Abstract:
A gas turbine of the type having turbine vanes retained in a cylinder and utilizing torque pins to transmit the torque load on the vanes to the cylinder is provided with improved structure for enabling insertion and withdrawal of the pin from engagement with the outer vane shroud in the vicinity of the cylinder flanges.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to the turbine section of a gas turbine, and more particularly to an apparatus and method for supporting the torque load on the turbine vanes. 
     Gas turbines employ a row of stationary vanes immediately upstream of each row of rotating blades to properly direct the hot gas flow to the rotating blades. A row of vanes comprises a plurality of vanes arrayed circumferentially around the flow path annulus. The vanes are retained in a turbine cylinder. To allow access to the turbine components, the turbine cylinder is split longitudinally into semi-circular upper and lower halves. The halves are joined together at horizontal joints by a plurality of bolts disposed along flanged portions of the cylinder halves extending the length of each cylinder. 
     Each vane comprises an airfoil, an outer shroud at its radially outboard end and an inner shroud at its radially inboard end. The flow of hot gas over the airfoil generates an axial force tending to urge the vane downstream. A support rail emanating radially from each outer shroud serves to restrain the motion of the vane in the axial direction by mating with the inner edge of a plate which is affixed at its outer edge to the turbine cylinder. Additional axial restraint may be obtained by a second support rail in the inner or outer shroud. 
     The flow of hot gas over the airfoil also generates a torque load on the vane, tending to urge it circumferentially around the turbine annulus. This load is absorbed by torque pins which engage the outer shroud support rail and transmit the load to the turbine cylinder. However, changes in the design of the turbine cylinder necessitated by the high temperature of modern gas turbines have made it impractical to use torque pins of the traditional type in the flanged area of the horizontal joints. This invention relates to a new type and method of using a torque pin which is suitable for use in the flanged areas. 
     2. Description of the Prior Art 
     In the past, torque pins were inserted and removed from outside of the cylinder through holes in the cylinder. This allowed the vanes to be removed without opening the turbine to disengage the pins. The pin was of cylindrical shape, a key being formed on one end adapted to engage a key-way in the vane outer shroud support rail. At installation the pin was inserted into the hole in the cylinder, pushing it radially inward until it engaged the vane. Since the diameter of the pin was only slightly smaller than that of the hole, the torque load on the vane was transmitted through the outer shroud and pin to the cylinder. A head formed on the end of the pin protruded through the hole in the cylinder and was seated in a counterbore on the outer surface of the cylinder. Motion in the radially outboard direction was prevented by a retainer bracket, affixed to the cylinder with screws, which spanned the head of the pin protruding from the cylinder, thus preventing the pin from accidentally disengaging. 
     In addition to the vanes, the turbine cylinder also contains a plurality of segments, arrayed around the turbine annulus, which form a ring encasing the tips of the rotating blades. To obtain optimum thermodynamic performance, the radial clearance between these segments and the tips of the rotating blades is maintained at a minimum. Hence, it is important that the turbine cylinder retain as nearly a perfectly cylindrical shape as possible. As a result of increases in the temperature of the hot gas flowing in the turbine cylinders of modern gas turbines, thermal stresses in the cylinder can cause it to ovalize and adversely affect the radial clearance between the segments and the rotating blades. To prevent this occurrence the thickness of the cylinder flanges and the diameter of the joint bolting has been increased and the spacing of the joint bolting has been decreased. As a result of these changes, however, there is insufficient clearance between the joint bolting to insert torque pins from outside of the cylinder to engage the vanes in the vicinity of the joint. 
     It is therefore desirable to provide an apparatus and method for transmitting the torque load on the vanes in the vicinity of the cylinder joint through pins which, although inserted in the turbine cylinder, do not interfere with the joint bolting and can be disengaged from outside the cylinder. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is the general object of the present invention to provide a method and apparatus for transmitting the torque load on the turbine vanes to the turbine cylinder. 
     More specifically, it is an object of the present invention to provide a method and apparatus for transmitting the vane torque load to a turbine cylinder whose horizontal joints have been strengthened, resulting in insufficient access for traditional style torque pins in the area of the joint flanges. 
     It is another object of the invention to allow disengagement of the torque pins from outside of the cylinder. 
     Briefly, these and other objects of the present invention are accomplished in a gas turbine with a plurality of vanes, the vanes being subjected to a torque load and retained in a cylinder. Pins are utilized to transmit the torque load to the cylinder. The cylinder has horizontal joints in which the flange thickness and bolt diameter have been increased and the bolts spacing decreased such that there is insufficient access for insertion of the torque pins from outside of the cylinder. 
     In accordance with one aspect of the invention a hole is provided in the inner surface of the cylinder, in the vicinity of each flange, which extends through only a portion of the cylinder&#39;s thickness. A second, smaller hole, extends from the first hole to the cylinder outer surface penetrating through the section of the flange between horizontal joint bolts which is too narrow for the first hole to penetrate without interfering with the bolts. A short torque pin with a rod affixed to its end is inserted, from inside the cylinder, into the first hole, the rod penetrating through the second hole and extending beyond the outer surface of the flange. A nut, larger than the diameter of the second hole, is threaded onto the protruding end of the rod and prevents it from slipping back into the cylinder. After the vane is installed the torque pin is engaged by backing off the nut so that the rod and pin can be moved radially inward. After engagement of the pin, a bracket is attached to the cylinder outer surface in the vicinity of the second hole. This bracket prevents the rod, and hence the torque pin from which it emanates, from moving radially outward and thereby accidentally disengaging. 
     In accordance with another important aspect of the invention, the torque pins can be disengaged and the vanes removed from outside the cylinder by removing the retaining bracket and withdrawing the pin. This aspect of the invention eliminates the need to open the cylinder to remove the vanes, a time-consuming and costly operation. 
     In accordance with still another aspect of the invention, rotation of the nut on the rod can be used to apply mechanical force for withdrawing a pin in the event the pin becomes jammed in the engaged position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevation view of a gas turbine. 
     FIG. 2 is a cross-section of the turbine taken through line 2--2 of FIG. 1 showing the outer casing, turbine cylinder and a row of stationary vanes. 
     FIG. 3 is a perspective view of the horizontal joint area of the turbine cylinder viewed from outside the cylinder, showing the horizontal joint flange and bolts in the top half of the cylinder. 
     FIG. 4 is a vertical cross-section through a horizontal joint in the vicinity of a torque pin. 
     FIG. 5 is a cross-section taken through line 5--5 in FIG. 4. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings wherein like numerals represent like elements, there is illustrated in FIG. 1 a gas turbine, the arrows indicating the direction of flow through the turbine. FIG. 1 shows the outer casings of the gas turbine including the turbine outer casing 9. FIG. 2 shows the turbine outer casing 9, a turbine cylinder and a row of stationary vanes 20. The turbine cylinder is split longitudinally into upper and lower semicircular halves 10 and 12 joined along a horizontal joint 13. As shown in FIGS. 2 and 3 heavy flanges 14 and 17 emanate from the longitudinal edges of the cylinder halves. Large bolts 16 extend through holes 18 in the flange and serve to compress the flanged portions of the top and bottom cylinder halves together, as shown in FIGS. 3 and 4. 
     Alternating rows of stationary vanes and rotating blades are retained inside the cylinder. The first row of vanes, shown in FIG. 2, is typical and is comprised of a plurality of vanes 20 arrayed circumferentially around the turbine flow path annulus. Referring to FIG. 5, it can be seen that at the radially outboard end of each vane is an outer shroud 22. A support rail 24 emanates from the outer shroud. The support rail is used to affix the vane to the cylinder and restrains motion of the vane in the axial direction. This is accomplished by mating the support rail with the inner edge of a plate 58, the plate being affixed at its outer periphery of the cylinder. Also retained in the cylinder are a plurality of segments 52 which form a ring encasing the tips of the rotating blades 54. To obtain optimum thermodynamic performance, the radial clearance 56 between these segments and the tips of the rotating blades is maintained at a minimum. A substantial loss of cylindricity in the cylinder will distort the shape of the ring formed by the segments 52 and result in insufficient clearance in the areas of the cylinder distorting radially inward (causing the blade tips to impact the segments) and excess clearance in the areas distorting radially outward (causing a loss in thermodynamic performance). Unfortunately, as a result of the high temperature of the hot gas in modern gas turbines, the cylinders are prone to distortion as a result of thermal stresses in the cylinder. To prevent this occurrence the thickness of the flanges at the horizontal joints and the diameter of the joint bolts have been significantly increased while the spacing of the bolts has been decreased. As a result, there is insufficient space between the bolts for a torque pin to be passed through the flange without interfering with the bolts. Hence the prior manner of utilizing torque pins, by inserting them from outside the cylinder through holes through the cylinder, is no longer practical for the vanes in the vicinity of the horizontal joints. 
     In accordance with the invention, this problem has been solved in the following manner. As illustrated in FIGS. 4 and 5, a first hole 32 is provided which extends radially from the inner surface of the cylinder 11 in the vicinity of each flanged portion of the cylinder. The hole penetrates through only a portion of the thickness of the flanged portion of the cylinder, stopping short before reaching the bolt holes 18. A second hole 34 extends from the bottom of the first hole within the cylinder to the outer surface 15 of the cylinder. Although there is insufficient clearance between bolt holes to allow the first hole to penetrate the entire thickness of the flanged portion of the cylinder, the second hole is of sufficiently small diameter to pass through the flanged portion of the cylinder between bolts without interfering with the bolts. 
     The torque pin 28, utilized in the vicinity of each of the flanged portions of the cylinder, is of cylindrical shape with a diameter slightly smaller than that of the first hole. A key 30 is provided on one end of the pin adapted to be inserted into a key-way 26 in a support rail 24 emanating from the outer shroud of the vane 22. In operation, the key is engaged in the key-way and the opposite end of the pin is disposed in the first hole, thereby transmitting the torque load on the vane through the outer shroud and pin to the cylinder. 
     A rod 36 emanates from the end of the pin opposite the key. At installation the pin is inserted into the first hole from inside the cylinder. The pin is oriented so that the key is facing radially inward and the rod penetrates through the second hole. The rod is sufficiently long to protrude from the outer surface of the cylinder when the torque pin is engaged. There is sufficient depth in the first hole 32 to allow the pin to be completely disengaged from the vane by withdrawing it radially outward. Thus, by grasping the end of the rod protruding from the outer surface of the cylinder the pin can be disengaged from outside the cylinder. 
     The end of the rod protruding from the cylinder features screw threads 38 thus allowing a nut 40 to be threaded onto the end of the rod. Since the face of the nut is larger than the diameter of the second hole 34, the nut prevents the pin from moving radially inward and slipping back into the cylinder when the vane into which it is engaged is removed. At installation the nut is rotated onto the rod so that it pulls the pin radially outward, into its disengaged position, holding it thus until the vane is installed. The nut also allows mechanical force to be applied for disengaging a jammed pin by rotating the nut after it has seated itself against the outer surface of the cylinder, thus drawing the rod radially outward. 
     A third hole 44 is drilled and tapped in the outside surface of the cylinder in the vicinity of each second hole. Accidental disengagement of the pin is prevented by installing a retainer bracket 42 utilizing a screw 48 disposed through a hole 46 in the bracket and threaded into the third hole 44. The retainer bracket has a relief 50 at one end whose depth is slightly greater than the height of the nut 40. A hole in the relieved portion, larger than the diameter of the rod but smaller than the nut, allows it to slip over the rod 36 but prevents the nut, and therefore the rod, from moving radially outward. 
     Although, for the purposes of illustration, the preferred embodiment of the invention has been described for use in the flanged portions of a turbine cylinder, the invention disclosed is applicable in any portion of a cylinder in which holes, of sufficient size to contain a pin capable of carrying the vane torque load, can not be provided through the entire thickness of the cylinder. 
     Many modifications and variations of the present invention are possible in light of the above techniques. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.