This invention relates to plug installation apparatus and more particularly to apparatus for installing plugs in heat exchanger tubes.
In tube-type heat exchangers, a first fluid flows through the tubes of the heat exchanger while a second fluid surrounds the outside of the tubes such that heat exchange occurs between the two fluids. Occasionally, one of the tubes can become defective such that a leak either is impending or occurs therein which allows the two fluids to mingle. When this occurs, it is sometimes necessary to plug the tube so that the fluid does not flow through the tube thereby preventing leakage from the tube.
In nuclear reactor power plants, the tube-type heat exchangers are commonly referred to as steam generators. When a defect occurs in the tubes of the nuclear steam generator that allows the fluid in the tubes to mingle with the fluid outside of the tubes, a more significant problem arises. Not only does this situation create an ineffective heat exchanger, but it also creates a radioactive contamination problem. Since the fluid flowing in the tubes of a nuclear steam generator is generally radioactive, it is important that it not be allowed to leak from the tubes and contaminate the fluid surrounding the tubes. Therefore, when a leak occurs in a nuclear steam generator heat exchange tube, the heat exchange tube is plugged so that the fluid is not permitted to flow through the tube. This prevents contamination of the fluid surrounding the tubes.
There are several kinds of plugs that may be used to plug the heat exchange tubes. One such device used to plug heat exchange tubes in nuclear steam generators is an explosive plugging device. With the explosive plugging devices, a metal plug is inserted in the heat exchange tube with an explosive contained within the plug. When the explosive is detonated, the plug is forced into close contact with the inside of the tube thus blocking flow through the tube. One problem associated with explosive plugging is that should it become necessary to replace the defective tube or a defective plug, the explosive plug must be drilled out which is a time-consuming procedure.
Another device used to plug heat exchange tubes is generally referred to as a mechanical plug. The mechanical plug comprises a cylindrical member closed at one end and having a tapered inner bore. An expander member is disposed in the cylindrical member such that when the expander member is drawn along the longitudinal axis of the cylindrical member, the cylindrical member is forced into close contact with the heat exchange tube due to the relative tapers of the inner surface of the cylindrical member and the expander member. In this type of device, no explosives are necessary to create the close contact between the plug and the heat exchange tube. Rather, the expansion of the plug is caused by the relative movement of the expander member in the plug. This gives the mechanical plug the characteristic of being able to be removed without being drilled out. In order to remove the mechanical plug, it is, thus, first desirable to relieve the internal pressure on the plug by moving the expander member to a position in the plug in which the tapered diameters of the plug and expander member are not in contact. Next, with the pressure on the plug relieved, the plug may then be pulled from the heat exchanger tube.
In order to quickly install a mechanical plug in the heat exchange tube, it is desirable to have a mechanism capable of both inserting the plug in the tube and of quickly moving the expander in the plug so as to lodge the plug in the tube. There are several mechanisms that can be used to accomplish this insertion of the plug in the tube. However, quick insertion of the plug in the tube is not the only criterion to be met in such a procedure. In addition to quickly inserting the plug in the tube, it is also necessary to be able to positively verify that the plug has been properly positioned in the tube prior to expansion of the plug. Improper installation of the plug in the tube can result in an improper seal between the plug and the tube or in damage to the tube. Also, it is important to be able to verify that the plug has been expanded to the proper limit in order to verify that the plug has effectively sealed the tube.
Therefore, what is needed is an improved plug installation apparatus that is capable of quickly installing a plug in a tube and capable of verifying that the plug has been properly installed.