Abstract:
The invention relates to an inspection probe for an internal wall of a duct, comprising at least one sensor mounted in a support adapted to be moved inside the duct while pressing said sensor flat against said internal wall. The support is formed by a shell which is molded onto the sensor and comprises a body provided with a window for positioning said sensor and means for attaching said sensor flat against the internal wall of the duct, said means being integrally molded with the body. 
     The invention has applications in the non-destructive testing of ducts in nuclear power plants.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a non-destructive inspection probe for an internal wall of a duct, more particularly an internal wall of a duct in a nuclear power plant. 
   The invention likewise relates to a set of probes comprising multiple inspection probes. 
   In many industrial installations it is necessary to periodically carry out a check on the internal walls of ducts to verify that they are intact and in the interests of their operational reliability and safety. Operators are therefore obliged to perform increasing numbers of checks, for example on areas linking together the various elements and, should the need arise, to perform repairs of any faults that may have been detected. 
   This is, for example, the case with the internal walls in respect of passages in vessel floors in nuclear power plants of the pressurised water type. 
   The reason for this is that these passages in the vessel floor feature one end, projecting beneath the convex floor, joined to a non-rigid measurement duct allowing the floor of the vessel to communicate with a control room located within the fabric of the reactor building. Each of the ducts and the corresponding passage in the vessel floor can be negotiated with the finger of a glove in which a measurement probe is moved. 
   In order to enhance the operational reliability of nuclear reactors it is necessary to check the condition of the vessel floor cross-pieces to make sure that these pieces are still intact after the reactor has been operating for some time, particularly in the area where these cross-pieces are welded to the floor of the vessel. 
   This is also the case with the tubes of the steam generators with which nuclear reactors are fitted, which need to be examined on a regular basis. 
   To carry out these checks it is known to use probes, notably Foucault current probes and ultrasonic probes, which are moved along the internal wall of the duct under test. 
   The probes that have hitherto been used, and in particular ultrasonic probes, comprise at least one sensor mounted in a substantially cylindrical metal jacket made, for example, of aluminium or stainless steel, which has means for pressing said probe flat against the internal wall of the duct. These pressing means are constituted by a metallic spring that is generally positioned beneath the sensor or by a brush arrangement with soft bristles, usually disposed radially in order, first and foremost, to centre the probe in the duct. 
   Another type of probe is currently used to check an internal wall of an annular space such as a cover cross-piece for a nuclear reactor vessel fitted with a heat sleeve constituted by a coaxial internal duct. 
   However, these types of probes do not allow uniform contact between the sensor and the internal wall to be obtained while the sensor is being displaced within the duct, on account of the distortions and irregularities in the surface of said internal wall after the installation has been operating for some years. 
   In fact, the effectiveness of the test depends upon the effectiveness of the contact between the sensor and the internal wall of the area of duct under test, so much so that these contact defects manifest themselves as distortions in the test signals supplied by the probe. 
   It is the object of the present invention to propose an inspection probe that avoids these drawbacks by providing reliable, uniform contact between the sensor and the internal wall and that makes it possible to prolong the probe&#39;s useful life, while at the same time reducing manufacturing costs. 
   BRIEF SUMMARY OF THE INVENTION 
   The object of the invention is therefore an inspection probe for the internal wall of a duct, comprising at least one sensor mounted in a support that is adapted to be moved along the duct while pressing said sensor against the internal wall, characterised in that the support is formed by a shell moulded onto said sensor and comprising, on the one hand, a body equipped with a window for positioning said sensor and, on the other hand, means for pressing said sensor flat against the internal wall of the duct, said means being integrally moulded with the body. 
   According to further features of the invention:
         the duct presents a circular cross-section and the body has a substantially circular cross-section that is slightly smaller than that of said duct;   the duct comprises an internal duct forming an annular space with said duct and the body has a substantially trapezoidal cross-section of a slightly lesser thickness then the width of said annular space;   the pressing means include at least one body portion that is resilient and juts out with respect to said body, designed to bear against the internal wall of the duct or against an inner wall of the annular space so as to exert a force in the direction of the window and press the sensor flat against said internal wall;   the pressing force which said resilient portion exerts on the sensor is between 2 and 25 newtons, preferably between 5 and 15 newtons;   said resilient portion extends over at least part of the length of the body of the shell;   said resilient portion extends the entire length of the body of the shell;   said resilient portion is located on the body, opposite the sensor&#39;s contact generator with the internal wall;   said resilient portion is located on the lateral edges of the body;   said resilient portion is formed by two non-rigid pressing wings;   the pressing wings are arranged 120° to either side of the sensor&#39;s contact generator with the internal wall;   the shell is made from at least one polymer, for example polyurethane;   the shell includes inserts, for example metal inserts;   the sensor is an ultrasonic sensor.       

   A further object of the invention is a set of inspection probes, characterised in that it comprises multiple inter-articulated probes of the type already mentioned. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     Further features and advantages of the invention will become apparent from the following description, which is given by way of example and refers to the accompanying drawings, wherein: 
       FIG. 1  shows a diagrammatic longitudinal section through an inspection probe according to the invention; 
       FIG. 2  shows a cross-section taken along line  2 — 2  in  FIG. 1 ; 
       FIG. 3  shows a cross-sectional view of a variant of the inspection probe according to the invention; 
       FIG. 4  shows a diagrammatic front view of a variant of an inspection probe according to the invention; 
       FIG. 5  shows a diagrammatic section taken along line  5 — 5  in FIG.  4 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The inspection probe according to the invention, which is represented schematically in the Figures, is for example intended for ultrasonic testing of an internal wall  2  of a duct  1 , for example internal walls of passages in the vessel floor in nuclear power plants of the pressurised water type. 
   The inspection probe, identified overall by reference number  10 , is designed for introduction into the duct  1  and, in the embodiment represented in the Figures, includes a transceiver-type ultrasonic sensor  11 . 
   According to one variant the probe  10  may have multiple sensors  11 . 
   The sensor  11  is mounted in a support which is formed by a shell  12  moulded onto said sensor and having, on the one hand, a body  13  and, on the other, means  14  for pressing said sensor  11  flat against the internal wall of the duct  1 . 
   According to a first embodiment depicted in  FIGS. 1  to  3 , the duct  1  presents a circular inner profile and the body  13  also presents a circular outer profile slightly smaller in section than the internal section of said duct  1 . The body  13  presents a window  13   a  for positioning the sensor  11  in such a way that the external face of said sensor  11  juts out very slightly from the outer face of the body  13  of the shell  12 . 
   In all cases the body  13  of the probe  10  presents an outer profile of complementary shape to the inner profile of the duct  1 , but slightly smaller in section than the internal section of said duct  1 . 
   As shown, especially in  FIGS. 2 and 3 , the pressing means  14  are integrally moulded with the body  13  and the shell  12  constituted by the body  13 , and the pressing means  14  form a part consisting of a single piece. 
   Generally speaking, the pressing means feature at least one resilient portion  14  of the body  13 , projecting with respect to said body, designed (as illustrated in the Figures) to rest against the internal wall  2  of the duct  1  so as to exert a force in the direction of the window  13   a  and press the sensor  11  flat against said internal wall  2 . 
   It is preferred if the pressing force which the resilient portion  14  exerts on the sensor  11  is between 2 and 25 newtons, preferably between 5 and 15 newtons, and said resilient portion  14  is located on the body  13 , in an arrangement diametrically opposite the contact generator for the sensor  11  with the internal wall  2 . 
   The resilient portion  14  may extend over at least part of the length of the body  13 , as depicted in  FIG. 1 , or it may extend the entire length of said body  13 , or else it may be constituted by multiple portions distributed the length of said body  13 . 
   According to one preferred form of embodiment depicted in  FIG. 2 , the resilient portion  14  is formed by two non-rigid wings,  14   a  and  14   b  respectively, which are integral with the body  13  and the free end of which bears against the internal wall  2  so as to each exert a pressing force the resultant of which is directed towards the window  13   a  of the body  13  so as to press the sensor  11  flat against the internal wall  2  of the duct  1 . The wings  14   a  and  14   b  are arranged on either side of the contact generator of the sensor  11  with respect to the internal wall  2 , preferably at an angle of 120°. 
   According to one variant represented in  FIG. 3 , the resilient portion  14  is constituted by at least one flange  15  which, when the shell  12  is introduced into the duct  1 , becomes compressed and exerts a force directed at the window  13   a  of the body  13  so as to press the sensor  13  flat against the internal wall  2  of said duct  1 . 
   The resilient portion  14  may take other forms and the chief condition to be fulfilled is that the difference between the internal section of the duct  1  and the external section of the body  13  must be decided so that the resilient portion  14  becomes compressed when the probe is introduced into the duct  1  and exerts a force on the sensor  11  that causes it to lie flat against the internal wall  2 . 
   The sensor  11  is connected to a data processing unit by wires  16  which lead to the outside of the shell  12  and which can serve as a cable for pulling the probe  10  along inside the duct  2 . 
     FIGS. 4 and 5  depict an alternative use of the probe in accordance with the invention, which is to test an internal wall  2  of an annular space. 
   As  FIG. 5  shows, the duct  1  features an internal duct  4  coaxial with said duct  1  and with the latter accommodating an annular space  5  delimited by the internal wall of the duct  1  and the external wall  6  of the duct  4 . 
   In this case the shell  12  comprises a body  23  having a substantially trapezoidal cross-section of a slightly lesser thickness than the width of the annular space  5 . The body  23  also presents a window  23   a  for positioning the sensor  11 , and in the exemplary embodiment depicted in  FIGS. 4 and 5  two windows  23   a  for positioning two sensors  11 . 
   The pressing means  14  are likewise integrally moulded with the body  23  and are formed by two non-rigid wings  24   a  and  24   b  located on the lateral edges of said body  23 . These wings  24   a  and  24   b  may extend over part or the full length of the body  23 . 
   To carry out the test on the internal wall  2  of the annular space  5 , the wings  24   a  and  24   b  bear on the wall  6  of said annular space  5 , i.e. on the external wall  6  of the internal duct  4 , so as to exert a pressing force directed at the wall  2  and press the sensors  11  flat against said wall  2 . 
   To carry out the test on the external wall  6  of the annular space  5 , the wings  24   a  and  24   b  bear on the wall  2  of said space  5 , i.e. on the internal wall  2  of the external duct  1 , so as to exert a pressing force directed at the wall  6  and press the sensors  11  flat against said wall  6 . 
   The shell  12  is made from a polymer, for example polyurethane, and it may include metallic inserts embedded in the polymer. According to one variant the shell  12  may be made from different, mutually compatible polymers. 
   The moulding techniques used to produce the shell  12  are of a conventional type, such as for example drop moulding, injection moulding or even dead moulding. 
   In the course of moving the probe  10  inside the duct  1  in order to inspect the internal wall  2 , the resilient portion  14  ensures uniform pressing of the sensor  11 , in spite of the distortions and irregularities in the surface of the internal wall  2 . 
   According to one variant, the body  13  or  23  of the shell  12  may feature one or more seats accommodated in said body, for the positioning of various components. 
   Moreover, the probe  10  may be operatively associated with other probes connected to one another in articulated fashion, for example by a cardan system or else by a “dolly axle” or “shock mount” type system, so as to constitute a set of probes that can be moved along the duct under test. 
   The design of the probe according to the invention makes possible lower manufacturing costs, simplifies the engineering principles involved when compared to the probes used up till now, and improves the reliability and service life of the inspection probe.