This invention relates to abrasive hones and particularly to segmented abrasive hones having a lubricating mechanism.
A typical nuclear steam generator comprises a vertically oriented shell, a plurality of U-shaped tubes disposed in the shell so as to form a tube bundle, a tube sheet for supporting the tubes at the ends opposite the U-like curvature, and a dividing plate that cooperates with the tube sheet forming a primary fluid inlet plenum at one end of the tube bundle and a primary fluid outlet plenum at the other end of the tube bundle. The primary fluid having been heated by circulation through the nuclear reactor core enters the steam generator through the primary fluid inlet plenum. From the primary fluid inlet plenum, the primary fluid flows upwardly through first openings in the U-tubes near the tube sheet which supports the tubes, through the U-tube curvature downwardly through second openings in the U-tubes near the tube sheet, and into the primary fluid outlet plenum. At the same time, a secondary fluid known as feedwater, is circulated around the U-tubes in heat transfer relationship therewith, thereby transferring heat from the primary fluid in the tubes to the secondary fluid surrounding the tubes causing a portion of the secondary fluid to be converted to steam. Since the primary fluid contains radioactive particles and is isolated from the secondary fluid by the U-tube walls and the tube sheet, it is important that the U-tubes and the tube sheet be maintained defect-free so that no breaks will occur in the U-tubes or in the welds between the U-tubes and tube sheet, thus preventing contamination of the secondary fluid by the primary fluid.
Occasionally, one or more of the heat transfer tubes may become internally dented due to a variety of possible reasons. One such reason for the internal denting is thought to be corrosion on the outside of the tube which presses in on the tube and causes the internal flow area of the tube to become constricted. Not only does this denting phenomenon restrict the flow through the particular heat transfer tube, but it also may lead to a failure in the tube at the point of denting which may allow the primary fluid to leak into the secondary fluid thus contaminating the secondary fluid. Of course, contamination of the secondary fluid must be prevented; therefore, such a dented tube must be repaired or replaced before the denting results in a crack in the tube. When it has been determined that a particular tube in a steam generator must be removed, the tube is cut and removed from its attachment to the tube sheet. Since corrosion products have been deposited between the tube and the tube sheet wherein the tube was positioned, it is necessary to remove the corrosion products from the hole in the tube sheet so that a new tube may be placed therein. Not only is it necessary to remove corrosion products from the hole in the tube sheet, but it sometimes is also necessary to slightly enlarge the hole in the tube sheet so that a new tube may be disposed therein and welded to the tube sheet. There are many devices known in the art for honing holes in tubular members so that the tubular member may be removed of corrosion products or may be enlarged. However, none of these hones have proved to be successful in applications to nuclear apparatus, such as in the replacement of tubes in nuclear steam generators. Because of the highly radioactive environment present in a nuclear steam generator, it is extremely important that the hone be able to remove the corrosion in a short amount of time and without failing. In addition, the tube sheet of a nuclear steam generator may have holes therein in excess of 20 inches in length that must be honed in a relatively short amount of time. Because of the high temperatures generated and because of the amount of corrosion encountered, the hones available to date were not capable of honing the holes in a tube sheet of a nuclear steam generator in a short period of time and without failing.
In U.S. Pat. No. 3,871,139 issued Mar. 18, 1975 in the name of Steven A. Rands, there is described a multiple-compliant-bristle, self-centering, self-sizing rotary abrasive hone made of multiple outwardly extending, flexible, extremely compliant plastic bristles having enlarged abrasive globules completely firmly attached to the outer ends of the bristles in a non-flaking and non-chipping manner. According to the patent to Rands, the hone is suitable for insertion into a recess or hole in a workpiece which is to be honed by relative movement of the abrasive hone with respect thereto. While the patent to Rands does describe a particular rotary hone, it does not teach a segmented flexible hone wherein a lubricant is conducted through the support for the bristles.
Therefore, what is needed is a segmented flexible hone capable of self-lubrication and of honing large sections of tubular members in an environment wherein human access is limited.