WO2014058336A1

WO2014058336A1 - А method and apparatus for monitoring a wall of a mechanical structure

Info

Publication number: WO2014058336A1
Application number: PCT/RU2012/000826
Authority: WO
Inventors: Mikhail Vladimirovich RYAZANOV
Original assignee: Siemens Aktiengesellschaft
Priority date: 2012-10-11
Filing date: 2012-10-11
Publication date: 2014-04-17

Abstract

An apparatus (1) adapted to monitor a wall (2) of a mechanical structure, said apparatus (1) comprising: an excitation unit (4) adapted to apply a magnetic excitation field to at least one magneto-elastic element (3) of said monitored wall (2), said magneto-elastic element (3) having a magnetic permeability sensitive to a change of mechanical stress in said wall; a recording unit (5) adapted to record a response signal generated by said at least one magneto-elastic element (3) in response to the applied magnetic excitation field; and a processing unit (6), adapted to evaluate the recorded response signal to detect a mechanical stress in said monitored wall (2).

Description

A METHOD AND APPARATUS FOR MONITORING A WALL

OF A MECHANICAL STRUCTURE

DESCRIPTION

The invention relates to an apparatus and a method to monitor a wall of a mechanical structure such as a pipeline for a fluid.

Mechanical structures in a wide range of applications can be damaged due to solid particle erosion caused by the attack of solid particles such as sand at high velocities. In particular, mechanical structures such as gas turbines, oil or gas production equipment, transmission pipe lines, boiler tubes are prone to erosion damages caused by solid particles. Localized erosive damage induced by solid particle impact may result to a loss of production in a production facility and/or to an increase in the maintenance cost of mechanical structures. The mechanical structures such as pipelines may start to leak causing environmental pollution and/or potential health and safety hazards . Several conventional techniques are used for monitoring and inspection of mechanical damages caused by solid particles.

A conventional technique is to use ultrasonic high- frequency sound waves transmitted through the material of the mechanical structure to be monitored. The transmitted sound wave is reflected back to the sound source by defects induced in the material and once the sound wave has reached the other side of the inspected material. The recorded sound wave is then used to map defects in the material and to measure the thickness of the respective material. However, ultrasonic inspection of a mechanical structure requires large equipment and huge operator experience. Another conventional technique to monitor mechanical structures uses resistive electrical sensors. Here, resistive electrical sensors are embedded in a wall of the mechanical structure to be monitored. These resistive electrical sensors provide an electrical indication due to resistance changes of wear or erosion of the monitored walls of the mechanical structure as exemplified in US patent 3015950. A main drawback of this conventional way to monitor a wall of mechanical structure is that the resistance change is very sensitive to temperature fluctuations .

Another conventional method for detecting wall thinning from erosion is described in US 4,922,748. This conventional way concerns drilling of holes in the outer surface of pipes at selected locations to depth greater than the thickness at which the pipes will rupture to leave predetermined residual wall thicknesses between the ends of the holes and the inner surfaces of the pipe walls. Further, tracer materials are inserted in the holes to be released in the pipes when the pipe wall thinning exceeds the residual wall thickness of the holes. Further, the presence or absence of tracer materials in the holes is determined to permit pipe wall thinning to be detected prior to pipe rupture. The main disadvantage of this conventional method is a decrease of mechanical integrity of the mechanical structure due to the formation of the necessary holes.

A further conventional technique to monitor a mechanical structure is the use of an inspection system detecting flaws in tubular walls using Hall effect sensors as described in US 2004/0100256. The inspection device operates inside by first saturating a tubular wall with magnetic flux. Flaws in the surface cause flux leakage and the magnitudes of flux leakages are measured with the Hall effect sensors disposed within the inspection device. The magnitude of flux leakage is related to the amount of ferromagnetic material loss resulting from the flaws. Eddy currents induced in the wall are also measured and combined with that Hall effect sensor measurements to define location and geometric shape of the flaw. The main disadvantage of this conventional technique is that it can only be applied to ferromagnetic metallic materials.

It is an object of the present invention to provide a method and an apparatus to monitor a wall of a mechanical structure and being robust against changes in the environment of the mechanical structure. This object is achieved by an apparatus comprising the features of claim 1.

The present invention provides an apparatus adapted to monitor a wall of a mechanical structure, said apparatus comprising : an excitation unit adapted to apply a magnetic excitation field to at least one magneto-elastic element of said monitored wall, said magneto-elastic element having a magnetic permeability sensitive to a change of mechanical stress in said wall; a recording unit adapted to record a response signal generated by said at least one magneto-elastic element in response to the applied magnetic excitation field; and a processing unit adapted to evaluate the recorded response signal to measure a mechanical stress in said monitored wall. An advantage of the apparatus according to the present invention is that the mechanical integrity of the investigated mechanical structure is not affected.

A further advantage of the apparatus according to the present invention is that it can be used to monitor any kind of mechanical structure consisting of a non- ferromagnetic material, in particular also a composite structural material.

In a further embodiment of the apparatus according to the present invention the processing unit is adapted to evaluate a wall thickness of the monitored wall on the basis of the detected mechanical stress changes in that wall .

In a further possible embodiment of the apparatus according to the present invention the excitation unit comprises an excitation coil adapted to generate the magnetic excitation field.

In a further possible embodiment of the apparatus according to the present invention the recording unit comprises at least one recording coil adapted to record the response signal generated by at least one magneto-elastic element in response to the applied magnetic excitation field.

In a further possible embodiment of the apparatus according to the present invention the excitation unit and the recording unit are integrated in a monitoring unit being movable along the wall to be monitored.

In a further possible embodiment of the apparatus according to the present invention the recording unit comprises a plurality of recording coils adapted to record response signals generated by the at least magneto-elastic element in response to the applied magnetic excitation field at predetermined locations of the wall.

In a further possible embodiment of the apparatus according to the present invention the excitation coils and/or recording coils are integrated in said wall and connected to the excitation unit and/or recording unit of the apparatus .

The invention further provides a method for monitoring a wall, comprising the features of claim 8. Accordingly, the present invention provides a method for monitoring a wall, comprising the steps of: providing said wall with at least one magneto-elastic element having a magnetic permeability sensitive to a change of mechanical stress in said wall; applying a magnetic excitation field to said at least one magneto-elastic element and evaluating a recorded response signal generated by said at least one magneto-elastic element in response to the applied magnetic excitation field to measure a mechanical stress in said monitored wall.

In a possible embodiment of the method according to the present invention the wall thickness of the monitored wall can be estimated from the detected mechanical stress changes in the monitored wall. The invention further provides a wall of a mechanical structure having the features of claim 10.

Accordingly, the invention further provides a wall for a mechanical structure, said wall comprising:

at least one embedded magneto-elastic element having a magnetic permeability sensitive to a change of mechanical stress in said wall.

In a possible embodiment the wall of a mechanical structure according to the present invention said magneto-elastic element is embedded in said wall at a depth from a surface of said wall where a wall thinning becomes critical to the mechanical structure.

In a possible embodiment of the wall according to the present invention the at least one embedded magneto-elastic element comprises an amorphous magnetic alloy.

In a possible embodiment of the wall according to the present invention the wall consists of a non-ferromagnetic material .

In a possible implementation the wall consists of a composite structural material or a diamagnetic material.

In still a further possible embodiment of the wall according to the present invention, the excitation coils and/or recording coils are embedded in said wall to apply a magnetic excitation field to the at least one embedded magneto-elastic element and to record a response signal generated by said at least one embedded magneto-elastic element in response to the applied magnetic excitation field.

In a possible embodiment of the wall according to the present invention the mechanical structure comprises a pipeline adapted to transport a fluid or gas or a chemical product .

In a still further possible embodiment of the wall according to the present invention, the mechanical structure comprises a wind turbine blade. In a still further possible embodiment of the wall according to the present invention, the mechanical structure comprises a boiler tube.

In the following possible embodiments of the apparatus and method according to the present invention are described in more detail with reference to the enclosed figures.

Fig. 1 shows a block diagram for illustrating a possible embodiment of an apparatus to monitor a wall according to the present invention; Fig. 2 shows a diagram for illustrating operation of possible embodiment of the apparatus according to the present invention;

Fig. 3 is a diagram for illustrating a possible embodiment of an apparatus according to the present invention; Fig. 4 shows a further diagram to illustrate a possible embodiment of an apparatus according to the present invention ;

Fig. 5 shows a diagram for illustrating a further possible embodiment of the apparatus according to the present invention;

Fig. 6 shows a flow chart for illustrating a possible embodiment of a method to monitor a wall of a mechanical structure according to the present invention.

Fig. 1 shows a block diagram of a possible embodiment of an apparatus 1 adapted to monitor a wall 2 of a mechanical structure. As can be seen in fig. 1, the wall 2 of the mechanical structure comprises at least one magneto-elastic element 3. This magneto-elastic element 3 can be embedded in the wall 2 of the mechanical structure. Apparatus 1 is adapted to monitor the wall 2 of the mechanical structure. Apparatus 1 comprises an excitation unit 4, and a recording unit 5. The excitation unit 4 is adapted to apply a magnetic excitation field to the at least one magneto- elastic element 3 of the monitored wall 2. Recording unit 5 is adapted to record a response signal, generated by the at least one magneto-elastic element 3 in response to the applied magnetic excitation field. The magneto-elastic element 3 can be embedded in the wall 2 of the mechanical structure, wherein the magnetic permeability is sensitive to a change of mechanical stress in said wall 2 as shown for example in fig. 2. Fig. 2 shows a relative change of a magnetic flux density B, wherein the magneto-elastic element 3 can be subjected to both tensile (TS) and compressive stresses (CS) . These stresses are mechanical stresses to which the wall 2 is subjected. As shown in the example of fig. 2 the magneto-elastic element 3 can consist of a Fe-Ni-Si-B amorphous alloy to which a magnetic field is applied having a field strength of 25 A/m. It can be seen that the Fe-based or Co-based amorphous magnetic alloys exhibit a large and stress sensitive change in the relative magnetic permeability and magnetic flux density. These materials can in a possible embodiment form wires or ribbons and can act as magneto-elastic elements or sensors to detect and assess mechanical stress changes in the wall 2. If the wall 2 is eroded by solid materials or particles the removal of material from the surface of the wall 2 causes a residual mechanical stress to accumulate in the remaining wall. The change of mechanical stress can be detected by means of the at least one magneto-elastic element 3 embedded in the wall structure 2 as shown in fig. 1. The magneto-elastic element 3 can for instance be integrated or embedded in the wall 2 of a pipeline which transports fluids such as gas or oil. The transported fluid can contain solid particles causing a wall thinning within the pipeline. The wall thinning can become critical in terms of pipe rupture or holes leaking the transported fluid. The thinning leads to an increased stress within the remaining wall so that the magnetic permeability of the magneto-elastic elements 3 changes because of mechanical stresses induced when the wall thicknesses is reduced beyond a predetermined threshold which can be defined by the distance between the magneto-elastic elements 3 and the wall surface. The wall 2 can be of a non-ferromagnetic material and can consist also of composite structural materials. The composite structural material can be for example a fiber with a polymer matrix. Within the magneto- elastic element 3, it is possible to detect local mechanical stresses in the mechanical structure. Further, it is possible to determine the quantity of the mechanical stress and the extent of thickness losses due to erosion processes caused by solid particles impact.

The apparatus 1 according to the present invention comprises a recording unit 5 adapted to record a response signal generated by the at least one magneto-elastic element 3 provided within the wall in response to the magnetic excitation field generated by the excitation unit 4. The apparatus 1 further comprises a processing unit 6 adapted to evaluate the recorded response signal to detect the mechanical stress changes in the monitored wall. The processing unit 6 can process the recorded response signal to detect a local mechanical stress induced in the investigated location within the monitored wall 2. In a further embodiment the processing unit 6 is further adapted to evaluate a wall thickness of the monitored wall 2 on the basis of the detected mechanical stress changes in the respective wall 2. In a possible embodiment the excitation unit 4 comprises an excitation coil EC adapted to generate the magnetic excitation field applied to the wall 2 to be monitored. The recording unit 5 also can comprise at least one recording coil RC adapted to record the response signal generated by the at least magneto-elastic element 3 in response to the applied magnetic excitation field. In a possible implementation of the apparatus 1 according to the present invention the excitation unit 4 and the recording unit 5 can be integrated in a monitoring unit 7 as illustrated in fig. 1. The monitoring unit 7 can be moved along the wall 2 to be monitored. In a possible embodiment the processing unit 6 is also integrated in the monitoring unit 7. In an alternative embodiment the monitoring unit 7 communicates with the processing unit 6 via a data interface. The data interface can be a wireless or a wired interface. In a possible embodiment the monitoring unit 7 is moved along the surface of the wall 2 to be monitored at a predetermined distance.

Fig. 3 shows a block diagram for illustrating a possible embodiment of the apparatus 1 according to the present invention. In the embodiment of fig. 3 coils are used for detecting a signal from the magneto-elastic element 3. At least one coil is used to generate a magnetic excitation field. Recording is performed by using another pick-up coil the inductance of which is influenced by the permeability of the magneto-elastic element 3. Fig. 3 shows an excitation coil EC and a recording coil RC. The excitation coil EC can be integrated in the excitation unit 4, whereas the recording coil RC can in a possible embodiment be integrated in the recording unit 5. In an alternative embodiment the excitation coil EC and/or the recording coil RC can be also integrated in the wall 2 to be monitored as shown in the implementation of fig. 5. The excitation coil EC is used to generate the magnetic excitation field, whereas the pick-up coil or recording coil RC receives the response signal. A function generator FG can be provided to generate a magnetic excitation field adapted to the wall 2 of the mechanical structure to be investigated. A signal detecting system SDS as shown in fig. 3 can be provided within the processing unit 6 as shown in fig. 1. Figs. 4, 5 show different exemplary embodiments of an apparatus adapted to monitor a wall 2 of a mechanical structure. In the shown examples the mechanical structure is formed by a pipeline, wherein the pipeline tube comprises a wall 2. In the example as shown in fig. 4 the magneto-elastic elements 3 are located at selective locations where material loss due to solid particle erosion may be critical in terms of structural and mechanical integrity of the wall. In the shown example there are provided nine different magneto-elastic elements 3 in the wall 2 of the pipeline. In the shown example an excitation magnetic field is induced locally by facing an appropriate region of the wall 2 with an excitation electric coil EC. The output signal is recorded with another solenoid, i.e. a recording coil RC. The recording coil RC can be integrated with the excitation coil EC in a single unit such as a monitoring unit 7 comprising an excitation unit 4 having an excitation coil EC and a recording unit 5 comprising a recording coil RC. The monitoring unit 7 can be moved along the surface of the monitored wall 2 of the pipeline. Fig. 5 shows an alternative embodiment of the apparatus 1 according to the present invention, wherein the magneto- elastic elements 3 are formed by long wires or ribbons embedded in the wall. Further in the wall of the investigated tube 2 a plurality of electrical coils is integrated as well. As shown in the embodiment an electrical coil forming an excitation coil EC as well as several recording coils RC are also embedded in the wall 2 of the mechanical structure. The integrated excitation coil EC is used to excite the magneto-elastic material of the magneto-elastic elements 3 integrated in the tube with a magnetic excitation field while the other recording coils RC being also integrated in the wall 2 are used for recording an output signal at predetermined locations as shown in fig. 5. The long magneto-elastic elements 3 can, for example, be formed by amorphous magnetic alloys.

As can be seen in the embodiments of figs. 4, 5 the invention further provides a wall 2 for a mechanical structure, wherein the wall 2 comprises at least one embedded magneto-elastic element 3 having a magnetic permeability sensitive to a change of mechanical stress in the respective wall. In a further implementation wires or ribbons made of an amorphous metal alloy are integrated for the purpose of detecting a change of mechanical stress within the wall 2 when the wall is subjected to wear or erosion processes. In a further embodiment the magneto- elastic elements 3 can be embedded in the wall 2 at a distance from the surface of the wall 2, where a wall thinning becomes critical to the mechanical structure. In a further embodiment the wall 2 consists of a non- ferromagnetic material such as a composite structure material or a diamagnetic metal. In a further possible embodiment of the wall 2 of a mechanical structure according to the present invention not only the magneto- elastic elements 3 are integrated in the wall 2 but also at least one excitation coil EC and several recording coils RC are integrated at different locations of the wall as shown in fig. 5. The excitation coil and/or recording coils are embedded in the wall 2 to apply a magnetic excitation field to the at least one embedded magneto-elastic element 3 and to record automatically a response signal generated by the at least one embedded magneto-elastic element 3 in response to the applied magnetic excitation field. In this embodiment not only the magneto-elastic element 3 is integrated in the wall structure as shown in fig. 4 but also an excitation coil EC and/or recording coils RC as shown in fig. 5.

Fig. 6 shows a flow chart of a possible embodiment of a method for monitoring a wall according to the present invention .

In a first step SI the wall 2 is provided with at least one magneto-elastic element 3 having a magnetic permeability sensitive to a change of mechanical stress in the wall 2. In an implementation the magneto-elastic elements 3 can be embedded in the wall 2 during its fabrication.

In a further step S2 a magnetic excitation field is applied to the at least one magneto-elastic element 3 provided within or along the wall 2. The magnetic excitation field can be provided by an excitation coil EC of an excitation unit 4.

In a further step S3 the recorded response signal generated by the at least one magneto-elastic element 3 in response to the applied magnetic excitation field is evaluated to detect the mechanical stress changes in the monitored wall 2. The evaluation of the recorded response signal can be performed by a processing unit. In a further possible step (not shown in fig. 6) a wall thickness of the monitored wall 2 can be estimated by a processing unit 6 on the basis of the detected mechanical stress changes in the wall 2.

The method according to the present invention enables a contactless monitoring of material loss for any kinds of walls such as pipes or tubes. These material losses can be caused by solid particle erosion. The monitoring of the wall can be performed without interrupting the equipment operation. Accordingly, a maintenance inspection by using the method according to the present invention can be performed without interrupting operation of an equipment such as a fluid transportation equipment. The method and apparatus according to the present invention has the advantage that a wall thinning can be detected before the wall thinning becomes critical. Accordingly, the apparatus and method according to the present invention allows one to prevent structural rupture in a mechanical structure.

In comparison to a conventional semiconductor strain gauge which shows a change in resistance of about 15 % when strained to their maximum recommended stress level an amorphous metal alloy based sensor forming a magneto- elastic element 3 is more sensitive to mechanical stress variations demonstrating a change in inductance of over 300 % when loaded to its maximum working level. Further, amorphous metal alloys which are used in a preferred embodiment of the apparatus according to the present invention exhibit superior mechanical properties. For example, amorphous metal alloys show superior mechanical properties such as very high tensile strength (> 2.000 MPa) and elastic modulus (> 120 GPa) to provide additional reinforcement of the mechanical structure against the solid particle erosion and structural failure. The method and apparatus according to the present invention can be used for a wide range of applications and mechanical structures including means to transport a fluid or gas or chemical product. The method and apparatus according to the present invention can be used for monitoring a wind turbine blade. In a further possible application of the method and apparatus according to the present invention can be used to monitor a wall thickness of a boiler tube. In a possible embodiment of the apparatus 1 according to the present invention the processing unit 6 can generate an alarm signal when the thickness of the investigated wall 2 falls under a predetermined critical level. In a possible implementation the apparatus 1 also forwards position data of the location where the wall thickness of a wall 2 reaches a critical level. In a possible implementation the apparatus 1 can be navigated autonomously along the wall 2 of the mechanical structure such as a pipeline.

Claims

CLAIMS :

1. An apparatus (1) adapted to monitor a wall (2) of a mechanical structure, said apparatus (1) comprising:

an excitation unit (4) adapted to apply a magnetic excitation field to at least one magneto-elastic element (3) of said monitored wall (2), said magneto-elastic element (3) having a magnetic permeability sensitive to a change of mechanical stress in said wall (2);

a recording unit (5) adapted to record a response signal generated by said at least one magneto-elastic element (3) in response to the applied magnetic excitation field; and

a processing unit (6), adapted to evaluate the recorded response signal to detect a change of mechanical stress in said monitored wall (2) .

2. The apparatus according to claim 1,

wherein the processing unit (6) is adapted to evaluate a wall thickness of the monitored wall (2) on the basis of the detected mechanical stress changes in said wall.

3. The apparatus according to claim 1 or 2,

wherein said excitation unit (4) comprises an excitation coil (EC) adapted to generate the magnetic excitation field.

4. The apparatus according to one of the preceding claims 1-3,

wherein said recording unit (5) comprises at least one recording coil (RC) adapted to record the response signal generated by said at least one magneto-elastic element (3) in response to the applied magnetic excitation field.

5. The apparatus according to one of the preceding claims 1-4, wherein said excitation unit (4) and said recording unit (5) are integrated in a monitoring unit (7) being movable along the wall (2) to be monitored.

6. The apparatus according to one of the preceding claims 1-4,

wherein said recording unit (5) comprises a plurality of recording coils (RC) adapted to record response signals generated by said at least one magneto-elastic element (3) in response to the applied magnetic excitation field at predetermined locations of the wall (2) .

7. The apparatus according to claim 6,

wherein said excitation coil (EC) and/or recording coils (RC) are integrated in said wall (2) and connected to the excitation unit (4) and/or recording unit (5) of said apparatus ( 1 ) .

8. A method for monitoring a wall comprising the steps of:

(a) providing (SI) said wall (2) with at least one magneto-elastic element (3) having a magnetic permeability sensitive to a change of mechanical stress in said wall (2) ;

(b) applying (S2) a magnetic excitation field to said at least one magneto-elastic element (3) ; and

(c) evaluating (S3) a recorded response signal generated by said at least one magneto-elastic element (3) in response to the applied magnetic excitation field to detect the mechanical stress changes in said monitored wall (2) .

9. The method according to claim 8,

wherein a wall thickness of the monitored wall (2) is evaluated from the detected mechanical stress changes in said monitored wall (2) .

10. A wall (2) for a mechanical structure, said wall (2) comprising :

at least one embedded magneto-elastic element (3) having a magnetic permeability sensitive to a change of mechanical stress in said wall (2) .

11. The wall (2) according to claim 10,

wherein said embedded magneto-elastic element (3) is embedded in said wall (2) at a depth from a surface of said wall where a wall thinning becomes critical to the mechanical structure.

12. The wall (2) according to claim 10 or 11,

wherein the at least one embedded magneto-elastic element (3) comprises an amorphous magnetic alloy.

13. The wall (2) according to one of the preceding claims 10-12,

wherein said wall (2) consists of a non-ferromagnetic material, in particular a composite structural material or a diamagnetic metal.

14. The wall (2) according to one of the preceding claims 10-13,

wherein excitation coils (EC) and/or recording coils (RC) are embedded in said wall (2) to apply a magnetic excitation field to the at least one embedded magneto- elastic element (3) and to record a response signal generated by said at least one embedded magneto-elastic element (3) in response to the applied magnetic excitation field.

15. The wall (2) according to one of the preceding claims 1-14, wherein said mechanical structure comprises :

a pipeline adapted to transport a fluid or gas chemical product;

a wind turbine blade,

a boiler tube.