EP4673629A1

EP4673629A1 - Spring insert assembly for non-bucketed stage groove in turbine rotor and turbine

Info

Publication number: EP4673629A1
Application number: EP24722106.2A
Authority: EP
Inventors: Steven Sebastian Burdgick; Kristopher John Frutschy; Cesar CORONA BRAVO; Jose Manuel Mendoza Perez; Hubert Kujawski; Geoffrey Scott CUSANO; Kane Douglas CHANDLER; Christopher EYRE
Original assignee: Ge Vernova Technology GmbH
Current assignee: Ge Vernova Technology GmbH
Priority date: 2023-04-26
Filing date: 2024-04-19
Publication date: 2026-01-07
Also published as: TW202443007A; WO2024223083A1

Abstract

A spring insert assembly (20) for a non-bucketed stage groove (18) in a turbine rotor (16) is described. Each of the spring inserts (64) have a base portion (46) inserted under hook lands (52) established in the non-bucketed stage groove, a neck portion (48) extending outward from the base portion, an extending cover (50) portion on the neck portion. The cover portion interfaces in mating engagement with cover portions of adjacent spring inserts in a tangential direction. The mating engagement between the cover portions of the spring inserts is a circumferential interference fit. The circumferential fit between the cover portions of the spring inserts creates an elastic twist in a predetermined direction between the cover portions and one of the base portions and the neck portions of the spring inserts.

Description

SPRING INSERT ASSEMBLY FOR NON-BUCKETED STAGE GROOVE IN TURBINE ROTOR AND TURBINE

BACKGROUND

TECHNICAL FIELD

[0001] Embodiments of this disclosure relate generally to steam turbines, and more specifically, to steam turbines with a non-bucketed stage groove in the turbine rotor for relieving thermal stresses, and transient thermal growth differences, with an assembly of spring inserts placed in the groove with an elastic twist in a predetermined direction to provide an improvement in performance of the groove and assembly of the spring inserts in the groove.

DISCUSSION OF ART

[0002] Steam turbine designs generally include static nozzle assemblies that direct a flow of steam into multiple stages or rows of turbine buckets that are connected to a rotating rotor. Said turbine buckets are also known as rotating blades. Some steam turbine designs include a non-bucketed stage groove formed circumferentially in the turbine rotor upstream of a first stage of turbine buckets. This non-bucketed stage groove, which can also be referred to as a stress relief groove or a BG0 groove, is typically used to help reduce and I or shield higher concentrated rotor stress at the groove in the rotor having the first stage of buckets. During operation of such steam turbines, the steam travels along the steam flow path from a steam inlet passage to the first stage of turbine buckets at a high flow rate. This high flow rate of steam can lead to the portion of the rotor underneath the first stage of buckets to have high stress concentration factor (Kt) values. In addition, the first stage of turbine buckets at this portion of the rotor can have very high inlet temperatures due to rotor bending that occurs at this location because of a gravity sag between the ends of the rotor. Placement of the non-bucketed stage groove in the rotor upstream of the first stage of buckets results in reduced Kt values at the location of this stage of buckets (inserts), while shielding some of the thermal and bending stress in the rotor that occur at the next downstream bucket stage.

[0003] In some steam turbine designs, rigid “inserts” are assembled in the non-bucketed stage groove to form a part of the steam flow path in order to match the inlet arcuate surface prior to the first stage of turbine buckets. These rigid inserts have a base portion with hooks that are configured to engage under the rotor undercut or hook lands established in the non-bucketed stage groove and a radial portion that extends up to the arcuate surface of the steam flow path. Use of these rigid inserts in the bucketed stage groove facilitate good rotor life, optimal steam flow swallowing and aero efficiency, with no span increase and no steam leakage.

[0004] Nevertheless, there are challenges associated with using these rigid inserts. One concern with the rigid inserts pertains to their assembly into the nonbucketed stage groove. In particular, the rigid inserts are assembled into the nonbucketed stage groove by twisting the hooks into the non-bucketed stage groove and then spinning the hooks under the rotor undercut. In this manner, the rigid inserts are stacked circumferentially about the non-bucketed stage groove and compacted tangentially. Shims are typically inserted in the non-bucketed stage groove in between placement of adjacent inserts. The insertion of the last few rigid inserts into the assembly becomes tight as space is needed tangentially to get those remaining inserts into the assembly in the radial direction. Due to the tightness in tangential space that is present with these remaining inserts, half shims can be placed in between the inserts instead of full inserts to allow for final closure of the inserts in the tangential direction. That is, a first half shim is placed in the small opening in the non-bucketed stage groove and slid in a first axially direction, and then a second half shim is push down the opening next to the first half shim and slid in an opposing axially direction with the use of a tooling device like a wedge placed therebetween to facilitate the insertion of both half shims in the groove, which is removed upon placement of the inserts. In this manner, the final rigid inserts can be placed radially in the last openings in the non-bucketed stage groove.

[0005] In order to facilitate the assembly of these rigid inserts with shims placed therebetween, both the full shims and the half shims can use circumferential dimples formed on their lateral surfaces for contact in the tangential direction with adjacent rigid inserts. During assembly, the dimples are compressed to provide room to enable the placement of shims between the inserts as well as to facilitate the contact and compaction of the rigid inserts in the tangential direction.

[0006] Problems can arise with this assembly of the rigid inserts in the nonbucketed stage groove with shims placed therebetween during operation as the turbine goes through thermal transients when the rotor, the stages of turbine buckets, the inserts and the shims heat up (e.g., during transient events such as start-up and shutdown). Typically, the inserts and the shims heat up at a different rate then the rotor and the buckets. As a result, during thermal transients, gaps can start to open up between the inserts and the shims, causing the shims to start loosening up and disengaging from the assembly of the rigid inserts while the turbine rotor is operating. This loosening and disengaging of the shims can result in an imbalance in the turbine rotor. [0007] The development of the gaps, loosening of the shims and their subsequent disengagement from the assembly of the rigid inserts stems from both the permanent deformation of the shim dimples as well as transient growth differences between the rotor and the inserts and shims. For example, the shim dimples, which ideally would be elastic upon removal of the insertion wedge to close up any tangential gap between the inserts and shims, turn out to compress plastically because of the thermal mismatch between the insert assembly and the rotor. Plastic deformation in the dimples can be non-uniform and as a result subsequent insert and shim movement can lead to non-uniform tangential gaps. Because the shim dimples are not reverting back to their shape to close up any tangential gaps, this leaves room for the shims to start loosening up and disengaging from the assembly of the rigid inserts while the turbine rotor is operating.

[0008] Another problem that can develop during thermal transients is that local thermal deformation can occur where the hot inlet steam can get down into the nonbucketed stage groove via the tangential gaps and cause a local “hot spot” that creates an imbalance in the turbine rotor. This imbalance can lead to rotor thermal bowing and excessive rotor vibration especially during startup. This imbalance in the rotor that is due to the local heating is unrelated to the above-mentioned thermal transient imbalance scenario that can arise from the loosening and disengaging of the shims. Actually, both thermal transient imbalance scenarios (i.e. , the imbalance from locating heating and the imbalance from the loosening and disengaging of the shims) can happen independently and unrelated from one another.

[0009] Attempts to ward off some of these problems include using different types of dimples on the shims. For example, spring shims can be inserted between the inserts instead of the dimpled shims. Also, arch shims can be used to supplement the spring shims by providing significantly more thickness to maintain elasticity in the spring shim. Nevertheless, these different types of shims do not totally solve the concern associated with dimpled shims, i.e. , that the shims are still susceptible to loosening and disengaging the non-bucketed stage groove.

[0010] Other attempts to preclude the shims from loosening and disengaging from the non-bucketed stage groove include welding the shims to the inserts. For example, in one implementation, welding is done between each shim and one adjacent insert. In addition, welding can be done at the top of the insert adjacent the shim. Welding the shims to the inserts, including full inserts and half inserts, can lead to a more robust assembly, but is time consuming, labor intensive and complicates the assembly of the rigid inserts in the non-bucketed stage groove, and thus is not ideal. Furthermore, even with welding, the shims are still susceptible to loosening and disengaging from the non-bucketed stage groove.

BRIEF DESCRIPTION

[0011] The following presents a simplified summary of the disclosed subject matter in order to provide a basic understanding of some aspects of the various embodiments described herein. This summary is not an extensive overview of the various embodiments. It is not intended to exclusively identify key features or essential features of the claimed subject matter set forth in the Claims, nor is it intended as an aid in determining the scope of the claimed subject matter. Its sole purpose is to present some concepts of the disclosure in a streamlined form as a prelude to the more detailed description that is presented later.

[0012] The aforementioned drawbacks associated with using an assembly of rigid inserts with shims placed therebetween in the non-bucketed stage groove create the need for a different insert assembly that can be placed in the groove that obviates issues such as shim liberation during turbine operation, non-uniform gapping in the groove due to the shims loosening and disengaging, and subsequent imbalance in the turbine rotor that leads to rotor thermal bowing and excessive rotor vibration, while maintaining positive features of the rigid insert designs such as facilitating good rotor life, optimal steam flow swallowing and aero efficiency, with no span increase and no steam leakage.

[0013] The solution provided by the various embodiments includes an assembly of spring inserts that can be placed in the non-bucketed stage groove with an elastic twist in a predetermined direction, which can also be referred to as an elastic pre-twist. Instead of using a rigid insert with a base portion and a radial portion that extends from the base to the steam flow path, the spring insert of these embodiments includes a base portion, a neck portion extending outward from the base portion, and an extending cover portion on the neck portion. These components of the spring insert as well as the non-bucketed stage groove can be configured with twist features that facilitate the elastic twist in the predetermined direction. For example, the cover portion of each spring insert can be skewed in a tangential direction. This allows the cover portion to interface in mating engagement with cover portions of adjacent spring inserts in the tangential direction, such that the mating engagement between the cover portions of the spring inserts is a circumferential interference fit. Also, the cover portions of the spring inserts can have an overlap with their edges in both the tangential direction and the axial direction.

[0014] With these twist features in the cover portions and those features configured in the base portion, the neck portion and the non-bucketed stage groove, the elastic twist of the spring inserts in the predetermined direction of the various embodiments can occur between the cover portions of the inserts and one of the base portions and the neck portions. That is, the twist features in the cover portions of the spring inserts allow for a twist I torsional spring-based base portion or neck portion for creating a twist reaction force that sets the elastic twist in the predetermined direction. This allows the cover portions to be skewed in the tangential direction.

[0015] In this manner, the elastic twist that results in the cover portions of the spring inserts skewed tangentially gives rise to a “stair-stepping” type of twisting of the covers that is beneficial during insertion and placement of the inserts in the nonbucketed stage groove. In particular, the stair-stepping type of twisting of the covers that arises from the elastic twist will allow for the tangential compaction that is necessary to radially insert those last few inserts in the non-bucketed stage groove during assembly. As a result, after all of the spring inserts have been assembled in the non-bucketed stage groove, the cover portions of those last few inserts will still have some elastic twist between the rest of the covers in the assembly that make a determinant system from an aeromechanics standpoint. Further, the remaining elastic twist between the cover portions creates the damping force necessary to create a predictable (damped) dynamic response for the spring insert assembly.

[0016] Not only is the assembly of the inserts improved with the elastic twist capability, but there is also an improvement in the performance of the non-bucketed stage groove with the assembly of spring inserts. For example, because the spring inserts are assembled with an elastic twist, the assembly of inserts will respond elastically and not plastically to the thermal strain mismatch that arises in transient events. As a result, tangential gaps will not arise between the inserts so that loosening and disengaging of any of the components of the assembly will not occur like that with conventional insert assemblies that use rigid inserts and shims placed therebetween. Furthermore, without the development of tangential gaps, steam leakage into the non-bucketed stage groove will not arise and cause a local hot spot that can lead to an imbalance in the turbine rotor such as thermal bowing and excessive rotor vibration during thermal or steady state operation of the steam turbine. The features of having cover portions with overlapping edges per certain embodiments can also contribute to further reduction in steam leakage into the nonbucketed stage groove that is attained with the inhibition of tangential gaps by greatly minimizing other possible steam leakage passages into the cavity defining the groove.

[0017] Said elastic twist (also known as elastic pre-twist) is a term commonly used in the field of turbine airfoils and design thereof. This term can mean that spring inserts are over twisted before assembly and then some of the twist comes out during operation and during years of creep untwisting.

[0018] In accordance with one embodiment, a spring insert assembly for a non-bucketed stage groove formed circumferentially in a turbine rotor and upstream of a first stage of turbine buckets and stator nozzles is provided. The spring insert assembly comprises: a plurality of spring inserts configured for insertion into the nonbucketed stage groove, each of the plurality of spring inserts including: a base portion having a base body configured to extend radially outward from the nonbucketed stage groove and a pair of opposing hook members extending from the base body and configured for insertion under hook lands axially established in the non-bucketed stage groove, the base body and the hook members each having a pair of lateral contact surfaces configured to interface in mating engagement with lateral contact surfaces of corresponding base bodies and hook members from adjacent spring inserts; a neck portion extending outward from the base body of the base portion and configured to extend radially outward from the non-bucketed stage groove, the neck portion having a pair of lateral face surfaces each configured to interface with lateral face surfaces of neck portions from adjacent spring inserts; and a cover portion on the neck portion with an extending cover body with a pair of lateral edges each configured to interface in mating engagement with lateral edges of cover bodies from cover portions of adjacent spring inserts in a tangential direction, wherein each of the lateral edges includes a protrusion configured to abut a protrusion from the lateral edges of the cover bodies of the adjacent spring inserts to form a cover-to-cover overlap arrangement in the tangential direction that creates an interference fit between the cover portions of the adjacent spring inserts, wherein the cover portion and one of the base portion and the neck portion is configured to elastically twist the spring insert in a predetermined direction in response to placement in the non-bucketed stage groove and engagement with adjacent spring inserts in the non-bucketed stage groove.

[0019] In accordance with another embodiment, a turbine is provided. The turbine comprises: a casing; a turbine rotor arranged inside the casing, the turbine rotor having a non-bucketed stage groove formed circumferentially therein; multiple stages of turbine buckets and stator nozzles downstream of the non-bucketed stage groove; a steam inlet passage between the casing and the turbine rotor to provide a flow of steam that travels through a downstream steam path that includes the nonbucketed stage groove and the multiple stages of turbine buckets; and a spring insert assembly as described herein.

DRAWINGS [0020] The present invention will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:

[0021] FIG. 1 shows a section from a longitudinal cross-sectional view of a steam turbine having multiple stages of turbine buckets and stator nozzles connected to a turbine rotor and a non-bucketed stage groove in the rotor upstream of the stages of buckets and nozzles in which a spring insert assembly according to an embodiment of the present invention can be placed therein;

[0022] FIG. 2 shows a more detailed view of the section depicted in FIG. 1 according to an embodiment of the present invention;

[0023] FIG. 3 shows a perspective view showing a portion of a turbine rotor like that depicted in FIGS. 1 and 2 with the non-bucketed stage groove and the spring insert assembly in the groove according to an embodiment of the present invention;

[0024] FIG. 4A shows a section view of the turbine rotor with the spring insert assembly circumferentially arranged in the non-bucketed stage groove according to an embodiment of the present invention, and FIG. 4B shows a perspective view of the spring insert assembly without the turbine rotor according to an embodiment of the present invention;

[0025] FIG. 5 shows a section of the non-bucketed stage groove with an assembly of rigid inserts and shims between the inserts according to the prior art;

[0026] FIGS. 6A and 6B show side views of a full shim and half-shims assembled to form a full shim, respectively, according to the prior art, and FIGS. 6C and 6D are sections of FIGS. 6A and 6B, respectively, that show further views of circumferential dimples on the lateral surfaces of the shims; [0027] FIG. 7 shows a perspective view of an assembly of spring inserts according to an embodiment of the present invention;

[0028] FIG. 8A shows a section view of an assembly of spring inserts in the non-bucketed stage groove with base portions of the inserts having a pocket formed between hook members that engage with hook lands of the turbine rotor according to an embodiment of the present invention, while FIG. 8B shows a top view of one of the inserts with more details of the base portion according to an embodiment of the present invention;

[0029] FIGS. 9A and 9B show side views of a section of the non-bucketed stage groove with the cover portion and base portion of a spring insert at various stages of disposal in the groove in relation to the hook lands of the turbine rotor according to embodiments of the present invention;

[0030] FIGS. 10A and 10B show views of an assembly of spring inserts with at least one of the inserts including two half-spring inserts according to embodiments of the present invention;

[0031] FIG. 11 shows a spring insert formed from two half-spring inserts according to one embodiment of the present invention;

[0032] FIG. 12 shows a more detailed view of the cover portions of adjacent spring inserts in the assembly with a smooth spline interface according to an embodiment of the present invention;

[0033] FIG. 13 shows a more detailed view of the cover portions of adjacent spring inserts in the assembly with chamfered surfaces with lines and arcs to form an interface with a gap between the inserts according to an embodiment of the present invention; [0034] FIG. 14 shows a more detailed view of a cover portion of a spring insert with a top surface having an arcuate shape and an axially extending side surface that is an arcuate surface according to an embodiment of the present invention;

[0035] FIG. 15 shows a more detailed view of a cover portion of a spring insert with an arcuate top surface and an axially extending side surface with a straight-line shape according to an embodiment of the present invention;

[0036] FIGS. 16A and 16B show various views of the non-bucketed stage groove with a protruding rail to react an elastic twist between the cover portions and the base portion of adjacent spring inserts in the tangential direction according to embodiments of the present invention;

[0037] FIGS. 17A and 17B show various views of the non-bucketed stage groove with an anti-rotation key disposed under the base portion of selected spring inserts to tangentially hold the selected spring inserts in place within the nonbucketed stage groove according to embodiments of the present invention.

[0038] FIGS. 18A and 18B show various views of the neck portions of the spring inserts having multiple features including a neck slot as a lightening feature according to embodiments of the present invention; and

[0039] FIG. 19 shows a more detailed view of a base portion of one spring insert in the non-bucketed stage groove with an angled hook interface therebetween according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0040] Example embodiments of the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments are shown. Indeed, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. For like numbers may refer to like elements throughout.

[0041] Throughout the discussion that follows, several descriptive terms may be used regularly herein. For example, it is often helpful to describe parts that are at differing radial, axial, circumferential and I or tangential positions. Accordingly, a set of axes will be referenced. These axes are based on a cylindrical coordinate system and point in an axial direction A, a radial direction R, and a circumferential direction C that extends around a longitudinal axis that aligns with the axial direction A. The axial direction A extends along the longitudinal axis of the turbine rotor (e.g., a central axis or center line of the rotor), the radial direction R extends transversely away (e.g., perpendicularly) from the longitudinal axis, the circumferential direction C extends around the longitudinal axis, and the tangential direction is relative to the circumferential direction C and the radial direction R. As used herein, the terms “axial” and I or “axially” refer to the relative position I direction of objects along axis A, which is substantially parallel with the axis of rotation of the turbine rotor (i.e. , the rotor center line). The term “radial” and I or “radially” refer to the relative position I direction of objects along the radial direction R, which is substantially perpendicular with axis A and intersects axis A at only one location. The term “circumferential” refers to movement or position around axis A (i.e., direction C). Finally, the term “tangential” and I or tangentially refers to the relative position I direction of objects along the C direction, at a tangent from the radial direction.

[0042] Also, as used herein, “downstream” and “upstream” are terms that indicate a direction relative to the flow of a fluid, such as the working fluid through a steam turbine or, for example, the flow of steam through a turbine section. The term “downstream” corresponds to the direction of flow of the fluid, and the term “upstream” refers to the direction opposite to the flow.

[0043] Turning now to the figures, FIG. 1 shows a section from a longitudinal cross-sectional view of a steam turbine 10, such as for example, a high pressure turbine, having multiple stages of turbine buckets 12 and stator nozzles 14 connected to a turbine rotor 16 and a non-bucketed stage groove 18 in the rotor upstream of the stages of buckets and nozzles in which a spring insert assembly 20 can be placed according to an embodiment of the present invention. The steam turbine further comprises an outer casing 22 and an inner casing 24 arranged in the outer casing. The turbine rotor 16 is rotatably mounted around a rotational axis 26 which can also be referred to as the rotor centerline. A steam inlet 28 is disposed in the inner casing 24 to receive a supply of operating steam 30. A steam inlet passage 32 leads the steam from the steam inlet 28 to the stages of turbine buckets 12 and stator nozzles 14 to form a portion of the steam flow path of the steam turbine 10. As shown in FIG. 1 , the steam inlet passage 32 can include a radial extending flow portion 34, an arcuate extending flow portion 36, and an axially extending flow portion 38.

[0044] A radial nozzle row 40, also known in the art as a guide vane row, can be placed through the radial extending flow portion 34 of the steam inlet passage 32 downstream of the steam inlet 28. With the radial nozzle row 40 disposed in this location of the steam inlet passage 32, the steam 30 can travel along the arcuate extending flow portion 36 over the non-bucketed stage groove 18 and the spring insert assembly 20 and the axially extending flow portion 38 towards the stages of turbine buckets 12 and stator nozzles 14 at a high flow rate. In this manner, the steam 30 flows through the stages of turbine buckets 12 and stator nozzles 14 to form another portion of the steam flow path of the steam turbine 10 that is substantially axially extending and is where the steam is expanded in the turbine and used to drive an electric generator to produce electricity or provide heat for other purposes.

[0045] FIG. 2 shows a more detailed view of the section depicted in FIG. 1 according to an embodiment of the present invention. In particular, FIG. 2 shows further details of the steam inlet 28, the steam inlet passage 32, the radial nozzle row 40, the non-bucketed stage groove 18 and the spring insert assembly 20 in the groove, and initial stages of the turbine buckets 12 and the stator nozzles 14 that are downstream of the groove and the spring inserts. As shown in FIG. 2, the upper radial portion of the non-bucketed stage groove 18 and spring insert assembly 20 match the arcuate shape of the abutting surface of the arcuate extending flow portion 36 of the steam inlet passage 32. FIG. 2 shows that the non-bucketed stage groove 18 can include a radial portion 42 extending inward from the surface of the arcuate extending flow portion 36 and a widen portion 44 extending axially from the radial portion 42 about the turbine rotor 16. To this extent, the widen portion 44 is widened in comparison to the radial portion 42.

[0046] Each of the spring inserts that form the spring insert assembly 20 can include a base portion 46, which can also be referred to as a dovetail or root portion, a neck portion 48 and a cover portion 50. The base portion 46 of the spring inserts are secured in the non-bucketed stage groove 18 under hook lands 52 established in the groove upon insertion and placement of the insert, such that the top surface of the cover portion 50 is substantially level with the surface of the arcuate extending flow portion 36 of the steam inlet passage 32. As shown in FIG. 2, the base portion 46, the neck portion 48, and the cover portion 50 can extend over a greater part of the radial depth of the non-bucketed stage groove 18. Discussed below are further details of the spring insert assembly 20 and individual features of each of the elements of the spring inserts that facilitate the insertion and placement of the inserts in the non-bucketed stage groove 18 per the various embodiments.

[0047] As shown in FIG. 3, the non-bucketed stage groove 18 can extend circumferentially over the entire periphery of the turbine rotor 16 and extend from its opening on the rotor surface essentially radially inwards, with the spring insert assembly 20 inserted and placed in the groove. A more detailed view of the nonbucketed stage groove 18 and the spring insert assembly 20 in the groove with respect to a section of the rotor near the groove 18 is shown in FIG. 4A, while FIG. 4B shows the circumferentially arranged spring insert assembly 20 with the rotor removed for clarity.

[0048] As noted above, conventional inserts placed in the non-bucketed stage groove comprise rigid inserts with shims inserted between adjacent inserts. FIG. 5 shows a section of a non-bucketed stage groove 54 in the turbine rotor 16 with an assembly of rigid inserts 56 and shims 58 between the inserts according to the prior art. The insertion of the last few rigid inserts 56 into an assembly of inserts becomes tight as space is needed tangentially to get those remaining inserts into the assembly in the radial direction. Due to the tightness in tangential space that is present with these remaining inserts, half shims can be placed in between the inserts instead of full inserts to allow for final closure of the inserts in the tangential direction. FIG. 6A shows a side view of a full shim 58, while FIG. 6B shows a side view of a full shim formed from two half-shims 60. [0049] To facilitate the assembly of the rigid inserts 56 with the shims placed therebetween, both the full shims 58 and the half shims 60 can have circumferential dimples 62 formed on their lateral surfaces for contact in the tangential direction with adjacent rigid inserts. For example, FIG. 6C shows a dimple 62 in the form of a flat dimple and FIG. 6D shows a dimple in the form of a ring stamp dimple. During assembly, the dimples 62 are compressed to provide room to enable the placement of shims between the inserts 56 as well as to facilitate the contact and compaction of the rigid inserts in the tangential direction. As noted above, the permanent deformation of the dimples 62 contributes to the development of gaps that form between the rigid inserts, loosening of the shims 58 and 60 and their potential for subsequent disengagement from the assembly of the inserts stems. Ideally, the dimples 62 should be elastic to close up any tangential gaps between the rigid inserts 56 and the shims 58 and 60, but instead the dimples turn out to compress plastically because of the thermal mismatch between the insert assembly and the rotor during thermal transients.

[0050] Because the dimples 62 behave plastically and not elastically, the dimples like those depicted in FIGS. 6A-6D will not revert to their uncompressed state upon insertion and placement against adjacent inserts, and any tangential gaps between the shims and the inserts will not be closed up. As a result, this leaves room for the shims to start loosening up and disengaging from the assembly of the rigid inserts while the turbine rotor is operating.

[0051] The solution provided by the various embodiments to obviate the problems associated with the conventional rigid inserts 56 and shims 58 and 60 placed between the inserts includes the assembly of spring inserts 20 that can be placed in the non-bucketed stage groove 18 with an elastic twist in a predetermined direction. This elastic twist can be referred to as an elastic pre-twist, which is a common term to those skilled in the art. For example, as used herein, an elastic pretwist of the spring inserts means that the inserts are over twisted before assembly. It is understood that some of the twist can come out during operation and during years of creep untwisting. Instead of using a rigid insert with a base portion and a radial portion that extends from the base portion to the steam flow path, each of the spring inserts of the various embodiments includes a base portion, a neck portion extending radially outward from the base portion, and an axially extending cover portion on the neck portion. These components of the spring inserts as well as the non-bucketed stage groove can be configured with twist features that facilitate the elastic twist in the predetermined direction. For example, the cover portion of each spring insert can be skewed in a tangential direction. This allows the cover portion to interface in mating engagement with cover portions of adjacent spring inserts in the tangential direction, such that the mating engagement between the cover portions of the spring inserts is a circumferential interference fit. Also, the cover portions of the spring inserts can have an overlap with their edges in both the tangential direction and the axial direction.

[0052] With these twist features in the cover portions and those features configured in the base portion, the neck portion and the non-bucketed stage groove, the elastic twist of the spring inserts in the predetermined direction of the various embodiments can occur between the cover portions of the inserts and one of the base portions and the neck portions. This twist causes allows the cover portions of the spring inserts to be skewed tangentially. As a result, the spring inserts of the assembly can be compacted tangentially over the circumferential arrangement of the assembly. [0053] The spring insert assembly configurations of the various embodiments described herein results in several technical effects. For example, the elastic -twist capability that is provided by the assemblies of the various embodiments leads to an improvement in the performance of the non-bucketed stage groove with the assembly of spring inserts. For example, because the spring inserts are assembled with an elastic twist, the assembly of inserts will respond elastically and not plastically to thermal strain mismatches that arise in transient events. As a result, tangential gaps will not appear between the inserts so that loosening and disengaging of any of the components of the assembly will not occur like that with conventional insert assemblies that use rigid inserts and shims placed therebetween. Although the improved performance of the non-bucketed stage groove with the assembly of spring inserts is apparent for transient conditions, the various embodiments can also lead to a performance improvement during steady state operation of the turbine rotor. Accordingly, it is understood that the various embodiments have utility beyond transient conditions, and thus the embodiments are not meant to be limited to only transient conditions.

[0054] Furthermore, without the development of tangential gaps, steam leakage into the non-bucketed stage groove will not arise and cause local hot spots that can lead to an imbalance in the turbine rotor such as thermal bowing and excessive rotor vibration during thermal or steady state operation of the steam turbine. The features of having cover portions with overlapping edges per certain embodiments can also contribute to further reduction in steam leakage into the nonbucketed stage groove that is attained with the inhibition of tangential gaps by greatly minimizing other possible steam leakage passage into the cavity defining the groove. [0055] Other technical effects associated with the spring insert assembly configurations of the various embodiments are that the embodiments maintain positive features of the rigid insert designs, such as for example, facilitating good rotor life, optimal steam flow swallowing and aero efficiency, with no span increase and no steam leakage.

[0056] FIG. 7 shows a perspective view of the spring insert assembly 20 according to an embodiment of the present invention. The spring insert assembly 20 of FIG. 7 shows two spring inserts 64, but it is understood that the number of inserts depicted in this figure can include a plurality of spring inserts like that depicted in FIGS. 4A and 4B. The actual number of spring inserts 64 that can be deployed in the non-bucketed stage groove 18 of the turbine rotor 16 can vary depending on the radius of the rotor which can differ between larger-sized rotors and smaller-sized rotors. Furthermore, those skilled in the art will appreciate that the number of spring inserts 64 assembled in the non-bucketed stage groove 18 of the turbine rotor 16 can typically range between 70 and 150 inserts per row. It is understood that this range is for illustrative purposes and is not meant to be limiting to any of the various embodiments.

[0057] Each of the spring inserts 64 in the embodiment depicted in FIG. 7 can include the base portion 46, the neck portion 48 and the cover portion 50. As shown in FIG. 7, the base portion 46 can have a base body 66 that is configured to extend radially outward from the non-bucketed stage groove 18 (FIGS. 1 and 2). A pair of opposing hook members 68 can extend from the base body 66 which are configured for insertion under the hook lands 52 (FIG. 2) axially established in the non-bucketed stage groove 18. The base body 66 and the hook members 68 each have a pair of lateral contact surfaces configured to interface in mating engagement with lateral contact surfaces of corresponding base bodies and hook members from adjacent spring inserts.

[0058] In one embodiment, the pair of lateral contact surfaces of the base body 66 can comprises a first lateral contact surface 70 and a second lateral contact surface 72. The first lateral contact surface 70 can form a pocket 74 between the pair of opposing hook members 68 and the second lateral contact surface 72 can have a projection 76 that extends beyond a periphery of the pair of opposing hook members in a tangential direction. To this extent, the pocket 74 and the projection 76 of each spring insert 64 can interlock correspondingly with the projection and pocket from the cover bodies of the adjacent spring inserts. Further details of the pocket 74 and the projection 76 interlocking correspondingly with the projection and pocket from the cover bodies of adjacent spring inserts are discussed in more detail with respect to FIGS. 8A and 8B.

[0059] FIG. 7 also shows that the base body 66 of the base portion 46 of the spring insert 64 can include a cut-out or a notch 78 formed in a lower radial surface of the base body between the pair of opposing hook members 68. The notch 78 can form a raised channel that extends through opposing internal side walls of the base body 66 to define an opening therethrough. As explained in more detail below with regard to other embodiments, the notch 78 can operate in a cooperative manner with a protruding rail formed in the non-bucketed stage groove and I or an anti-rotation key, both of which can be used to react the elastic twist between the cover portion and the base portion in the tangential direction in relation to the adjacent spring inserts. As used herein, to react the elastic twist between the cover portion and the base portion means to take the torsional elastic strain between the cover and the base. For example, the torque force, created by the interference, or elastic twist (pre-twist), is reacted between the cover and the circumferential rotor rail. Other embodiments as described below can react a twist between the cover portion and the neck portion.

[0060] The neck portion 48 of the spring insert 64 as shown in FIG. 7 can extend outward from the base body 66 of the base portion 46. The neck portion 48 can have a pair of lateral face surfaces 80 each configured to interface with lateral face surfaces of neck portions from adjacent spring inserts. For clarity, the neck portion 48 depicted in FIG. 7 only is labeled with one lateral face, however it is understood that the opposing side includes a second lateral face. In one embodiment, the neck portion 48 can have an axial width that is reduced in comparison to the axial width of the base portion 46 and the cover portion 50. The reduced neck portion 48 in relation to the base portion 46 and the cover portion 50 can be beneficial to react a twist between the cover portion and the base portion, or a twist between the cover portion and the neck portion. Regardless of where and how the twist is brought about and reacted, FIG. 7 shows that a gap 82 will form between the lateral face surfaces 80 of the neck portions 48 of adjacent spring inserts 64 as a result of the elastic twist that is configured through the placement and assembly of the inserts in the non-bucketed stage groove 18.

[0061] As shown in FIG. 7, the cover portion 50 of the spring insert 64 can include an extending cover body 84 (e.g., axially extending) with a pair of lateral edges 86 each configured to interface in mating engagement with the lateral edges of the cover bodies from the cover portions of adjacent spring inserts in a tangential direction as well as an axial direction. In one embodiment, each of the lateral edges 86 can include a protrusion 88 that is configured to abut with a protrusion from the lateral edges of the cover bodies 84 of the adjacent spring inserts to form a cover-to- cover overlap arrangement in the tangential direction and axial direction that creates an interference fit between the cover portions of the adjacent spring inserts. In this manner, the cover-to-cover overlap arrangement with this interference fit can prevent the flow of steam from flowing between the inserts.

[0062] In one embodiment, as shown in FIGS. 7 and 12, the cover-to-cover overlap arrangement formed from the abutting of the protrusions 88 of the lateral edges 86 of the cover bodies 84 of the adjacent spring inserts 64 can comprise a smooth spline interface 90 between the lateral edges.

[0063] The extending cover body 84 of the cover portion 50 of each spring insert 64 can comprise an arcuate top surface 92 that is configured to match a flow path of steam (i.e. , the steampath contour) provided to the first stage of turbine buckets and stator nozzles. More specifically, that is, the arcuate top surface 92 is configured to match the sidewall of the inlet steampath. In one embodiment, as shown in FIGS. 7 and 14, the cover portion 50 of each of the spring inserts 64 can comprise a pair of opposing axially extending side surfaces 94 each configured to interface with axially extending side surfaces of the cover portions from the adjacent spring inserts. To this extent, the interfacing axially extending side surfaces 94 can comprise an arcuate shape that matches the flow path of steam provided to the first stage of turbine buckets and stator nozzles.

[0064] With the spring insert cover configuration depicted in FIG. 7, embodiments of the present invention can be configured to provide an elastic twist between one of the base portion 46 and the neck portion 48 in a predetermined direction in response to placement of the spring inserts 64 in the non-bucketed stage groove 18 (FIGS. 1 and 2) and engagement with adjacent spring inserts in the groove. In one embodiment, the elastic twist can occur between the cover portion 50 and the base portion 46. For example, as shown in FIGS. 7, 8A and 8B, the surfaces of the first lateral contact surface 70 of the base body 66 of the base portion 46 of the spring insert 64 that define the pocket 74 can axially interlock with the projection 76 from the second lateral contact surface 72 of the base body of the base portion of an immediately adjacent spring insert. The location of this axial insert-to- insert twist interlock that occurs between the spring inserts 64 is depicted in FIGS. 8A and 8B with reference element 96. With the base portions of the inserts axially interlocked, and the features of the configuration of the cover portions 50 of the inserts (e.g., the cover-to-cover overlap arrangement in the tangential direction and the axial direction that creates interference fit between the cover portions), the elastic -twist can occur between the cover portions and the base portions of the inserts. [0065] In particular, with this configuration of the cover portions 50 and the base portions 46, a force can be created at one of the comers of the cover bodies 84 and at an opposite corner due to the cover-to-cover overlap arrangement in the tangential direction and the axial direction. As a result, there will always be a force on the spring insert. Since the base portions 46 are axially interlocked, the force from the cover portions 50 will create the twist between the tangential faces of the cover portions and the tangential faces of the base portions of the spring inserts 64. In this manner, the neck portions 48 of the spring inserts 64 will twist between the cover portions 50 and the base portions 46. This twist at the neck portions results in the gap 82 between the lateral face surfaces 80 of the neck portions 48 of adjacent spring inserts 64 as shown in FIG. 7.

[0066] Additionally, the elastic twist that arises from the cover-to-cover overlap arrangement in the tangential direction and the axial direction and the axially interlocking of the base portions 46 of the spring inserts 64 will cause the spring inserts to be skewed tangentially, and as a result, their cover portions will form a stair-stepping pattern. This stair-stepping pattern that arises from the twisting of the covers will enable the spring insert assembly 20 with the capability to put more spring inserts 64 in the non-bucketed stage groove 18 than what would be expected with an assembly formed from rigid inserts. This can be beneficial during the placement and installation of the last few spring inserts 64 in the non-bucketed stage groove during assembly.

[0067] FIGS. 9A and 9B provide examples showing the placement and installment of the spring insert 64 in the non-bucketed stage groove 18 during assembly. In particular, FIGS. 9A and 9B show side views of a section of the nonbucketed stage groove 18 with the cover portion 50 and base portion 46 of the spring insert 64 at various stages of disposal in the groove in relation to the hook lands 52 of the turbine rotor 16. For example, FIG. 9A shows how the spring insert 64 can be twisted for placement in the non-bucketed stage groove 18. As shown in FIG. 9A, the hook members 68 of the base portion 46 and the cover portion 50 are twisted so that the spring insert 64 can fit in the non-bucketed stage groove 18. In this state, the hook members 68 are not yet in mating engagement with the hook lands 52, and the cover body 84 of the cover portion 50 is generally aligned between the radial width of the non-bucketed stage groove 18. In FIG. 9B, the spring insert is twisted at a predetermined twist angle so that the hook members 68 will be underneath the hook lands 52 to be in mating engagement, and the cover body 84 will be skewed at a predetermined skew angle with respect to the non-bucketed stage groove 18 including the hook lands 52. It is understood that the predetermined twist angle used to twist the spring insert 64 for insertion and placement in the non-bucketed stage groove 18 can vary and will depend on factors such as the groove width and the desired cover skew angle. In general, an illustrative predetermined twist angle can range from about 20° degrees to 60° degrees.

[0068] The elastic twist feature associated with the various embodiments makes the assembly of the last few spring inserts 64 into the non-bucketed stage groove 18 more readily achievable in comparison to an assembly formed from rigid inserts. As noted above, the insertion of the spring inserts 64 into the assembly of inserts can become tight as space is needed tangentially to get those remaining inserts into the assembly in the radial direction. Due to this tightness in the tangential space, half-spring inserts can be used instead of spring inserts to allow for final closure of the inserts in the assembly in the tangential direction.

[0069] The half-spring inserts, which are used to form the spring inserts that are inserted in those last remaining rows of inserts, can also be configured to have twist features per any of the various embodiments described herein to enable an elastic twist that occurs between the cover portion and one of the base portion and the neck portion of these half-spring inserts. FIGS. 10A and 10B show one embodiment in which an anti-twist feature can be built into the base portions of the half-spring inserts that are used to form a spring insert. In particular, the embodiment depicted in FIGS. 10A and 10B utilizes an axial insert-to-insert twist interlock feature like that described with respect to FIGS. 7, 8A, and 8B, except that this feature is deployed with the half-spring inserts 98 utilized to form a spring insert. That is, the anti-twist feature of the base portion of the spring insert depicted in FIGS. 7, 8A, and 8B can be built into the base portions of the half-spring inserts that are used to form a spring insert.

[0070] As shown in FIG. 10A, each half-spring insert 98 can include a halfspring insert base portion 100, a half-spring insert cover portion 102, and a half- spring insert neck portion 104 extending between the half-spring insert base portion 100 and the half-spring insert cover portion 102. The half-spring-insert base portion 100 can have a pair of axially extending ends. A first axially extending end of the half-spring insert base portion 100 can include a hook member 106 configured for insertion under the hook lands 52 in the non-bucketed stage groove 18 and a second axially extending end of the half-spring insert base portion can include a coupling end 108 configured for an axial mating engagement with a coupling end of a halfspring insert base portion of an axially adjacent half-spring insert 98. In one embodiment, the coupling ends 108 of each of the half-spring-insert base portions 100 can take the form of a tongue and groove mating arrangement. In this manner, the axial mating engagement between the half-spring inserts 98 by way of the tongue and groove mating arrangement will lock the two half-spring inserts axially in place in the non-bucketed stage groove 18, preventing any twist between the halfspring inserts.

[0071] It is understood that the axial mating engagement between the halfspring inserts 98 in this embodiment as well as the embodiments depicted in FIGS.

7, 8A and 8B are not limited to a tongue and groove mating arrangement. Those skilled in the art will appreciate that other forms of mating arrangements can be configured in the base portions and neck portions of the spring inserts and halfspring inserts to facilitate an axial mating engagement. Examples can include, but are not limited to, a protruding rail in the non-bucketed stage groove like that discussed with respect to FIGS. 16A and 16B; an anti-rotation key like that discussed with respect to FIGS 17A and 17B, and a pair of opposing neck protrusions like that discussed with respect to FIGS. 18A and 18B. Additionally, a pinned engagement can be used to facilitate an axial mating engagement between the half-spring inserts.

[0072] With the half-spring inserts 98 in mating engagement, a pocket 74 can be formed between the half-spring inserts. Although not shown in FIG. 10A and 10B, the base body of the spring insert formed from the half-spring inserts 98 can also have a projection 76 on the side that opposes the pocket like that described with respect to FIGS. 7, 8A and 8B, that can extend beyond a periphery of the resultant pair of opposing hook members in a tangential direction. To this extent, the pocket 74 and the projection of the spring insert formed from the half-spring inserts 98 can interlock correspondingly with the projection and pocket from the cover bodies of the adjacent spring inserts in the tangential direction.

[0073] FIG. 10A shows that the half-spring insert neck portion 104 of the halfspring inserts 98 can each include a pair of opposing axial face surfaces 110. Each face surface 110 can be configured to tangentially interface with a face surface of a neck portion of an immediately adjacent spring insert or a half-spring insert without contact thereof. As shown in FIG. 10A, the half-spring insert neck portion 104 of each half-spring insert 98 can also include an inner edge face surface 112 that is configured to oppose an inner edge face surface of the half-spring insert neck portion of the axially adjacent half-spring insert upon putting the half-spring inserts in mating engagement.

[0074] The formation of the spring insert from the half-spring inserts 98 as depicted in the embodiment of FIGS. 10A and 10B brings about a resultant cover portion from the half-spring insert cover portions 102. Like the embodiments described with respect to FIGS. 7, 8A, and 8B, the resultant cover portion of the embodiment of FIGS. 10A and 10B can have a cover-to-cover overlap arrangement in the tangential direction and the axial direction with immediately adjacent spring inserts. This cover-to-cover overlap arrangement in the tangential direction and the axial direction creates an interference fit between the cover portions of the inserts. As a result, the use of the half-spring inserts 98 to form the spring insert will also lead to the elastic twist between the cover portions and the base portions of the inserts like that described previously with respect to FIGS. 7, 8A, and 8B.

[0075] The resultant cover portion that is attained from the mating of the halfspring inserts 98 can have a separation at a location 114 where the half-spring insert cover portions 102 are axially adjoined. This separation can be closed by applying a weld to the half-spring inserts 98 at the location 114. For example, a typical “U” or “J-prep” weld interface could be used at the corner interface between the half-inserts as location 114. The weld will secure the mating of the half-spring insert cover portions 102 to make a more robust assembly and prevent leakage of steam between the half-spring inserts.

[0076] FIG. 10B shows a top view of the half-spring inserts 98 used to form a spring insert in FIG. 10A in a spring insert assembly 20 that includes other spring inserts 64. In particular, this view illustrates the half-spring inserts 98 in assembly with the other spring inserts 64 after the elastic twist. In this manner, the spring insert assembly 20 is relieved tangentially to close tangential gaps between the inserts.

[0077] It is understood that the half-spring inserts described with respect to FIGS. 10A and 10B represent only one possible design option. Furthermore, the forms of engagement to couple the half-spring inserts 98 to form a spring insert is illustrative of one configuration. Those skilled in the art will appreciate that the halfspring inserts can be configured differently, and thus the embodiments depicted in FIGS. 10A and 10B are not meant to be limiting. For example, instead of having a slot like the race-track slot formed in the neck portion of the spring inserts including those formed from the half-spring inserts, the neck portions can include other shaped slots or no slots at all. Furthermore, it is understood that although FIGS. 10A and 10B show only one spring insert formed from a pair of half-spring inserts, there may be situations in which a row may have more than one spring insert formed from a combination of two half-spring inserts. For example, there could be such a small tangential opening when inserting those last remaining spring inserts in the nonbucketed stage groove, that it might necessitate the use of two sets of half-spring inserts (two adjacent in the tangential direction).

[0078] FIG. 11 shows a spring insert assembly 20 having spring insert 116 formed from two half-spring inserts 118 according to another embodiment. As shown in FIG. 11 , each half-spring insert 118 can include a half-spring insert base portion 120, a half-spring insert cover portion 122, and a half-spring insert neck portion 124 extending between the half-spring insert base portion and the half-spring insert cover portion. The half-spring insert neck portion 124 can include a pair of opposing axial face surfaces 126 each configured to interface with axial face surfaces of the neck portions of immediately adjacent inserts.

[0079] The half-spring insert neck portion 124 can also include various axial end face surfaces. One end face surface of the axial end face surfaces can include a hook member 128 configured for insertion under the hook lands 52 in the nonbucketed stage groove 18. Another axial end face surface of the axial end face surfaces can include a half-spring insert neck contact surface 130 configured to interface with a corresponding half-spring insert neck contact surface of the other half-spring insert 118 coupled therewith. [0080] FIG. 11 further shows that other axial end face surfaces of the halfspring insert neck portion 124 of each of the half-spring inserts 118 can include an inner edge face contact surface 132 that is configured to mate with the inner edge face contact surface of the half-spring insert neck portion of the axially adjacent halfspring. In one embodiment, the inner edge face contact surfaces 132 of each of the half-spring insert neck portions 124 can take the form of a tongue and groove mating arrangement. In this manner, the axial mating engagement between the half-spring inserts 118 by way of the tongue and groove mating arrangement will lock the two half-spring inserts axially in place in the non-bucketed stage groove 18, preventing any twist between the half-spring inserts.

[0081] It is understood that the elements of the half-spring inserts 98 depicted in FIG. 11 are illustrative of one design and those skilled in the art will appreciate that variations to this design are possible. For example, the grooves that are formed between the various hooking members shown with the half-spring insert neck portions 124 of the half-spring inserts 118 can be taller or shorter depending on stage of the inserts in the non-bucketed stage groove 18. In addition, the axial mating engagement between the half-spring inserts 98 in this embodiment is not meant to be limited to a tongue and groove mating arrangement. The previously mentioned axial mating engagements are applicable to the embodiment as well.

[0082] Like the embodiments described with respect to FIGS. 10A and 10B, the formation of the spring insert 116 from the half-spring inserts 118 in FIG. 11 will yield a resultant cover portion from the half-spring insert cover portions 122. In this manner, the resultant cover portion includes a cover-to-cover overlap arrangement in the tangential direction and the axial direction with immediately adjacent spring inserts. The cover-to-cover overlap arrangement in the tangential direction and the axial direction can create an interference fit between the cover portions of the inserts. As a result, the use of the half-spring inserts 118 to form the spring insert 116 will also lead to the elastic twist between the cover portions and the base portions of the inserts like that described with respect to FIGS. 7, 8A, 8B, 10A and 10B.

[0083] Irrespective of whether the configuration of the half-spring inserts take the form of the inserts depicted in FIGS. 10A-1 OB, or FIG. 11 , or some other configuration, all of these inserts can be put together in a spring insert assembly with spring inserts using a common approach. For example, one approach of putting together a spring insert assembly that utilizes spring inserts and half-spring inserts can include a twist assembly of the majority of the spring inserts like that described above. That is, the spring inserts can be twisted for placement in the non-bucketed stage groove 18 and rotated once in the groove so that the inserts are twisted at a predetermined twist angle. To this extent, the hook members can be underneath the hook lands 52 of the turbine rotor 16 to be in mating engagement, and the covers will be skewed at a predetermined skew angle with respect to the non-bucketed stage groove 18.

[0084] After the twist assembly of a row of spring inserts, other steps can be performed. These steps include attaching manual or hydraulic tooling to radially protruding threaded bosses applied to the inserts that can be used to facilitate the assembly of the inserts. The manual or hydraulic tooling can then be used to perform a swage row open of the spring inserts in the non-bucketed stage groove 18.

[0085] The installment and placement of the half-spring inserts can then be performed after these operations. In general, each half-spring insert can be inserted into the tight radial opening in the non-bucketed stage groove 18 and slid into engaged with one another using any of the mating arrangements approaches described above (e.g., a tongue and groove arrangement). This will lock the halfinserts together.

[0086] With the half-spring inserted and placed in the non-bucketed stage groove 18, remaining steps of the assembly can then be performed. These steps can include releasing the row of the inserts (i.e. , a tangential elastic strain release), welding the top cover portions of the adjoined half-spring inserts, and grinding off the threaded bosses from the inserts.

[0087] While for purposes of simplicity of explanation, the aforementioned operations used to assemble the spring inserts and half-spring inserts in the nonbucketed stage groove 18 are described as a series of acts. It is to be understood and appreciated that these operations are not limited by the order of acts, as some acts may occur in a different order and I or concurrently with other acts.

Furthermore, those skilled in the art will understand and appreciate that other methodology or operations could alternatively be utilized to assemble the spring inserts and half-inserts in the non-bucketed stage groove. Moreover, not all of the described operations may be required to implement the spring insert assembly in the non-bucketed stage groove.

[0088] It is understood that these operations can be used to configure the spring insert assembly in a number of configurations. For example, the operations can be used to configure the elastic twist of the spring inserts in a clock-wise direction like that shown in FIG. 9B. In another embodiment, the elastic twist of the spring inserts can be configured in a counter-clock-wise direction. In still another embodiment, the elastic twist of the spring inserts can be configured in varying combinations of clock-wise and counter-clock-wise directions. Examples can include, but are not limited to, having the elastic twist all in one direction (e.g., clockwise direction or counter-clock-wise direction) and in alternating directions. A twist in one direction means that the cover force will always be at the same location on all covers in the spring insert assembly. It is understood that these alternating elastic twists can be applied to inserts individually or groups of inserts to create twist loads in a multiple of direction configurations. For example, this could mean that half of the covers have a force on the same point of contact between covers, while the other half of covers can have the contact force on the opposite (tangential) corner.

[0089] Further, it is understood that the spring inserts described in FIGS. 7, 8A, 8B, and 10A represent only one possible design option for spring inserts that can be assembled in the non-bucketed stage groove 18. The manner in which the elastic twist is generated in the assembly with this type of spring insert depicted in FIGS. 7, 8A, 8B, and 10A represents only one approach that can be utilized to attain the elastic twist in the assembly. Those skilled in the art will appreciate that the spring inserts 64 of FIGS. 7, 8A, 8B, and 10A can be configured differently. In addition, those skilled in the art will appreciate that the elastic twist can be implemented differently than that described with respect to FIGS. 7, 8A, 8B, and 10A.

[0090] For example, instead of having an assembly of spring inserts having a cover-to-cover overlap arrangement that comprises a smooth spline interface 90 between the lateral edges 86 of the cover bodies 84 of adjacent spring inserts 64 as shown in FIGS. 7 and 10A, this cover-to-cover overlap arrangement can include a chamfered interface surface as shown in FIG. 13. A cover-to-cover overlap arrangement with a smooth spline interface can be difficult to produce because of the challenges that it presents from machining and tolerances inspection points of view. A chamfered interface surface address these challenges as a chamfered interface surface significantly reduces the complexity in machining and tolerances.

[0091] As shown in FIG. 13, the lateral edges 86 of the cover bodies 84 of the cover portions 50 of the spring inserts 64 can include a chamfered surface 134 with a blend of lines 136 and arcs 138. In this manner, the protrusions 88 of the lateral edges 86 of the cover bodies 84 will abut with one another, but a gap 140 is formed therebetween due to the lines 136 and arcs 138 of the chamfered surface 134.

[0092] Instead of having the cover body 84 of the cover portion 50 of each spring insert 64 with an arcuate top surface 92 and interfacing axially extending side surfaces 94 that comprise an arcuate shape as shown in FIGS. 7 and 14, these side surfaces can include a straight-line shape as shown in FIG. 15. Interfacing axially extending side surfaces with an arcuate shape can be expensive from drafting and machining points of views. Interfacing axially extending side surfaces with a straight- line shape will reduces these costs, simplify machining tolerance capability and improve stack-up of the spring inserts. FIG. 15 shows the cover body 84 of the cover portion 50 of a spring insert 64 with an arcuate top surface 92 and extending side surfaces 142 that comprises a straight-line shape.

[0093] FIGS. 16A and 16B show an embodiment that provides an alternative to having the base portions 46 of the spring inserts in an axial insert-to-insert twist interlock to create the elastic twist between the cover portions 50 and the base portions of the inserts as described with respect to FIGS. 7, 8A, 8B and 10A. In the embodiment of FIGS. 16A and 16B, a protrusion feature, such as for example, a protruding rail 144 can be formed in a bottom region of the non-bucketed stage groove 18 of the turbine rotor 16 to react the elastic twist between the cover portions 50 and the base portions 46. The protruding rail 144 can extend circumferentially about the non-bucketed stage groove 18. As shown in FIG. 16B, the protruding rail 144 can include a gate opening 146 formed in the rail to facilitate placement of the plurality of spring inserts 64 on the rail for tangential movement thereon. In particular, with the gate opening 146, the spring inserts can be rotated and inserted in the non-bucketed stage groove 18, and twisted into position such that the notch 78 formed in the base portion 46 of the spring insert 64 can sit over the rail 144 to enclose the top and side surfaces of the rail. The spring insert 64 can then be tangentially slid along the rail 144 in the non-bucketed stage groove 18 of the rotor 16. This allows an assembly of spring inserts to be placed on the rail 144 via the gate opening 146 and slid into position in the non-bucketed stage groove 18. Once all of the spring inserts have been placed in the non-bucketed stage groove 18 and moved into position via the use of the rail 144 and the gate opening 146, the spring insert assembly 20 can be tangentially packed together. To this extent, the rail 144 along with the tangential packing of the spring insert assembly 20 can axially lock the spring inserts in place.

[0094] With the configuration depicted in FIGS. 16A and 16B, the protruding rail 144 can be used to react the elastic twist between the cover portion 50 and the base portion 46 in the tangential direction for each of the spring inserts 64 in the spring insert assembly 20 in relation to each of their adjacent spring inserts. In particular, the rail 144 can serve as a bottom axial twist interface with the base portion 46 of the spring inserts 64 to react a twist load between their cover portions 50 and base portion. FIG. 16A shows radial rail surfaces 148 of the rail 144 that can take out the cover to base twist that is generated with this embodiment.

[0095] FIGS. 17A and 17B show another embodiment that provides an axial insert-to-insert twist interlock to create the elastic twist between the cover portions 50 and the base portions 46 of the spring inserts. In this embodiment, an anti-rotation key 150 can be disposed under the base portion 46 of selected spring inserts 64 to tangentially hold the selected spring inserts in place within the non-bucketed stage groove 18. As shown in FIG. 17B, the anti-rotation key 150 can be put in right before the last spring insert is disposed in the assembly in the non-bucketed stage groove 18. To this extent, the anti-rotation key 150 can supply a circumferential stop between the turbine rotor 16 and the spring insert assembly 20 for at least one spring insert 64. That is, the physical feature of the anti-rotation key 150 inhibits or will not allow the tangential movement of the at least one spring insert 64, thereby stopping tangential movement of the row of inserts. In this manner, the anti-rotation key 150 will hold the row of spring inserts 64 fixed from tangential movement and sliding around in the non-bucketed stage groove 18 during the operation of the rotor 16.

[0096] With the configuration depicted in FIGS. 17A and 17B, the anti-rotation key 150 can be used to react the elastic twist between the cover portion 50 and the base portion 46 in the tangential direction for each of the spring inserts 64 in the spring insert assembly 20 in relation to each of their adjacent spring inserts. In particular, the anti-rotation key 150 can serve as a bottom axial twist interface with the base portion 46 of the spring inserts 64 to react a twist load between their cover portions 50 and base portion.

[0097] In one embodiment, the anti-rotation key 150 can be used to operate in conjunction with a protruding rail 144 and gate opening 146 formed in a bottom region of the non-bucketed stage groove 18 of the turbine rotor 16 as depicted in FIGS. 16A and 16B to react the elastic pre-twist between the cover portions 50 and the base portions 46. To this extent, the anti-rotation key 150 and the rail 144 along with the tangential packing of the spring insert assembly 20 in the non-bucketed stage groove 18 can operate cooperatively to axially lock the spring inserts 64 in place. As a result, the anti-rotation key 150 can interface with the radial rail 144 on the bottom of the non-bucketed stage groove 18 of the rotor 16 between the raised rail and a stepped interface with at least one spring insert 64. This allows the antirotation key 150 and the rail 144 to react the elastic twist between the cover portion 50 and the base portion 46 in the tangential direction for each of the spring inserts 64 in the spring insert assembly 20 in relation to each of their adjacent spring inserts. In particular, the anti-rotation key 150 and the rail 144 can serve as a bottom axial twist interface with the base portion 46 of the spring inserts 64 to react a twist load between their cover portions 50 and base portion.

[0098] It is understood that the anti-rotation key 150 can be used with any and all of the various embodiments described herein. Accordingly, it is not necessary to use the anti-rotation key 150 in conjunction with the rail 144, and thus the description of the use of these components together is not meant to be limiting to any of the embodiments described herein.

[0099] The embodiments depicted in FIGS. 16A and 16B, as well as FIGS. 17A and 17B, show another aspect of the spring insert 64. In particular, these figures show that the spring inserts 64 can be configured with a neck portion 48 that is axially and tangentially reduced in width in comparison to the neck portion of the spring inserts depicted in FIGS. 7, 8A, 8B and 10A. For example, in one embodiment, the neck body of the neck portion can have an axial width that is less than an axial width of the base portion 46 and an axial width of the cover portion 50. Reduced neck portions 48 will mean that less stress will be placed on this component from a twist load, which can be advantageous for creating the twist between the cover portions 50 that have that interference fit due to the cover-to- cover overlap arrangement in the tangential direction and the base portions 46A. In addition, reduced neck portions 48 can be beneficial to the design of the spring inserts 64 in that it provides a weight savings for each of the inserts.

[00100] Instead of providing the elastic twist between the cover portions 50 and the base portions 46 like the heretofore embodiments, FIGS. 18A and 18B disclose an alternative embodiment. In particular, the embodiment of FIGS. 18A and 18B uses axially extending projections in a lower radial region of the neck portion 48 of the spring inserts 64. These projections off the lower radial region of the neck portion 48 can have the cover twist forces interact on the non-bucketed stage groove 18 of the rotor 16 in the axial direction. This neck feature of FIGS. 18A and 18B that provides twist reaction with the non-bucketed stage groove 18 is an alternative to the axial insert-to-insert twist interlock described with respect to FIGS. 7, 8A, 8B and 10A.

[00101] As shown in FIGS. 18A and 18B, the neck features on the neck portion 48 of the spring insert 64 can include a neck body 152 extending outward from the base body of the base portion 46 and a pair of opposing neck protrusions 154 extending from the neck body. Each of the neck protrusions 154 are configured to contact against inner axial rotor surfaces in the non-bucketed stage groove 18 at locations 156. To this extent, the elastic twist that occurs between the cover portion 50 and the neck portion 48 due to the circumferential interference of the covers and neck protrusions 154 generates a twist force at locations 156 as shown in FIG. 18B that reacts on the inner axial rotor surfaces of the non-bucketed stage groove in the axial direction. In this manner, this cover to neck protrusion twist force can react at the locations 156 which leads to the cover twist force interacting on the nonbucketed stage groove 18 in the axial direction.

[00102] The embodiment depicted in FIGS. 18A and 18B shows another aspect that can be configured with the neck portion 48 of the spring inserts 64. In particular, these figures show that the neck portion 48 of the spring inserts 64 can include a radially extending slot 158 to reduce torsional stiffness and pull load of the spring insert 64 between the cover portion 50 and the base portion 46. In one embodiment, the radially extending slot 158 can include a shaped hole or race track shaped hole. The radially extending slot 158 is advantageous in that it can reduce mass of the spring insert assembly 20. Reduced mass means that reduced centrifugal force will be applied to the spring inserts which can lead to less stress on the inserts. It is understood that the radially extending slot 158 is applicable to any embodiments of the spring inserts and is not meant to be limited to the one depicted in FIGS. 18A and 18B which illustrate the aforementioned neck twist features.

[00103] FIG. 19 shows another embodiment which can have applicability to any and all of the various embodiments described herein. In particular, the embodiment of FIG. 19 is directed to providing an angled hook interface 160 between the hook lands 52 in the non-bucketed stage groove 18 of the turbine rotor 16 and the hook members 68 of the base portion 46 of the spring inserts 64 in the groove. As shown in FIG. 19, a top surface of the hook members 68 and an inner surface of the hook lands 52 can each comprise an angled surface to form the angled hook interface 160 upon the insertion of the hook members under the hook lands.

[00104] The angled hook interface 160 of the embodiment of FIG. 19 is in contrast to the embodiments depicted in FIGS. 8A, 16A, 17A, 18A and 18B which show an edged interface between the top surface of the hook members 68 and an inner surface of the hook lands 52. The angled hook interface 160 between the top surface of the hook members 68 and an inner surface of the hook lands 52 as shown in FIG. 19 allows for a determinant axial position of the spring insert 64 within the rotor 16. In particular, the angled hook interface 160 not only can take out the twist, but it also can help with locating the spring insert 64 in an axial position in the nonbucketed stage groove 18. For example, once the spring insert is loaded up with a twist force, the angled hook interface 160 can help with the centering of the hook members 68 under the hook lands 52. To this extent, the angled hook interface 160 can reduce the rotor local stress concentration at the hook members 68 and reduce the rotor radial shear stress component.

[00105] In light of the various embodiments described herein, it should be apparent that in addition to the aforementioned technical effects, the spring insert assembly configurations of the various embodiments can provide many commercial advantages. For example, the embodiments can be applied to both new-build steam turbines and turbines in service. Also, design of the spring insert assembly of the various embodiments make it possible to use different material for the spring inserts. For example, instead of using an expensive nickel alloy material which is still an option with the various embodiments, the spring inserts can be made from a standard (industry common) steel. Also, the design of the spring insert assembly of the various embodiments can use less parts, and can be assembled more quickly with less hand-fitting in comparison to a design that includes rigid inserts.

Furthermore, the design of the spring insert assembly of the various embodiments is more determinant during both transient and steady state turbine operation than existing designs that utilize the assembly of rigid inserts and shims for the nonbucketed stage groove. [00106] The above description of illustrated embodiments of the subject disclosure, including what is described in the Abstract, is not intended to be exhaustive or to limit the disclosed embodiments to the precise forms disclosed. While specific embodiments and examples are described herein for illustrative purposes, various modifications are possible that are considered within the scope of such embodiments and examples, as those skilled in the relevant art can recognize. For example, parts, components, steps and aspects from different embodiments may be combined or suitable for use in other embodiments even though not described in the disclosure or depicted in the figures. Therefore, since certain changes may be made in the above-described invention, without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention.

[00107] In this regard, while the disclosed subject matter has been described in connection with various embodiments and corresponding figures, where applicable, it is to be understood that other similar embodiments can be used or modifications and additions can be made to the described embodiments for performing the same, similar, alternative, or substitute function of the disclosed subject matter without deviating therefrom. Therefore, the disclosed subject matter should not be limited to any single embodiment described herein, but rather should be construed in breadth and scope in accordance with the appended claims below. For example, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Within the scope of the disclosure are also embodiments produced by combination in any order and number of embodiments, examples, and features thereof disclosed in the description and in the claims.

[00108] In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, terms such as “first,” “second,” “third,” “upper,” “lower,” “bottom,” “top,” etc. are used merely as labels, and are not intended to impose numerical or positional requirements on their objects. The terms “substantially,” “generally,” and “about” indicate conditions within reasonably achievable manufacturing and assembly tolerances, relative to ideal desired conditions suitable for achieving the functional purpose of a component or assembly. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted as such, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.

[00109] In addition, the term "or" is intended to mean an inclusive "or" rather than an exclusive "or." That is, unless specified otherwise, or clear from context, "X employs A or B" is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then "X employs A or B" is satisfied under any of the foregoing instances. Moreover, articles "a" and "an" as used in the subject specification and annexed drawings should generally be construed to mean "one or more" unless specified otherwise or clear from context to be directed to a singular form.

[00110] What has been described above includes examples of systems and methods illustrative of the disclosed subject matter. It is, of course, not possible to describe every combination of components or methodologies here. One of ordinary skill in the art may recognize that many further combinations and permutations of the claimed subject matter are possible. Furthermore, to the extent that the terms "includes," "has," "possesses," and the like are used in the detailed description, claims, appendices and drawings, such terms are intended to be inclusive in a manner similar to the term "comprising" as "comprising" is interpreted when employed as a transitional word in a claim. That is, unless explicitly stated to the contrary, embodiments “comprising,” “including,” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property.

[00111] This written description uses examples to disclose several embodiments of the invention, including the best mode, and also to enable one of ordinary skill in the art to practice the embodiments of invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to one of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

[00112] Further aspects of the invention are provided by the subject matter of the following clauses:

[00113] A spring insert assembly for a non-bucketed stage groove formed circumferentially in a turbine rotor and upstream of a first stage of turbine buckets and stator nozzles, the spring insert assembly comprising: a plurality of spring inserts configured for insertion into the non-bucketed stage groove, each of the plurality of spring inserts including: a base portion having a base body configured to extend radially outward from the non-bucketed stage groove and a pair of opposing hook members extending from the base body and configured for insertion under hook lands axially established in the non-bucketed stage groove, the base body and the hook members each having a pair of lateral contact surfaces configured to interface in mating engagement with lateral contact surfaces of corresponding base bodies and hook members from adjacent spring inserts; a neck portion extending radially outward from the base body of the base portion and configured to extend radially outward from the non-bucketed stage groove, the neck portion having a pair of lateral face surfaces each configured to interface with lateral face surfaces of neck portions from adjacent spring inserts; and a cover portion on the neck portion with an extending cover body with a pair of lateral edges each configured to interface in mating engagement with lateral edges of cover bodies from cover portions of adjacent spring inserts in a tangential direction, wherein each of the lateral edges includes a protrusion configured to abut a protrusion from the lateral edges of the cover bodies of the adjacent spring inserts to form a cover-to-cover overlap arrangement in the tangential direction that creates an interference fit between the cover portions of the adjacent spring inserts, wherein the cover portion and one of the base portion and the neck portion is configured to elastically twist the spring insert in a predetermined direction in response to placement in the non-bucketed stage groove and engagement with adjacent spring inserts in the non-bucketed stage groove.

[00114] The spring insert assembly of the preceding clause, wherein the pair of lateral contact surfaces of the base body comprises a first lateral contact surface and a second lateral contact surface, the first lateral contact surface forming a pocket between the pair of opposing hook members and the second lateral contact surface having a projection that extends beyond a periphery of the pair of opposing hook members in a tangential direction, wherein the pocket and projection are configured to interlock correspondingly with the projection and pocket from the cover bodies of the adjacent spring inserts, wherein the elastic twist occurs between the cover portion and the base portion in the tangential direction in relation to the adjacent spring inserts.

[00115] The spring insert assembly of any of the preceding clauses, wherein the cover-to-cover overlap arrangement comprises a smooth spline interface between the lateral edges.

[00116] The spring insert assembly of any of the preceding clauses, wherein the lateral edges of the cover bodies including the protrusion comprises a chamfered surface with a blend of lines and arcs, wherein the cover-to-cover overlap arrangement comprises a gap therebetween due to the chamfered surfaces of the lateral edges.

[00117] The spring insert assembly of any of the preceding clauses, wherein at least one of the plurality of spring inserts comprises two half-spring inserts coupled together to form a spring insert, each half-spring insert comprising: a half-spring insert base portion having a pair of extending ends, a first extending end of the halfspring insert base portion including a hook member configured for axial insertion under one of the hook lands in the non-bucketed stage groove and a second extending end of the half-spring insert base portion including a coupling end configured for an axial mating engagement with a complementary fitting end of a half-spring insert base portion of an axially adjacent half-spring; a half-spring insert cover portion; and a half-spring insert neck portion extending between the half-spring insert base portion and the half-spring insert cover portion, the half-spring insert neck portion including a pair of opposing face surfaces, wherein each axial face surface is configured to tangentially interface with a face surface of a neck portion of an immediately adjacent spring insert or a half-spring insert.

[00118] The spring insert assembly of any of the preceding clauses, wherein the axial mating engagement between the half-spring inserts forms a tongue and groove mating arrangement configured to lock the two half-spring inserts axially in place in the non-bucketed stage groove, preventing any twist between the half-spring inserts.

[00119] The spring insert assembly of any of the preceding clauses, wherein the cover portion of each of the plurality of spring inserts comprises an arcuate top surface configured to match a flow path of steam provided to the first stage of turbine buckets and stator nozzles.

[00120] The spring insert assembly of any of the preceding clauses, wherein the cover portion of each of the plurality of spring inserts comprises a pair of opposing extending side surfaces each configured to axially interface axially extending side surfaces of the cover portions from the adjacent spring inserts, wherein the extending side surfaces comprise one of an arcuate shape that is configured to match the flow path of steam provided to the first stage of turbine buckets and a straight-line shape.

[00121] The spring insert assembly of any of the preceding clauses, wherein the base body of the base portion of the spring insert includes a cut-out or a notch formed in a lower radial surface of the base body between the pair of opposing hook members. [00122] The spring insert assembly of any of the preceding clauses, wherein the non-bucketed stage groove comprises a protruding rail that extends circumferentially thereabout with a gate opening formed in the rail to facilitate radial placement of the plurality of spring inserts on the rail for tangential movement thereon, wherein the protruding rail is used to react the elastic twist between the cover portion and the base portion in the tangential direction in relation to the adjacent spring inserts.

[00123] The spring insert assembly of any of the preceding clauses, further comprising an anti-rotation key disposed under the base portion of selected spring inserts to tangentially hold the selected spring inserts in place within the nonbucketed stage groove, wherein the anti-rotation key interfaces with the protruding rail to supply a circumferential stop between the turbine rotor and at least one of the plurality of spring inserts.

[00124] The spring insert assembly of any of the preceding clauses, wherein the neck portion comprises a neck body extending outward from the base body and a pair of opposing neck protrusions extending from the neck body, each of the neck protrusions configured to contact against axial rotor surfaces in the non-bucketed stage groove, the elastic twist occurs between the cover portion and the neck portion, wherein the cover portion generates a twist force that interacts with the neck protrusions and reacts on the inner axial rotor surfaces of the non-bucketed stage groove in the axial direction.

[00125] The spring insert assembly of any of the preceding clauses, wherein the neck portion comprises a neck body having an extending slot therethrough to reduce torsional stiffness of the spring insert between the cover portion and the base portion. [00126] The spring insert assembly of any of the preceding clauses, wherein a top surface of the hook members of the base portion and an inner surface of the hook lands in the non-bucketed stage groove each comprises an angled surface, wherein the hook members are configured to form an angled hook interface with the hook lands.

[00127] The spring insert assembly of any of the preceding clauses, wherein the elastic twist of one of the plurality of spring inserts is one of a counter-clock-wise direction, a clock-wise direction in relation to a radial axis extending through the nonbucketed stage groove, and combinations thereof.

[00128] A turbine, comprising: a turbine rotor arranged inside the casing, the turbine rotor having a non-bucketed stage groove formed circumferentially therein; multiple stages of turbine buckets and stator nozzles downstream of the nonbucketed stage groove; a steam inlet passage between the casing and the turbine rotor to provide a flow of steam that travels through a downstream steam path that includes the non-bucketed stage groove and the multiple stages of turbine buckets; and a spring insert assembly according to any of the above paragraphs.

Claims

WHAT IS CLAIMED IS:

1 . A spring insert assembly (20) for a non-bucketed stage groove (18) formed circumferentially in a turbine rotor (16) and upstream of a first stage of turbine buckets (12) and stator nozzles (14), the spring insert assembly comprising: a plurality of spring inserts (64) configured for insertion into the non-bucketed stage groove, each of the plurality of spring inserts including: a base portion (46) having a base body (66) configured to extend radially outward from the non-bucketed stage groove and a pair of opposing hook members (68) extending from the base body and configured for insertion under hook lands (52) axially established in the non-bucketed stage groove, the base body and the hook members each having a pair of lateral contact surfaces (70,72) configured to interface in mating engagement with lateral contact surfaces of corresponding base bodies and hook members from adjacent spring inserts; a neck portion (48) extending outward from the base body of the base portion and configured to extend radially outward from the non-bucketed stage groove, the neck portion having a pair of lateral face surfaces (80) each configured to interface with lateral face surfaces of neck portions from adjacent spring inserts; and a cover portion (50) on the neck portion with an extending cover body (84) with a pair of lateral edges (86) each configured to interface in mating engagement with lateral edges of cover bodies from cover portions of adjacent spring inserts in a tangential direction, wherein each of the lateral edges includes a protrusion (88) configured to abut a protrusion from the lateral edges of the cover bodies of the adjacent spring inserts to form a cover-to-cover overlap arrangement in the tangential direction that creates an interference fit between the cover portions of the adjacent spring inserts, wherein the cover portion (50) and one of the base portion (46) and the neck portion (48) is configured to elastically twist the spring insert in a predetermined direction in response to placement in the non-bucketed stage groove (18) and engagement with adjacent spring inserts (64) in the non-bucketed stage groove.

2. The spring insert assembly (20) according to claim 1 , wherein the pair of lateral contact surfaces (70,72) of the base body (66) comprises a first lateral contact surface (70) and a second lateral contact surface (72), the first lateral contact surface forming a pocket (74) between the pair of opposing hook members (68) and the second lateral contact surface having a projection (76) that extends beyond a periphery of the pair of opposing hook members in a tangential direction, wherein the pocket and projection are configured to interlock correspondingly with the projection and pocket from the cover bodies of the adjacent spring inserts (64), wherein the elastic twist occurs between the cover portion (50) and the base portion (46) in the tangential direction in relation to the adjacent spring inserts.

3. The spring insert assembly (20) according to claim 1 , wherein the cover-to- cover overlap arrangement comprises a smooth spline interface (90) between the lateral edges.

4. The spring insert assembly (20) according to claim 1 , wherein the lateral edges of the cover bodies including the protrusion comprises a chamfered surface (134) with a blend of lines (136) and arcs (138), wherein the cover-to-cover overlap arrangement comprises a gap (140) therebetween due to the chamfered surfaces of the lateral edges.

5. The spring insert assembly (20) according to claim 1 , wherein at least one of the plurality of spring inserts comprises two half-spring inserts (98) coupled together that form said at least one spring insert, each half-spring insert comprising: a half-spring insert base portion (100) having a pair of extending ends, a first extending end of the half-spring insert base portion including a hook member (106) configured for axial insertion under one of the hook lands (52) in the non-bucketed stage groove (18) and a second extending end of the half-spring insert base portion including a coupling end (108) configured for an axial mating engagement with a complementary coupling end of a half-spring insert base portion of an axially adjacent half-spring; a half-spring insert cover portion (102); and a half-spring insert neck portion (104) extending between the half-spring insert base portion and the half-spring insert cover portion, the half-spring insert neck portion including a pair of opposing face surfaces (110), wherein each face surface is configured to tangentially interface with a face surface of a neck portion of an immediately adjacent spring insert or a half-spring insert.

6. The spring insert assembly (20) according to claim 5, wherein the axial mating engagement between the half-spring inserts (98) forms a tongue and groove mating arrangement configured to lock the two half-spring inserts axially in place in the non-bucketed stage groove (18), preventing any twist between the half-spring inserts.

7. The spring insert assembly (20) according to claim 1 , wherein the cover portion (50) of each of the plurality of spring inserts (64) comprises an arcuate top surface (92) configured to match a flow path of steam provided to the first stage of turbine buckets and stator nozzles.

8. The spring insert assembly (20) according to claim 7, wherein the cover portion of each of the plurality of spring inserts comprises a pair of opposing extending side surfaces each configured to axially interface with extending side surfaces of the cover portions from the adjacent spring inserts, wherein the extending side surfaces comprise one of an arcuate shape (94) that is configured to match the flow path of steam provided to the first stage of turbine buckets and a straight-line shape (142).

9. The spring insert assembly (20) according to claim 1 , wherein the base body

(66) of the base portion (46) of the spring insert (64) includes a cut-out or a notch

(78) formed in a lower radial surface of the base body between the pair of opposing hook members (68).

10. The spring insert assembly (20) according to claim 1 , wherein the non-bucketed stage groove (18) comprises a protruding rail (144) that extends circumferentially thereabout with a gate opening (146) formed in the rail to facilitate radial placement of the plurality of spring inserts on the rail for tangential movement thereon, wherein the protruding rail is used to react the elastic twist between the cover portion (50) and the base portion (46) in the tangential direction in relation to the adjacent spring inserts.

11 . The spring insert assembly (20) according to claim 10, further comprising an anti-rotation key (150) disposed under the base portion (46) of selected spring inserts (64) to tangentially hold the selected spring inserts in place within the nonbucketed stage groove (18), wherein the anti-rotation key interfaces with the protruding rail (144) to supply a circumferential stop between the turbine rotor (16) and at least one of the plurality of spring inserts.

12. The spring insert assembly (20) according to claim 1 , wherein the neck portion (48) comprises a neck body extending outward from the base body (46) and a pair of opposing neck protrusions (154) extending from the neck body, each of the neck protrusions configured to contact against axial rotor surfaces in the nonbucketed stage groove (18), the elastic- twist occurs between the cover portion (50) and the neck portion, wherein the cover portion generates a twist force that interacts with the neck protrusions and reacts on the inner axial rotor surfaces of the nonbucketed stage groove in the axial direction.

13. The spring insert assembly (20) according to claim 1 , wherein the neck portion (48) comprises a neck body having an extending slot (158) therethrough to reduce torsional stiffness of the spring insert between the cover portion (50) and the base portion (46).

14. The spring insert assembly (20) according to claim 1 , wherein a top surface of the hook members (68) of the base portion (46) and an inner surface of the hook lands in the non-bucketed stage groove each comprises an angled surface, wherein the hook members are configured to form an angled hook interface (160) with the hook lands.

15. The spring insert assembly (20) according to claim 1 , wherein the elastic twist of one of the plurality of spring inserts is one of a counter-clock-wise direction, a clock-wise direction in relation to a radial axis extending through the non-bucketed stage groove, and combinations thereof.

16. A turbine (10), comprising: a casing (22,24); a turbine rotor (16) arranged inside the casing, the turbine rotor having a non-bucketed stage groove (18) formed circumferentially therein; multiple stages of turbine buckets (12) and stator nozzles (14) downstream of the non-bucketed stage groove; a steam inlet passage (32) between the casing and the turbine rotor to provide a flow of steam (30) that travels through a downstream steam path that includes the non-bucketed stage groove and the multiple stages of turbine buckets and stator nozzles; and a spring insert assembly (20) according to any of claims 1 -15.