Pipe penetration system – general electric company

A major design consideration of a gas turbine is the thermal and mechanical stresses due to the connection between the ductwork and the pipes that penetrate the duct. Specifically, the need to accommodate the insertion of hot pipes through relatively cool inlet and exhaust exterior duct walls. If the piping system does not fully accommodate all relative movements, the pipe penetration point eventually may fail. Gas turbine ducts often are required to be penetrated with pipes to supply steam for cooling, to provide oil for lubrication, or for other many other purposes. The pipe penetration must be designed to contain very high temperature, high velocity, and poisonous exhaust gases. If a leakage point in the duct occurs, the leak could lead to hazardous conditions for plant personnel and for the surrounding turbine equipment.


The failure of the duct due to the structural characteristics of the duct materials also is a concern.

The relative movement of the pipe (in three dimensions) may be about two (2) to about four (4) inches (about 5.1 to about 10.2 centimeters) or so as compared to the duct. This design condition generally happens more severely during thermal transients where the pipe quickly expands relative to the duct due to internal heating of the penetrating pipe and insulation protecting the exterior shell. In addition, the pipe is hotter than its connection point to the duct such that the connection also needs to be thermally compliant.

A penetrating pipe is generally welded to a slightly larger pipe stub that protrudes from the duct wall. This type of connection works well as long as there are no appreciable thermal differences between the penetrating pipe and the pipe stub or appreciable movement/growth of the penetrating pipe upstream of the penetration. To address the thermal stress issue, designers generally locate the highest mechanical stress points away from the maximum thermal stress points by encasing the penetrating pipe in a larger cylindrical or conical shroud that is insulated and welded to the ductwork and to the pipe. These designs can accommodate some degree of thermal discrepancies, but add complications to the turbine system as a whole by requiring pipe loops and expansion joints to minimize the relative movement at the pipe penetration.

Thus, there is a desire for a pipe penetration system that can accommodate large axial, vertical, and radial displacements during operation of the gas turbine. The pipe penetration system should contain the internal air or gas flows yet be flexible enough to accommodate thermal and mechanical stresses. Such a system should be economical and should be able to be installed without special machining or tooling so as to result in a simplified piping system.

According to the present invention there is provided a penetration system as defined in claim 1. The penetration system further may include a pipe flange attached to the pipe and a pipe stub flange attached to the pipe stub. The bellows may include a first flange for connecting with the pipe flange and a second flange for connecting to the pipe stub flange. The thermal sleeve may include carbon steel or similar types of materials. The bellows may include carbon steel, stainless steel, nickel-chromium-iron alloys, or similar types of materials. The bellows includes a number of folds defined to accommodate the thermal movement of the penetrating pipe. The bellows expands as the pipe deflects. The bellows deflects laterally, vertically, and axially with the thermal growth or deflection of the penetrating pipe.

The present application further describes a penetration system for a pipe entering a duct wall at a pipe stub. The penetration system includes a thermal sleeve surrounding the pipe stub and adjacent to the duct wall and a metal bellows positioned below the thermal sleeve and about the pipe such that the metal bellows expands as the pipe expands.

The penetration system further may include a pipe flange attached to the pipe and a pipe stub flange attached to the pipe stub. The bellows may include a first flange for connecting with the pipe flange and a second flange for connecting to the pipe stub flange. The thermal sleeve may include a truncated conical closeout. The metal bellows deflects laterally, vertically and radially as the pipe deflects.

Referring now to the drawings, in which like numerals refer to like elements throughout the several views, Figs. 1 and 2 show a pipe penetration system 100 as is described herein. The pipe penetration system 100 is used with an insulated duct wall 110 of a conventional gas turbine engine. Likewise, the pipe penetration system 100 is used with a penetrating pipe 120. As described above, the penetrating pipe 120 may be used to supply steam for cooling, provide lubrication, remove exhaust, or any other desired purpose. The duct wall 110 may be made out of carbon steel, or similar types of high temperature resistant materials. Similarly, the penetrating pipe 120 is generally may be made out of stainless steel, Inconel (high strength austenitic nickel-chromium-iron alloys), or similar types of high temperature resistant materials. The penetrating pipe 120 may have a flange 125 welded thereon or the penetrating pipe 120 may be attached by other connection means.

The penetrating pipe 120 may be inserted through the duct wall 110 via a conventional pipe stub 130. The pipe stub 130 is generally slightly larger than the penetrating pipe 120 and protrudes from the duct wall 110. The pipe stub 130 may be made out of stainless steel, or similar types of high temperature resistant materials. The pipe stub 130 may include a pipe stub expansion joint flange 135 at the lower end thereof.

The pipe penetration system 100 may include a thermal sleeve 140 that surrounds the pipe stub 130 at the connection to the duct wall 110. The thermal sleeve 140 may have a slightly larger diameter than that of the pipe stub 130. The thermal sleeve 140 may end in a truncated conical closeout 150 about the penetrating pipe 130 so as to reduce thermal stress. The thermal sleeve 140 may be made out of carbon steel, or similar types of materials consistent with the material of the duct wall 110. The thermal sleeve 140 may be attached to the duct wall 110 via welding or similar types of connection means.

The pipe penetration system 100 further includes a metal bellows 160. The bellows 160 may be positioned beneath the thermal sleeve 140. The bellows 160 may include a number of curved folds 170 so as to expand and deflect as needed. The number of folds may be defined by the expected amount of lateral and axial displacement. The bellows 160 may be made out of carbon steel, stainless steel, Inconel (nickel-chromium-iron alloys), or similar types of materials with good ductile qualities. One end of the bellows 160 may be bolted to the pipe stud flange 135 via a first flange 180. The other end of the bellows may be bolted to the penetrating pipe flange 125 at a second flange 190. Other types of connection means may be used herein.

The use of the thermal sleeve 140 greatly reduces the temperature at the duct wall 110. Likewise, the use of the bellows 160 allows the penetrating pipe 120 to move in any direction. The pipe penetration system 100 as a whole thus allows for large displacements (axially, vertically, and radially) as well as accommodating thermally induced strains. Specifically, the pipe penetration system 100 accommodates high relative displacements between the duct wall 110 and the penetrating pipe 120. The pipe penetration system 100 addresses the potential high stresses at the duct wall 110 to the pipe 120 by thermally isolating the penetrating pipe 120 so as to lower the interface temperature. The pipe penetration system 100 thus accommodates large thermal movements while still being leak proof. The pipe penetrations system 100 allows for complete adjustment and requires no special installation tools or methods. The pipe penetration system 100 generally utilizes common and inexpensive manufacturing processes.

Variations on the pipe penetration system 100 also can be used in other applications. For example, the pipe penetration system 100 could be used in a gas turbine inlet bleed heat system. In such a system, a large hot supply pipe 120 carrying highpressure compressor air has to penetrate a duct wall 110. The pipe 120 should be thermally and mechanically decoupled from the duct 110. Many other applications may be used herein.