Abstract:
A device for discovering, identification and monitoring, of mechanical flaws in metallic structures is disclosed, based on magneto-graphic/magnetic tomography technique to identify stress-related defects. The device can determine the position of the defect or stress including depth information. The device includes registration means that optimized for use with metallic structures of various types, shapes and sizes. Applications include a real-time quality control, monitoring and emergency alarms, as well structural repairs and maintenance work recommendations and planning. Examples of the device implementation include pipes for oil and gas industry monitoring, detection of flaws in rolled products in metallurgical industry, welding quality of heavy duty equipment such as ships, reservoirs. etc. It is especially important for loaded constructions, such as pressured pipes, infrastructure maintenance, nuclear power plant monitoring, bridges, corrosion prevention and environment protection.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of the U.S. patent application Ser. No. 13/920,216 filed on Jun. 18, 2013, published as US Patent Application Publication No. 20140368191 A1. This application is also a continuation-in-part of the U.S. patent application Ser. No. 14/551,295 filed on Nov. 24, 2014. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates broadly to a system and method for inspecting a subsea pipeline as well as a device and method for continuous (extended) metallic structures inspection and monitoring for possible mechanical defects; in particular, to contact magnetic scanner device and method, using magnetic tomography for a real-time structural defects measurement and assessment. 
       BACKGROUND ART 
       [0003]    This invention can be used in various fields where constructions are tested for continuity defects in a contact fashion or combined with the remote method. Examples of device and method implementation may include pipes for oil and gas industry, detection of flaws in rolled products in metallurgical industry, welding quality of heavy duty equipment such as ships and reservoirs, etc. It is especially important for inspection of loaded constructions, such as pressured pipes, infrastructure maintenance, nuclear power plant monitoring, bridges, corrosion prevention and environment protection. 
         [0004]    Similar to the modes of transportation like roads, railroads, and electric transmission lines, the pipelines have an important role in the nation&#39;s economy, belonging to the long linear assets. They typically cross large distances from the points of production and import facilities to the points of consumption. Like the other modes of transportation, pipe lines require very large initial investment to be built, having long exploitation periods when properly maintained. Like any engineering structure, pipelines do occasionally fail. While pipeline rates have little impact on the price of a fuel, its disruptions or lack of capacity can constrain supply, potentially causing very large price spikes. That&#39;s why pipelines, such as ones used in the oil and gas industry, require regular inspection and maintenance before potentially costly failures occur. 
         [0005]    The major causes of pipeline failures around the world are external interference and corrosion; therefore, assessment methods are needed to determine the severity of such defects when they are detected in pipelines. Pipeline integrity management is the general term given to all efforts (design, construction, operation, maintenance, etc.) directed towards ensuring continuing pipeline integrity. 
         [0006]    Traditional contact methods of assessing the structural integrity typically complemented by flaw detection using in-line inspection (ILI), detecting and evaluating various metal defects organized by area (clusters), assessing their danger by calculating a level of stress-deformed state (SDS), and deciding on a permissible operating pressure with evaluated factor of repair (EFR), based on residual pipe wall thickness (for defects of “metal loss”—corrosion type). 
         [0007]    Pipelines, e.g. those used in the oil and gas industry, need regular inspection and maintenance before potentially costly failures occur. A traditional method of assessing the technical condition of a pipeline typically includes flaw detection using in-line inspection (ILI) for detecting location and evaluating parameters of separate metal defects, joining defects into clusters by an expert evaluation method (without indicating the rules of joining), calculating a level of stress deformed condition (SDC) in cluster zones to assess their danger, and calculating a permissible operating pressure and evaluated factor of repair (EFR) for clusters of corrosion origin based on residual pipe wall thickness with defects of “metal loss” (corrosion) type. 
         [0008]    As a contact technique, pigging devices has been used for many years to maintain larger diameter pipelines in the oil industry. Today, however, the use of smaller diameter pigging devices is increasing in many plants as plant operators search for increased efficiencies and reduced costs. Unfortunately, the ILI using intelligent pigging is unavailable for a wide range objects that require full disruptive inspection and significant spending on repair preparation. While the ILI method is suitable for the initial flaw detection, it is less efficient for the relative degree (ranking) of the risk-factor evaluation, as well as for defective pipeline serviceability calculation. 
         [0009]    Pipe-line pigging device can detect the following types of defects: i) changing in geometry: dents, wavy surface, deformed shape of cross-section; ii) metal loss, having mechanical, technological or corrosion nature; material discontinuity: layering and inclusions; iii) cracks; iv) all types of welding defects. 
         [0010]    Pipe-line pigging is a very expensive and labor consuming method. The major limitation of this method is the fact that a large part of pipe-lines are not prepared for the pigging device operation, e.g. due to lack of input/output chambers for pig-flow device launching and pipe-line cleaning access, partially blocked pipe cross-section due to the welding artifacts, geometrical abnormalities and large slopes (small radius turns) of the pipe-line layout. In order to make the pipe-line pigging method possible, a significant preparation has to be done in advance, in particular, the high residual level magnetization (saturated magnetic fields) of the pipe line has to be performed before using the pig-flow device. This causes future technical problems of the pipeline demagnetization that required for actual pipe repair after the pigging. 
         [0011]    Moreover, the evaluation of the absolute values of mechanical flaws by pigging device is particular difficult due to the multiple additional factors that have to be taken into account, e. g. bearing capacity of the soil, local cyclical loads (temperature, etc.). 
         [0012]    Aside of the remote methods, there are numerous contact non-destructive testing devices for access to the surface of the metallic construction (ultrasound-, eddy-current-, magnetic-powder-defectoscopy). The main disadvantages of such methods is the time-consuming procedure of surface preparation that reduces the scope of applicability and leads to high cost, low registration sensitivity and selectivity for hidden internal defects identification. 
         [0013]    Typically, a pipeline company will have a thorough pipeline safety program that will include a routine for the identification of pipeline defects and review of pipeline integrity. Such a plan should include, but not be limited to i) a review of previous inspection reports by a third party expert; ii) excavation of sites identified by this review for visual examination of anomalies; iii) repairs as necessary; and iv) addressing factors in the failure and verify the integrity of the pipeline. 
         [0014]    It is important to mention that the pipeline safety program can be only as effective as the interpretation of internal inspection reports. 
         [0015]    There are several magnetographic devices that have been disclosed for non-destructive inspection of ferrous materials. In magneto-graphic inspection and defectoscopy the tested area of the material is placed in proximity to the magnetic medium. The changes of the surface-penetrating impede flux due to the material flows or deviations can be recorded. The resulting “magnetogram” of the material can provide the information about the location, size, and type of the defect or abnormality. In general, this information can be converted into the report about the quality of the material. Obtaining the magnetogram (magnetic picture) of the material in the course of the non-destructive inspection process is very challenging and typically requires additional forms of inspection, such as roentgenogram or an X-ray image. 
         [0016]    For example, U.S. Pat. No. 4,806,862 (Kozlov) offers a contact method of magnetographic inspection of quality of materials, where a magnetic substance (such as liquid) is applied to be magnetized together with the tested material. According to the invention, the intensity of the magnetizing field is established by the maximum curvature of the surface of a drop of a magnetic fluid applied onto the surface of the material to be inspected, so that the resulting magnetogram can be used to assess the quality of the material. 
         [0017]    In another magnetographic U.S. Pat. No. 4,930,026 (Kljuev), the flaw sensor for magnetographic quality inspection is disclosed, which includes a flaw detector and a mechanism for driving the magneto-sensitive transducer. During the scanning procedure, the magnetic leakage fluxes penetrate through the surface of the material in places where flaws occur, resulting in a magnetogram of the tested material. 
         [0018]    There is another magnetic technique that has been proposed by U.S. Pat. No. 6,205,859 (Kwun) to improve the defect detection with magnetostrictive sensors for piping inspection. The method involves exciting the magnetostrictive sensor transmitter by using a relatively broadband signal instead of a narrow band signal typically used in order to avoid signal dispersion effects. The amplified detected signal is transformed by a short-time Fourier transform providing the identifiable signal patterns from either defects or known geometric features in the pipe such as welds or junctions. 
         [0019]    There is a known contact device with two single component collinear flux-gate magnetometers have been reported for the contact magnetometric monitoring and defects detection, RU 2062394. This device characterized by limited applicability due the slow data reception and processing and low sensitivity that makes impossible to detect minor deviations of stress-strain state (STS) from the background values, also leading to the low resolution threshold and a high false alarm rate. 
         [0020]    The deviations of F-value can be classified as follows: X1—for negligible defects (good technical condition of the metal); X2—for defects that require planned repairs (acceptable technical condition); X3—for defects that require immediate repairs (unacceptable, pre-alarm technical condition, alarm). 
         [0021]    The absolute values X1-X3 of the F-value (comprehensive value of magnetic field anomaly) should be defined for each particular case, depending upon the following factors: i) Material type (e.g. steel); ii) Topological location with the local background magnetic fields variation range, iii) Distance to the object (e.g. pipe-line installation depth), iv) General condition of the deformation-related tension within construction under testing, v) etc. 
         [0022]    As a result, the only relative changes (variations) of the magnetic field can be evaluated for the given defective segment (relatively to the flawless segment), by comparing to its relative F-values. Thus, the very moment of the ultimate stress-limit crossing can be identified for each defective segment during the real operation (i.e. under pressure/loaded) condition. It can be done by monitoring the development of the defects within its F-value interval, namely, starting from the good technical condition X1 up until the yield-strength limit approaching and material breakdown. It provides a real possibility to predict the defect&#39;s speed development, resulting in increased accuracy in priority order definition for upcoming maintenance steps. 
         [0023]    The aforementioned techniques are not satisfactory to be used for efficient prediction in defects development timeline and not capable of providing a real-time alert about the strength-limits approaching, i.e. when probable construction failure is about to occur. 
         [0024]    The closest remote technology to the disclosed invention is shown in RU 2264617 that describes the Magnetic Tomography (MT) technique. This technique includes a remote magnetic field vectors measurement in Cartesian coordinates with the movement of measuring device (magnetometer) along the pipe-line, the recording of the anomalies of magnetic field (on top of background magnetic field), processing of the data and report on found pipe-line defects with their localization shown in resulting magnetogram. The technique provides a good sensitivity, also capable of discovering the following types of defects: i) Changing in geometry: dents, wavy surface, deformed shape of cross-section; ii) Metal loss, having mechanical, technological or corrosion nature; material discontinuity: layering and inclusions; iii) Cracks; iv) Welding, flaws, including girth weld defects. Moreover, such method provides a risk-factor ranking of the discovered pipe-line defects accordingly to material tension concentration (factor F). Accordingly this technique was taken as initial prototype for the disclosed technology. 
         [0025]    MT determines the comparative degree of danger of defects by a direct quantitative assessment, of the stress deformed condition of the metal. Conventional surveys only measure the geometrical parameters of a defect. Their subsequent calculations to assess the impact of the defect on the safe operation of the pipe do not take into consideration the stress caused by the defect. Therefore conventional surveys may fail to detect dangerously stressed areas of the pipe or, conversely, classify a defect as one which requires urgent attention when, in reality, the stress level may be low and the defect presents no immediate threat to the operation of the pipe. Since MT directly measures the stress caused by defects it is an inherently more accurate guide to the safe operation of the pipeline than conventional survey methods. 
         [0026]    There are several methods for integrity assessment of extended structures (e.g. metallic pipes) that have been proposed in literature. Thus, U.S. Pat. No. 4,998,208 (Buhrow, et al) discloses the piping corrosion monitoring system that calculates the risk-level safety factor producing an inspection schedule. There is another method disclosed in U.S. Pat. No. 6,813,949 (Masaniello, et al.), which addresses a pipeline inspection system having a serviceability acceptance criteria for pipeline anomalies, specifically wrinkles, with an improved method of correlating ultrasonic test data to actual anomaly characteristics. 
         [0027]    The main disadvantages of previous methods are: i) The scope of its application is limited by large-scale linear objects. Located at a considerable distance from each other, ii) Difficult real-time implementation of the device, iii) It is impossible to identify the location of individual defects, visualize and specify the exact position on the internal or external tested surfaces; iv) There is also a lack of visualization of the obtained information in a form of the resulting tomogram where all the locations of the defective segments with associated respective risk factors (absolute mechanical stress values) are shown. 
         [0028]    There is a need in developing a combination of contact and remote techniques in order to increase sensitivity, resolution and visual representation of the stress-related anomalies within the structure, as well as a probability of operation failure (i.e. risk-factor). 
         [0029]    The defect areas risk-factor criteria and ranking (such as material stress: F-value) is used for planning a required sequence of repair and maintenance steps. Such criteria were developed by comparing a risk-factor calculated using the defect geometry in calibration bore pits with a predicted risk-factor obtained by the remote magneto-metric data (i.e. comprehensive F-value of particular magneticanomaly). 
         [0030]    However, there are several limitations to the above method. For example, ILI using intelligent pigging is unavailable for a range of objects that are non-piggable, or requires significant spending to prepare an object for pigs running. While the ILI method is suitable for the first task (the flaw detection itself), it is less advantageous for evaluating the comparative degree of the flaw&#39;s danger (e.g. by ranking), or for calculating serviceability of pipeline sections with various defects. Also, traditional calculations consist only in the evaluation of danger of groups of defects (clusters) like “metal loss”. The task of evaluating the corrosion rate (corrosion prognosis or monitoring) is not solved, and is typically settled by repeated runs of tools-defectoscopes. 
         [0031]    Furthermore, in the above traditional method, there is no evaluation of cracks stability, that is, no prognosis for the rate of crack-like defects development, especially in a longitudinal direction. There is also no evaluation of danger of other types of defects (e.g. welds) due to operation conditions, as the evaluation of metal properties degradation in aggressive conditions and with anomalies of stress-deformed condition (SDC) is not carried out. For example, there are pipeline sections with sags, bends, stresses/stretches/twists, that is, with loss of a pipeline stability, e.g. due to land-washing during heavy rains, in land-slipping areas, precipices, ravines and zones of seismic activity. In addition, the main problem—the degree of stress concentration in a particular pipeline section—is not considered; it must be considered by engineers of the integrity department of the company/operator by e.g. expert evaluation. 
         [0032]    As an alternative to the above method, a magnetometric tomography method (MTM) has been proposed. MTM is a non-contact method of non-destructive testing (NDT) and technical diagnostics based on remote scanning the magnetic field of a ferro-magnetic pipeline in a system of orthogonal coordinates. Additionally, manual processing and calibrating are used to define locations of sections with metal defects of various types, identify the type of the most dangerous defects, and evaluate serviceability of defective sections according to the degree of mechanical stress concentration. 
         [0033]    However, MTM is currently available only to on-shore (i.e. land-based) applications. Also, the current detection capability of such a magnetometer is only up to a maximum distance of 20 times the pipe diameter. Thus, such conventional MTM systems are not suitable for many subsea (i.e. underwater) pipelines, which may be located at significant depths. The inspection speed is also limited to only about 2 meters per second (m/s), and the recording of distance is typically manual. Also, the analysis of the collected data is substantially manual, i.e. it relies again on expert evaluation. 
         [0034]    A need therefore exists to provide a system and method for inspecting a subsea pipeline that seeks to address at least some of the above problems. 
       SUMMARY OF THE INVENTION 
       [0035]    A device for discovering, identification and monitoring of mechanical defects in extended metallic structure, such as pipe, a rail, a rolled metal product, a reservoir, a bridge, a vessel a cable, electrical power transmission lines, or vertical pipelines, is disclosed. The device includes a pulse generator being used to irradiate a part of the metallic structure, a sensor array registering a response from this part of the structure and a GPS and depth sensor. The sensor array is located in proximity of the structure and measures its magnetic field gradient at a distance of up to 20 cm from the structure without any surface preparation treatment. The sensor array includes a number of 3-component arrays, positioned along the 3 orthogonal dimensions. An analogue-to-digital converter digitizing the sensor signal which is wirelessly transmitted to the calculation unit. 
         [0036]    By “vertical pipelines” inventor means any pipelines going between resting or buried on or in the seabed to the sea surface by any angles are “vertical pipelines” for the purpose of this invention. Where parts of the pipelines are transitioning between different depths such that a coordination of position and depth of the pipeline is determined. 
         [0037]    A calculation unit exploits an inverse magnetostrictive (Villari) effect of changing material&#39;s magnetic susceptibility wider applied mechanical stress. Such changing results in gradient distribution of the magnetic field along the area of the structure that has a magnetic field anomaly. The distribution, in turn, reflects a presence and a value of the magnetic field anomaly at the given location. An absolute value of the mechanical stress, which corresponded to said anomaly, is further deducted, thus characterizing a mechanical defect of the structure, optionally using, a pre-determined information such as look-up tables, standards, thresholds or an alternative contact measurement such as a contact probe. 
         [0038]    The sensor array functions without removing the non-metallic cladding of the structure, such as a concrete wall around a metallic pipe, for example. The sensor array measurements can also be performed from inside the pipeline. 
         [0039]    The device detects foreign objects that are present in vicinity of the structure, measuring a relative distances and angles between themselves and the found anomaly. The discovered information is visualized by representing a topological map of the structure in real coordinates, showing simultaneously a structure layout, the foreign objects in vicinity, the location and calculated three-dimensional values of the mechanical stress. 
         [0040]    The device is also capable of measuring a natural Earths background magnetic field without engaging the pulse generator. Such measurement is subtracted from the sensor signal to improve accuracy of the anomaly(s) location. 
         [0041]    The device is operated by the battery with a residual charge indicator to ensure a quality and reliability of the identification in the field conditions and can perform without interruption of the structure normal operation. 
         [0042]    A method for discovering, identification and monitoring of mechanical defects of various nature, causing the concentration of mechanical tension in metallic structures, is also disclosed. The method includes an irradiating a part of the metallic structure with electromagnetic pulses, performing mechanical stress measurement of the metallic structure by a sensor array placed in proximity of the structure and producing a digitized sensor signal and digitizing the sensor signal. The method also includes analyzing the digitized signal in a calculation unit using the inverse magnetostrictive effect providing information about the presence and the value of the magnetic field anomaly at the given location of the structure. The method calculates absolute values of the mechanical stress around the anomaly, thus unveiling and characterizing the mechanical defect of the structure. 
         [0043]    Accordingly, the present invention is directed to a system and a method for inspecting a subsea pipeline which makes it possible to inspect the pipeline on the continental shelf at depths of 200 meters or more or a vertical pipeline with an accurate determination of the location of the defect area and its type. An object of the present invention is to provide a system for inspecting a subsea pipeline or vertical pipeline, comprising: a submersible magnetometric tomography method (MTM) module movable adjacent the subsea or vertical pipeline for detecting a defect along the subsea or vertical pipeline; and means for determining a position, including depth, of the submersible MTM module, thereby determining the position, including depth, of the defect. 
         [0044]    In one aspect of the present invention in the system the means for determining the position and depth of the submersible MTM module comprises means for determining the position and depth of the submersible MTM module relative to a surface vessel; and means for determining an absolute position of the surface vessel. In another aspect of the present invention in the system the means for determining the position including depth of the submersible MTM module relative to the surface vessel comprises at least one of an odometer, a Doppler velocity log, a pressure sensor, and a microelectromechanical systems (MEMS) accelerometer coupled to the submersible MTM module. In another aspect of the present invention in the system the means for determining the absolute position of the surface vessel comprises a global positioning system (GPS) receiver. In another aspect of the present invention in the system time stamps of data from the submersible MTM module and the means for determining the position of the MTM module are synchronized based on a GPS time signal. In another aspect of the present invention the system further comprising means for categorizing the defect based on at least a density of magnetic field strength distribution along a pipeline axis in an anomaly zone. In another aspect of the present invention in the system the means for categorizing the defect ranks the defect as one of one, two and three corresponding to immediate repair, scheduled repair and no repair, respectively. In another aspect of the present invention the system further comprising means for determining a safe operating pressure of the pipeline. In another aspect of the present invention the system further comprising means for determining a safe operation term of the pipeline. In another aspect of the present invention in the system he submersible MTM module is mounted to a remotely operated vehicle (ROV) or autonomous underwater vehicle (AUV). In another aspect of the present invention in the system the submersible MTM module is disposed at least about 1 meter from the ROV or AUV engines. 
         [0045]    Another object of the present invention is to provide a method for inspecting a subsea or vertical pipeline, the method comprising the steps of: detecting a defect along the subsea or vertical pipeline using a submersible magnetometric tomography method (MTM) module adjacent the subsea or vertical pipeline; and determining a position of the submersible MTM module, thereby determining the position of the defect. 
         [0046]    In one aspect of the present invention in the claimed method the step of determining the position of the submersible MTM module comprises: determining the position of the submersible MTM module relative to a surface vessel; and determining an absolute position of the surface vessel. In another aspect of the present invention the method further comprising synchronizing time stamps of data from the submersible MTM module and equipment for determining the position of the submersible MTM module based on a GPS time signal. In another aspect of the present invention the method further comprising categorizing the defect based on at least a density of magnetic field strength distribution along a pipeline axis in an anomaly zone. In another aspect of the present invention the method further comprising ranking the defect as one of one, two and three corresponding to immediate repair, scheduled repair and no repair, respectively. In another aspect of the present invention the method further comprising determining a safe operating pressure of the pipeline. In another aspect of the present invention the method further comprising determining a safe operation term of the pipeline. 
         [0047]    The present invention makes it possible to determine the exact location of the submersible MTM module on the pipeline when you move it under the water along the pipeline and thus pinpoint the location of the defect, if it is registered. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0048]    The present invention will now be discussed in further detail below with reference to the accompanying figures in which: 
           [0049]      FIG. 1  shows a block-diagram of the device for discovering, identification and monitoring of mechanical defects in metallic structures using contact method, optionally, in combination with a non-contact technique. 
           [0050]      FIG. 2  shows a general principle of operation of the contact and non-contact magneto-graphic techniques used in metallic structure defects monitoring and integrity assessment. 
           [0051]      FIG. 3  shows an example of a single magneto-graphic measurement. The diagram represents the three areas of a magnetic field anomalies (a), (b) and (c) corresponding to the respective local mechanical stresses. The area (c) shows the evidence of the metal stress yielding-limit crossing. 
           [0052]      FIG. 4  shows a block-diagram for metallic structure integrity assessment and maintenance planning method. 
           [0053]      FIG. 5  shows an image illustrating an implementation of a system for inspecting a subsea pipeline according to an example embodiment. 
           [0054]      FIG. 6  shows a block diagram illustrating communication interfaces of the system of  FIG. 1 . 
           [0055]      FIG. 7  shows a block diagram illustrating an arrangement of components on the ROV of  FIG. 5  according to an example embodiment. 
           [0056]      FIG. 8  shows an exploded view of an implementation of the underwater unit of  FIG. 7  according to an example embodiment. 
           [0057]      FIG. 9  shows a schematic diagram illustrating an operation of the system of  FIG. 5  according to an example embodiment. 
           [0058]      FIG. 10  shows a flow chart illustrating a method for inspecting a subsea pipeline according to an example embodiment. 
           [0059]      FIG. 11  shows a block diagram illustrating a computing device for implementing the method and system of the example embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0060]    The present invention describes the contact magnetic scanner device that uses a magnetic tomography (MT) for contact magnetographic identification and analysis of mechanical flaws/defects, optimized for extended metallic constructions inspection. The invention can be used in combination with a non-contact identification. And can be applied to variety of extended metallic structures, such as a pipe, a rail, a rolled metal product, a reservoir, a bridge, a vessel a cable, or electrical power transmission lines. 
         [0061]    The use of MT device has following advantages: 1) Applicable for the unpiggable pipelines or other objects where in-line inspection method is inapplicable; 2) the objects to be inspected include but not limited to: compressor stations pipelines, pipeline inclusions, water-supply pipelines in cities; 3) the use of MT device doesn&#39;t require any preparation of the pipeline for testing such as cleaning, opening the pipe, or stopping pipeline operation; 4) the use of MT device doesn&#39;t require magnetizing of the object&#39;s pipes; 5) MT device capable of detecting flaws of various types including long crack-like pipe-line defects and welding defects; 6) the use of MT device doesn&#39;t have limitation on the structure diameter, configuration and protective coatings, for example, change of pipe diameter/wall-thickness, turns and their directions, transported product (e.g. gas, oil, or water), inside pressure, pipeline protection e.g. cathodic protection, etc). 
         [0062]    The MT device is capable to evaluate the degree of danger of defects by the level of concentration of mechanical tensions rather than defect geometry (e.g. length-width-depth) and particularly suitable for running a database on condition certification of objects of any length and any monitoring period. 
         [0063]    The MT device implementation guarantees minimal customer resources use for monitoring preparation and repair works such as: i) reduces work volume and total costs of pipe access works; ii) greatly reduces time of full diagnostic-repair evaluation-repair planning-repair cycle; iii) gives pipe corrosion prognosis and estimates levels of tense-deformed state of the pipeline under current operating conditions. 
         [0064]    The MT device application provides a remote metal flaws monitoring, which is particularly suitable for hidden ferromagnetic constructions of extended length. 
         [0065]    The general combined block-diagram of the method is given in  FIG. 1 . 
         [0066]    The magnetic tomography device is based on Using of the inverse magnetostrictive (Villari) effect—i.e. the changing of the material magnetic susceptibility under applied mechanical stress. Generally, such technique uses “natural” magnetization of the ferrous pipes by magnetic field of the Earth. The changing of magnetic susceptibility results in distribution of magnetic field gradient along the structure surface area under measurement, thus providing information about the presence and the value of the magnetic field anomaly at the given location of the structure. 
         [0067]    The term “contact measurement”, as used herein is defined as the measurement being used from a small distance from the surface of the structure under testing. For the preferred embodiment of the invention, such distance is defined as a small if it is less than 20 cm from the surface of the structure. Furthermore, for the preferred embodiment of the invention applying an additional (pulsed) magnetic field is used. 
         [0068]    The term “remote measurement”, as used herein is defined as the measurement being used from a substantial distance from the structure under testing. Unlike to the contact measurement (non-destructive or distractive), the remote sensor is not necessary located in a close proximity to the structure. For the preferred embodiment of the invention, the substantial distance have value of 1-50 m, making the disclosed device especially effective for testing structures located deep underground or underwater. 
         [0069]    The remote measurement is capable of identifying, the anomalies by deviation of the Earth&#39;s magnetic field at each location from a background value, without applying an additional magnetic field during the measuring. 
         [0070]    The contact measurement device is also capable localizing coordinates of foreign objects in vicinity of the structure and making, a linkage between the anomalies&#39; locations and the foreign objects locations around. In the preferred embodiment of the invention, the device finds coordinates of foreign objects which can be present in vicinity of the structure and measures a distance/angle between those foreign objects and the structure&#39;s anomaly. 
         [0071]    The both remote and contact measurements are further capable of localizing coordinates of the structure and detecting anomalies with localized coordinates within the extended metallic structure based on measuring a value of the Earth&#39;s magnetic field at multiple locations in vicinity of the structure. 
         [0072]    The present invention discloses the Contact Magnetic Scanner a device for the contact detection of the defects in metallic structures. The present invention effectively overcomes the aforementioned disadvantages of contact defect monitoring and detection. 
         [0073]    Similarly to the remote method, the contact method at a given measurement point, the presence of the magnetic field anomaly and its magnitude (the local stress at the remote area) is determined based on a comparison between the increments (modules) of the Earth&#39;s magnetic field values (magnetic moments), Such calculation method is based on a dipole approximation of the remote stress-concentrator. The solution of the problem of the magnetic moment calculation results from a system of algebraic equations, which, for example, described in the U.S. Pat. No. 4,309,659. 
         [0074]    The disclosed device expands the scope of device applications for different types of metallic structures (e.g. confined extended, small and large), ii) provided real-time operational means by including, data preprocessing and calibration, iii) increases the identification sensitivity of the defects located at the surface and within the volume of the object by including an additional pulse-magnetization unit, v) using a contact tomography technique in order to add 3D visualization capabilities using a 3D model of the tested object. The information visualization (display) unit of the device represents a topological map of the structure in real coordinates, showing; simultaneously a structure layout, the foreign objects in vicinity, the calculated values of a mechanical stress and the location of the found anomalies. 
         [0075]    The disclosed device uses pre-determined information for structure anomaly identification and localizing. Such pre-determined information can be a look-up table, preset standards and thresholds, an alternative contact measurement, or combination of the above. 
         [0076]    Moreover, the device can combine a contact and non-contact measurement increasing the reliability and accuracy of information about the necessary repair or stop alarm. It can be done using the risk-factor ranking tables based on the absolute values of stress, compared against the values from regulatory documentation (for particular object). 
         [0077]    In the preferred embodiment of the invention, the device performs the identification of anomalies without interruption of the structure normal operation. 
         [0078]    Increasing the efficiency of the method by applying a 3D visualization-assisted maintenance and repair schedule with the real values of mechanical stress) to the actual structural layout, such as a pipe-line integrated into the existing topology. 
         [0079]    Such technological outcome can be achieved, mainly, due to the following innovative means: i) Contact (object surface) identification of the local defects and their respective risk-factors; ii) Comparing the remote measurement with ones obtained locally; iii) Comparing the resulting measurements against the values from regulatory. documentation (for particular object), iii) Graphical 3D visualization of the obtained information using the actual topological layout of the area and the structure in absolute geographical coordinates. 
         [0080]    For the remote registration of magnetic field anomalies in extended metallic structures (such as a pipe) is performed in a predetermined coordinate system relatively to the structure (axis) with a known (fixed) remote sensor array aperture. The coordinates of each single measurement along the structure can be chosen accordingly to the cross-section size and burial depth of the (underground, underwater) structure. It results in the matrix distribution of magnetic field gradient along the structure surface area under each single measurement. The presence and the value of the magnetic field anomaly at the given location are derived from the comparison of different increments of the Earth&#39;s magnetic induction vector modulus. 
         [0081]    Similarly to the remote measurements, the contact measurement also includes device to measure the magnetic field vector in Cartesian coordinates, by moving the registration device (magnetometer) along (above) the metallic structure (of arbitrary configuration, in general) and registration of the magnetic field anomalies, Such anomalies are calculated by a deviation from the background values (calculated using matrix transformations). 
         [0082]    The contact device also connected the data recording unit and decoding system that provides conclusive information about the presence and location of the defects in the form of magnetograms that shows the location of the defective pipe sections and their degrees of risk. 
         [0083]    Similarly to the remote measurements, the contact measurement of the extended object (such as pipeline) uses the recording of the magnetic field that is carried out in a pre-defined coordinate system at specifically defined measuring points by a set of sensors having a pre-selected aperture (base) K2. This aperture corresponds to the axis of the extended object with a measuring step K1. 
         [0084]    The exact location of measurement points is defined from the diameter and underground depth (e.g. of the pipeline), using coefficients K1, K2 and K3, where: K1—is the measuring step (registration of the magnetic field induction) 0.2 in, for example, K2—the aperture (the base) of the sensors, chosen from the ratio 0.7 D≦K 2≦1,4 D, where D—is the diameter of the structure (pipeline), K3—is the depth of the pipeline, or the shortest distance from the metallic construction to the surface, [m]. 
         [0085]    In the case of a non-linear (or small) extended object the contact registration c the magnetic field is carried out in a fixed coordinate system. In this case, registration is possible at different relative positions of the sensors and their arbitrary orientation with respect to the object (coplanar or collinear). 
         [0086]    To verify the anomaly angular position along the structure (pipeline) circumference, the angular scanning step K1 should not larger than 30 degrees with the pre-defined distance between the sensors K2, to ensure the required accuracy of calculations. 
         [0087]    The block-diagram of such device is shown in  FIG. 1 . with the reference to  FIG. 1 , the device for contact and, optionally, non-contact measurements comprises of a sensor array for remote measurements ( 1 ), a sensor array for proximity (contact) measurements ( 20 ), a quartz generator ( 2 ), a frequency divider ( 3 ), analogue-to-digital converter (A/D) ( 4 ), a control unit ( 5 ), a threshold unit ( 6 ), a light- and sound-alarm unit ( 7 ), a battery with a charge indicator ( 8 ), a calculation unit ( 9 ), a (resulting) information unit ( 10 ) with a display unit ( 23 ), a non-volatile memory unit ( 11 ), a recording unit ( 12 ), a case-analysis unit ( 13 ), a pulse generation lint ( 21 ), an odometer unit ( 23 ), a GPS unit and pressure sensor(s) ( 14 ), navigation unit (gyroscope/accelerometer) ( 17 ) and a logic unit ( 15 ). The device performs in a following manner. 
         [0088]    The remote sensor array ( 1 ) registers induction gradients of the magnetic field ( 16 ) within construction under testing. 
         [0089]    The proximity sensor array ( 20 ) registers induction gradients of the magnetic field ( 19 ), the gradients corresponding to reflections of the EM pulses from the structure; the EM pulses generated by the Pulse generator ( 21 ). The signal from the proximity sensor is used as a calibrating measurement. 
         [0090]    By using A/D converter ( 4 ), the both digitized signals (remote and contact) are: i) inputted into calculation unit as a preliminary data; ii) recorded by the memory unit ( 11 ). The Quartz generator ( 2 ) controls the frequency of the A/D converter ( 4 ). 
         [0091]    The control unit ( 5 ) through the logic unit ( 15 ) controls the case analysis unit ( 13 ) with predetermined database and lookup tables, the recording unit ( 12 ), the GPS unit ( 14 ), the navigation unit ( 17 ) and the memory unit ( 11 ). 
         [0092]    The calculation unit ( 9 ) receives the information from units ( 12 ), ( 13 ), ( 14 ), ( 17 ), ( 20 ), ( 22 ) through the memory unit ( 11 ), controlled by logic unit ( 15 ). 
         [0093]    The real-time information from ( 4 ) is compared with the information from the threshold unit ( 6 ). By these means, the visualization of the real-time data against the threshold values is provided, enabling the alarming (by the unit ( 7 )) an operator about potentially dangerous operational conditions of the structure. The remaining charge of the battery ( 8 ) is monitored. The calculation unit ( 9 ) is responsible for the information processing, providing the information to the resulting, and visualization unit ( 10 ). 
         [0094]    The calculation unit ( 9 ) unit receives the digitized signal, uses the inverse magnetostrictive effect of changing of material magnetic susceptibility under applied mechanical stress resulting in gradient distribution of the magnetic field along an area of the structure that has a magnetic field anomaly, the distribution of magnetic field gradient providing an information about a presence and a value of the magnetic field anomaly at the given location of the structure and a mechanical stress, corresponded to the anomaly. 
         [0095]    The calculation unit ( 9 ) further calculates absolute values of a mechanical stress around all found anomalies in the metallic structure using the measured values of the Earths magnetic field for each anomaly and applying the calibration coefficient As a result, the calculation unit is capable of identifying and localizing of said signal anomalies. 
         [0096]    In one embodiment of the invention the calculation unit is located at a distance from the sensor array, and the digitized signal is transmitted to the calculation unit via wireless connection. 
         [0097]    The measured magnetic field values from 2 inputs ( 16 ) and ( 19 ) local stress at the remote area are recorded at each measurement point, (both for contact and optional remote sensor independently), then further compared with other measurements within a respective segment of the metallic construction. By these means the anomalies (levels of stress-deformation) that deviate from the baseline magnetic field values are selected. Thus, the location of each stress-related deformation is derived from the maximum concentration value of the magnetic field after comparing it with the previous measurements. 
         [0098]    The visualization unit has a 3-dimensional display means ( 23 ) in order to provide a 3-D representation of the density of magnetic field strength distribution, found detects and its risk-factors along with the topological (3D) map of the structure under testing. 
         [0099]    The resulting and visualization init ( 10 ) also accommodates inputs from the threshold unit ( 6 ) and the light-sound-alarm unit ( 7 ) which enables identification of the parameters&#39; deviation from the background level, as well as (e.g. wirelessly) informing an operator about the deviation value in real-time, respectively. 
         [0100]    Moreover, the resulting and visualization init ( 10 ) is capable of comparing the remote signals ( 16 ) with in-contact measurement ( 19 ) and producing a set of calibration coefficients in order to calibrate the resulting calculated data of found magnetic anomalies. 
         [0101]    The situational case-analysis unit ( 13 ) enables the analysis of the information in the context of pre-determined technological information and schemes, which, in combination with the GPS unit and pressure sensor(s) ( 14 ), provides more accurate topological mapping. 
         [0102]    In the preferable configuration of the device, a GPS sensor ( 14 ) is complemented by a. navigation unit that includes gyroscope(s) and/or set of accelerometer(s) ( 17 ), and odometer unit ( 22 ) enabling the recording of the device&#39;s angle-positioning relatively to the extended metallic structure cross-section at each moment of the magneto-graphical measurements. The recorded angle-positioning data (including positioning, relatively to horizon) is used further to correct the magneto-graphical measurements due to structural bending/turning-related deviations. 
         [0103]    Accordingly, the absolute coordinates of discovered defects relatively to the (visible) reference objects can be obtained with the following registration in the database during the equipment assessment report. 
         [0104]    In the preferable configuration of the mentioned device, each sensor arrays ( 1 ) and ( 20 ) consist of a few 3-component arrays, positioned along the 3 orthogonal dimensions. Alternatively, each array includes a few single-component sensors, such as optically pumped quantum analyzers. Using the optically pumped quantum analyzers in the sensor array ( 1 ) allows higher flaw-detection accuracy in underground constructions, well-suited for detecting relatively small values of mechanical stress, and/or deeper underground installation. 
         [0105]    Since die sensor array ( 1 ) and ( 20 ) can be rotated above the surface of the structure during the scanning procedure, it is possible to implement a polar coordinate system for detects detection, in combination with the data from the gyroscope/accelerometer unit ( 17 ). 
         [0106]    The recording process is arranged in a discrete manner, enabling an independent storage and access for different recorded portions (memory segments) of the scanning. 
         [0107]    In the preferable configuration of the disclosed device, the unit ( 9 ) calculates: i) magnetic field gradients distributed along the square area within the defined segment of the structure, ii) the values of the local mechanical stress within the defined segment of the structure. 
         [0108]    The device allows identifying the location of defects using both in-contact and remote magnetic measurements. 
         [0109]    Moreover, it expresses the calculations in real-time, also providing the visualization of the information in the form of tomograms with reference to the 3D model of the controlled object. 
         [0110]    Moreover, the device provides automated evaluation of the defects risk factor at respective identified location, allows automatic processing, interpretation and archiving of non-destructive testing results. 
         [0111]    In the alternative configuration of the disclosure, the calculation unit ( 9 ) can be realized similarly to the U.S. Pat. No. 4,309,659 patent. 
         [0112]    Moreover, in the alternative configuration of the disclosure, the recording unit ( 12 ) can be realized similarly to the RU2037888 patent. 
         [0113]    The principle of operation of the device shown in  FIG. 1 . is explained further in  FIG. 2 . The  FIG. 2   a  shows the structure ( 1 ) without defects, with the preliminary magnetic tomography charts (magnetogram) ( 2 ) showing the measured background (calibrated to zero) level of magnetization. The  FIG. 2   b  shows the same structure ( 1 ) with the potential defects ( 3 ), ( 4 ) corresponded to the deviations of the tomography charts ( 5 ). The  FIG. 2   c  show the same structure ( 1 ) with the processed tomography charts ( 5 ) showing the location of the defect ( 4 ) that require an immediate attention (unacceptable, pre-alarm technical condition, alarm), based on the local mechanical stress value estimate. 
         [0114]    As mentioned before, the magnetogram ( 2 ) attributes and characterizes the section of the structure by registering and analyzing changes in the magnetic field of the structure such as pipeline. These changes are related to stress, which, in turn, is related to defects in the metal and insulation. Magnetic measurements data is collected from the surface and includes the detected anomalies. Such detected anomalies are function of a local stress and/or local mechanical tension and structural changes in the metal. Moreover, a post-processing of this experimental data enables the visualization of the flaws in the structure. 
         [0115]    The device can operate on the metallic structure which is covered by a non-metallic cladding and the sensor array performs the measurement without removing the cladding, for example, when the metallic structure is a pipeline and the cladding is a pipeline insulation cover. Moreover, the device (sensor array) is capable of performing measurements from inside the structure, such as a pipeline. 
         [0116]    The described. MT device does not measure the dimensions of geometric defects alone, but, instead, provides a stress measurement caused b these defects and identifies their character, location and orientation in accordance with the location and orientation of the area of stress. Linear and angular coordinates of flaws in the metal and coating are have been experimentally defined within a tolerance of +/−0.25 m. 
         [0117]    The device explained by  FIG. 1  and  FIG. 2  can effectively identify and analyze the magnetic field anomalies in areas with stress concentrators caused by: i) defects or changes in structural conditions (such as metal loss, cracks, dents, lamination and inclusions); ii) erosion, seismic activity, or third-party damage. 
         [0118]      FIG. 3  shows the example of a single magneto-graphic measurement. The diagram represents the three areas of a magnetic field anomalies (a), (b) and (c) corresponding to the respective local mechanical stresses. The area (c) shows the evidence of the metal stress yielding-limit crossing. 
         [0119]    In parallel, the in-contact (proximity) defectoscopy has been performed at the location (c). The actual dimensions of defects (cracks and corrosion) have been evaluated. The magnetographic device calibration has been done based on a difference between the measured signal (versus background) and the actual parameters of the defect(s) found. Then, the calibrated values of the anomalies have been used as a criterion. For this particular case, the calibrated values appeared to be 3-10 times higher comparing to the background signal value. The follow-up magnetographic measurements ha been performed in a real-time. 
         [0120]    The presented MT device helps to plan necessary structural maintenance procedures and define their priorities. The device is particularly efficient when the magneto-graphic material (Magnetic Tomography) inspection is applied to extended metallic constructions, revealing its flaws against the topological map of the structure. 
         [0121]    Moreover, the device enables direct monitoring of the defective construction segments with still acceptable technical conditions. It allows a long-term database support for the follow up monitoring, certification, prognosis and operational timeline for the structure. 
         [0122]    The present invention also describes the magnetographic method maintenance timeline planning method (priority steps), optimized for extended metallic constructions. The block-diagram of the method is given in  FIG. 4 . 
         [0123]    The method includes (with reference to  FIG. 4 ): Precise scanning ( 401 ) using the non-destructive magneto-graphic (such as MT) anomalies detection technique ( 412 ) for (axial) localization of the extended metallic structure (e.g. subterranean or submarine pipeline), as well as surrounding scanning ( 402 ) for identification of other possible objects in the vicinity of the structure, including hidden objects (pipes, cables) detection ( 424 ) and identification of the defective segments or areas of the said structure, in general, by using thermo-visual imaging, magneto-graphic methods or by other remote (non-contact, non-destructive) methods; accurate location of different types of anomalies by using thermal and magnetic non-contact scanning sensors moving in Cartesian coordinates. Registering and processing of the obtained data and assessing resulting anomalies in accordance with their risk-factor and structural topology (mapping) ( 403 ). Identification of the absolute geographical coordinated for characteristic elements of the construction under testing ( 403 ), preferably by using a GPS sensor(s) and pressure sensor(s) ( 413 ) and (inertial) navigation system (gyroscope and/or accelerometers)  415 . Non-contact detection ( 424 ) of the construction defects and flawless segments. In-contact measurement of at least one found defect ( 405 ) (e.g. visual, spectral, magneto-graphic). Calculation of the local metal stress at each found anomaly ( 406 ) and calibration ( 407 ), using calibrating coefficients obtained by in-contact method ( 405 ) and regulatory documentation and stress/risk look-up tables ( 409 ). Processing the obtained information about discovered defects and its ranking accordingly to the risk factor (value of mechanical stress) ( 408 ). Graphical visualization of the results in the form of the topological map of the construction using absolute values of geographical coordinates ( 410 ). The topological map would reflect the maintenance schedule to be applied to the construction following from the recorded mechanical stress values at the defective segments of the construction ( 409 ), ( 410 ). The method includes preventive warning means ( 414 ) to inform about defects that require immediate attention, e.g. unacceptable operational condition. The aforementioned method provides operational and monitoring prognosis ( 411 ) with an optimal priority planning for required maintenance steps for construction under testing. 
         [0124]    In the preferred embodiment of the invention the non-destructive detection of anomalies in the structure is performed using magnetographic technique such as MT. 
         [0125]    The main goals of the present invention are: i) to increase the method&#39;s applicability area; ii) to increase the accuracy of the priority scheduling for required maintenance and repair procedures iii) to broaden the spectrum of the potentially scheduled repair procedures, based on the additional data. 
         [0126]    The invention is a system for inspecting a subsea vertical pipeline which has a movable submersible magnetometric tomography method (MTM) module for detecting a defect or stress along the subsea pipeline; a pressure sensor for determining a depth of the submersible MTM module. 
         [0127]    The system further having a module with a sensor array with at least three sensor positioned in three orthogonal dimensions. 
         [0128]    The system further having a compass for registering azimuth data of the defect and stress position on the pipeline at the determined depth. 
         [0129]    The system wherein the system outputs a 3D map of the inspected pipeline on a computer screen; the map showing the defects and stress concentrator. 
         [0130]    The system further having means for categorizing the defect and condition stress effect based on at least a density of magnetic field strength distribution along a pipeline axis in an anomaly zone. 
         [0131]    The system further having a camera for registering an image of the defect, which is visible or non-destructive testing (NDT) or non-destructive examination (NDE) tools for hidden defects and internal corrosion. 
         [0132]    The system further having additional means for determining a position, including depth via pressure sensor, of the submersible MTM module relative to a sea surface and relative to a linear coordinate of pipe axis comprising at least one of an odometer, a Doppler velocity log and a microelectromechanical systems (MEMS) accelerometer coupled to the submersible MTM module. 
         [0133]    The system further having an engine for moving the sensors along the pipeline adjacent to the pipeline. 
         [0134]    The system wherein a distance between the sensors and a surface of the pipeline is from 0, being on the pipe surface, to a distance equal to 15 time a diameter of the pipe. 
         [0135]    The system further having a range finder to determine a distance between the sensors and the surface of the pipeline. 
         [0136]    The system further having a control unit to adjust operation of the engine in order to keep the distance between the sensors and the surface of the pipeline from 0, being on the pipe surface, to a distance equal to 15 time a diameter of the pipe. 
         [0137]    The system further having a processing unit. 
         [0138]    The system wherein the means for categorizing the ranging of dangerous as one of one, two and three corresponding to immediate repair, scheduled repair and no repair, respectively taking into account stress concentration, stress effect, material strength, condition stress effect, or stressing sequence. 
         [0139]    The system further having means for determining a safe operating pressure of the pipeline, taking into account stress concentration, stress effect, material strength, condition stress effect, or stressing sequence. 
         [0140]    The system further having means for determining a safe operation term of the pipeline. 
         [0141]    The system wherein the submersible MTM module is mounted to a remotely operated vehicle (ROV) or autonomous underwater vehicle (AUV). 
         [0142]    The system wherein the submersible MTM module is disposed at least about 1 meter from the ROV engines. 
         [0143]    The invention also providing a method for inspecting a subsea pipeline, the method comprising the steps of: detecting a defect or stressing along the subsea pipeline using a submersible magnetometric tomography method (MTM) module adjacent the subsea pipeline; determining a depth of the submersible MTM module by use of a pressure sensor, and determining a position, including depth via pressure sensor, of the submersible MTM module, thereby determining the position, including depth via pressure sensor, of the defect or stress concentrators. 
         [0144]    The method wherein the step of determining the position, including depth via pressure sensor, of the submersible MTM module comprises: determining the position, including depth via pressure sensor, of the submersible MTM module relative to a surface vessel, relative to positioning system with underwater markers; and determining an absolute position of the surface vessel. 
         [0145]    The method further involving synchronizing time stamps of data from the submersible MTM module and equipment for determining the position, including depth via pressure sensor, of the submersible MTM module based on a GPS time signal. 
         [0146]    The method further involving categorizing the defect based on at least a density of magnetic field strength distribution along a pipeline axis in an anomaly zone. 
         [0147]    The method further involving ranking the defect as one of one, two and three corresponding to immediate repair, scheduled repair and no repair, respectively. 
         [0148]    The system further involving monitoring and automatic alarm control emergency shutdown (ESD) in situation with the destination of deformations of Yield Stress, Specified Minimum Yield Stress (SMYS), yield strain, Ultimate Tensile (UT) Strength, Rupture Pressure Ratio (RPR), buckling stress, fatigue limit under cyclic loading for fatigue cracks, or stress corrosion crack or cracking (SCC). 
         [0149]      FIG. 5  shows an image illustrating an implementation of a system  100  for inspecting a subsea pipeline  130  according to an example embodiment.  FIG. 6  shows a block diagram illustrating communication interfaces of the system of  FIG. 5 . 
         [0150]    In the example embodiment, system  100  comprises a control unit  102  disposed on-board a surface vessel  110  and an underwater unit  112  mounted to a remotely operated vehicle (ROV)  120  that is adjacent to, but not in contact with, the subsea pipeline  130 . The ROV  120  is typically tethered to the surface vessel  110  via an umbilical cable or tethering line  106 , as will be appreciated by a person skilled in the art. An operator (not shown) on-board the surface vessel  110  can control the ROV  120  to move along the subsea pipeline  130 . The surface vessel  110  in the example embodiment is capable of receiving signals (e.g. time and position signals) from a global positioning system (GPS) satellite  140 . In addition, the surface vessel  110  and the underwater unit include respective navigation and tracking equipment  104 ,  114 . The navigation and tracking equipment  104  comprises GPS navigation equipment for the surface vessel  110  as well as equipment for tracking the ROV  120 . 
         [0151]    As can be seen from  FIG. 6 , the underwater unit  112  comprises an embedded computer  214  in communication with a hub  212  of the ROV  120  ( FIG. 5 ). The hub  212  of the ROV  120  is in communication with the control unit  102  via a hub  202 . The control unit  102  further comprises a controller  204  and a computing device in the form of a personal computer (PC)  208 . The controller  204  is in communication with a GPS Time Receiver  206  and navigation equipment  104  of the surface vessel  110 . Suitable communication interfaces between relevant components as described above include, but are not limited to RS-485, RS-232, RS-422 and Ethernet, as will be appreciated by a person skilled in the art. 
         [0152]    Some portions of the description which follows are explicitly or implicitly presented in terms of algorithms and functional or symbolic representations of operations on data within a computer memory. These algorithmic descriptions and functional or symbolic representations are the means used by those skilled in the data processing arts to convey most effectively the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities, such as electrical, magnetic or optical signals capable of being stored, transferred, combined, compared, and otherwise manipulated. 
         [0153]    Unless specifically stated otherwise, and as apparent from the following, it will be appreciated that throughout the present specification, discussions utilizing terms such as “scanning”, “calculating”, “determining”, “replacing”, “generating”, “initializing”, “outputting”, or the like, refer to the action and processes of a computer system, or similar electronic device, that manipulates and transforms data represented as physical quantities within the computer system into other data similarly represented as physical quantities within the computer system or other information storage, transmission or display devices. 
         [0154]    The present specification also discloses apparatus for performing the operations of the methods. Such apparatus may be specially constructed for the required purposes, or may comprise a general purpose computer or other device selectively activated or reconfigured by a computer program stored in the computer. The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general purpose machines may be used with programs in accordance with the teachings herein. Alternatively, the construction of more specialized apparatus to perform the required method steps may be appropriate. The structure of a conventional general purpose computer will appear from the description below. 
         [0155]    In addition, the present specification also implicitly discloses a computer program, in that it would be apparent to the person skilled in the art that the individual steps of the method described herein may be put into effect by computer code. The computer program is not intended to be limited to any particular programming language and implementation thereof It will be appreciated that a variety of programming languages and coding thereof may be used to implement the teachings of the disclosure contained herein. Moreover, the computer program is not intended to be limited to any particular control flow. There are many other variants of the computer program, which can use different control flows without departing from the spirit or scope of the invention. 
         [0156]    Furthermore, one or more of the steps of the computer program may be performed in parallel rather than sequentially. Such a computer program may be stored on any computer readable medium. The computer readable medium may include storage devices such as magnetic or optical disks, memory chips, or other storage devices suitable for interfacing with a general purpose computer. The computer readable medium may also include a hard-wired medium such as exemplified in the Internet system, or wireless medium such as exemplified in the GSM mobile telephone system. The computer program when loaded and executed on such a general-purpose computer effectively results in an apparatus that implements the steps of the preferred method. 
         [0157]    Referring back to  FIGS. 5 and 6 , in the example embodiment, the underwater unit  112  senses and records the magnetic field (e.g. in micro Tesla (μT) unit in the X-axis, Y-axis and Z-axis respectively) emitted by the stressed pipe wall as the ROV  120  moves along the pipeline  130 . Magnetic field data is typically captured on about every 2 centimeters (cm) distance passed in the example embodiment, by using at least one of e.g. an odometer, a Doppler velocity log and a microelectromechanical systems (MEMS) accelerometer to track the distance passed. The underwater unit  112  does not capture readings of magnetometric data at the same spot when the ROV  120  is not moving. 
         [0158]    In addition, in the example embodiment, the GPS time signal received by the GPS Time Receiver  206  is provided to all components of system  100 , including the underwater unit  112 , such that all data of system  100  is synchronized to GPS time. For example, the time stamps on a navigation log of the surface vessel  110  are matched with those on a magnetometer log of the underwater unit  112 . 
         [0159]      FIG. 7  shows a block diagram illustrating an arrangement of components on the ROV  120  of  FIG. 1  according to an example embodiment. As can be seen from  FIG. 7 , the underwater unit  112  is enclosed in a water-proof capsule and mounted to the ROV  120 . The underwater unit  112  comprises a submersible magnetometric tomography method (MTM) module  302  (e.g. Model No. Scythian MBS SKIF-04 manufactured by Transkor-K) for sensing and recording magnetic field data and navigation and positioning equipment  114  for recording positional data including depth via pressure sensor. 
         [0160]      FIG. 8  shows an exploded view of an implementation of the underwater unit  112  of  FIG. 7  according to an example embodiment. In addition to the submersible MTM module  302  and the navigation and positioning equipment  114 , the underwater unit  112  comprises an embedded computer  214  (as also shown in  FIG. 2 ), a power supply in the form of batteries  402 , and a water-proof casing  404  forming the capsule. The casing  404  is typically fabricated from a non-ferromagnetic material. Also, the underwater unit  112  is preferably disposed at least about 1 meter (m) from the engines of the ROV  120  in the example embodiment to minimise echo 
         [0161]      FIG. 9  shows a schematic diagram illustrating an operation of the system  100  of  FIG. 1  according to an example embodiment. As can be seen in  FIG. 9 , inputs to the navigation and positioning equipment  114  ( FIG. 5 ) in the example embodiment includes a GPS time pulse  502  as received by the GPS Timer Receiver  206  ( FIG. 6 ) and synchronized throughout the system  100 , Doppler velocity log data  504  and MEMS accelerometer data  506 . The Doppler velocity log data  504 , which is typically in terms of speed measured in cm/s, is converted to distance data  508  (e.g. in cm) via a function  510 , e.g. using the embedded computer  214  ( FIG. 6 ). Similarly, the MEMS accelerometer data  506 , which is typically in terms of acceleration measured in m/s 2 , is converted to distance data  512  (e.g. in cm) via successive functions  514 ,  516 . The time pulse  502  and distance data  508 ,  512  are then provided to a Kalman filter  518  for generating a single distance pulse  520 , e.g. a 2 cm pulse, with corresponding time data  522 . In the example embodiment, the Kalman filter  518  is capable of selecting the best reading from two or more sources (i.e. inputs), as will be understood by a person skilled in the art. 
         [0162]    At the same time, in the example embodiment, the submersible MTM module  302 , which senses and records the magnetic field emitted by the pipe wall at about 2 cm intervals, generates magnetometric data  524  corresponding to the distance pulse  520  and time data  522  above. The distance pulse  520 , time data  522  and magnetometric data  524  are transmitted to the control unit  102  ( FIG. 5 ) for further processing, e.g. calculating position, including depth via pressure sensor, of any defect/anomaly, calculating severity of such defect/anomaly. 
         [0163]    The system  100  of the example embodiment is capable of operating in either an on-line mode or an off-line mode. In the on-line mode, the system  100  receives both magnetometric data with GPS time stamps and navigation data in real-time. In the off-line mode, the system  100  receives real-time magnetometric data, but receives navigation data only after the mission has been completed, e.g. via a removable device such as a Universal Serial Bus (USB) flash drive. Typically, the navigation data includes at least the absolute coordinates of the ROV  120  (hence, the underwater unit  112  and any defect/anomaly) with GPS time stamps, and Kilometer Post data (distance traveled by the ROV  120  along the pipeline since the beginning of the movement) In the example embodiment, the navigation data is provided in American Standard Code for Information Interchange (ASCII) codes. The magnetometric data and navigation data are saved together in a database of the PC  208  of the control unit  102  ( FIG. 6 ) for further processing. 
         [0164]    Table 1 shows details of the navigation data in the example embodiment. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Field 
                 Description 
               
               
                   
                   
               
             
             
               
                   
                 DD/mm/yy 
                 date 
               
               
                   
                 Hh:mm:ss.ss 
                 IPPS GPS time 
               
               
                   
                 XF.xx 
                 Easting of ROV 
               
               
                   
                 YF.yy 
                 Northing of ROV 
               
               
                   
                 SF.xx 
                 KP of ROV 
               
               
                   
                   
                 (Distance along the Pipeline) 
               
               
                   
                 CFF 
                 ROV depth 
               
               
                   
                 XVV.x 
                 ROV heading 
               
               
                   
                 sDVVV 
                 CP Values 
               
               
                   
                   
                 (Controlled Parameter) 
               
               
                   
                   
               
             
          
         
       
     
         [0165]    Table 2 shows details of the magnetometric data in the example embodiment. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Field 
                 Description 
               
               
                   
                   
               
             
             
               
                   
                 DD/mm/yy 
                 date 
               
               
                   
                 Hh:mm:ss.ss 
                 IPPS GPS time 
               
               
                   
                 H x   
                 X-axis magnetometric value 
               
               
                   
                 H y   
                 Y-axis magnetometric value 
               
               
                   
                 H z   
                 Y-axis magnetometric value 
               
               
                   
                   
               
             
          
         
       
     
         [0166]    For example, the PC  208  calculates the coordinates of the ROV  120  relative to the surface vessel  110  at a particular time stamp based on the ROV  120  navigation data. These coordinates are then combined with the absolute coordinates of the surface vessel  110  received from the GPS satellite at that time stamp to determine the absolute coordinates of the ROV. If an anomaly in the magnetometric data is found at the same time stamp, such anomaly is associated with the coordinates that have been determined. By compiling and processing all data collected from an inspection mission, locations of potential defects, which correspond to the anomalies in magnetometric data, are determined in the example embodiment. 
         [0167]    Furthermore, the system of the example embodiment is capable of evaluating a danger degree of a defect, calculating a pipeline safe operating pressure and calculating a pipeline safe operation term. An integral index F of danger degree of a defect that takes into account the extent of magnetic anomaly, amplitude and shape of distribution of magnetic field intensity vector over the background values is calculated in the example embodiment based on the following formula: 
         [0000]    
       
         
           
             
               
                 
                   F 
                   = 
                   
                     A 
                     · 
                     
                        
                       
                         ( 
                         
                           1 
                           - 
                           
                             
                               Q 
                                
                               
                                   
                               
                                
                               φ 
                             
                             
                               Q 
                                
                               
                                   
                               
                                
                               α 
                                
                               
                                   
                               
                                
                               H 
                             
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0168]    where A denotes a corrective coefficient characterizing influence of defects of pipelines upon the magnetic field change and is typically determined after a calibration procedure; Q AH , Q Φ  denote density of magnetic field strength distribution along a pipeline axis in anomaly zone and in a “calm” background area, A/ M , respectively. The density is typically determined as a length of a section of a curve. 
         [0169]    In the example embodiment, the curve comprises a geometrical place of points of intensity of a magnetic field in space, thus: 
         [0000]        dQ =√{square root over( dH   x   2   +dH   y   2   +dH   z   2 )}  (2)
 
         [0170]    where dH x , dH y , dH z  denote values of change of magnetic field strength vector, A/ M   2 , respectively. 
         [0171]    In the example embodiment, Q AH  and Q Φ  are calculated by integrating dQ by length of anomaly and background sections, respectively. 
         [0172]    The calculated values of index F are maintained e.g. in a database of revealed defects, and also in diagrams of anomalies distribution. Table 2 provides a ranking of sites (i.e. locations) with magnetic anomalies based their danger degree. On sites with the first danger rank, the first priority repair-reconstruction works are carried out. On sites with the second danger rank, planned repair-reconstruction works are scheduled. On sites with the third danger rank, the operation of the pipeline is allowed without repair-reconstruction works. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Danger degree of magnetic 
               
               
                 No 
                 Value of integral index F 
                 anomaly, rank 
               
               
                   
               
             
             
               
                 1 
                 from 0 to 0.2 
                 first 
               
               
                 2 
                 from 0.22 to 0.55 
                 second 
               
               
                 3 
                 from 0.55 to 0.99 
                 third 
               
               
                   
               
             
          
         
       
     
         [0173]    Additionally, in the example embodiment, the safe operating pressure P safe  is calculated based on the respective danger degree of the defect. 
         [0174]    For sections with defects of the first danger rank (i.e. 0≦F&lt;0.2), 
         [0000]      at  F&lt; 0.1: P   safe =0.9 P   oper +0.1 P   oper   ·F   (3)
 
         [0000]      at 0.1≦ F&lt; 0.2: P   safe =0.9 P   oper +0.05 P   oper   ·F   (4)
 
         [0175]    For sections with defects of the second danger rank (i.e. 0.2≦F&lt;0.55): 
         [0000]        P   safe =1.01 P   oper +0.05 P   oper   ·F   (5)
 
         [0176]    For sections with defects of the third danger rank (i.e. F≧0.55): 
         [0000]        P   safe =1.06 P   oper +(0.95 P   design −1.06 P   oper )· F   (6)
 
         [0177]    where P oper  denotes pressure in a pipeline at the moment of inspection, measured in megapascals (MPa); P design  denotes design pressure in a pipeline (in MPa); and P safe  denotes calculated safe operating pressure in a pipeline (in MPa). 
         [0178]    If the value of calculated safe operating pressure P safe  exceeds the design pressure P design , the pipeline is preferably operated at the design pressure. The assessment of pipeline technical condition can also be carried out based on the coefficient of safe pressure “CSP” where: 
         [0000]    
       
         
           
             
               
                 
                   CSP 
                   = 
                   
                     
                       P 
                       oper 
                     
                     
                       P 
                       safe 
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
         [0179]    In the example embodiment, at CSP≧1, a defect is assessed as extreme and subject to the first priority repair. 
         [0180]    For a pipeline short-term operation, the maximum admissible operating pressure P max  (also known as MAOP) is calculated in the example embodiment: 
         [0000]        P   max   =P   safe ·τ  (8)
 
         [0181]    where τ denotes a coefficient of the short-term increase of pressure, which is determined by the operating organization and may range from 1.1 to 1.15 in the example embodiment. 
         [0182]    The pipeline safe (i.e. accident-free) operation term T safe  is calculated in the example embodiment on the condition that the pipeline is operated at the calculated safe pressure, as described above with respect to Equations (3)-(6). After having repaired all revealed defects the pipeline safe operation term is fixed no more than 90% from calculated value. lease explain what is meant by “fixed no more than 90% from For each revealed defect, the calculations are carried out in the example embodiment by the following formula: 
         [0000]        T   safe   =K   p   ·K   F   ·K   t   (9)
 
         [0183]    where K p  denotes a coefficient considering the pressure in the pipeline; K F  denotes a coefficient considering danger degree of a defect; and K t  denotes a coefficient which takes into account the term of a pipeline operation. 
         [0184]    For example, if the pipeline is operated at the design pressure, K p =1, otherwise: 
         [0000]        Êδ=e  1− P  design  P  oper  (10)
 
         [0000]      Also,  K F=− 2           Lg           1− F   (11)
 
         [0185]    K t  considers the influence of operation factors, in particular, the probability of a pipeline failure within the first 3 years of operation because of construction-assembly defects and because of corrosion damage after 5-7 years of operation. 
         [0000]        K t= 10· TΔ                       T   (12)
 
         [0186]    where T denotes the normative operation term of a pipeline (measured in years), and ΔT denotes the operation term of a pipeline since the moment of its putting into operation (measured in years). 
         [0187]      FIG. 10  shows a flow chart  600  illustrating a method for inspecting a subsea pipeline according to an example embodiment. At step  602 , a defect along the subsea pipeline is detected using a submersible magnetometric tomography method (MTM) module adjacent the subsea pipeline. At step  604 , a position, including depth via pressure sensor, of the submersible MTM module is determined, thereby the position, including depth via pressure sensor, of the defect is determined. 
         [0188]    The method and system of the example embodiment can advantageously allow non-piggable subsea pipelines from an on-shore location. Even for piggable subsea pipelines, the need for pipeline preparation prior to inspection (e.g. (clean-up of a pipe internal cavity, geometric inspection before runs of diagnosing tool-defectoscopes, placement of reference points, magnetization of a pipeline metal) is advantageously eliminated. Additional facilities for pig launching/receiving are also not required. Thus, a cost reduction may be achieved compared to conventional methods such as intelligent pigging. 
         [0189]    Additionally, the method and system of the example embodiment can have a high sensitivity due to the non-contact registration of the pipeline magnetic field and the filtration of relevant signal over noise. This means that metal defects causing stress-deformed conditions are typically not missed during inspection. Advantageously, the magnetic field change of the whole defective section (cluster)—not a separate defect—is registered in the example embodiment. That is, the method and system of the example embodiment can provide a quantitative assessment of stress concentrator F for all interconnected defects of the registered magnetic anomaly (or stress-deformed condition anomaly resulting from a cluster). 
         [0190]    Furthermore, the method and system of the example embodiment can advantageously be a single tool for inspection of different sizes of pipelines, and allow evaluating the danger degree of defects of various types on the basis of the unified quantitative index F of stress-concentrator value. Preferably, this allows calculating EFR for the defects of “metal loss” type and other types such as: “crack-like defects”, weld defects, “continuity failure”, “geometry change”, etc. Thus, the calculations of serviceability for all types of defects—not only “metal loss” type—can be made possible. 
         [0191]    The method and system of the example embodiment can be implemented on a computer system  700 , schematically shown in  FIG. 11 . It may be implemented as software, such as a computer program being executed within the computer system  700 , and instructing the computer system  700  to conduct the method of the example embodiment. 
         [0192]    The computer system  700  comprises a computer module  702 , input modules such as a keyboard  704  and mouse  706  and a plurality of output devices such as a display  708 , and printer  710 . 
         [0193]    The computer module  702  is connected to a computer network  712  via a suitable transceiver device  714 , to enable access to e.g. the Internet or other network systems such as Local Area Network (LAN) or Wide Area Network (WAN). 
         [0194]    The computer module  702  in the example includes a processor  718 , a Random Access Memory (RAM)  720  and a Read Only Memory (ROM)  722 . The computer module  702  also includes a number of Input/Output (I/O) interfaces, for example I/O interface  724  to the display  708 , and I/O interface  726  to the keyboard  704 . 
         [0195]    The components of the computer module  702  typically communicate via an interconnected bus  728  and in a manner known to the person skilled in the relevant art. 
         [0196]    The application program is typically supplied to the user of the computer system  700  encoded on a data storage medium such as a CD-ROM or flash memory carrier and read utilising a corresponding data storage medium drive of a data storage device  730 . The application program is read and controlled in its execution by the processor  718 . Intermediate storage of program data maybe accomplished using RAM  720 . 
         [0197]    It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.