US2800299A - Nozzlebox structure for high temperature steam turbine - Google Patents

Description

July 23, 1957 R. SHEPPARD ETAL I 2,800,299 NOZ ZLEBOX STRUCTURE FOR HIGH TEMPERATURE STEAM TURBINE Filed Sept. so. 1955 FT .l.

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United States Patent F NOZZLEBOX STRUCTURE FOR HIGH TEMPERA- TURE STEAM TURBINE Raymond Sheppard, Schenectady, and George E. Maxwell, Scotia, N. Y., assignors to General Electric Company, a corporation of NewYorlr Application September 30, 1955, Serial No. 537,808

4 Claims. (Cl. 253-=-78) This invention relates to elastic fluid turbines for very high pressures and temperatures, specifically to the nozzlebox and supporting arrangements therefor of a turbine adapted for use with steam on the order of 1100" F.

This invention represents an improvement in nozzlebox and inlet conduit construction of the general type incorporated in the supercritical pressure turbine disclosed in the copending application of Jack E. Downs, Serial No. 491,290, filed March 1, 1955, and assigned to the same assignee as the present application.

Such high pressure, high temperature steam turbines are customarily fabricated with an outer casing surrounding and spaced from an inner high pressure casing. Because of differences in the temperature of these two casings, and difiiculties in securing precise alignment of the inner casing within the outer casing, very substantial design problems need be solved with respect to the conduit which admits the high pressure steam through the outer casing to the nozzle sections supported within the inner casing. For ease in manufacture and disassembly' for inspection and servicing, it is highly desirable that the nozzlebox assembly be readily removable from the inner casing, and that it be so arranged that it can be assembled complete on the inner casing before the outer casing is assembled around the inner casing. .The austenitic or stainless steel alloys of which the high temperature components are fabricated have a substantially higher coefiicient of thermal expansion than the lower temperature-alloys used in steam turbine construction, and are at the same time more subject to cracking due to thermal fatigue, resulting from repeated heating and cooling cycles. This makes it essential that the high temperature nozzlebox parts be readily available for inspection to detect any evidence of such cracking. Operation of a steam turbineat extremely high temperatures over a long period of time may tend to cause abutting parts to seize or gall, perhaps due to high temperature corrosion or to the deposition of solid impurities entrained in the steam. It is therefore particularly important that parts which are to be disassembled be so designed that they can be readily separated in spite of these tendencies to stick together after being in assembled relation for an extended period.

Other problems arise from the urgent necessity to maintain the nozzles in a precise desired relation with the bucket-Wheel to which they supply motive fluid. This precise alignment must be maintained irrespective of thermal distortions or misalignment between the inner casing, outer casing, and the inlet conduit members.

Accordingly, an object of the present invention is to provide an improved high temperature nozzlebox and inlet conduit construction for a high pressure elastic fluid turbine having special means for accurately maintaining alignment of the nozzlebox assembly relative to the inner turbine casing, which permits free thermal expansion of the nozzlebox parts relative to the inner casing, yet without sloppy fits between the respective parts when in 2,800,299 Patented July 23, 1957 cold condition or when coming up to normal operating temperature.

the accompanying drawings in which Fig. l is a longi-' tudinal sectional view of a nozzlebox structure incorporating the invention, showing its relation to the inner and outer turbine casings, Fig. 2 is a transverse sectional view taken on the plane 2-2 in Fig. 1, Fig. 3 is a detail view of one of the locating key elements shown in Fig. 2, and Fig. 4 is a sectional view of this key means taken on the plane 4-4 in Fig. 3.

Generally stated, the invention is practiced by providing special locating lugs extending from the nozzlebox proper to engage sockets in the casing, and securing the remote end of an inlet conduit portion formed integral with the nozzlebox by means of special locating and fastening means which perform the dual function of securing the outer end of the inlet conduit portion to the inner casing of the turbine, while always maintaining this conduit portion exactly coaxial with the casing opening in which the conduit portion is disposed.

Referring now more particularly to Fig. l, the invention is illustrated as applied to a high pressure, high temperature steam turbine intended to be mounted with its rotor axis horizontal and having an outer casing 1 surrounding and spaced from an inner casing 2. This inner casing defines a vertically extending cylindrical boss portion. 3 with a cylindrical bore 4, in which is disposed an' in a multiple ring packed joint indicated generally at 7. This joint serves to seal against the leakage of high pressure steam, while permitting limited displacement of the conduit portion 5 in a plane transverse to the axis of the conduit. Such joints are well known in the art, one form being disclosed more particularly in Patent 2,649,315, issued August 18, 1953 in the name of P. G. Ipsen and assigned to the same assignee as the present application.

As also more particularly disclosed in the Ipsen patent, the packing rings 7 are supported in a cylindrical fitting 8 having an inner conduit portion 8a welded to the inlet conduit 9 and an outer annular axially extending thinwalled portion 10 terminating in a thick flange portion 11. Flange 11 is secured to the boss portion 1a of the outer casing 1 by a circumferential row of studs 12 which first pass through a heavy ring member 13, the function of which is to transmit evenly to the highly stressed flange 11 the forces exerted by the nuts. This general combination of slip joint 7 and cylindrical fitting member 8,

with its heavy flange 11 and stress distributing ring 13 has become quite conventional in the steam turbine art and does not form a part of the present invention.

This invention particularly relates to the construction of the nozzlebox 6 with its inlet conduit portion 5 and K the means for securing conduit 5 to the boss portion 3 of inner casing 2, and maintaining it exactly coaxial in the cylindrical opening 4. V

The nozzlebox 6 may be fabricated as a casting, or forged in several pieces and welded together-to form an arcuate casing as illustrated in Fig. 1. The far wall of the nozzlebox defines an arcuate opening in whichare disposed radial partitions or vanes forming the nozzle arc 6a. These discharge jets of motive fluid into the buckets of the first stage bucket-wheel (not shown). It is, of course, essential that the nozzle arc 6a be under all operating conditions accurately spaced and aligned relative to the bucket-wheel. To this end, the nozzlebox 6 is accurately located by a plurality of locating lugs 6b, 6c, and a third lug 6d, shown in dotted lines since it is onthe same side of the nozzlebox as the bucket-wheel, that is, behind the section plane on which Fig. l is taken. These three locating lugs may be cast integral with the nozzlebox, or may be fabricated separately and welded to the nozzlebox proper. Each is provided with a carefully machined key portion adapted to engage a cooperating groove or recess in the inner turbine casing 2. As will be'apparent from Fig. 1, the locating lugs 6b, 6c engage an annular groove 2a in the casing. Thus these two lugs accurately locate the nozzlebox in an axial direction, leaving it free to shift only in a plane normal to the axis of the turbine. Such transverse shifting is prevented in the horizontal direction by engagement of the third key 6d with a recess 2b, in a manner which will be apparent from Fig. 1.

The inlet conduit portion indicated generally by the reference numeral 5 in Fig. 1 may be cast integral with the nozzlcbox 6 or may also be forged in several components welded together and to the nozzlebox. As shown in the drawing, a conduit portion 5b is formed integral with nozzlebox 6, while a second portionSc is fabricated separately and welded as shown at 5d.

Secured to or formed integral with the innermost conduit portion 5b is a radially spaced axially extending cylindrical conduit portion See. The outer surface of this cylindrical extension cooperates with a multiple ring slip joint indicated generally at 14. This packing may be of the same general type as shown at 7. The outer surface of cylindrical portion 5e may be provided with a thin layer of a hard corrosion resistant material such as that known to the trade as Stellite. This prevents sticking or galling of the packing rings.

The special means for securing the inlet conduit portion 5 to the inner casing boss portion 3, and for maintaining the conduit exactly coaxial with the bore 4, comprises a special split annular member 15 and a solid ring member 16, the construction and arrangementof which.

may be seen more particularly by comparison of'Figs. 1 and 2.

The special lock ring member 15 is made in two or more arcuate segments, as shown in Fig. 2, and has a downwardly extending skirt portion defining at the end thereof an inwardly projecting annular flange 17. This flange engages an annular groove 18 around the end of the boss portion 3, in a manner which will be apparent from Fig. 1. It will be obvious that it isnecessary to make ring 15 in two or more arcuate pieces in order to assemble them in a radial direction so as to engage the flange 17 with the circumferential groove 18. The central portion 19 of the ring 15 abuts the annular upper end surface of the cylindrical member 5e of the inlet conduit. Thus the nozzlebox and inlet conduit are prevented from moving upwardly. The upper surface of the lock ring portion 19 abuts a radially extending locating flange portion 5 of the inlet conduit. As may be seen in Fig. 2, flange 5 is of a substantial radial width, and is provided with four equally spaced keyways 5g, 5h, 5k and 51.

It will be seen that the central portion 19 of lock ring 15 is carefully fitted between the upper end surface of conduit portion 5e and the lower surface of flange portion 5f, thus locating the conduit and nozzlebox assembly accurately in a vertical direction. It is to be noted also'that the clamp ring 16 and the lock ring 15 are made of the same material as the inner shell 2 (for instance a ferritic alloy), in order that there shall be no differential thermal expansion causing ring 15 to grow in diameter away from boss portion 3 and thereby cause looseness in a sidewise direction between the ring 15 and the cylindrical boss portion 3. Thus the centering members 15 and 16 can be very carefully fitted so nozzlebox 5b is centrally located relative to bore 4, both when the parts are cold and when hot.

The clamp ring member 16 is either fabricated as a single integral ring member, as shown in Fig. 2, or it may also be formed in segments, provided of course that the segments of the ring 16 are oriented to bridge the joints between the segments of lock ring 15. As will be apparent from the drawings, the clamp ring 16 is secured to the lock ring 15 by a circumferential row of threaded fastenings 20.

It will be apparent from the above how the clamp ring 16.and lock ring 15 secure the conduit relative to the casingportionfl, .but it remains to be seen how the conduit is exactly centered relative to the bore 4. This is accomplished by radial key means comprising the four keyways 5g, 5h, 5k, 51, cooperating with special key members projecting radially inwardly from the clamp ring 16, in a mannertwbich will be more apparent from Figs. 3 and 4. These key assemblies are identical in construction, as may be seen in Fig. 2. As shown in Fig. 3, the clamp ring 16 has an inwardly projecting lug portion 16a of a dimension in the'tangential direction substantially smaller than the Width of the keyway 5h. The substantial clearance space thus defined between the lug 16a and the keyway is occupied by a pair of similar L-shaped blocks identified 16b. As.will be seen by a comparisonof Figs. 3 and 4, each L- block has one leg overlying the lug 16a and secured thereto by .a threaded fastening 160. The other leg is disposed between the side surface of lug 16a and the adjacent surfaceof the keyway 16h. The advantage of this construction :isthat the separate L-block members 16b may be readily removed by removing the threaded fastenings during the process of accurately fitting the key members to the cooperating keyway. This may be much more readily accomplished by removal of the separate blocks 16b, ascompared with the more difficult job of accurately machining the lug portion 16a to fit the keyway 5h. If extreme accuracy is not required, the separate blocks 16b could obviously be dispensed with and the lug 16a itself machined to engage-keyway 5h with an appropriate class of fit.

It is to be particularly'noted that the opposite keyways 5g, 'Sh-arein the same plane transverse to the axis of the turbine as thenozzlebox locating lugs 6b, 6c. Likewise, the opposite keyways 5k, 5l are in the same vertical plane as the locating lug 6d. Thus the nozzlebox and its associated conduit portion are very accurately located relative to casing 2 in perpendicular planes. Since, as noted above, the nozzlebox assembly is located in the vertical direction by abutment of the lock ring portion 19 with the flange 5i and cylindrical member 5e, the nozzlebox-conduit assembly is very accurately located in all three dimensions relative to casing 2.

Brief reference may be made to special cooling means incorporated in this construction. In order to prevent excessive transfer of heat from the inner conduit portion 5b to the packing rings 14, a special heat shield member 21 is disposed in the annular space between the conduit and the spacedcylindrical portion See. This heat shield is a cylindrical member defining an inner annular clearance space with theouter wall of the conduit and an outer annular clearance space with the inner surface of cylindrical pontion15e. The inner clearance space is subdivided into two annular insulating spaces 21a, 21b by three annular ribs, only one of which is identified in dotted lines at 210. It will be obvious from Fig. 1 that there is one of these ribs at either end of the cylindrical shield 21, the third being roughly at the middle of the length of the shield member. The outer clearance space is occupied by a helically extending rib 21d as shown in dotted lines. Thus the outer annular clearance space is subdivided to form a single helically extending passage for cooling steam which enters by way of .a port 5m. This basic combination of a cylindrical shield member having internal annular ribs defining stagnant heat insulating spaces and an outer helical rib defining a flow path for a cooling medium, and the theory on which such a heat shield system operates, is described more specifically in the aboveddentified Downs application, Serial No. 491,290.

comparatively cool steam may be supplied to the bore 4 from any suitable location in the turbine, for instance fromthe space at the downstream side of the first stage hucketwheel. This steam, for instance, may be on the order of 1,050 =F., and flows by way of the port 5111 through the helical passage 21d, leaving by way of one or more radial holes a drilled in the lock ring segments 15.

A similar cooling shield member may be interposed between the cylindrical pipe fitting portion 14) and the adjacent portion 1a of the outer casing, as illustrated at Ma in Fig. 1. This shield also defines an inner annular dead space and an outer helical path for the flow of cooling steam as shown by the arrows in Fig. 1, this coolant leaving by way of one or more passages 11a drilled in the heavy flange 11. This arrangement reduces the iiow of heat from the hot inlet conduit 3 to the comparatively cooler flange 11 and boss portion 1a.

The method of assembly of this improved nozzlebox may be outlined as follows.

After fabrication of the nozzlebox 6 iscompleted, the packing rings 14 are assembled in casing 2 and the heat shield member 21 is disposed in its annular recess. The end conduit portion 50 will then be welded at 5:1. The complete nozzlebox-conduit assembly 6, 5 may then be inserted into bore 4 so that the locating lugs 6b, 6c, 6d engage their respective recesses in casing 2. The lock ring segments 15 are then assembled in a radial direction so that flanges 17 engage groove 18, and the central portion 19 of the lock ring fits snugly between cylindrical conduit portion 5e and the locating flange 5 The integral ring 16 is then assembled axially over the end of conduit 5 and secured with the threaded fastenings 20. The l.- blocks 16b are then carefully machined to exactly fit the clearance space between the locating lugs 16a and the walls of the respective keyways 5g, 5h, 5k, 5L Thus the nozzlebox-conduit assembly is firmly secured and accurately located relative to the upper casing half =2. The other nozzleboxes would then be similarly assembled, after which the rotor would be installed and the upper casing half 2 bolted to the lower casing half (not shown). The upper half of the outer casing 1 may then be lowered over the inner casing, so that the packing rings '7 receive the conduit end portion 5a. Disassembly is of course performed in the reverse order.

It will be seen that the only threaded fastenings involved in disassem-bly are the threaded members 20, which are subjected to the comparatively lower temperature steam in the space between the inner casing Z and the outer casing 1. Thus these threaded fastenings, being not very highly stressed anyhow, have little tendency to stick or gall. The lock ring 15, which takes the pressure forces on the nozzlebox assembly, has no associated threaded parts which might be subject to galling. The

segments of ring 15 are readily displaced radially outward for disassembly. Thus, by removal of the simple clamp ring 16 and the segmental lock ring 15, the nozzlebox assembly may be readily removed as a unit from the casing 2. The simplicity and ruggedness of the parts used makes it feasible to use a common set of casting patterns or forging dies for the nozzlebox and inlet conduit parts, for a range of turbine sizes, thus eifecting aIsubstantial reduction in manufacturing costs' Such standard nozzlebox assemblies would of course be provided with nozzle arcs 6a of a difierent arcuate length, or of appropriate eifective areas, corresponding to the capacity desired for the particular turbine.

As will be appreciated by those skilled in the art, the comparatively thin-walled steam inlet conduit 9, 8, the nozzlebox conduit portion 5, and the nozzlebox proper 6 will be fabricated of suitable high temperature alloys, for instance those known as austenitic stainless steels, for operating temperatures on the order of 1100 P. On the other hand, the inner casing 2 and the outer casing 1 may be made of lower temperature ferrit-ic alloy steels. As

noted above, the lock ring 15 is preferably made of thesame alloy as the casing boss portion 3 in order to avoid problems arising from differential thermal expansion between the lock ring and casing.

While only one specific structure has been described in detail herein, it will be obvious to those acquainted with the turbine art that numerous changes and substitutions of mechanical equivalents might be made. As suggested above, the built-up construction for the locating keys engaging the keyways 5g, 5h, 5k, SI, may be dispensed with, or these locating keys could take many other equivalent forms. For instance, the locating flange 5 might be provided with radially extending lugs engaging appropriate keyways formed in the clamp ring 16. Thus the proper class of fit could be obtained by repeatedly removing the ring 16 and carefully machining the keyways in it until the proper fit with the keys is obtained. As also suggested above, the clamp ring 16 may be either an integral ring or a plurality of segments. The special heat shield member 21 could of course be dispensed with for lower temperatures of operation.

Other changes will occur to those familiar withthej turbine art, and it is of course intended to cover by the appended claims all such modifications as fall with-in the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. Elastic fluid turbine nozzlebox assembly comprising an arcuate nozzlebox with a projecting inlet conduit, said inlet conduit being of generally circular cross section and having adjacent the nozzlebox an axially extending cylindrical conduit portion forming a radially extending annular abutment surface, a radially extending locating flange portion on said inlet conduit and spaced axially from the annular abutment surface of said cylindrical conduit portion at the side thereof remote from the nozzlebox, a casing member surrounding the nozzlebox and having a generally cylindrical casing boss coaxially surrounding said cylindrical conduit portion and having also a plurality of spaced locating recesses, packing means disposed between the outer surface of said cylindrical conduit portion and the inner surface of said casing boss, and means securing the inlet conduit relative to the casing boss comprising locating lug means cooperating with the nozzlebox and said locating recesses in the casing memher, a segmental lock ring member having a circumferential depending flange portion with a circumferential end portion adapted to engage radially with a circumferential groove in the outer surface of the casing boss, the lock ring member having also a central portion shaped to fit the axial space between said locating flange portion of the inlet conduit and said annular abutment surface of the cylindrical conduit portion, a clamp ring secured to hold together the segments of said lock ring member, and radial key means cooperating with said clamp ring and said locating flange portion for maintaining the inlet conduit coaxial within the casing boss.

2. Elastic fluid conduit and casing assembly comprising a casing member defining a generally cylindrical projecting casing boss, a conduit of circular cross section disposed coaxially within said casing boss andhaving an axially extendingvcylindrical conduit portion defining a radially extending annular abutment surface, said conduit having also a radially extending locating flange portion spaced axially from said annular abutment surface, packing means disposed between the outer surface of said cylindrical conduit portion and the inner surface of said casing boss, and means for supporting the conduit in coaxial relation with the casing boss including a segmental lock ring member having a circumferential depending flange portion surrounding the end of the casing boss with a circumferential end portion adapted to engage radially with a circumferential groove in the outer surface of the casing boss, the lock ring member having .also a central portion shaped to fit the axial space between said locating flange portion and said annular abutment surface, clamp means securing together the segments of the lock ring member, and radial key means cooperating with said clamp means and locating flange portion for maintaining the conduit coaxial within the casing boss.

3. Elastic fluid conduit and casing assembly comprising a casing member having a generally cylindrical projecting casing boss, a conduit of generally circular cross section disposed within said casing boss portion and having a first radially extending portion defining a first annular abutment surface, said conduit having also a second radially extending locating flange portion spaced axially from said first abutment surface, and means for supporting the conduit in coaxial relation within the casing boss including a, segmental lock ring member having a circumferential depending flange portion surrounding the end of the casing boss portion with an inwardly projecting end portion adapted to engage radially with a circumferential groove in the outer surface of the casing boss, the lock ring member having also a central portion shaped to fit the axial space defined between the locating flange portion and said first annular abutment surface, clamp means securing together the segments of the lock ring member, and radial key means cooperating with said clamp means and locating flange for maintaining-the conduit coaxial within the cylindrical casing boss portion.

4. Elastic fluid turbine nozzlebox assembly comprising an arcuate nozzlebox with a projecting inlet conduit of circular cross-section and having an axially extending cylindrical conduit portion defining a first'radially extending annular abutment surface, a radially extending locating flange portion on said inlet conduit and spaced axially from said annular abutment surface at the side thereof remote from the nozzlebox, a casing member having a generally cylindrical casing boss surrounding said cylindrical conduit portion and spaced portions defining locating recesses, and means supporting the nozzlebox assembly in said casing member comprising a plurality of locating lugs associated with the nozzlebox and shaped to engage said locating recesses in the casing member, a segmental lock ring member having a circumferential depending flange portion adapted to engage radiallywith a circumferential groove in the outer surface of the casing boss, the lock ring member having also a central portion adapted to fit the axial space between said locating flange portion and said annular abutment surface, a clamp ring disposed around said locating flange portion, means securing said clamp ring to the segmental lock ring member, and radial key means disposed between the clamp ring and the locating flange portion for maintaining the inlet nnduit coaxial within the casing boss.

References Cited in the file of this patent UNITED STATES PATENTS 2,112,738 Doran Mar. 29, 1938 2,527,445 Pentheny Oct. 24, .1950 2,527,446 Jenks, et a1. Oct. 24, 1950

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