The Ethernet interface may constitute or form part of the respective output of the testing unit. When the first testing unit comprises a permanent magnet and Hall Effect sensor, the first testing unit may output a voltage, the value of which is dependent on the monitored first magnetic field. Accordingly, fluctuations in the output voltage may correspond to fluctuations in the first magnetic field which may correspond to a defect in the proximal surface of the plate.

When the first testing unit comprises an inductive proximity sensor, the first testing unit may output an oscillating current or voltage, the amplitude of which may be dependent on the monitored first magnetic field. Accordingly, fluctuations/changes in the output voltage/current amplitude may correspond to fluctuations in the first magnetic field which may correspond to a defect in the proximal surface of the plate.

The first testing unit may be configured to output data when a threshold value has been reached, for example when a predetermined voltage/current/magnetic flux threshold value is detected by the first sensor module. The first testing unit may be configured to output data when the oscillation amplitude of an inductive proximity sensor is above, or below, a certain threshold value.

The output may comprise a standard electronic interface. For example an analogue or digital connector, for example, an Ethernet or USB interface to output data to a computing device for further analysis.

The first testing unit may provide a sensory output, such as a visual indicator, or audible output. For example, the output may be an LED which activates when a change in the magnetic field caused by defects are detected. Alternatively, the output may comprise a dial or digital display which outputs information on properties relating to the magnetic field, e.g. magnetic flux or an output current or voltage induced by the magnetic field. In such cases, the first sensor module may output a voltage, the value of which is dependent on the first magnetic field, and this voltage, or the amplitude of this voltage, may be used to provide one of the above sensory outputs.

The first testing unit may be configured to detect a defect in the proximal surface of the plate. The first testing unit may further be configured to output indicative data when a defect in the proximal surface of the plate is detected. The first sensor module may be configured to determine whether a defect in the proximal surface of the plate is detected. The output of the first testing unit may be configured to output data when a defect in the proximal surface of the plate is detected.

The determination may be made by identifying a change in the voltage or current. The determination may be made by identifying a change in the amplitude of voltage or current oscillations. Determining whether a defect in the proximal surface of the plate is detected may comprise comparing a voltage, current or magnetic flux value (or an amplitude of an oscillating voltage, current or magnetic flux value) from the first sensor module to a threshold value. It may be determined that defects are detected when the absolute or amplitude of the oscillating voltage/current/magnetic flux value is lower than or higher than the threshold value. The processor may be configured to output data indicating that defects are detected.

The first testing unit may be configured to detect the defect depth - that is, the extent to which the defect extends perpendicularly into a surface of the plate. The amplitude of an output signal (e.g. of a steady state reading or an oscillating signal) or change thereof may be proportional to the depth of the detected defect.

The first testing unit or first sensor module may comprise a processor and data storage device. The processor and data storage device may form part of the first sensor module or the output. The data storage unit may be configured to store data relating to the first magnetic field - for example voltage over time.

The processor may be configured to undertake any action described herein with reference to the first testing unit.

The processor may be configured to determine whether a defect in the proximal surface of the plate is detected. The processor may be configured to output indicative data when a defect in the proximal surface of the plate is detected. The processor may be configured to use the data stored on the data storage device to identify a defect in the proximal surface of the plate. The processor may be configured to monitor the first magnetic field. The processor may also be configured to provide oscillator functionality when the first magnetic field generating module comprises a coil and an oscillator.

The first testing unit may comprise a plurality of magnetic field generating modules and/or sensor modules. The plurality of magnetic field generating modules and/or sensor modules may be arranged in an array. The use of a plurality of modules may increase the surface area which can be tested at any given time, thus increasing the speed with which a tank floor plate can be tested.

The first testing unit may comprise a plurality of permanent magnets. The first testing unit may comprise a plurality of Hall Effect sensors, arranged to test an area of a tank floor plate. The Hall Effect sensors may be arranged in an array.

The first testing unit may comprise an array of inductive proximity sensors, arranged to test an area of a tank floor plate.

The plurality of sensor modules and/or magnetic field generating modules may be arranged on a plane and may be arranged in the same orientation. The plurality of sensor modules and/or magnetic field generating modules may be arranged in a grid formation, or in a staggered grid formation - that is a grid formation in which adjacent rows or columns are staggered or misaligned with respect to each other. The use of a staggered grid formation may ensure better surface coverage.

The first testing unit (or processor thereof) may be configured to process data from all of the sensor modules. The first testing unit may be configured to use the plurality of sensor modules/magnetic field generating modules to differentiate between changes in the magnetic field(s) caused by defects and changes in the magnetic field(s) caused by other phenomena.

The first testing unit may be configured to compare the changes in the magnetic fields monitored by the sensor modules such that localised defects can be differentiated from array-wide phenomena. The first testing unit may be configured to filter out testing device-wide effects. That is, features of the tank floor plate which affect the magnetic fields of all of first the magnetic field generating modules may be identified and filtered out, since these changes are likely to be caused by testing unit-wide phenomena, such as a change in the distance between the testing unit and the tank floor plate, a weld line or a change in the coating thickness. Disturbances caused by mechanical movement of the testing device - for example due to tilting, lifting or jerking of the testing device - may be prevented from negatively affecting the identification of defects.

The first testing unit may be configured to identify differences in sensor module readings between sensor modules within the array to identify localised changes in the tank floor plate. This may be achieved by subtracting an average sensor module reading from the absolute reading of each sensor modules. These localised changes in magnetic field effects may be more likely to be caused by defects, rather than large scale phenomena such as a reduction in covering thickness or a change in ride height of the testing device.

The first magnetic field generating module may be arranged to generate a first magnetic field which penetrates the proximal surface but not the distal surface of the plate. In order to ensure that the first magnetic field penetrates the proximal surface but not the distal surface of the plate, the first magnetic field generating module may be arranged such that it is spaced from the proximal surface of the plate when in use, for example by a predetermined (e.g. calculated) amount.

Any reference to the spacing between the first magnetic field generating module and a proximal surface of the plate (or carrier surface) may refer to a direction substantially perpendicular to the surface of the plate.

The testing device may comprise a carrier surface. The carrier surface may be arranged to support the first and/or second testing units. The carrier surface may be arranged to contact the plate to be tested during use.

The carrier surface may comprise part of the carriage, or part of one, or both of, the testing devices. The contact surface may constitute a lower surface of the carriage and may be arranged to be the closest surface of the testing device to the tank bottom plate during use. The carrier surface may comprise a skid, wear plate or shield for protecting the first and/or second testing units from damage, or for holding them in a specific arrangement. The carrier surface may be a protection plate. The carrier surface may comprise a thin wear plate arranged to ensure a constant spacing between the plate being tested and the first magnetic field generating module and first sensor module. The carrier surface may be arranged to protect the first magnetic field generating module and the first sensor module from being damaged by contact with the plate being tested.

The first testing unit may be arranged on the carrier surface. The first sensor module may be arranged on the carrier surface. The first magnetic field generating module may be arranged to generate a first magnetic field which extends substantially perpendicularly to the carrier surface (and hence the tank bottom plate during use).

The carrier surface may be arranged to contact with the tank floor plate during testing, or to be suspended a fixed distance above the tank floor plate. The first magnetic field generating module may be configured to generate a first magnetic field which clearly penetrates the carrier surface. The first magnetic field generating module may be configured to generate a first magnetic field which extends past the carrier surface of the carriage by a predetermined amount - for example up to 5mm, up to 10mm, up to 20mm or up to 50mm.

The first magnetic field generating module may be spaced from the carrier surface by a predetermined amount. The first magnetic field generating module may be arranged spaced from the carrier surface such that during use the first magnetic field generating module is spaced from a proximal surface of a plate so that the first magnetic field penetrates the proximal surface but not the distal surface of the plate.

Given that the nominal thickness of a tank floor plate will be known and the contact surface may contact the upper surface or be arranged a known distance above the tank floor plate (for example through knowledge of the dimensions of the rest of the carriage), the distance past the carrier surface that the first magnetic field extends can be selected to penetrate the proximal, but not distal, surface of the plate. The distance between the first magnetic field generating module and the carrier surface may be dependent on the thickness of the coating (if any) on the plate and the strength of the magnetic field generated by the first magnetic field generating module.

The testing device or first testing module may be configured such that the spacing between the carrier surface and the first magnetic field generating module can be adjusted.

The spacing between the carrier surface and the first magnetic field generating module may be adjustable.

The first magnetic field generating module and the first sensor module may be aligned on an axis extending perpendicularly to the proximal surface of a plate during use, or perpendicular to the carrier surface.

The first magnetic field generating module may be arranged such that it is spaced from the first sensor module during use, for example by a predetermined amount.

The permanent magnet may be arranged such that it is spaced from the Hall Effect sensor, for example by a predetermined amount. The spacing between the permanent magnet and the Hall Effect sensor may be such that the Hall Effect sensor is working within its operable limits and can detect changes in the magnetic field caused by a defect in the proximal surface of the plate only.

Reference to the spacing between the first magnetic field generating module and the first sensor module may refer to spacing in a direction perpendicular to the surface of a plate being tested.

The spacing between the first sensor module and the first magnetic field generating module may be adjustable.

The testing device may comprise a second testing unit. The second testing unit may be configured to detect a defect in the proximal surface of the plate and to detect a defect in the distal surface of the plate. Where it is stated to herein that a testing unit is configured to detect a defect in the plate; or a defect in the proximal surface and distal surface of the plate; or a defect in at least one of the proximal surface and distal surface of the plate, in certain cases this may mean that the testing unit is configured to detect a defect in the proximal surface and is configured to detect a defect in the distal surface. Similarly, where it is stated that changes in the magnetic field caused by a defect in the plate (or the proximal and distal surfaces of the plate) can be detected, in certain cases this may mean that changes in the magnetic field caused by a defect in the proximal surface can be detected and changes in the magnetic field caused by a defect in the distal surface can be detected.

The second testing unit may be detachable such that it can be connected and disconnected from the testing device (mechanically and electrically); for example, the second testing unit may be releasably connectable to the carriage.

The second testing unit may comprise a second magnetic field generating module. The second magnetic field generating module may be configured to generate a second magnetic field. The second magnetic field may penetrate the plate. The second magnetic field may penetrate the plate to the distal surface of the plate. The second magnetic field may completely penetrate the thickness of the plate. The second magnetic field may penetrate 100% of the thickness of the plate. The second magnetic field may penetrate the proximal surface and the distal surface of the plate. The second magnetic field generating module may be configured to generate a second magnetic field, sufficient to detect, or be affected by, defects on the distal surface of the tank bottom plate (as well as defects on the proximal surface of the tank bottom plate).

The second magnetic field may penetrate a surface coating on the proximal surface of the plate, and the plate. The surface coating may be up to 12 mm thick. Accordingly, a surface coating may be at least 1 mm, 3mm, 5mm, 8mm or 12mm thick.

The second magnetic field generating module may be configured to generate a second magnetic field, wherein the second magnetic field is larger or stronger than the first magnetic field. The second magnetic field generating module may be configured to generate a second magnetic field configured to penetrate a plate to a greater depth than the first magnetic field. The penetration of the second magnetic field into a plate - i.e. in a direction perpendicular to a plate to be tested - may be larger than the penetration of the first magnetic field. This may allow the second testing unit to detect defects in the proximal and distal surfaces of the plate.

The second magnetic field generating module may comprise an electromagnet, for example a selectively operable electromagnet.

The second magnetic field generating module may comprise an electromagnet. The second magnetic field generating module may be configured such that the electromagnet can be selectively activated.

The second magnetic field generating module may comprise supporting circuitry configured to activate and deactivate the electromagnet.

The electromagnet may be configurable or adjustable such that the second magnetic field can be generated which penetrates the entire depth of the plate to be tested. The second magnetic field generating module may be configured to vary the power of the electromagnet. This may be used to account for different dimensions (e.g. thicknesses) of the plate to be tested.

The second magnetic field generating module may comprise a permanent magnet.

The second magnetic field generating module may be arranged with a north and south pole provided laterally spaced and close to a carrier surface of the testing device or the proximal surface of the tank floor plate. The second magnetic field generating module may be arranged such that the magnetic field travels laterally (with respect to the direction the testing device is facing) across a width of the plate, or longitudinally such that the magnetic field travels in the same direction that the testing device is facing.

The second testing unit may comprise a second sensor module. The second sensor module may be configured to monitor - which may be interpreted to include detecting, using or measuring - the second magnetic field. The second sensor may monitor the second magnetic field such that changes in the second magnetic field can be detected. These changes may be caused by defects. The second sensor module may be configured such that its output is dependent on the magnetic field which it is exposed to/which it monitors.

The second sensor module may be arranged adjacent the bottom of the testing device. The second sensor may be arranged such that it is adjacent the tank floor plate during use. The second sensor module may be arranged on the carrier surface (which may be, for example, a wear plate), which may be in contact with the plate floor surface during use.

The second sensor module may comprise a sensor configured to detect a magnetic field. That is, the second sensor module may comprise a sensor, the output of which is affected by or dependent on the presence of a magnetic field. Exemplar sensors may include a Hall Effect sensor.

Changes in the second magnetic field may be caused by a defect in the proximal surface of the plate, or a defect in the distal surface of the plate, or a defect in both the proximal and distal surfaces of the plate. Changes in the second magnetic field may be caused by a defect in the proximal, or distal half of the plate (or both). Changes in the second magnetic field may be caused by small-scale or large-scale a defect in the proximal or distal surface of the plate.

Changes in the second magnetic field may comprise a steady state change in the magnetic flux, or fluctuations in the magnetic flux.

The magnetic field may be largely unaffected by the presence of a coating. As such, changes in the magnetic field caused by a defect in the plate (for example the proximal surface and/or distal surface of the plate) may be largely unaffected by the presence or absence of a coating.

The second testing unit may be configured to use a magnetic flux leakage method to detect a defect in the plate (for example the proximal surface and a distal surface of the plate).

The second magnetic field generating module may be configured to generate a magnetic field through the tank floor plate; the second sensor module may be configured and arranged to detect leakage of the magnetic flux (or field) from the plate caused by a defect in either or both of the proximal and distal surfaces of the plate.

The magnetic behaviour of metal with defects is different to that of metal without defects. As such, defects on either surface of a piece of metal through which a magnetic field is present cause the lines of magnetic flux to‘bow’ out of either side of the piece of metal. This magnetic flux leakage can be detected by means of a magnetic field detecting sensor.

The magnetic flux leakage method may be configured to detect the defect depth - that is, the extent to which the defect extends into a surface of the plate. The amplitude of an output signal may be proportional to the depth of the detected defect.

Although the depth of the defects (e.g. the size) may be determined by the magnetic flux leakage method, it may be unable to determine whether the defects are on the proximal or distal surface of the plate.

The second testing unit may comprise an output arranged to output data relating to the second magnetic field. All of the comments made above with respect to the output of the first testing unit apply to the second testing unit, mutatis mutandis. It is to be noted that where comments are made with respect to only the proximal surface for the first testing unit, the comments will apply to the proximal and distal surface for the second testing unit, mutatis mutandis.

The second testing unit may be configured to detect a defect in the plate. The second testing unit may be configured to detect a defence in at least one of the proximal surface and distal surface of the plate. The second testing unit may further be configured to output indicative data when a defect in plate (for example at least one of the proximal surface and distal surface of the plate) is detected.

The second sensor module may be configured to determine whether a defect in the plate (for example at least one of the proximal surface and distal surface of the plate) is detected. The determination may be made by comparing a measured flux level, or voltage level, to a threshold value. The output of the second testing unit may be configured to output data when a defect in plate (for example at least one of the proximal surface and distal surface of the plate) is detected.

The second testing unit may be configured to detect a defect in at least one of the proximal surface and distal surface of the plate and to output indicative data when a defect in at least one of the proximal surface and distal surface of the plate is detected.

The second testing unit may comprise a processor and data storage device. The data storage unit may be configured to store data relating to the second magnetic field - for example voltage over time.

The processor may be configured to determine whether a defect in the plate (for example at least one of the proximal surface and distal surface of the plate) is detected. The processor may be configured to output indicative data when a defect in the plate (for example at least one of the proximal surface and distal surface of the plate) is detected.

The processor may be configured to compare a voltage or magnetic flux value to a threshold value and to take certain actions dependent on the result of said comparison.

The second testing unit may be a magnetic flux leakage detecting module. The second testing unit may therefore be configured to output a voltage dependent on the detected magnetic field. Fluctuations in the output voltage may indicate defects. A threshold voltage value may be set which, when the output voltage reaches the threshold value, indicates that defects are present in the tested area of the tank floor plate.

The testing device may further comprise a carriage. The carriage may be configured to support the first testing unit. The carriage may be configured to support the second testing unit. The carriage may comprise a support for locating and attaching the first and/or second testing unit to the carriage.

The carriage may be arranged to move the first and second testing units over a plate to be tested. The carriage may comprise wheels or rollers or a low friction surface (e.g. the carrier surface) allowing the device to be moved over a plate. The carriage may be configured to support a plurality of first magnetic field generating modules and/or first sensor modules in an array as described herein.

The carriage may comprise the carrier surface. The carrier surface may protect the first and/or second testing unit from damage caused by impact with the plate. The carrier surface may support the first and/or second testing unit, first and/or second magnetic field generating module, and first and/or second sensor module.

The carriage may comprise a frame configured to support at least one of: the first sensor module, the second sensor module, the first magnetic field generating module and the second magnetic field generating module at a predetermined distance from the plate to be tested.

The frame may be configured to allow the distance between the plate being tested and any of the above-mentioned components to be adjustable. The frame may be configured to support each, or a plurality of, the above-mentioned features at a predetermined distance from the plate. The frame may be configured such that this predetermined distance for each of the supported features may be independently adjustable.

The data that is output by the first testing unit output and the second testing unit output may be usable to identify and differentiate between a defect in the proximal surface of the plate and the distal surface of the plate. The data output from the first and second testing units may be combined to identify and differentiate between a defect in the proximal surface of a plate being tested and the distal surface of the plate being tested.

The testing device may further comprise a processing module. The processing module may comprise an input configured to receive data from the outputs of the first and second testing units; a data storage unit configured to store data received from the first and second testing units; a processor configured to use the data from the first and second testing units to identify and differentiate between defects present on the proximal and distal surface of the plate.

The processing module may be a laptop, which may be connected to the outputs of the first and second testing units. The processing module may comprise the testing device output.

The processing module may be configured to: use data output by the first testing unit to determine whether a defect in the proximal surface of the plate is detected by the first testing unit; and use data output by the second testing unit to determine whether a defect in the plate (for example at least one of the proximal surface and distal surface of the plate) is detected by the second testing unit.

The processing module (or processor thereof) may be configured to use the data output by the first testing unit to determine whether a defect in the proximal surface of the plate is detected by the first testing unit. The processing module (or processor thereof) may be configured to use the data output by the second testing unit to determine whether a defect in the plate (for example at least one of the proximal surface and distal surface of the plate) is detected by the second testing unit.

The processing module may be configured to: determine that defects are present on a proximal surface of the plate when: a defect in the proximal surface is detected by the first testing unit; and a defect in the plate (for example the at least one of the proximal surface and the distal surface of the plate) is detected by the second testing unit; and determine that defects are present on a distal surface of the plate when: a defect in the plate (for example the at least one of the proximal surface and the distal surface of the plate) is detected by the second testing unit; and a defect in the proximal surface of the plate is not detected by the first testing unit.

The processing module may be configured to compensate for the relative spacing between the first testing unit and second testing unit, such that the readings provided for the same absolute location of a tested plate are aligned.

The processing module may further comprise an output configured to output data indicative of whether defects are detected and the surface on which those defects are detected.

The processing module may be configured to communicate information relating to the monitored magnetic fields and/or detected defects to a user in real-time The processing module may be configured to communicate information relating to detected defects to a user in real-time.

Further according to the disclosure is a testing unit configured to detect a defect in a proximal surface of a plate of a storage tank. The testing unit may comprise: a magnetic field generating module configured to generate a magnetic field which penetrates the proximal surface of the plate. The testing unit may further comprise a sensor module configured to monitor the magnetic field such that changes in the first magnetic field caused by a defect in the proximal surface of the plate can be detected. The testing unit may further comprise an output arranged to output data relating to the first magnetic field.

The testing unit may be for use in a testing device, or a tank floor testing device, as described anywhere herein.

The testing unit may be connectable and disconnectable from the rest of a testing device. Any discussion made herein relating to features of the first testing unit may apply to this testing unit, mutatis mutandis.

The testing unit may be used in a tank testing device - for example a tank floor testing device.

Further according to the disclosure is a method of detecting a defect in a tank plate, for example a tank bottom plate. The plate may extend through a thickness from an upper proximal surface to a lower distal surface. The method may comprise: detecting a defect in a proximal surface of a plate. This may be done by generating a first magnetic field to penetrate the proximal surface of that plate and monitoring the generated first magnetic field to detect changes in that first magnetic field caused by a defect in the proximal surface. The method may further comprise detecting a defect through a thickness from the proximal surface to the distal surface of the plate by generating a second magnetic field to penetrate the plate. The method may further comprise monitoring the generated second magnetic field to detect changes in the second magnetic field caused by a defect in the plate (for example the proximal and distal surface of the plate). The method may further comprise identifying differentiating between a defect in the proximal surface of the plate and the distal surface of the plate using the monitored first and second magnetic field.

Further according to the disclosure is a method of detecting a defect in a tank bottom plate. The method may comprise: monitoring for a defect in the proximal surface of the plate using a first testing unit. The method may further comprise: monitoring for a defect in the plate (for example the at least one of the proximal surface and distal surface of the plate) using a second testing unit. The method may further comprise: determining that a defect is present on a proximal surface of the plate when: a defect in the proximal surface is detected by the first testing unit; and a defect in the plate (for example the proximal surface and distal surface of the plate) is detected by the second testing unit. The method may further comprise: determining that a defect is present on a distal surface of the plate when: a defect in the proximal surface of the plate is not detected by the first testing unit; and a defect in the plate is detected by the second testing unit (for example in at least one of the proximal surface and distal surface of the plate).

The method may comprise detecting a defect in the proximal surface of the plate using a first testing unit and/or detecting a defect in the plate using a second testing unit.

Any discussion made herein relating to the testing device applies, mutatis mutandis, to corresponding features of the testing unit, as well as the methods described as part of this disclosure. As such, methods according to the disclosure may comprise steps involving the use of the testing device or features thereof as described anywhere herein.

Further according to the disclosure is the use of a testing device as described anywhere herein, to identify and differentiate between a defect in the proximal surface of the plate and the distal surface of the plate.

It is to be understood that any disclosure and description of features provided above in relation to one of the first and second testing units, magnetic field generating modules, sensor modules or outputs, applies equally, mutatis mutandis, to the other of the first and second testing units, magnetic field generating modules, sensor modules or outputs. BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a schematic view of a testing device according to the disclosure;

Figures 2A and 2B illustrate a carriage for use with the testing device of figure 1 ;

Figure 3 is perspective view of a first testing unit according to the disclosure;

Figure 4 is front view of the first testing unit of figure 3;

Figure 5 is a cross section of the first testing unit of figure 3;

Figure 6 is a schematic view of an induction proximity sensor for use with the disclosure;

Figure 7 is a further schematic view of the induction proximity sensor of figure 6;

Figure 8 is a block diagram of supporting circuitry of a first testing unit according to the disclosure;

Figure 9 is a schematic view of a first testing unit according to the disclosure;

Figure 10 is a schematic view of a second testing unit according to the disclosure;

Figure 11 is a side view of a testing device according to the disclosure;

Figures 12A-12C illustrate exemplar data for use with a testing device according to the disclosure; and

Figures 13A-13C illustrate further exemplar data for use with a testing device according to the disclosure.

DETAILED DESCRIPTION OF DRAWINGS Figure 1 is a schematic side view of a testing device 10 according to the disclosure. The testing device 10 comprises a first testing unit 1 1 and a second testing unit 13. In this example, the first testing unit 11 and second testing unit 13 are supported by a carriage 14 with the first testing unit 1 1 arranged in front of the second testing unit 13, adjacent a tank floor plate 12 over which the testing device 10 is moved to test for corrosion.

Figure 2A illustrates a carriage 14 for use with a testing device 10 (for example as shown in figure 1 ). In figures 2A and 2B, the carriage 14 supports only a second testing unit 13. The carriage 14 is shown in use for testing for a defect in a tank floor plate 12, on which it is located. The tank floor plate 12 is the flat base plate of a tank used to store and transport materials used in the production of oil and gas. The tank floor plate 12 is made of a ferromagnetic material and is being checked for corrosion.

The carriage 14 supports the second testing device 13 at its lower end. The second testing unit 13 is located close to the tank floor plate 12 to allow magnetic fields generated by the second testing unit to penetrate the plate 12 (the same is true for the first testing unit, when present). Here, the carriage 14 comprises a container in which the second testing unit 13 is installed. The first testing unit 11 (for example as shown in figure 1 ) can also be installed in the container, or connected to the front of the container. Two wheels 18 are arranged on either side of the carriage such that the testing device 10 (as shown in figure 1 ) can be rolled along the upper surface of the floor plate 12. The carriage 14 in figure 2A also comprises a frame which supports a processing module in the form of a laptop 20. The laptop 20 is located towards the top of the carriage 14 so that it can be viewed easily and used by a user operating the testing device. A handle 22 is provided on the carriage 14 adjacent the laptop to allow a user to push the carriage 14 over the plate 12.

In use, the carriage 14 is rolled over the entire upper (proximal) surface of the tank floor plate 12, preferably in parallel contiguous strips. The laptop 20 records the location and details of detected defects (e.g. areas of corrosion) present in the plate 12 and can then provide a report to the user, who can take any necessary action. Figure 2B is a side view of the carriage 14 of figure 2A. It can be seen in figure 2B that there is only a small amount of clearance between the second testing unit 13 and the upper surface of the tank floor plate 12.

In the carriage 14 of figures 2A and 2B, the first and second testing units can both be housed in the support 16. It is also possible for the first testing unit to be separably attachable to the front of the carriage 14, both electrically and mechanically.

Figures 3 to 5 illustrate an example first testing unit 1 1 - configured to be separably connectable to the carriage 14 of a testing device 10, for example as shown in figure 1. The first testing unit 11 of figures 3 to 5 is arranged to connect to the carriage but be self-supporting on the plate to be tested.

The first testing unit 1 1 of figures 3 to 5 comprises a body 42 which includes a carrier surface in the form of a lower plate 46 suspended from a pair of support arms 48. Each support arm 48 comprises a damper 52 for allowing variation in the height of the lower plate 46 relative to the tested plate. The body 42 further comprises four casters 50 located towards the four corners of the body 42 such that the first testing unit 11 can be sat on a plate to be tested and rolled thereover, either as part of, or separate from, the rest of a testing device 10 as illustrated in figure 1.

The lower plate 46 supports an array of twenty-seven magnetic field generating modules and sensor modules integrally formed as inductive proximity sensors 44. The support arms 48, casters 50 and lower plate 46 are arranged to support the array of inductive proximity sensors 44 at a predetermined height above a tank floor plate on which the first testing unit 1 1 rests. The predetermined height is selected such that the magnetic field generated by the inductive proximity sensors 44 penetrates only the upper (proximal) surface of a tank floor plate on which the first testing unit 1 1 rests. In the presently-described first testing unit 11 , the inductive proximity sensors 44 are supported such that the lower end of the sensors 44 are between 2 and 12 mm from the proximal surface of the tank floor plate.

The first testing unit 1 1 further comprises mechanical fasteners 49 and electrical connectors (e.g. an output - not shown in figures 3 to 5) for both mechanically and electrically connecting the first testing unit 11 to a carriage 14 and/or other part of the testing device 10 (figure 1 ).

Figure 6 illustrates an example inductive proximity sensor 44 for use in a first testing unit 11 according to the disclosure (for example as shown in figures 3 to 5). The inductive proximity sensor 44 provides both the first magnetic field generating module and the first sensor module by means of an oscillator coil and supporting circuitry configured to generate an oscillating magnetic field and measure the amplitude of the oscillating voltage of the coil in order to monitor the magnetic field induced and hence detect any defects in a plate located within the oscillating magnetic field. The presence of a defect - e.g. corrosion - in the tested plate affects the Eddy-currents generated in the tested plate and hence the defects can be detected through the changes to the induced magnetic field.

The inductive proximity sensor 44 is supported between 2 and 12mm above the plate 12 being tested. The arrow“A” indicates the direction in which the inductive proximity sensor 44 is arranged to move with the carriage 14 (see, for example, figure 1 ) during use. The inductive proximity sensor 44 is configured to output indicative data when corrosion in the proximal surface of the plate is detected, as shown in figure 6, where corrosion 54 is located below the inductive proximity sensor 44 and the output signal 56 indicates the detection of corrosion 54 by an increase in the output value as the proximity sensor 44 passes over the defect. The output signal 56 also provides an indication of the thickness of the corrosion 54.

Figure 7 shows the inductive proximity sensor 44 of figure 6 testing a plate 12 with a coating 58. The presence of the coating 58 does not affect the magnetic field and, as such, the inductive proximity sensor 44 can still detect the presence of corrosion 54 underneath the coating 58, provided the magnetic field induced by the oscillation coils is sufficient to pass through the coating 58 into the proximal surface of the plate 12.

Figure 8 schematically illustrates exemplar supporting circuitry for use with a first testing unit. Each of the twenty-seven inductive proximity sensors 44 is connected to a preamplifier auto-zero or self-zero op-amp arrangement 60 which auto-zeros the output over time to negate the effects of offset, drift and noise. This is beneficial as material properties of tank floor plates are rarely consistent across an entire floor plate. These fluctuations in material properties can affect the first and second magnet fields and thus affect an output from the first and/or second testing units. The auto-zeroing effect of the Preamplifier Self Zero Setting reduces the impact of these effects.

The outputs of all of the self-zeroing op-amp arrangement are converted from an analogue to digital signal through an analogue-to-digital converter instrumentation arrangement 62 and transmitted to a PC 66 - for example a laptop connected to the carriage 14 - via an Ethernet-interface 64.

Figure 9 is a schematic for an alternative first testing unit 11 according to the disclosure. The first testing unit 11 comprises a permanent magnet 26 which forms part of the first magnetic field generating module, a Hall Effect sensor 28 and a carrier surface in the form of a wear plate 30.

The permanent magnet 26 is located at a predetermined distance from the tank floor plate 12, to ensure that the magnetic field generated by the permanent magnet 26 penetrates the proximal (upper) surface of the tank floor plate 12a, but does not penetrate the distal (lower) surface of the tank floor plate 12b.

The wear plate 30 forms part of the testing device 10 and is arranged to provide a bottom surface of the testing device 10 (see, for example, figure 1 ) adjacent the tank floor plate 12. The wear plate 30 may comprise a flat metallic plate attached to the carriage 14. In the testing unit 1 1 of figure 9, a Hall Effect sensor 28 is attached to the upper side of the wear plate 30. This arrangement ensures that the Hall Effect sensor 28 is arranged close to the tank floor plate 12. The Hall Effect sensor 28 is arranged between the permanent magnet 26 and the tank floor plate 12 so as to be located within the magnetic field generated by the permanent magnet 26.

The Hall Effect sensor 28 is arranged at a distance‘d’ from the permanent magnet 26 in a direction perpendicular to the tank floor plate 12. This spacing‘d’ is selected such that the Hall Effect sensor 28 can detect any fluctuations in the magnetic field caused by a defect in the proximal surface of the tank floor plate 12. In figure 9, the tank floor plate 12 has a plastic coating 32, which has a thickness of much less than the thickness of the tank floor plate 12. This plastic coating 32 does not affect the operation of the first testing unit 1 1.

In use, the first testing unit 1 1 is moved over the surface of the tank floor plate 12 as the testing device 10 is rolled over the tank floor as shown in figures 1 and 11. The permanent magnet 26 generates a magnetic field which penetrates the proximal surface of the tank floor plate 12a. The Hall Effect sensor 28 provides an output voltage dependent on the sensed magnetic field. Thus, the output of the Hall Effect sensor 28 fluctuates when corrosion located under the first testing unit 1 1 causes fluctuations in the magnetic field passing through the proximal surface of the plate 12a.

Figure 10 is a schematic image of a second testing unit 13 according to the disclosure. Figure 10 schematically illustrates a magnetic flux leakage system suitable for use as a second testing unit 13. The system of figure 10 comprises an electromagnet core 34 and a magnetising system 36. When active, the magnetising system 36 and core 34 provide a magnetic field 72 which passes through the entire thickness of the tank floor plate 12.

If corrosion 96 is present in the part of the plate 12 in which the magnetic flux is present, the corrosion will cause“leakage” of the magnetic flux (both above and below the plate 12). This leakage is monitored by a sensor 38. Corrosion on the tested section of plate 12 causes magnetic flux leakage regardless of whether it is located on the upper (proximal) surface 12a or lower (distal) surface 12b of the plate 12. As such, the magnetic flux leakage system does not discriminate between corrosion on the top and bottom surfaces. The amount of magnetic flux leakage is proportional to the depth that the defect (e.g. corrosion) extends into the plate in a direction perpendicular to the plate surfaces.

Figure 11 schematically illustrates a testing device 10 according to the disclosure. The testing device comprises a first testing unit 11 -as illustrated in figures 3 to 5 - and a second testing unit 13 - for example as illustrated in figure 10. In the illustrated device 10, the second testing unit 13 uses a magnetic flux leakage method for detecting defects such as corrosion of the plate 12 being tested. Accordingly, the second testing unit 13 generates a magnetic field 72 which passes through the thickness of the plate 12 which is being tested. A sensor 38 is arranged to monitor the magnetic field and detect changes in the magnetic field caused by a defect in the plate 12 (for example the proximal and the distal surface of the plate 12). The first testing unit 1 1 is connected to the front of the second testing unit 13 and comprises an array of inductive proximity sensors 44 as discussed above.

Figures 12 and 13 illustrate exemplar outputs from the first and second testing units and how they may be used to determine whether a defect is present on the proximal (top) or distal (bottom) surface of a plate. In both of the examples provided in figure 12 and figure 13, the first testing unit and the second testing unit are configured to output a signal when a defect is detected.

Figure 12A illustrates a plate 12 being tested. The plate 12 has a defect 90 in its upper surface. Figure 12B illustrates an output from a first testing unit. The first testing unit is configured to detect changes in the first magnetic field caused by a defect in the top surface. As the defect 90 is in the upper surface of the plate 12, the first testing unit outputs an indicative signal 92 at the location of the defect 90. Figure 12C illustrates an output from a second testing unit. The second testing unit is configured to detect changes in the second magnetic field caused by a defect in the plate (for example the proximal and distal surface of the plate) and thus output a signal when a defect is detected in either of the top or bottom surface of the plate. The second testing unit also outputs an indicative signal 94 at the location of the defect 90. A processor of the testing device, which may be the laptop computer 20, is configured to determine that a defect is present in the top surface of the plate 12 because the defect 90 was detected by both of the first testing unit and the second testing unit.

Figure 13A illustrates a plate 12 being tested. The plate 12 has a defect 96 in its lower surface. Figure 13B illustrates an output from a first testing unit. The first testing unit is configured to detect changes in the first magnetic field caused by a defect in the top surface. As the defect 96 is in the lower surface of the plate 12, the first testing unit does not detect any change in the first magnetic field and does not output an indicative signal 92. Figure 13C illustrates an output from a second testing unit. The second testing unit is configured to detect changes in the second magnetic field caused by a defect in the plate (for example the proximal and distal surface of the plate). The second testing unit outputs an indicative signal 94 at the location of the defect 96 because changes to the second magnetic field, caused by the defect 96 in the lower surface of the plate 12, are detected. A processor of the testing device, which may be the laptop computer 20, is configured to determine that a defect 96 is present in the lower surface of the plate 12 because the defect 96 was detected only by the second testing unit.

Implementations of certain aspects of the subject matter and the operations described in this specification can be realized in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Implementations of aspects of the subject matter described in this specification may be realized using one or more computer programs, i.e., one or more modules of computer program instructions, encoded on computer storage medium for execution by, or to control the operation of, data processing apparatus. Alternatively or in addition, program instructions can be encoded on an artificially-generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. A computer storage medium can be, or be included in, a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially-generated propagated signal. The computer storage medium can also be, or be included in, one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices).

The present invention has been described above purely by way of example. Modifications in detail may be made to the present invention within the scope of the claims as appended hereto.

Claims

1. A testing device for detecting a defect in a tank plate, such a plate extending through a thickness from an upper proximal surface to a lower distal surface, the device comprising:

a first testing unit configured to detect a defect in a proximal surface of a plate; a second testing unit configured to detect a defect through a thickness from a proximal surface to a distal surface of a plate; and

wherein the device is configured to use data output from the first testing unit together with data output from the second testing unit so as to identify and differentiate between a defect in a proximal surface of a plate and a defect in a distal surface of that plate.

2. The testing device according to claim 1 , wherein:

the first testing unit comprises:

a first magnetic field generating module configured to generate a first magnetic field for penetrating a proximal surface of a plate; and a first sensor module configured to monitor a generated first magnetic field such that changes in that first magnetic field caused by a defect in a proximal surface of a plate can be detected; and

an output configured to output data relating to a monitored first magnetic field.

3. The testing device according to claim 2, wherein the first magnetic field generating module is configured to generate a first magnetic field for penetrating only partially through a thickness of a plate.

4. The testing device according to any of the preceding claims, wherein the second testing unit comprises:

a second magnetic field generating module configured to generate a second magnetic field for penetrating through a thickness of a plate from a proximal surface to a distal surface; and

a second sensor module configured to monitor the generated second magnetic field such that changes in that generated second magnetic field caused by a defect in a plate can be detected; and an output configured to output data relating to the monitored second magnetic field.

5. The testing device according to any of the claims 2 to 4, wherein the first magnetic field generating module comprises a permanent magnet arranged to generate the first magnetic field.

6. The testing device according to any of the claims 2 to 5, wherein the first sensor module comprises a Hall Effect sensor arranged to monitor the generated first magnetic field.

7. The testing device according to any of the claims 2 to 6, wherein the testing device comprises a carrier surface and the first testing unit is arranged on the carrier surface.

8. The testing device according to any of the claims 2 to 7, wherein the second testing unit is configured to use a magnetic flux leakage method to detect a defect in a plate.

9. The testing device according to any of the preceding claims further comprising: a carriage configured to support the first and second testing units and arranged to move the first and second testing units over a plate.

10. The testing device according to any of the preceding claims, wherein the first testing unit comprises a plurality of magnetic field generating modules and/or sensor modules arranged in an array.

1 1. The testing device according to claim 10, wherein the first testing unit is configured to compare the changes in the magnetic fields monitored by the sensor modules such that localised defects can be differentiated from array-wide phenomena.

12. The testing device according to any of the preceding claims, wherein the testing device is configured to determine that a defect is present on a proximal surface of a plate when:

a defect in the proximal surface is detected by the first testing unit; and a defect in the plate is detected by the second testing unit; and determine that a defect is present on a distal surface of a plate when:

a defect in a proximal surface of the plate is not detected by the first testing unit; and

a defect in the plate is detected by the second testing unit.

13. The testing device according to any of the preceding claims, further comprising a processing module comprising:

an input configured to receive data from outputs of the first testing unit and second testing unit;

a data storage unit configured to store data received from the first and second testing units;

a processor configured to use the data from the first and second testing units to identify and differentiate between defects present on a proximal and distal surface of a plate.

14. The testing device according to claim 13, wherein the processing module further comprises an output configured to output data indicative of whether defects are detected and the surface of on which those defects are detected.

15. A method of detecting a defect in a tank plate, such a plate extending through a thickness from an upper proximal surface to a lower distal surface, the method comprising:

i) detecting a defect in a proximal surface of a plate by generating a first magnetic field to penetrate the proximal surface of that plate; and monitoring the generated first magnetic field to detect changes in that first magnetic field caused by a defect in the proximal surface;

ii) detecting a defect through a thickness from the proximal surface to the distal surface of the plate by generating a second magnetic field to penetrate the plate; and monitoring the second magnetic field to detect changes in the second magnetic field caused by a defect in the plate; and the method comprising: identifying and differentiating between a defect in the proximal surface of the plate and the distal surface of the plate using the monitored first and second magnetic fields.