EP2342554A1

EP2342554A1 - Improvements in the detection of deposits comprising at least one ferromagnetic material on or close to the external wall of a tube

Info

Publication number: EP2342554A1
Application number: EP09783746A
Authority: EP
Inventors: Antoine Gemma
Original assignee: Electricite de France SA
Current assignee: Electricite de France SA
Priority date: 2008-10-03
Filing date: 2009-10-05
Publication date: 2011-07-13
Also published as: WO2010037869A1; US20110241660A1; FR2936875B1; ZA201102438B; KR20110083639A; JP2012504756A; CN102171558A; FR2936875A1

Abstract

The present invention relates to a method for the detection of fouling or clogging deposits comprising at least one ferromagnetic material, such as nickel, magnetite or similar material, on or close to the external wall of a tube, characterized in that it comprises at least the following steps: a magnetized source is positioned inside the tube and immobilized heightwise therein; the source is rotated about itself by being driven by means of an electric motor; and the intensity of the current drawn by said electric motor during this rotational movement is measured and the curve obtained is analysed in order to detect, and where appropriate evaluate, the clogging.

Description

Improvements in the detection of deposits containing at least one ferromagnetic material on or near the outer wall of a tube

FIELD OF THE INVENTION

The present invention relates to the general field of magnetic detection methods and devices and more particularly to the field of methods and devices for detecting fouling or clogging by deposits of ferromagnetic materials on or in the vicinity of cooling tubes of a steam generator of a pressurized water nuclear reactor called REP.

BACKGROUND TECHNIQUE

In the field of nuclear power plants of the PWR type according to the acronym "pressurized water reactor", it is well known that the heat produced in the reactor core is transmitted by means of a closed circuit called primary circuit in which circulates from water to a so-called secondary circuit whose water transformed into steam supplies the turbines for the production of electricity.

With reference to FIG. 1, which represents a torn perspective steam generator, each PWR nuclear power plant generally comprising three or four steam generators, said steam generator consists of a confinement enclosure 5 receiving the primary circuit 10 and the secondary circuit 15. The heat exchange between the primary circuit 10 and the secondary circuit 15 is through a plurality of inverted U-shaped tubes 20. Said tubes 20 are held in place by spacer plates 25 immobilized by tie rods fixed at the bottom of the steam generator.

Referring to Figure 2 which shows a perspective view of a detail of the spacer plates 25 and tubes 20, said plates spacers 25 comprise cross-shaped holes 4 called quadrifollings through which pass said cylindrical tubes.

It is known that clogging deposits 35 are formed at the quadrifollings 25 (FIG. 2) between the tubes 20 and the spacer plates 25. These deposits 35 have the consequence, on the one hand, in normal operation, of modifying the mechanical stresses. on the tubes 4 and secondly, in case of incident or accident, to increase the efforts on the spacer plates 25, thus increasing the risk of rupture of the tubes 20. In addition, it is also known that so-called fouling deposits are formed on the outer surface of the tubes 20, causing a decrease in the performance of the heat exchange in the steam generator.

In order to remove these clogging or fouling deposits, it is well known to clean the tubes and spacer plates by chemical cleaning processes. These methods involve injecting chemical reagents into the secondary circuit of the steam generators in order to destructure and dissolve these oxide deposits such as magnetites.

However, the amount of reagents to be injected depends on the amount of oxides present in the steam generators.

Therefore, it is first necessary to determine the amount of oxides.

For this purpose, methods and devices for detecting magnetite deposits using a low-frequency eddy-axial axial probe are well known, said probe being introduced into the tubes of the steam generator, the measurements of which are correlated with television images. or online standards representative of the deposits encountered.

This type of method has the disadvantage of requiring a data acquisition analysis time of about 1 month significantly burdening costs. In addition, the measurements obtained by this type of process have a low accuracy. In addition, the method and the device for detecting deposits described in US Pat. No. 4,088,946 are known. The device includes an eddy current probe that is moved at a constant rate in a tube to detect deposits. In the same way as before, this probe has a low precision and requires the acquisition of video images.

Other methods and devices for detecting deposition on the outer wall of tubes having the same disadvantages are described in particular in French patent application FR 2,459,490 and in US Pat. No. 4,700,134.

BRIEF DESCRIPTION OF THE INVENTION

One of the aims of the invention is thus to remedy these drawbacks by proposing a method and a device for detecting deposits comprising at least one ferromagnetic material on or near the outer wall of a tube, more particularly intended for deposit detection on or near the tubes of a steam generator of a nuclear power plant PWR type, simple and inexpensive design, with high accuracy and high reliability. It has already been proposed by the applicant company in its French patent application FR0853200 (not published today) a detection device comprising, as illustrated in FIG. 3, a probe 105, for example a magnet (s). ) permanent (s), and means 110 which comprise an electric motor 120, a gearbox 160 and a shaft 150 and which, thanks to a system of the screw and nut type, to move the probe inside the tube 115 with a given servo, for example at constant speed. Depending on the thickness of the ferromagnetic deposits (nickel, magnetite, or the like) on or near the wall of the tube 115, the motor supply current varies. The analysis of the variation of this current thus makes it possible to detect the existence of fouling or clogging in the tube.

As is readily understood, such a solution, if it makes it possible to detect the presence and to estimate the volume of the deposits around the tube and in the tube / spacer plate connection, does not make it possible to detect which are the obstructed foliated passages and the depth where deposits are located at a spacer plate.

The new solution presented here makes it possible to overcome these disadvantages. In particular, there is provided a method for detecting fouling or clogging deposits comprising at least one ferromagnetic material, such as nickel, magnetite or the like, on or near the outer wall of a tube, characterized in that it comprises at least the following stages of: positioning and locking in altitude of a magnetised source inside the tube,

- rotation of the source on itself by driving by means of an electric motor and measuring the intensity of the current of said electric motor during this rotation drive, - analysis of the curve obtained to detect and if necessary evaluate the clogging at said spacer.

In this way, it is possible to have information on the distribution of deposits around the tube and thus to detect which are the foliated passages obstructed. Advantageously, after rotation of the source, it is moved incrementally aloft inside the tube and, after blocking, the preceding steps are repeated.

Thus, one traverses the tube portions, including the spacer plates, over a full depth. The invention also proposes a device that implements such a method. DRAWINGS

Other advantages and features will emerge more clearly 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 a non-magnetic tube conforming to the invention, from the attached drawings in which:

FIG. 1, already discussed, is a torn perspective view of a steam generator of PWR power plants;

FIG. 2, already discussed, is a perspective view of a detail of the tubes passing through the quadrifollages of the spacer plates, said quadrifollings comprising so-called clogging deposits;

- Figure 3, already discussed, is a schematic representation, in longitudinal section, of the detection device according to the invention introduced into a tube with a fouling deposit; FIG. 4 is a schematic perspective representation illustrating a detection device according to a possible embodiment of the invention; Fig. 5 is a block diagram illustrating various steps for a possible embodiment for the invention; FIGS. 6a and 6b respectively illustrate different possible positions of the permanent magnet with respect to the foliated passage tube, as well as the acquisition curve obtained by moving said permanent magnet with respect to the various unobstructed foliated passages, FIG. as for it, three successive positions of the rotating magnetic probe with respect to the folate passage of the tube represented in FIG. 6a;

FIGS. 7a to 7c correspond to FIGS. 6a to 6c in the case this time where four foliated passages are obstructed;

FIGS. 8a and 8b correspond to FIGS. 6a and 6b in the case where three foliated passages are obstructed;

FIGS. 9a and 9b correspond to FIGS. 6a and 6b in the case where two foliated passages are obstructed; - Figures 10a and 10b correspond to Figures 6a and 6b in the case where a folate passage is obstructed;

FIG. 11 illustrates the control cycle of a device of the type of that illustrated in FIG. 4; FIG. 12 illustrates an example of acquisition curves obtained with such a device.

DETAILED DESCRIPTION

Referring to FIG. 4, there is shown a detection device 200 which comprises, in a tube 215, a magnetized source probe 205 which comprises, for example, one or more permanent magnets, as well as means 210 for the rotational drive of said source 205 in said tube 215.

In the example described, the source 205 comprises a single permanent magnet 206 supported by a plate 207 of soft iron itself mounted on a support 208 made of stainless steel. The magnetic plane PM of the permanent magnet 206 has also been shown in the figure. It is radial with respect to the cylinder constituted by the tube 215.

Said rotation drive means 210 consist in particular of an electric geared motor 211. The electric motor of this geared motor 211 is connected to a device 212 for measuring the supply current of said motor, for example an ammeter, itself connected to a computer 213 of PC type. An algorithm in the form of software recorded on a physical medium, such as the hard disk and / or the memory of the computer 213, stores and analyzes the curves of variations of intensity or power of the power supply. electric motor to determine the obstructed foliated passages at the spacers, as well as the depths (altitudes) where the deposits are.

A propulsion sheath 300 or a geared motor type system and screw / nut also ensures the positioning of the probe at a given altitude therein. A locking system 301 makes it possible, for example by clamping, to maintain the probe at this altitude while the gearmotor 211 rotates it in the tube 215.

Such a structure is used in the manner illustrated in FIG. 5. The probe is initially positioned at altitude, at the height of the spacer plate 265 that is to be tested (step I).

The position of the probe at altitude in the tube is then blocked by means 301 (step II). Once thus positioned: the probe 200 is rotated on itself by the geared motor 211, with a given servocontrol, for example at a constant speed; and during this rotation, the consumption current of the electric motor of the gearmotor 211 (step III) is acquired.

Once the servocontrol current acquired on one revolution or more, the probe is unlocked and incrementally displaced by means of the propulsion sheath 300 or any other equivalent means (step IV). Steps II to IV are then repeated on the one hand as a function of the number of increments necessary to cover the width of the spacer plate and on the other hand according to the desired accuracy thereon.

After acquiring all the analysis plans corresponding to these different incremental steps, the computer 213 analyzes the various current or power consumption curves (step V).

For example, the current or power consumption compared with the input signal is compared in the case of a spacer plate free from clogging. The comparison can also be made on other calibrated reference signals representative of dimensional data (standard tubes).

The behavior of the rotating magnetic probe in the case where the foliated passages PF at the spacer 265 are not obstructed is illustrated in Figures 6a to 6c. When the probe 205 passes from point A to point B, it is attracted by the material present at point B. This attraction is maximum in the middle of the centering sector. Beyond this point, the attractive forces on the probe decrease (distance from the material) and become minimal when the probe 205 arrives at the point C (center of the folate passage).

In the same way, the probe 205 will be in minimal attraction at the points C, E, G, and in maximum attraction at the points, D, F, H.

In the case now that the four foliated passages are obstructed (FIGS. 7a to 7c), the attraction remains maximal in the middle of the centering sectors (point B for example), but is less important than in the previous case of a folate passage. unobstructed due to the presence of a deposit in it. Past this midpoint, the forces of attraction decrease and become minimal when the probe reaches point C, E or G.

In the case of an obstructed FP foliated passage, the attraction forces are lower than in the case of an unobstructed foliated passage. The attraction forces depend on the gap between the permanent magnet and the deposits. When the foliated passages PF are not obstructed, the attractive forces are important at the centering sectors of the tube. On the other hand, when the passages are obstructed, there are fewer variations in the gap and therefore less variations in the attraction forces. The power variation supplied by the motor is correlated with the volume of the deposits (see double arrow DE in FIG.

In the same way, in the case of acquisition curves with three obstructed foliated passages, two or only one, the shape of the signals and the corresponding amplitudes before or after the folate passages make it possible to detect the presence of clogging in the foliated passages ( Figures 8a, 8b, 9a, 9b, 10a, 10b).

Figure 11 illustrates the control cycle of the motions given to the permanent magnet 206. Said magnet 206 is first positioned at a certain height relative to the spacer.

Then, he is rotated on himself on a lap or more

(rotation R). Once the current or power intensity signal has been acquired, the longitudinal displacement of the probe 205 in the tube 215 (increment I) is incremented and then rotated again R over one complete revolution.

As illustrated in FIG. 11, these operations are repeated to scan the entire height of the spacer 265. Thus, a succession of curves is retrieved, which can for example be the subject of a 3D representation.

FIG. 12 is a 3D representation on which the curves obtained for four analysis planes PA-A, PA-B, PA-C, PA-D (equidistant from 3 mm) were carried. A fifth curve has been shown which corresponds to a reference curve.

For example, it can be seen from this FIG. 12 that the acquisition made in the last analysis plane (plane PA-D) has the same shape as the reference curve: the clogging stops between the analysis plans PA-C and PA-D.

In the case illustrated, the sealing depth is approximately 7.5 mm. The shape of the curve in the plane of the PA-C analysis shows amplitudes lower than the level of the peaks: the thickness at the level of the deposits is greater at this level. The algorithm implemented by the computer 213 implements the comparison with the reference curve and analyzes the amplitudes of the peaks to deduce the distribution of the deposits and, where appropriate, their thickness.

By way of example, the magnetic probe can admit a rotation of 450 degrees and incremental steps of 0.5 to 1 mm.

As will be understood, such a solution allows a greater accuracy in the detection of clogging and a greater accuracy of the depths where the deposits are. It will be noted that the analysis of the clogging of the spacer plates of a steam generator tube can be done advantageously by using, in a first step, an axial sounding with a structure of the type described in application FR0853200 (structure of FIG. moving a magnetic 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 the thickness and / or the volume of said deposit as a function of the variations in the intensity of the current measured in the electric motor), followed in a second step by a rotary sounding of the type just described.

Claims

1 - Method for detecting clogging or clogging deposits comprising at least one ferromagnetic material, such as nickel, magnetite or the like, on or near the outer wall of a tube, characterized in that comprises at least the following steps of:

positioning and locking in altitude of a magnetised source inside the tube, rotation of the source on itself by driving by means of an electric motor and measurement of the intensity of the current of said electric motor during this rotational drive,

- Analysis of the curve obtained to detect and if necessary evaluate the clogging. 2 - Process according to claim 1, characterized in that after rotation of the source, it is moved incrementally aloft inside the tube and in that, after locking, the preceding steps are repeated.

3 - Process according to one of the preceding claims, characterized in that the magnetized source consists of at least one permanent magnet.

4 - Process according to any one of claims 1 or 3, characterized in that the rotation of the magnetized source in the tube is a rotation at a constant speed. 5 - Process according to any one of claims 1 to 4, characterized in that the analysis step comprises a step of comparing the variation of the intensity or the power of the current measured in the engine with a model of reference and / or a calibrated model. 6 - Process according to any one of claims 1 to 5, characterized in that it implements a prior axial detection which comprises at least the following steps of: - displacement of 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

determination of the position and / or the thickness and / or volume of said deposit as a function of the variations of the intensity of the current measured in the electric motor.

7 - Apparatus for detecting clogging or clogging deposits comprising at least one ferromagnetic material, such as nickel, magnetite or the like, on or near the outer wall of a tube, characterized in that has:

at least one magnetized source,

means capable of positioning and blocking at altitude said magnetised source inside the tube,

means which rotate said magnetised source inside said tube and which comprise an electric motor,

means for measuring the intensity or the power of the current of said electric motor during driving in rotation of the source, and

means for analyzing variations in the intensity of the current measured in the electric motor.

8 - Device according to claim 7, characterized in that it comprises means for incrementally moving said probe inside the tube.

9 - Device according to one of claims 7 or 8, characterized in that the magnetic source consists of at least one permanent magnet.

10 - Device according to any one of claims 7 to 9, characterized in that the drive means rotate the magnetized source in the tube at a constant speed rotation. 11 - Application of the method according to any one of claims 1 to 6 for the detection of deposits in the quadrifolliages of the spacers of a steam generator of a pressurized PWR nuclear reactor.