Patent Application
20140130566
1. Field of the Invention
The present invention relates to tube expanders, and, more particularly, the present invention relates to hydraulic tube expanders with expansions performed from within a tube by a computer controlled process.
2. Description of the Related Art
While the present invention may be used in a variety of industries, the environment of a pressurized water reactor (PWR) nuclear power plant will be discussed herein for illustrative purposes. There are two major systems utilized in a PWR to convert the heat generated in the fuel into electrical power. In the primary system, primary coolant is circulated past the fuel rods where it absorbs the emitted heat. The heated fluid, which is in liquid form due to the elevated pressure of the primary loop, flows to the steam generators where heat is transferred to the secondary system. After leaving the steam generators, the primary coolant is pumped back to the core to complete the primary loop. In the secondary loop, heat is transferred to the secondary coolant, or, feedwater, from the primary side in the steam generators, producing steam. The steam is used to rotate a turbine, generating electricity. The secondary coolant leaves the turbine, passes through a condenser to remove residual heat, and the liquid feedwater is pumped back to the steam generators.
Inside of the steam generator, the hot reactor coolant flows inside of the many tubes and the feedwater flows around the outside of the tubes. There are two forms of steam generators: once-through steam generators, in which the tubes are straight, and U-bend steam generators, which are more common and in which the tubes contain a U-shaped bend.
In general, heat exchangers, and steam generators in the nuclear industry in particular, are susceptible to vibration-induced wear between the tubing and internal heat exchanger tube supports. This vibration is due to flow-induced forces acting on the tubing during normal operation, and can occur anywhere along the tube length, including the U-bend region of the tubes where flow is more predominantly cross-flow rather than axial. Typical steam generators include supports, called anti-vibration bars (AVBs), that are disposed between adjacent columns of the U-shaped tubes to prevent vibration and other movement of the tubes. However, unless the tubes are in physical contact with the AVBs, the AVBs will not prevent all movement of the tubes. Although precision machining and installation is employed, a small gap can exist between the AVBs and the U-bend portion of the tubes. Moreover, AVBs typically are not designed with specific features to prevent instability in the in-plane direction (that is, within the plane defined by the U-bend tube). Any spacing between the tubes and the AVBs can prevent the AVBs from providing adequate resistance to in-plane tube movement.
An apparatus and a process for alleviating spacing between the AVBs and the U-tubes are herein presented. The inventive hydraulic expander is configured for use in a tube containing a U-bend region, such as a U-bend tube of a steam generator in a pressurized water nuclear reactor power system. The tool includes a sheath for transmitting hydraulic fluid therethrough. The sheath is flexible, allowing it to bend and pass through the U-bend tubes. The sheath may include a number of layers, with an outer protective tube overlying an inner tube through which the hydraulic fluid is transmitted. A first end of the sheath is in fluid communication with a supply of pressurized hydraulic fluid, such as water.
The tool further includes an inflatable bladder that is fluidly coupled to a second end of the sheath. The bladder and metal end caps have a length that allows it to pass through the bend region of the tubes. The expansion bladder length, which is measured along a longitudinal axis of the bladder, may be approximately 0.5 in. to 1 in. The sheath transmits hydraulic fluid to the bladder. The bladder is firmed of an elastic material such as urethane and is adapted for radial expansion when hydraulically pressurized to exert outward force on the inner surface of the tube. In this manner, the expansion tool can exert a force to plastically deform the tube outward such that it is moved into contact with the AVBs. The friction imparted by this contact can prevent flow-induced vibration or other movement of the steam generator tubes.
The tool may also include an eddy current probe, such as an eddy current coil, that is connected to the sheath. Through use of the eddy current probe in known manner, the position of the AVB can be determined and the bladder aligned with the AVB to ensure the correct portion of the tube is expanded.
The tool may also include one or more spacers that are connected to the sheath. The spacers are configured to align the hydraulic expander within the tube to allow it to be inserted around the curved U-bend portion of the tube.
The present invention is described with reference to the accompanying drawings, which illustrate exemplary embodiments and in which like reference characters reference like elements. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.
The bladder 11 is fluidly coupled to the sheath 10. When hydraulically charged with a predetermined amount of fluid pressure, the bladder 11 expands to exert a radially outward force onto the inner diameter of the tube in which it has been inserted. Preferably, the bladder 11 is formed of a urethane material. The bladder 11 and metal end caps 12, 15 are shortened such that it can fit within and be transmitted through the U-bend portions of the heat exchanger tubes. A preferred length of the bladder 11 is approximately 0.5 in. to 1 in. The reduced length and diameter allow access to the entire U-bend radius while allowing the proper expansion length to be made to improve the heat exchanger vibration conditions. Therefore an expansion can be placed at any location along the U-bend where tube vibration is expected. The assembly is capable of creating a range of diametric expansions, from 0.003 in. or smaller up to greater than 0.060 in.
The repair method uses a single expansion bladder 11 that is centered within the AVE (or, as an alternative, it can be positioned on both sides of the AVB to pin the AVB in position). Due to the length of this expander 11 and the height of the AVB, there is some overhang of the bladder 11 on either side of the AVB. This allows for better positioning of the expander within the U-tube since the expander can be mispositioned some amount without affecting the process.
The hydraulic expansion process is managed by a computer-controlled system. A preferred control system is described U.S. Pat. No. 5,606,792, the disclosure of which is incorporated herein by reference in its entirety. This system consists of computer controls, a hydraulic expansion box to provide the high pressure water, high pressure tubing, and the expander.
The process hydraulically expands ¾ in.×0.043 in. wall alloy 690 steam generator tubes in the U-bend region of the steam generators (although this process could also be used to expand other size tubes, such as 9/16 in. and ⅞ in. outside diameter tubing, or tubes in other types of heat exchangers which have U-bend tube vibration issues). This process is used to decrease the gap and increase the friction between the tubes and the AVBs in the U-bend portion of the steam generator, preventing in-plane motion of the U-tubes during plant operation. Laboratory qualification testing is performed to determine the expansion parameters that are input into the control computer to assure accurate and consistent tube-to-AVB tube expansions. This consistency is required in order to achieve the proper fit between the tube-and-AVB to improve the steam generator operation.
The expansion process is controlled by pressurizing the bladder 11. As the water is being injected, the displacement of the piston and the pressure within the hydraulic expansion box are monitored. The point at which the tube yields is determined by the computer control system by noting the change in slope of the pressure vs. piston displacement curve. Past this point, the piston continues to be displaced until an additional amount of water is added to the system (this preset volume of water is determined during testing). When the preset volume of water is reached, the control system automatically shuts off the pressurization process and depressurizes.
A hydraulic system calibration is performed after the equipment is setup and the expander is placed on the expansion sheath. The purpose of the system calibration is to eliminate the elasticity of the system (elastic deformation of the high pressure tubing and the compressibility of water) from the expansion process.
After the system calibration is complete, the expander 11 is ready for use in the heat exchanger. The tool 1 is inserted into the tube such that the bladder 11 and eddy current coil 14, if used, are positioned beyond the AVB location that is being expanded. The expansion sheath is withdrawn from the tube until the location of the center of the AVB is determined using the eddy current coil 14 in known manner. As an option, the expansion sheath is inserted into the tube to a known depth as indicated by graduated marks on the sheath or an appropriately positioned hardstop clamped on the sheath. The expansion sheath 10 is then withdrawn from the tube an additional predetermined amount such that the center of the bladder 11 is aligned with the center of the AVB that is being expanded. The expansion process then commences.
There are preset safeguards built into the control system to eliminate the possibility of damage to the tube or expansion system. These include a maximum pressure limit for the system and a maximum allowed piston travel. The system automatically shuts down and depressurizes if either of these limits are reached.
This equipment and process eliminates the need to work on top of the tube bundle, since all work is performed from inside the tube. This beneficially reduces radiological exposure to workers and facilitates performance of the work because work from the outside of the tubes may be difficult from an access standpoint.
An expansion parameter is employed during use of the inventive system to achieve an expected expansion size. This parameter represents a volume of water that will be added to the system after the tube yields. Parameter values are correlated with the amount of tube expansion by performing a series of expansions in a mockup setting. This mockup includes of multiple columns of tubes with multiple tubes per column. Thin bars between various tube columns simulate the AVBs. The expander is placed in the tube at the location of the AVBs and the computer-controlled expansion process begins. The computer control automatically senses when the tube yields (based on the decrease in pressure vs. piston displacement slope as illustrated in
The mockup tube OD is measured at the AVB location (where the expansion was performed) and this expansion data, along with the volume of water that was input into the computer (the expansion parameter), is stored in a computer spreadsheet. Additional expansions are made, with varying e parameters and different tubing, to arrive at data curves.
While the preferred embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not of limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail (such as positioning the expander to a preset length dimension instead of using eddy current) can be made therein without departing from the spirit and scope of the invention. Thus the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
Furthermore, while certain advantages of the invention have been described herein, it is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.
This patent application claims the benefit of U.S. Provisional Patent Application No. 61/725,541 filed on Nov. 13, 2012, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61725541 | Nov 2012 | US |
