Patent Number: 046769463
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Insulating blanket 10 of this invention, as shown in FIGS. 1 and 2, includes a filler layer 11, a waterproof sheet 12 adjacent one surface of the filler layer, and a mesh casing 13 surrounding the composite of filler layer and waterproof sheet. Blanket 10 is shown by way of example only as being a thick substantially rectangular sheet, about 12.times.12 inches in size and about 2 inches in thickness. Blanket 10 may be fabricated in a variety of different sizes, shapes and thicknesses for wrapping around various shaped pipes and equipment and for maintaining a specified reduction in heat loss. Filler layer 11 consists of one or more bodies of thermal insulating fibers. Preferably, as shown in FIG. 2, filler layer 11 consists of two thick sheets 20, 21 of glass fiber wool or ceramic fiber wool, and these sheets 20, 21 are separated by a mesh septum 14. Both glass and ceramic fiber wool have a low thermal conductivity and are resistant to chemical attack. The density and insulating value of the filler layer is selected in accordance with the temperature of the system which is to be insulated. Septum 14 lies in substantially parallel relationship between sheets 20 and 21 and divides filler layer 11 substantially in half. Septum 14 is a flexible knitted mesh of metal wire and is designed to enhance the strength of the blanket and to cut sheets 20 and 21 into small pieces if torn by a high force liquid stream. Waterproof sheet 12 is disposed adjacent one surface of filler layer 11 and is cut to approximately the same size as filler layer 11. Waterproof sheet 12 prevents moisture from getting into filler layer 11 (which reduces the blanket's insulating characteristics) and also increases the strength of blanket 10. Waterproof sheet 12 is preferably made of silicone rubber, and more preferably of a stainless steel wire mesh completely embedded or encapsulated by silicone rubber --such as ERCO-SIL 36S sold by Eastern Refractories Company, Inc., Belmont, Mass. Waterproof sheet 12 is completely impervious to moisture and preferably is at least about 25 mils thick, more preferably at least about 45 mils thick. Waterproof sheet 12 is preferably made by calendering a thick paste of silicone rubber over each side of a fine wire mesh screen --to completely fill the apertures of the screen, form integral layers of silicone rubber on each side of the screen, and provide substantially planar opposing surfaces of sheet 12. The composite of filler layer 11 and waterproof sheet 12 is completely surrounded by or encased within mesh casing 13, with sheet 12 being positioned between the outer surface of the blanket and filler layer 11. Casing 13 is made of metal wire, such as stainless steel or Inconel. The presence of wire mesh casing 13 on the outer surface of the blanket is essential to improving the resistance of the blanket to damage by liquid jet streams. Casing 13 breaks up jet streams which may impinge on the outer surface of the blanket, and thus reduces the force of the streams hitting the underlying layers. In addition, the mesh casing serves to cut up the filler layer into small pieces which will not clog the sump screen if an excessive jet stream tears the waterproof sheet and filler layer. For purposes of strength, for retaining the filler layer within the casing, and for cutting up the filler layer, if torn, into small pieces which will not clog the sump screen, the mesh casing 13 preferably has of from about 40 to about 100 apertures per square inch, more preferably of from about 48 to about 76 apertures per square inch, and most preferably about 60 apertures per square inch (i.e., 60 density). The wire should have a diameter of from about 0.005 to about 0.015 inches, preferably of from about 0.006 to about 0.011 inches, and more preferably about 0.011 inches. Casing 13 forms a continuous envelope and means 15 are provided for securing the edges of the casing, such as metal clips or hog rings 15, which also pass through waterproof sheet 12. Also, preferably, septum 14 consists of the same wire mesh as casing 13 and the ends of septum 14 are secured by hog rings 15 on opposing sides of the blanket (see FIG. 2). Thus, septum 14 extends along the sides of the outer filler layer sheet 20 and between the outer and inner filler layer sheets 20, 21. Blanket 10 is intended to be wrapped around a pipe or like equipment with its outer surface (adjacent waterproof sheet 12) facing away from the pipe. Metal pins or lacing anchors 16, secured by locking washers 17, are disposed about the blanket to reinforce the same, preferably, about one every square foot (i.e., at 12 inch centers). Anchor 16 is an integral member consisting of, in spaced relation, a first hook 18, a spindle 19, and a second hook 20. First hook 18 is disposed adjacent the outer surface of the blanket to provide means for attaching the blankets to each other and to the pipes and equipment. Spindle 19 extends transversely through each of filler layer 11, waterproof sheet 12, casing 13, and septum 14. The end of spindle 19 adjacent the inner side of the blanket passes through locking washer 17 and is bent to form flat hook 20. Illustrative of the invention, a thermal insulating blanket approximately 24.times.24 inches in size and approximately two inches thick, was constructed having a filler layer of ERCO-MAT F glass fiber wool (sold by Eastern Refractories Company, Inc., Belmont, Mass.). Two one-inch sheets of the glass fiber wool were separated by a septum of Inconel knitted mesh, 60 density, 0.011 inch diameter wire. A waterproof sheet of ERCO-SIL 36S, also sold by Eastern Refractories Company, Inc., having a nominal thickness of about 45 mils, covered the outer surface of the filler layer. A casing of Inconel knitted mesh, 60 density, 0.011 inch diameter wire, surrounded the filler layer and waterproof sheet. The edges of the casing and septum were secured by stainless steel hog rings which also passed through the waterproof sheet. Sixteen stainless steel lacing anchors were spaced about the perimeter of the blanket, with a seventeenth anchor disposed at the center of the blanket. This blanket has withstood a liquid jet stream at a stagnation pressure of 65 psi directed at an angle of 45.degree. , without tearing, for about 20 minutes, in accordance with the test conditions described in Durgin, W. W., and Noreika, J. F., "The Susceptibility Of Fibrous Insulation Pillows To Debris Formation Under Exposure To Energetic Jet Flows," NUREG/CR-3710 (SAND 83-7008), Alden Research Laboratory and Sandia National Laboratory, U.S. Nuclear Regulatory Commission, Washington, D.C. 20555. Further, this blanket gives effective heat insulation at temperatures of from about 200.degree. to about 1,000.degree. F. (93.degree.-538.degree. C.), and can be removed from and reapplied to pipes without loss of integrity. Further, if the filler layer is torn by excessive jet forces during a LOCA, those portions of the filler layer removed by the water during failure come out in a finely chopped condition of less than approximately 0.5 inches in diameter. Having described the invention in detail, those skilled in the art will appreciate that numerous modifications may be made thereof without departing from the spirit of the invention. Therefore, it is not intended that the scope of the invention be limited to the specific embodiment as illustrated and described herein. Rather, it is intended that the scope of the invention be determined by the appended claims and their equivalents.