Tube traveler

#This invention relates to disassembling tube type heat exchangers and more particularly to an extractor for pulling individual tubes from a tube sheet in heat exchangers, boilers, and the like.

#Many heat exchangers are of an indirect type which employ tubes for carrying a heat transfer fluid. A large number of the tubes are mounted to extend in a parallel grid between two supporting tube sheets in such heat exchangers. The tubes are pressed into or expanded into engagement with openings through the tube sheet for forming a fluid tight seal. A heat transfer fluid, such as water, is circulated through the parallel tubes between the two tube sheets while a different temperature fluid, such as combustion gases or heated water is circulated past the exterior of the tubes between the two tube sheets for achieving indirect heat transfer between the two fluids. It is sometimes necessary to remove tubes from the tube sheets in which they are mounted. This may be necessary for many reasons, such as leaks in the tubes or excessive scale accumulations within the tubes.

#The tubes commonly are held in the tube sheets by expanding the ends into engagement with the internal walls of openings through the tube sheets and are securely held therein by hoop stresses created by the expanding process. Various methods are used for relieving these hoop stresses to remove tubes from the tube sheets. One method used for removing the hoop stresses holding the tubes within the tube sheets is by cutting axial slots within the expanded end portion of the tube passing through the tube sheet, as disclosed in U.S. Pat. No. 3,628,246 which issued Dec. 21, 1971. Another method used for relieving tube stresses involves engaging the interior walls of the tube with expandable jaws on a mandrel and, subsequently, retracting a hydraulic cylinder connected to the mandrel to pull the tube end from the tube sheet, as disclosed in U.S. Pat. No. 3,835,520 which issued Sept. 17, 1974. After the hoop stresses are removed, it is necessary to pull the entire length of the tube through the tube sheet. This may be a difficult and time consuming process since tubes in some indirect heat exchangers, such as those used in nuclear reactors, may be on the order of 30 to 70 feet long and of considerable weight.

#FIG. 1 is a perspective view showing a tube extractor in accordance with the present invention, pulling a tube from a tube sheet in a heat exchanger;

#FIG. 2 is a vertical cross-sectional view of a tube extractor taken along line 2--2 of FIG. 1;

#FIG. 3 is a horizontal cross-sectional view of a tube extractor taken along line 3--3 of FIG. 1; and

#Turning now to the drawings and particularly to FIG. 1, a tube extractor 10 constructed in accordance with the present invention is shown in the process of extracting a tube 11 from a tube sheet 12 in an indirect heat exchanger 13. The tube 11 is one of a plurality of tubes 14 which extends between the tube sheet 12 at one end of the heat exchanger 13 and a similar tube sheet (not shown) at an opposite end of the heat exchanger 13. Normally, each of the tubes 14 will have an end 15 which has been expanded to engage the walls of an opening 16 through the tube sheet 12. The openings 16 are arranged in the tube sheet 12 in a grid pattern for maintaining a preselected spacing between the tubes 14 during operation of the heat exchanger 13. When the heat exchanger 13 was originally assembled, the tubes 14 were initially inserted into the tube sheet openings 16 and the tube ends 15 were expanded to sealingly engage the walls of the openings 16. Sufficient hoop stresses remain within the tube ends 15 to prevent fluid leakage between the tube ends 15 and the tube sheet 12.

#Due to various reasons, it is sometimes necessary to replace one or more of the tubes 14 in a heat exchanger 13. Tube replacement may be necessary, for example, because of excessive scale accumulation within the tubes 14 or cracking of any of the tubes 14. To replace the tubes 14 in the heat exchanger 13, it is first necessary to relieve the hoop stresses in the tube ends 15. This is accomplished by pulling the tube ends 15 from the tube sheet 12 by any conventional manner such as that disclosed in the above-mentioned U.S. Pat. No. 3,835,520. Several of the tubes 14 are shown in FIG. 1 as having their ends 15 pulled through the tube sheet 12. After the ends 15 are pulled through the tube sheet 12, the extractor 10 is used for pulling or walking the length of the tubes 14 from the tube sheet 12. The tube extractor 10 effectively pulls the tubes 14 from the tube sheet 12 even though the tubes may be of considerable length, such as up to 70 or more feet long in large heat exchangers, and of considerable weight.

#The tube extractor 10 generally consists of a pneumatic motor 17 attached to a housing formed from an upper housing plate 18, an upper gear transmission housing 19, an intermediate housing plate 20, two opposed lower housing sides 21 and a lower housing plate 22. The housing components 18-22 are held together by any conventional manner such as by four bolts 23. The motor 17 shown in the drawings is of a pneumatic type, although an electric motor or other conventional type of motor may also be used in the tube extractor 10. It is desirable that the motor 17 be of a variable speed type to permit control over the speed at which the tube 11 is walked or advanced through the tube extractor 10. The motor 17 receives power from an air compressor (not shown) or other suitable source of compressed air connected to an air line 24. The air line 24 is connected through a manually controlled throttle valve 25 to the motor 17 for controlling the speed of the motor 17. The throttle valve 25 also acts as a deadman's release valve which automatically stops the tube extractor 10 in the event that an operator becomes incapacitated. During operation of the tube extractor 10, an operator manually positions the throttle valve 25 to pull the tube 11 through the tube sheet 12 at a controlled speed up to a predetermined maximum speed determined by the maximum speed of the motor 17 and the transmission gear ratio within the tube extractor 10. In an exemplary tube extractor 10, a tube 11 was advanced up to a maximum speed of 168 feet per minute and the tube extractor 10 exerted a pull force of 2650 pounds on the tube 11 without slippage.