Patent Application
20130224005
This invention relates to a seal for containment of gas leakage across two opposed flanges of a pressure vessel structure such as a turbine casing. This invention also relates to a method of sealing a pressure vessel structure such as a gas turbine casing.
In some pressure vessel applications, a gasket or seal is employed together with a flange connection to prevent a gas such as air from escaping through flange joints. For various technical reasons, some flange joints are employed which are not capable of totally sealing an air leak and some quantity of escaping air is acceptable, particularly where the amount of escaping air does not deleteriously affect the overall system of which the air is a part.
Gas turbines ordinarily utilize an air compressor having a cylindrical casing enclosing a cylindrical bladed rotor therein. Air at atmospheric pressure is ducted into the compressor at one open end of the cylinder to be compressed by the rotating blades of the rotor interengaging with blades in the casing. Air at elevated pressure is taken from the opposite end of the casing to be directed to combustion and exhaust system regions of the gas turbine apparatus which operate at a lower pressure. The compressor casing as well as intermediate parts of the casing between the compressor and the combustion system usually comprises a multipart arrangement of component sections suitably fastenered together with appropriate flanges. It has been found that excess air leakage may occur through the usual flat metal on metal engaging surface of the flanges of the multipart assembly, for example, because of thermal distortion of the flanges. Air leakage becomes an increasing problem where the casing structure includes curved and angled parts. It is difficult for the otherwise desirable machined surface flanges to maintain desired air sealing characteristics when the casing includes sections which are curved or at an angle to each other and the flanges are angled accordingly. For example, a flange may be utilized to seal to a horizontal as well as to a vertical surface and may utilize a single right angle flange to do so. The use of a gasket seal between the flanges is not only a deterrent to the more desirable metal to metal surface contact of the flanges, but also becomes a problem where the gasket seal might only be used where most air leakage occurs and therefore becomes an obstruction in the overall coextensive contact of the flange surfaces.
According to one embodiment of the present invention, a seal for a turbine casing is provided. The turbine casing includes a plurality of sections joined at flanges provided on each section. Each flange includes a bore and a counterbore. The seal comprises a compression sleeve seal having a length that is greater than a counterbore-to-counterbore length of two flanges; a fastener configured to extend through the compression sleeve seal; and a nut threadable on each end of the fastener. The compression sleeve seal is compressible between each flange and each nut to create a first seal and is radially extensible to create a second seal against each bore.
According to another embodiment of the present invention, a method of sealing a turbine casing is provided. The turbine casing includes a plurality of sections joined at flanges provided on each section, each flange including a bore and a counterbore. The method comprises inserting a compression sleeve seal having a length that is greater than a counterbore-to-counterbore length of two flanges into the bores of two mating flanges; inserting a fastener into the compression sleeve seal; tensioning the fastener; threading a nut on each end of the fastener into contact with each end of the compression sleeve seal; and releasing the tension to compress the ends of the compression sleeve seal to form a first seal between each nut and each flange and radially extend the compression sleeve seal between the ends to form a second seal against the bores.
Referring to
Referring to
The nuts 14 are turned until they contact the ends 20 of the compression sleeve seal 12 which may sit slightly proud of the flange face. The release of the fastener 16 from tension compresses the fastener 16 along its longitudinal axis and creates a primary seal between the nuts 14 and the flanges 4, 6. Through Poisson's effect, the compression sleeve seal 12 extends out radially from its longitudinal axis to create a secondary seal against the bores 8, 18 of the flanges 4, 6 to seal the potential leak path.
Referring to
Referring to
The compression sleeve seal 12 may be formed of metal, for example steel (e.g. a Cr—Mo—V steel). The material of the turbine casing may be, for example, steel (e.g. a Cr—Mo—V steel).
The use of the compression sleeve seal may allow sealing of the sections of the turbine casing without the use of gaskets and/or rope seal grooves which may have a complicated structure and/or tend to break off into the gas stream path. The compression sleeve seal is also preloaded and does not rely on the gas flow to seat the seal, as is required in existing butterfly valves. The compression sleeve seal also provides primary and secondary seals in the flange bores and does not require caps on the tops of the fasteners.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
