The present invention relates to the general field of processes and devices for magnetic detection and more particularly the field of processes and devices for detection fouling or clogging by deposits of ferromagnetic materials on or near cooling tubes of a steam generator of a pressurised nuclear water reactor known as PWR.
In the field of electronuclear plants of PWR type according to the acronym “Pressurised Water Reactor”, it is well known that heat produced in the core of the reactor is transmitted by means of a closed circuit known as the primary circuit in which water circulates to a so-called secondary circuit whereof the water transformed into steam powers turbines to produce electricity.
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It is known that clogging deposits 35 form at the level of the quadrifoliages 25 (
Also, it is likewise known that so-called fouling deposits form on the external surface of tubes 20 causing a drop in performance of thermal exchange in the steam generator.
To eliminate these clogging or fouling deposits, it is known to clean the tubes and spacer plates by chemical cleaning processes. These processes consist of injecting chemical reagents into the secondary circuit of steam generators to demolish and dissolve these oxide deposits such as magnetites.
However, the quantity of reagents to be injected depends on the quantity of oxides present in the steam generators.
Consequently, the quantity of oxides needs to be determined in advance.
For this purpose, processes and devices are well known which detect deposits of magnetites using an axial probe with low-frequency Foucault current, said probe being introduced into the tubes of the steam generator, whereof the measurements are correlated with televisual images or online standards representative of deposits encountered.
The drawback to this type of process is that it needs analysis time of around 1 month for acquisition of data, considerably driving up costs. Also, measurements obtained by this type of process exhibit low precision.
The process and device for detecting deposits described in US patent U.S. Pat. No. 4,088,946 are also known. Said device comprises a probe with Foucault current which is moved at a constant speed in a tube to detect deposits.
In the same way as earlier, this probe exhibits low precision and needs acquisition of video images.
Other processes and devices for detection of deposit on the external wall of tubes having the same drawbacks are described especially in French patent application FR 2 459 490 and in US patent U.S. Pat. No. 4,700,134.
One of the aims of the invention is therefore to rectify these drawbacks by proposing a process and a detection device for deposits comprising at least one ferromagnetic material on or near the external wall of a tube, more particularly designed for detection of deposit on or near tubes of a steam generator of a electronuclear plant of PWR type, which is simple in design and minimally costly and has high precision and is substantially reliable.
For this purpose and in keeping with the invention, a process for detecting deposits is proposed, comprising at least one ferromagnetic material, such as nickel, magnetite or similar, on or near the external wall of a tube, significant in that it comprises at least the following steps of moving a magnetised source inside the tube in the direction of its length by means of an electric motor, measuring the intensity of the current in the electric motor, and determining the position and/or thickness and/or volume of said deposit as a function of the variations in intensity of the current measured in the electric motor.
The magnetised source preferably consists of at least one permanent magnet.
Also, said magnetised source is moved in the tube at a constant speed, said magnetised source being moved in a first direction and then in its opposite direction.
Also, the step for determining the position and/or thickness and/or volume of said deposit comprises a comparison step of the variation in intensity of the current measured in the motor with a reference model and/or a calibrated model.
Another object of the invention relates to a detection device executing the process significant in that it comprises at least one magnetised source, moving means of said magnetised source inside of said tube in the direction of the length comprising an electric motor, means for measuring the intensity of the current in said electric motor and means for determining the position and/or thickness and/or volume of said deposit as a function of variations in intensity of the current measured in the electric motor.
Said magnetised source preferably consists of at least one permanent magnet.
Said moving means of the magnetised source consist of a piston whereof one of the ends bears said magnetised source and whereof the opposite end comprises a bolt cooperating with an endless screw solid with the rotary drive axle.
Also, the rotary drive axle consists of the output axle of a reducer coupled to an electric motor.
By way of advantage, the device comprises blocking means of drive means inside a tube.
Other advantages and characteristics will emerge from the following description of several variant embodiments, given by way of non-limiting examples, of the device for detecting magnetic deposits on or near an amagnetic tube according to the invention, from the attached diagrams, in which:
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The moving means 110 of the magnetised source 105 consist of a piston 135 whereof one of the ends bears said magnetised source 105 and whereof the opposite end comprises a bolt 140 cooperating with an endless screw 145 solid with a rotary drive axle 150. Said rotary drive axle 150 consists of the output axle of a moto-reducer 155 constituted by a reducer 160 coupled to an electric motor 120. Said electric motor 120 is powered by fixed voltage regulated such that, to compensate for the increase in power necessary to pass the hard points associated with attraction of the magnets of the magnetised source 105, the intensity of the current motor increases.
In fact, having a magnetised source 105 called a probe, constituted by one or more permanent magnets, near a deposit 165 comprising at least one ferromagnetic material, such as nickel, magnetite or similar, on or near the external wall of the tube 115, results in attraction forces which vary as a function of the volume of the deposit 165, the distance between the probe 105 and the deposit 165, and the relative position between the probe 105 and the deposit 165. Moving this probe 105 is motorised at a constant speed, under the effect of attraction forces, results in variation in intensity of the supply current of the motor 120 which calibrates, detects the presence and estimates the volume of the deposit 165. Maximal force is attained when the minimum volume of the magnetic material is equal to the volume of the magnet of the probe 105. The attraction forces generated by the permanent magnets of the probe can be active or resistant, can favour displacement or oppose displacement. The control process by magnetic probe of the fouling and clogging consists of motorising in the tube 115 displacement of a probe 105 at a constant speed, comprising one or more permanent magnets, and making acquisition of the current motor whereof the intensity varies as a function of the presence, distance and volume of deposits.
Also, acquired signals are compared to the signal tube or to calibrated reference signals representative of dimensional data of deposit forms.
Also, to keep the device in place inside the tube 115 during displacement of the probe, the device comprises blocking means 165 of the moving means 110 inside said tube 115. Said blocking means 115 will be able to consist of all means well known to the person skilled in the art, such as mechanical means or plastic deformation means for example.
Also, the means for measuring the intensity of the current 125 consist of a device of ammeter type connected to a computer 170 of PC type by means of an acquisition card USB 175. An algorithm in the form of registered software on a physical medium, such as a hard drive and/or computer memory 165, the position and/or the thickness and/or volume of a deposit on or near the external wall of the tube 115, as a function of variations in intensity of the current measured in the electric motor 120, measurements of the intensity being transmitted to the computer 170 by means of the acquisition card USB 175.
An explanation now follows of the function of the device for detecting deposits comprising at least one ferromagnetic material, such as nickel, magnetite or similar, on or near the external wall of an amagnetic tube, in reference to
The device according to the invention, in reference to
When the probe 105 is moved at constant speed in the amagnetic tube 115, it is necessary to exert motorisation force of the probe depending on its position relative to the deposit 165.
The probe 105 is moved at constant speed, the voltage being regulated, the power function of the electric motor 120 with continuous current written as P(t)=U×l(t).
The intensity l(t) varies as a function of the relative position between the permanent magnets of the probe 105 and the deposit 165, said relative position generating a variation in attraction forces.
In some phases (input and output of the zone of the deposit 165), the attraction forces tend to draw on mechanics and generate axial restrictions which are compensated by the current motor.
The marker points on the curves of
A highly characteristic point of these curves is the point of inflection (B) which indicates that the probe is in material equilibrium, that is, that there is as much magnetic material on either side of the normal axis of the probe 105.
It is evident that the value of these forces depends on the volume of deposits encountered.
To retain displacement at constant speed the motor 120 must compensate for the effect of attraction forces when they are powered or resistant.
When they are powered, they are more substantial than the advance force. In reference to
In the case of the particular embodiment of the invention in which transmission consists of a transmission via screw/bolt, magnetic forces generate an axial force on the axle of the moto-reducer. These magnetic forces are sometimes so powered that they become resistant for mechanics.
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Consequently, the device according to the invention detects the presence of a deposit around the tube and determines the length of these deposits and their thickness.
Also, the device according to the invention enables direct on-screen reading of results by comparing the acquired signals to the reference tube signal or to calibrated signals.
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Tests conducted using the device according to the invention have shown that the variation in volume of deposits could be detected by comparison to a reference signal, the reference signal consisting of variations in intensity of the current motor when the probe is moved in a tube comprising no deposit, or by the difference in plate input and output signals. If there is a clogging deposit, it is present on one side of the spacer plate only, which compares the corresponding signals.
In the case of comparative input/output analysis, to boost precision for detection and characterisation of deposits, it is necessary to make a double acquisition (out and back) since the behaviour of the probe is different if entry is made via the clogged side or exit is made via the clogged side.
The first assay, in reference to
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To analyse the signals, characteristic points must be located on the curve. A variation in intensity of the current motor at these points will reveal the presence of a variation in volume of material, that is, the presence of a clogging deposit.
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In the current part (B), the attraction forces due to deposit at the plate intake hold the probe, leading to an increase in intensity.
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Consequently, the device according to the invention detects clogging of the quadrifoliage passages of the spacer plates with fine sensitivity, and determines the depth of this clogging and its thickness.
Also, the device according to the invention enables direct on-screen reading of results by comparing signals acquired at the reference tube signal or at calibrated signals.
Finally, it is understood that the examples given hereinabove are only non-limiting particular illustrations as to fields of application of the invention.
Number | Date | Country | Kind |
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0853200 | May 2008 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP09/55949 | 3/15/2009 | WO | 00 | 2/28/2011 |