Patent Number: 046735461
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, FIG. 1 is a schematic view of a typical loop seal 10. At one pipe, the loop seal pipe interfaces with the pressurizer 12 at the loop seal nozzle 14. For approximately the first two feet (as measured along the centerline) of the loop seal piping, a constant supply of steam is present within the piping during normal operation. This regime ends at a steam/water interface 16. Proceeding from this interface is a straight section 18, a curved section 20, and another straight section 22 ending at an opposite end in a loop seal pipe/safety valve interface 24. FIG. 2 depicts three loop seal temperature profiles calculated for an actual loop seal system. The lowest curve, denoted by circles plotted on the curve, represents a completely uninsulated loop seal pipe exposed directly to ambient temperature. The intermediate curve, denoted by triangles plotted on the curve, represents a loop seal insulated in a conventional manner with standard reflective-type insulation. The highest curve denoted by squares plotted on the curve, represents a loop seal enclosed with reflective type insulation according to the present invention. It is readily seen that the present invention provides an elevated temperature at the critical loop seal pipe/safety valve interface 24. The temperature at interface 24 is about 300.degree. F., considerably higher than 120.degree. F. achieved by the alternative means described above. For all three curves, no temperature decay should occur for about the first two feet of piping, as measured along the loop seal pipe centerline, because of the constant presence of steam in this portion of loop seal pipe 10. The temperature profile for an uninsulated loop seal pipe (lower curve) or a loop seal insulated with a conventional piping insulation configuration quickly degrades with distance from the pressurizer. A principal reason for the superior results obtained by the practice of the present invention is the capture of radiative and convective heat from the pressurizer surface by the loop seal pipe 10. The remaining figures illustrate a typical loop seal insulation assembly in accordance with the present invention. It was noted earlier that typically three loop seals are present at different azimuths near the top head of a pressurizer. These three loop seals are clustered together rather than spaced equidistant around the top of the pressurizer head. While FIGS. 3 through 10 disclose an illustrative embodiment of a first insulation assembly, similar assemblies will be used for the second and third loop seals of a pressurizer, with suitable modifications made to accomodate existing interferences, existing top head insulation, and the like. One of the features of this invention is its flexibility in allowing small adjustments in the placement of individual insulation panels in order to achieve the desired elevated temperature at the safety valve/flange interface. FIG. 3 shows a plan view of a typical loop seal insulation housing in accordance with the invention. Reflective type insulation panels 26 are placed over existing top head insulation 28 shown in phantom. A portion of existing top head insulation 28 is removed to correspond with the inner case 30 of loop seal insulation panels 26, thereby exposing a portion of the outer surface of the pressurizer to the loop seal piping. Angle 32 is attached by screws 34 or other suitable attachment means to the existing top head insulation 28. Likewise, angle 36 is attached by screws 34 or other suitable attachment means to the top flat portion of existing top head insulation 28. Self-locking buckles 38 hold the reflective type insulation panels 26 in place, and allow selective removal or replacement of individual panels 26 as well understood in the art. Reinforcement plates 40 are popriveted or otherwise attached to the outer case of existing top head insulation 28. The insulation assembly of the present invention is designed to physically and thermally accomodate and adjust for interferences such as hangers, gratings 42 (FIG. 4), grating supports 44 (FIG. 9) and other components already installed in the vicinity of the loop seal piping and top head of the pressurizer. Individual insulation panels 26A and 26B straddle a portion of the loop seal nearest the pressurizer and are buckled to angle 32. Insulation panels 26C and 26D are buckled to each other at their juncture, and to panels 26B and 26A respectively, and encompass the intermediate portion of loop seal pipe 10. Vertically below panels 26C and 26D are located insulation panels 26M and 26N, encompassing the curved portion 20 of loop seal pipe 10. Angles 46 are attached, preferably spot-welded, to panels 26G and 26H, and popriveted or otherwise suitably attached to panels 26E and 26F, as best seen in FIG. 6. FIG. 10 illustrates angles 48 and 50 buckled to insulation panels 26B and 26A respectively, and screwed or otherwise attached to existing top head insulation. It should be noted that the preferred embodiment described above is illustrative only, and a similar arrangement may be utilized, with appropriate changes to accomodate the specific interferences and existing equipment found at a particular plant site.