Stiffening system for steam turbine casing   

Abstract: A steam turbine casing stiffening system is disclosed. In one embodiment, a steam turbine inner casing stiffening system is disclosed, including: an inner casing segment; and a stiffening member affixed to and extending radially outward from an external surface of the inner casing segment, the stiffening member configured to support at least a portion of the inner casing segment.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to a steam turbine casing. Specifically, the subject matter disclosed herein relates to a steam turbine casing including an externally disposed stiffening system.

Conventional steam turbine casings include stiffening structures disposed along the interior of the inner casing wall. In some instances, these stiffening structures extend through the width of the inner casing wall and remain flush with the outer portion of the inner casing wall. However, in all instances, these conventional stiffening structures include stiffening members extending into the steam flow path on the interior of the inner casing wall. These stiffening structures may cause clearance and flow-related issues in the steam turbine.

A steam turbine casing stiffening system is disclosed. In one embodiment, a steam turbine inner casing stiffening system is disclosed, including: an inner casing segment; and a stiffening member affixed to and extending radially outward from an external surface of the inner casing segment, the stiffening member configured to stiffen at least a portion of the inner casing segment.

A first aspect of the invention includes a steam turbine inner casing stiffening system having: an inner casing segment; and a stiffening member affixed to and extending radially outward from an external surface of the inner casing segment, the stiffening member configured to stiffen at least a portion of the inner casing segment.

A second aspect of the invention includes a steam turbine inner casing stiffening system having: an inner casing segment having a first half and a second half; and a plurality of stiffening members disposed about and extending radially outward from an external surface of the first half or the second half of the inner casing segment, the plurality of stiffening members configured to stiffen at least one of the first half or the second half of the inner casing segment.

A third aspect of the invention includes a steam turbine having: a rotor member; and a stator member at least partially surrounding the rotor member, the stator member including: an external casing; and an inner casing stiffening system disposed between the external casing and the rotor member, the inner casing stiffening system including: an inner casing segment; and a stiffening member affixed to and extending radially outward from an external surface of the inner casing segment, the stiffening member configured to stiffen at least a portion of the inner casing segment.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which:

FIG. 1 shows a three-dimensional perspective view of a steam turbine inner casing stiffening system according to embodiments of the invention.

FIG. 2 shows a three-dimensional perspective view of a steam turbine inner casing stiffening system according to embodiments of the invention.

FIG. 3 shows a partial cut-away top view of inner casing stiffening system according to embodiments of the invention.

FIG. 4 shows a partial cut-away bottom view of inner casing stiffening system according to embodiments of the invention.

FIG. 5 shows a three-dimensional perspective view of a plurality of stiffening bars, arranged in different circumferential positions, according to embodiments of the invention.

FIG. 6 shows a rough schematic cut-away top view of a portion of a steam turbine apparatus according to embodiments of the invention.

It is noted that the drawings of the invention are not to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION

Aspects of the invention provide for a steam turbine casing. Specifically, the subject matter disclosed herein relates to a steam turbine inner casing including an externally disposed stiffening system.

As described herein, conventional steam turbine casings include stiffening structures disposed along the interior of the inner casing wall. In some instances, these stiffening structures extend through the width of the inner casing wall and remain flush with the outer portion of the inner casing wall. However, in all instances, these conventional stiffening structures include stiffening members extending into the steam flow path on the interior of the inner casing wall. These stiffening structures may cause clearance and steam sealing issues within the steam turbine.

In contrast to conventional stiffening structures for steam turbine inner casings, aspects of the invention provide for an external stiffening system for an inner steam turbine casing, providing for minimal impact on the steam flow path. In some embodiments, the stiffening system includes substantially parallel axially extending members disposed (e.g., affixed) annularly about the outer surface of the inner steam turbine casing.

In other embodiments, the stiffening system includes substantially parallel annularly extending members disposed axially about the outer surface of the inner steam turbine casing. In this embodiment, the stiffening system may include a plurality of annular rings disposed along (e.g., affixed to) the outer surface of the inner casing in the axial direction.

In other embodiments, the stiffening system includes both annularly extending members and axially extending members providing stiffening along the outer surface of the inner casing. In yet other embodiments, stiffening members may extend partially axially and partially annularly along the outer surface of the inner casing. In any case, the technical effect of the stiffening systems described herein is to provide mechanical stiffening for a steam turbine inner casing without disrupting the steam flow path and sealing surfaces inside the inner casing.

Turning to FIG. 1, a three-dimensional perspective view of a steam turbine inner casing stiffening system 2 is shown according to embodiments. In this embodiment, the steam turbine inner casing stiffening system 2 includes an inner casing segment 4, and a stiffening member 6 (a plurality shown) affixed to and extending radially outward from an external surface 8 (or, wrapper external surface) of the inner casing segment 4. In one embodiment, the stiffening member 6 is configured to stiffening (e.g., mechanically support) at least a portion of the inner casing segment 4. In contrast to conventional stiffening systems for inner casing segments (e.g., inner casing segment 4), the stiffening system 2 shown and described herein includes radially outwardly extending stiffening member(s) 6, which do not extend into the steam flow path defined on the internal surface 10 of the inner casing segment 4.

In one embodiment, the stiffening member(s) 6 extend axially along the external surface 8 of the inner casing segment 4. That is, in some cases, stiffening member(s) 6 may extend in a direction substantially parallel with the axis of the steam turbine (indicated in phantom by the line A-A. This may allow for axial support of the inner casing segment. In some embodiments, the stiffening member(s) 6 may extend along an axial length of more than one stage of the steam turbine (which is further explained herein with respect to the stages shown and described with reference to the internal surface 10). Further, the stiffening member(s) 6 may extend along or across turbine section joint segments 12 where adjacent axial sections of the inner casing are joined. In some embodiments, stiffening member(s) 6 may have substantially smooth radially inwardly facing surfaces (not shown in this embodiment), which may be configured to fit substantially flush against the substantially smooth external surfaces 8 of inner casing segment 4. These substantially smooth radially inward facing surfaces are dissimilar to the radially inward facing surfaces of conventional stiffening structures for inner casing segments, as those conventional stiffening structures are located along the internal surfaces (e.g., internal surface 10) of the inner casing segment and are corrugated to mate with internal steam flow path components.

In one embodiment, at least one stiffening member 6 may include an attachment member 14 configured to receive a displacement member (not shown) for actuating movement of the inner casing segment 4. In one embodiment, the attachment member 14 may be a loop (either closed or adaptable to open), a hook, a notch, etc., configured to receive a displacement member, which may similarly be a loop (either closed or adaptable to open), a hook, a notch, etc., configured to mate with the attachment member 14. One or more displacement members may attach to the one or more attachment members 14 (e.g., as shown, at least two) to actuate movement of the inner casing segment 4. In some cases, attachment member(s) 14 may allow for placement, removal and/or replacement of inner casing segment 4 from a steam turbine system.

It is understood that as shown, inner casing segment 4 includes a portion of an upper half of a steam turbine inner casing. In a complete steam turbine inner casing section, this inner casing segment 4 will be joined at a horizontal joint surface with a second inner casing segment (e.g., a lower half of a steam turbine inner casing) that will form one or more steam paths around a rotor. As shown, inner casing segment 4 (and its counterpart lower casing segment, shown and described with respect to FIG. 2) is part of a double-flow steam turbine system. However, it is understood that the teachings described herein may be applied to axial flow steam turbine systems as well.

Also included in inner casing segment is an inlet 16 for receiving steam flow through a steam flow path 18. In the case that the inner casing segment 4 is an upper half of a double-flow steam turbine inner casing segment (e.g., in a low pressure section), inlet 16 will allow steam to flow through flow path 18 and divide between axially forward and axially rearward sections of the steam turbine. Inlet 16 has an external surface 20 and an internal surface (not shown), and in some embodiments, a stiffening member 6 may be affixed to an external surface 20 of inlet 16. In one embodiment, the stiffening member(s) 6 may extend axially across surface 20 (sometimes referred to herein as axially extending stiffening members), while in another embodiment, stiffening member(s) 6 may extend at least partially radially along the surface 20 of inlet 16 (e.g., substantially parallel with flow path 18).

In another embodiment, axially extending stiffening member(s) 6 may include, or be operably connected with one or more annularly extending stiffening members 22, configured to provide radial support to the inner casing segment 4. In some cases, annularly extending stiffening members 22 may be connected to axially extending stiffening members 6 via welds, pins, clamps, adhesives, etc. In other cases, these stiffening members (6, 22) may be integrally cast or formed form a continuous pieces of material. As described herein, stiffening members (e.g., axially extending stiffening members 6 and/or annularly extending stiffening members 22) may be formed of a metal (e.g., steel) or composite capable of providing support to the inner casing segment. While stiffening members (e.g., axially extending stiffening members 6 and/or annularly extending stiffening members 22) are shown running substantially parallel, or substantially perpendicular with the steam turbine\'s central axis A, it is understood that one or more stiffening members may be configured to extend at least partially annularly and at least partially axially along external surface 8 (e.g., diagonally between portions of external surface). In this case, the stiffening member may provide both axial and radial support to inner casing segment 4.

It is understood that the axially extending stiffening member(s) 6 described herein may allow for axial stiffening of inner casing segment 4, thereby aiding in the retention of axial joints formed between one or more casing segments (e.g., inner casing segment 4 and an adjoining segment, further described herein). However, in some embodiments, where the steam turbine inner casing is radially sealed, the annularly extending stiffening members 22 may aid in retaining radial joints formed between one or more casing segments.

Turning to FIG. 2, a three-dimensional perspective view of a steam turbine inner casing stiffening system 24 is shown according to embodiments of the invention. In this embodiment, the inner casing stiffening system 24 includes a second inner casing segment 26 (e.g., a lower half of an inner casing segment configured to mate with the inner casing segment 4 of FIG. 1). It is understood that like numbering between figures may represent substantially like elements. As shown, the inner casing stiffening system 24 includes stiffening bars 28 configured to retain the inner casing segment 26 within an external casing segment (e.g., a lower external casing segment) as is known in the art. As is similarly described with reference to FIG. 1 and inner casing segment 4, one or more stiffening bars 6 may be disposed about one or more of the external surfaces 8 of second inner casing segment 26, thereby providing support to second inner casing segment 26. Further, annularly extending stiffening bars 22 may also be disposed about one or more of the external surfaces 8 of second inner casing segment 26, e.g., to provide radial support.

Turning to FIGS. 3-4, a partial cut-away top view of inner casing stiffening system 2 (including inner casing segment 4), and a partial cut-away bottom view of inner casing stiffening system 24 (including second inner casing segment 26), respectively, are shown according to embodiments of the invention. As mentioned herein, in some instances, the inner casing is referred to as a “wrapper.” For ease of reference in FIGS. 3-4, inner casing segment 4 is referred to as upper casing segment, while second inner casing segment 26 is referred to as lower casing segment.

Upper casing segment 4 and lower casing segment 26 include a plurality of steam flow channels 30, which extend substantially annularly about a rotor apparatus (omitted for clarity of illustration). That is, the steam flow channels 30 illustrated in FIGS. 3-4 extend between the lower casing segment 26 and upper casing segment 4 so as to provide a continuous steam flow path about the central axis A (indicated in phantom) when the casing segments are adjoined. Separating the steam flow channels 30 are annular ledge rings 32, which allow for fluid isolation between different stages of the low pressure steam turbine. As will be described further herein, ledge rings 32 extend substantially radially inwardly from the inner casing wall, and aid in defining the steam flow channels 30. In contrast to conventional inner casing stiffening systems, aspects of the invention allow for minimal impact on the steam flow channels 30 by the stiffening system (including, e.g., stiffening bars 6 and/or stiffening bars 22) described herein. For example, as shown in FIGS. 3-4, only a portion of stiffening bar 6 may extend through the interior surface 10 of upper casing segment 4.

FIG. 5 shows a three-dimensional perspective view of a plurality of stiffening bars 6, arranged in different circumferential positions, according to embodiments of the invention. As described with reference to FIG. 1, stiffening bars 6 may include substantially smooth radially inward surfaces (or, faces) 34, which may be configured to attach flush against one or more external surfaces of an inner casing segment (e.g., external surfaces 8). Additionally, as described with reference to FIG. 1, one or more stiffening bars 6 may include at least one attachment member 14.

FIG. 6 shows a rough schematic cut-away top view of a portion of a steam turbine 36 according to embodiments of the invention. The steam turbine 36 may include a rotor member 38 affixed to one or more buckets 40, and a stator member 42 at least partially surrounding the rotor member 38. The stator member 42 may include an external casing 44 and an inner casing stiffening system 46 (hidden from this cut-away view) Inner casing stiffening system 46 may be positioned radially inward of external casing 44 (between external casing 44 and rotor member 38), and may include an inner casing 48 (having a plurality of inner casing segments, such as inner casing segments 4, 24). It is understood that the inner casing stiffening system 46 may include one or more components described with reference to the inner casing stiffening systems 2, 24 of FIGS. 1-2. That is, although not visible from this perspective, inner casing stiffening system 46, a portion of which is included in steam turbine apparatus 36, may include one or more inner casing segments (e.g., inner casing segments 4, 24) and one or more stiffening members (e.g., stiffening members 6, 22) described herein. In contrast to conventional steam turbine apparatuses, the steam turbine apparatus 36 shown according to embodiments allows for stiffening of the inner casing 48 with minimal effect on the steam flow path between the rotor member 38 (and buckets 40) and the interior surfaces of inner casing 48.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the 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 those skilled 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.