Boots – shoes – and leggings
Patent
1991-03-12
1993-10-26
Harvey, Jack B.
Boots, shoes, and leggings
7386223, G05D 1702
Patent
active
052572072
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention is in the field of mechanical engineering and more specifically relates to a method for monitoring gasket compression during bolt tensioning in pressurized fluid systems to prevent leakage of a fluid. Typical applications of the present invention would be on piping systems used in nuclear power generating plants or in other applications with high internal pressures and where consequences of leakage are severe.
2. Background Art
Piping systems, pressure vessels, pumps, and valves that contain high pressure and/or aggressive liquids or gasses are normally closed by flanged and bolted connections and are sealed by special gaskets. Traditionally, the bolts used in such devices have been tensioned by use of a torque wrench, but alternative methods are in use.
In one alternative method of tensioning the bolts, a special device called a hydraulic tensioner is used. One type of hydraulic tensioner employs hydraulic pressure to pull on the end portion of the bolt, and with the bolt thus stretched, the nut, which is unloaded, is tightened. Bolt tensioners are described in the following U.S. Pat. Nos. 3,749,362; 4,249,718; 4,438,901; and 4,433,828.
Although, in many cases, bolt tensioners are easier, more convenient, and more accurate to use than a torque wrench, such tensioners merely apply force, and still include no apparatus or method for monitoring the compression of the gasket.
In U.S. Pat. No. 3,643,501, Pauley describes a differentiator that turns off a power wrench when the tension applied to a fastener begins to exceed the elastic limit of the fastener. This range of tension is far greater than that with which the present invention is concerned, and Pauley's invention is based on a different physical effect than the present invention.
In U.S. Pat. No. 4,102,182, Brown, et al, describe a tensioning procedure in which limits on the slope of the torque versus angle curve are employed.
In U.S. Pat. No. 4,400,785, Wallace, et al, use a microprocessor to measure successive areas under the torque versus angle curve to determine whether a tightening criterion has been met.
In U.S. Pat. No. 4,228,576, Eshghy uses a torque or tension versus angle curve to monitor or control tightening of fasteners.
None of the above patents provides a tensioning method that considers the unique needs of pressure-sealing gaskets. In contrast, the present invention is concerned only with situations in which a gasket is to be compressed to a specific desired extent, and identifying the bolt tension at which that specific gasket compression takes place.
DISCLOSURE OF INVENTION
The present invention is intended for use with a bolt tensioner on flanged and bolted connections of the type in which gasket compression is limited by a metal compression stop. The compression stop may either be part of the gasket or part of the flange. The invention permits the user to determine the bolt tension at which proper gasket compression takes place, which allows the user to verify that the gasket was of proper density and that the proper bolt preload was added.
Since high pressure sealing gaskets can be of different densities yet indistinguishable in size, shape, and color, a connection cannot be confirmed as being properly tensioned without verifying proper gasket behavior. If the gasket is too soft, the gasket will compress fully to the compression stop with too little bolt tension, and may leak regardless of how much additional bolt tension is added. If the gasket is too dense, full gasket compression may not occur at maximum bolt tension, leaving the full bolt tension on the gasket surface. In this latter condition, future gasket relaxation reduces bolt tension and may result in a leak. This condition also allows the bolts to be subjected to increased fatigue loading. To avoid leakage, full gasket compression (to the compression stop) must occur at proper bolt tension, with additional bolt tension added to withstand variable internal and external loads. This leaves the gasket properly loaded,
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Harvey Jack B.
McKown Daniel C.
Ramirez Ellis B.
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