Patent Number: 043953808
Section: summary

The invention relates to the remote examination of pipes having communicating tubular extensions to determine whether or not such extensions are obstructed and relates particularly to the testing, at various times and from a remote position, of the flow through nozzles extending from headers in a cooling water spray system. In nuclear power plants, there is a containment building overlying the reactor. The building is circular and dome-like, and within the dome, there are a plurality of ring-shaped headers from which a plurality of nozzles extend. In the event of an accident, e.g. loss of reactor coolant circulation, a flow of water is automatically supplied through risers to the normally dry headers to spray from the nozzles to cool the interior of the building. Regulatory agencies usually require that the cooling spray headers and nozzles be tested every three years to demonstrate that they are not obstructed to an extent that the spray system is inadequate. The interior of the dome of the building may be as high as 140 feet above the floor of the building and the headers are near the dome. Although the building may also include a polar crane which is rotatable and which has a catwalk above the floor, the headers may be fifty feet or more above such catwalk. Therefore, the headers and nozzles are relatively inaccessible, and it is relatively time consuming and expensive to erect structures, such as scaffolding, to permit close examination of the nozzles. In addition, the headers and nozzles are usually made of stainless steel and great care must be taken to prevent exposing them to corrosive materials, such as small parts per million of halogens or compounds thereof, and therefore testing techniques as would involve such exposure must be avoided. Normally, the testing of the headers and nozzles is conducted while the reactor is shut down, and because the reactor shutdown time should be as short as possible, and because other tests may also be necessary during such shutdown time, it is necessary to conduct the header and nozzle testing within a short period of time. Usually, the spray system involves a large number, e.g. over 250, nozzles, and therefore, a system of testing is required which will permit the testing of each individual nozzle relatively rapidly. In those cases where the headers are only 15-30 feet from a platform or catwalk, it has been possible to supply air under pressure to the headers and check the air flow from each nozzle with a streamer on a long pole. However, even this technique can require three days of two shifts per day to complete the necessary testing. In other cases, where the headers are farther away from a platform or support, it had been proposed to test the outflow of air from the nozzles by means of a streamer supported by a tethered, helium-filled balloon, but this is time consuming and difficult to accomplish. Consideration has been given to supplying smoke or visible steam to the headers, and to then visually observe the issuance thereof from the nozzles. This is also impractical not only because the smoke or steam issuing from the nozzles obscures them making it difficult to ascertain that each nozzle is properly functioning, but also because such may include undesirable corrosive materials. I have discovered from tests that when heated air is forced through such headers and nozzles there is an unexpected effect, namely, a blocked nozzle does not reach a temperature as high as a nozzle through which the air flows freely. It is possible, therefore, to distinguish a blocked nozzle from an open nozzle on the basis of temperature. The explanation for this effect is not entirely clear because it would be expected that the temperature along the length of a nozzle would be substantially the same, and would be substantially the same as the temperature of the header to which it is attached due to the conductivity of the metal. However, it has been found that the temperature of an open nozzle, along its length, is many degrees higher than the temperature along the length of a blocked nozzle even though the temperature of both an open nozzle and a blocked nozzle a short distance from the header to which it is attached is less than the temperature of the header when heated air under pressure is supplied to the header. While there are various ways to measure remotely the temperatures of the nozzles, e.g. thermocouples, it is undesirable to make permanent installations requiring wires, etc., for remote observation, and it would be expensive and time-consuming to install such in already existing installations. I have further discovered that, considering both the distances involved and the nozzle temperature differences involved, infrared scanning techniques and apparatus, as developed today, are adequate to permit distinguishing between the temperature of a blocked nozzle and the temperature of an open nozzle with such apparatus located on a platform or catwalk normally located below the headers, at distances of up to 100 feet or more therefrom. Thus, by successively scanning the nozzles from a remote point while heated air is supplied to the headers under pressure, the location of any blocked nozzle or nozzles can be determined. One object of the invention is to provide a method of remote testing of the fluid flow through nozzles, which does not require any physical contact or interconnections with the nozzles. Another object of the invention is to provide a method of remote testing of the fluid flow through nozzles, which can be performed easily and in a relatively short time even though many nozzles are involved. In the preferred embodiment of the invention, clean air under pressure, e.g. at 100 lbs. p.s.i., and at a temperature substantially above ambient temperature, e.g. at a temperature of at least 100.degree. F., is supplied to a header having nozzles secured thereto, and the header and each nozzle is scanned with infrared scanning apparatus to provide thermograms thereof which are observed to determine whether or not the thermogram of each nozzle conforms to the thermogram of an open or a blocked nozzle. If desired a plurality of nozzles may be scanned simultaneously so that a plurality thereof appear in the same thermogram.