Patent Application
20090162139
The present application relates generally to gas turbines and more particularly relates to the use of insulated bolts between a turbine shell and a compressor discharge casing or between any number of components with a temperature gradient therethrough.
In a conventional gas turbine engine, the turbine shell, the compressor discharge casing, and other elements may be joined by a number of bolts. The bolts, however, may get hot from the hot compressed air in the interior portion of the compressor discharge casing and elsewhere. As the bolts get hotter, the bolts may be subject to creep. The creep may result in a loss of bolt pretension and a reduced lifetime.
Current solutions to preventing creep in high temperature environments include the use of larger bolts or bolts made out of temperature resistant materials such as Inconel (a nickel-chromium alloy). The size of the bolts, however, can only increase so much because of space limitations. Likewise, the use of materials such as Inconel may be much more expensive than bolts made of standard steel or similar materials.
There is thus a desire for a bolted joint connection that reduces the impact of thermal influences but at less expense than with known high heat resistant materials. The bolts preferably will be substantially creep resistant while being reasonably sized and available at a reasonable cost.
The present application thus provides for a turbine/compressor stator joint. The turbine/compressor stator joint may include a flange, an aperture extending through the flange, and a bolt extending through the aperture. The bolt may include a shank and a layer of insulation surrounding the shank.
The present application further provides for a method of closing a joint positioned about a hot air pathway. The method may include the steps of covering a bolt shank with a layer of insulation, positioning the bolt shank within an aperture of the joint, positioning a layer of nut insulation about the bolt shank and the joint, and tightening a nut about the bolt shank and the joint.
The present application further provides for a hot air joint. The hot air joint may include a flange, an aperture extending through the flange, and a bolt extending through the aperture. The bolt may be made out of steel. The bolt may include a shank and a layer of shank insulation surrounding the shank.
These and other features of the present application will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims.
Referring now to the drawings, in which like numerals refer to like elements throughout the several views,
In this example, the turbine section 60 may have (4) four successive stages represented by four (4) wheels, a first wheel 71, a second wheel 72, a third wheel 73, and a fourth wheel 74. The wheels 71-74 are mounted onto the rotor shaft 50. Each wheel 71-74 carries a row of buckets that include a number of blades, a first blade 81, second blade 82, third blade 83, and the fourth blade 84. The blades 81-84 are arranged alternatively between fixed nozzles that include a number of vanes, a first vane 91, a second vane 92, a third vane 93, and fourth vane 94. Thus, a four staged turbine is illustrated wherein a first stage includes the blade 81 and the vane 91; a second stage includes the blade 82 and the vane 92; a third stage includes the blade 83 and the vane 93; and a fourth stage includes the blade 84 and the vane 94. The turbine section 60, however, may include any number of stages and differing configurations.
The turbine section 60 may include an outer shell 100 and an inner shell 110. The outer shell 100 may be secured at one end to a compressor discharge casing 120 and a turbine exhaust frame 130 at the other. The outer shell 100 may be joined to the compressor discharge casing 120 and to the turbine exhaust frame 130 by a number of bolts 140. The bolts 140 may be of conventional design and materials, oversized, or made of heat resistant materials.
Chart I below shows a temperature distribution within the flange 210 and the shank 240 of the bolt assembly 230 under typical operating conditions. As is shown, the temperature of both the flange 210 and the shank 240 initially increases from the compressor discharge casing 120 through the flange 210 and then decreases again towards the outer turbine shell 100.
Chart II shows the average temperature distribution for the flange 210 and the shank 240. As is shown, the temperature distribution of the shank 240 does not have the peak as is shown in Chart I when the shank insulation 310 is used.
The nut insulation 360 reduces the heat that can enter the shank 240 from the flange 210 and may dissipate some of the heat from the flange 210 to the air due to the increased surface area. Certain geometries may be cut into the nut insulation 360 so as to increase the heat transfer area to the cooling air about the flange 210. For example, castellation or fins may be used. One can also reduce the heat transfer area between the washer 360 and the flange 210 and/or the washer 360 and the nut 250 or between the nut 250 and the flange 210 by scalloping or castellating the nut contact surface.
Chart III shows the average temperature distribution between the flange 210 and the shank 240. Again, the temperature distribution of the shank 240 is reduced from the baseline case of Chart I although the initial peak shown in Chart I does return.
Chart IV below shows the greatest decrease in the temperature of the shank 240. In this case, a temperature difference of about 105° F. (about 40.6° C.) is achieved by use of the shank insulation 310 and the nut insulation 360. Moreover, the temperature within the flange 210 is reduced by about 48.5° F. (about 9.2° C.) as compared to the baseline case of Chart I.
The use of the shank insulation 310 and the nut insulation 360 thus reduces the pathways that allow heat to enter into the bolt assembly 230 by reducing the conductivity along the pathways and also by shielding the pathways. Likewise, the increased surface area that is exposed to the cooling air also may help to remove the heat. As a result, the bolt assembly 230 may be made out of standard materials at a reduced cost but with reduced creep.
Although the invention has been discussed in the context of a turbine/compressor shell joint, the shank insulation 310 and the nut insulation 360 described herein can be used at the turbine shell/turbine exhaust frame joint or at any other desired location within the turbine. This invention also can be used wherever there may be a temperature differential along a bolt relative to a flange. The shank insulation 310 and the nut insulation 360 also may be used wherever a bolt or a similar joinder device is exposed to high temperatures.
It should be apparent that the foregoing relates only to the preferred embodiments of the present application and that numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.
