Patent Description:
Turbine systems are used widely to generate power. One common form of turbine system is a steam turbine system. Many steam turbine (ST) systems include a number of sequential turbines that handle different pressure steam, e.g., a high pressure (HP) turbine, an intermediate pressure (IP) turbine and a low pressure (LP) turbine. In one approach the HP-IP steam turbines are arranged in a casing with an opposed flow configuration because it is most cost efficient compared to a system including separate HP and IP steam turbine casings. The HP steam turbine and the IP steam turbine can be provided together in a casing that includes two, coupled casing half-shells. Steam may be delivered to such a system using 'close coupled' or casing mounted valves, which are more cost-efficient because they eliminate expensive connecting piping. In this setting, valves are directly mounted to the outer casing such that steam is directed tangentially into the casing from opposed sides of the casing. A steam dam is provided between the inlets in the casing in the HP or IP steam turbine to direct the steam axially into the HP or IP steam turbine and prevent flow oscillations. Typically, the steam dam is cast into the casing. One challenge with this approach is that the added material can create a high local stress that requires additional maintenance, and thus can reduce the availability of the steam turbines.

Document <CIT> discloses a self-aligning flow splitter in a steam turbine diaphragm stage. Said flow splitter includes a flow splitter body and two end portions. The body includes a flow divider proximate to central portion and a hook proximate to each end portion. The hook is coupled with a flange. A configuration of the hook and the flange retains the blow splitter body within a nozzle assembly.

A first aspect of the invention provides a casing half shell for a turbine system as claimed in claim <NUM>. The casing half shell comprising: a body having an open interior for enclosing parts of the turbine system; a first working fluid flow path in the body for directing a first working fluid flow in the open interior in a first direction; a second working fluid flow path in the body for directing a second working fluid flow in the open interior in a second direction that is opposed to the first direction; and a working fluid dam extending radially and axially in the body between the first working fluid flow path and the second working fluid flow path, the working fluid dam including a stress-mitigating slot extending radially therein.

A second aspect of the invention provides a steam turbine (ST) system as claimed in claim <NUM>. The steam turbine system comprising: at least one of a high pressure (HP) turbine and an intermediate pressure (IP) turbine; a casing including a body having an open interior for enclosing the at least one of the high pressure (HP) steam turbine and the intermediate pressure (IP) steam turbine; a first working fluid flow path in the body for directing a first working fluid flow in the open interior in a first direction; a second working fluid flow path in the body for directing a second working fluid flow in the open interior in a second direction that is opposed to the first direction; and a steam dam extending radially and axially in the body between the first working fluid flow path and the second working fluid flow path to redirect the first and second working fluid flows to the at least one of the high pressure (HP) steam turbine and the intermediate pressure (IP) steam turbine, the steam dam including a stress-mitigating slot extending radially therein; and a fill member mounted in the stress-mitigating slot.

The illustrative aspects of the present disclosure are designed to solve the problems herein described and/or other problems not discussed.

As an initial matter, in order to clearly describe the current disclosure it will become necessary to select certain terminology when referring to and describing relevant machine components within a turbine system. When doing this, if possible, common industry terminology will be used and employed in a manner consistent with its accepted meaning. Unless otherwise stated, such terminology should be given a broad interpretation consistent with the context of the present application and the scope of the appended claims. Those of ordinary skill in the art will appreciate that often a particular component may be referred to using several different or overlapping terms. What may be described herein as being a single part may include and be referenced in another context as consisting of multiple components. Alternatively, what may be described herein as including multiple components may be referred to elsewhere as a single part.

In addition, several descriptive terms may be used regularly herein, and it should prove helpful to define these terms at the onset of this section. These terms and their definitions, unless stated otherwise, are as follows. 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 the turbine system or, for example, the flow of air through the combustor or coolant through one of the turbine's component systems. The term "downstream" corresponds to the direction of flow of the fluid, and the term "upstream" refers to the direction opposite to the flow. It is recognized that in an opposed flow configuration, upstream and downstream directions may change depending on where one is in the turbine system. The terms "forward" and "aft", without any further specificity, refer to directions, with "forward" referring to the front end of the turbine system, and "aft" referring to the rearward of the turbine system. It is often required to describe parts that are at differing radial positions with regard to a center axis. The term "radial" refers to movement or position perpendicular to an axis. In cases such as this, if a first component resides closer to the axis than a second component, it will be stated herein that the first component is "radially inward" or "inboard" of the second component. If, on the other hand, the first component resides further from the axis than the second component, it may be stated herein that the first component is "radially outward" or "outboard" of the second component. The term "axial" refers to movement or position parallel to an axis. Finally, the term "circumferential" refers to movement or position around an axis. It will be appreciated that such terms may be applied in relation to the center axis of the turbine system, e.g., an axis of a rotor thereof.

Where an element or layer is referred to as being "on", "engaged to", "disengaged from", "connected to" or "coupled to" another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on", "directly engaged to", "directly connected to" or "directly coupled to" another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., "between" versus "directly between", "adjacent" versus "directly adjacent", etc.).

As indicated above, the disclosure provides a casing half shell for a turbine system such as a steam turbine (ST) system, and a related method. The ST system may include, for example, at least one of a high pressure (HP) steam turbine and an intermediate pressure (IP) steam turbine. For purposes of description only, the ST system is illustrated as a high pressure-intermediate pressure (HP-IP) steam turbine (ST) system. The casing half shell can be used in, for example, an HP ST system, an IP ST system, and/or an HP-IP ST system. In any event, the casing half shell includes a body having an open interior for enclosing parts of the turbine system. Where the casing half shell is, for example, a lower half shell casing, it may also include a first inlet in the body for delivering a first working fluid flow into the open interior in a first direction; and a second inlet in the body for delivering a second working fluid flow into the open interior in a second direction that is opposed to the first direction. Alternatively, when the casing half shell is an upper casing half shell, it may be devoid of the inlets. In any event, a working fluid dam extends radially and axially in the body at a location where tangentially opposing working fluid flow paths meet. In a lower casing half shell, the location may be between the first inlet and the second inlet. In contrast to conventional working fluid dams, the working fluid dam includes a stress-mitigating slot extending radially therein. The slot reduces stress in a high stress-prone area that may form in the dam and forces stresses radially outward in the casing half shell to either maintain current stress or relieve the high stress from the working fluid dam. A fill member is mounted in the stress-mitigating slot to otherwise provide full functioning of the working fluid dam.

<FIG> shows a cross-sectional schematic view of an illustrative turbine system <NUM> in the form of a high pressure and intermediate pressure (HP-IP) steam turbine (ST) system <NUM>. While the disclosure will be described as applied to HP-IP ST system <NUM>, the teachings of the disclosure may be applicable to other forms of ST systems such as an HP steam turbine system or an IP steam turbine system. The teachings of the disclosure are also applicable to turbine systems <NUM> in which a working fluid other than steam reacts in the casing in opposing tangential directions, e.g., gas turbines, jet engines, low pressure steam turbines, compressors, etc. The example shows a double casing half-shell, opposed flow configuration. In this setting, HP-IP ST system <NUM> may include a high pressure (HP) steam turbine <NUM> and an intermediate pressure (IP) steam turbine <NUM>. HP-IP system <NUM> also includes a casing <NUM> having an open interior <NUM> for enclosing HP steam turbine <NUM> and IP steam turbine <NUM>. More particularly, casing <NUM> may include a pair of casing half shells <NUM>, <NUM> that are coupled together to collectively form open interior <NUM>. A lower casing half shell <NUM> may include body <NUM>, and upper casing half shell <NUM> may include body <NUM>. Here, body <NUM>, <NUM> may have a generally semi-circular shape. Casing half shells <NUM>, <NUM> are fastened together using any now known or later developed system, e.g., bolts. A seam between casing half shells <NUM>, <NUM> is hidden behind rotor <NUM> in <FIG>, but is shown in the perspective view of <FIG>. Casing half shell <NUM> (and <NUM>) for a turbine system, e.g., HP-IP ST system <NUM>, may be provided in any now known or later developed fashion, e.g., via casting and related finishing processes.

A variety of thrust bearings and journal bearings <NUM> may support rotor <NUM>. Rotor <NUM> has an axis A. Each turbine <NUM>, <NUM> includes a plurality of axially spaced rotor wheels <NUM> to which a plurality of rotating blades <NUM> are mechanically coupled. More specifically, blades <NUM> are arranged in rows that extend circumferentially around each rotor wheel <NUM>. A plurality of stationary vanes (not shown for clarity) extend circumferentially around rotor <NUM>, and the vanes are axially positioned between adjacent rows of blades <NUM>. The stationary vanes cooperate with blades <NUM> to form a stage and to define a portion of a steam flow path through each turbine <NUM>, <NUM>. HP steam turbine <NUM> may have smaller blades than IP steam turbine <NUM>. It is recognized that where HP and IP systems are separate, separate casings <NUM> may be used.

Embodiments of the disclosure will be described and illustrated mainly relative to an IP steam turbine <NUM> section of HP-IP ST system <NUM>. It is emphasized that the teachings of the disclosure equally applicable to HP steam turbine <NUM> section of HP-IP ST system <NUM>, and to upper or lower casing half shell portions thereof.

<FIG> shows a bottom perspective view of casing <NUM>; <FIG> shows a top, perspective view of lower casing half shell <NUM> (with upper casing half shell <NUM> (<FIG>) removed); and <FIG> shows a top, perspective view of upper casing half shell <NUM> (flipped over with lower casing half shell <NUM> (<FIG>) removed). <FIG> show a portion of open interior <NUM> including a space <NUM> for IP steam turbine <NUM> (<FIG>) and a space <NUM> for HP steam turbine <NUM> (<FIG>). Spaces <NUM>, <NUM> are separated by a packing head (not shown) mounted to a packing head main fit <NUM>. A casing flow guide <NUM> may extend axially from packing head main fit <NUM>. Spaces <NUM>, <NUM> may include any form of diaphragm mounting elements <NUM> for receiving diaphragms (not shown) that extend about outer ends of rotating blades <NUM> (<FIG>). Each casing half shell <NUM>, <NUM> includes similar, mating diaphragm mounting elements <NUM>.

With reference to <FIG>, <FIG> and <FIG>, relative to, for example, space <NUM> for IP steam turbine <NUM> (<FIG>), each casing half shell <NUM>, <NUM> includes a first working fluid flow path <NUM> in body <NUM>, <NUM> for directing a first working fluid flow <NUM>, e.g., steam, in open interior <NUM> in a first direction FD, and a second working fluid flow path <NUM> in body <NUM>, <NUM> for directing a second working fluid flow <NUM>, e.g., steam, in open interior <NUM> in a second direction SD. Relative to lower casing half shell <NUM>, first working fluid flow path <NUM> may be created, in part, by a first inlet <NUM> (<FIG>) in body <NUM> for delivering first working fluid flow <NUM>, e.g., steam, into open interior <NUM> in first direction FD, and second working fluid flow path <NUM> may be created, in part, by a second inlet <NUM> (<FIG> and <FIG>) in body <NUM> for delivering second working fluid flow <NUM>, e.g., steam, into open interior <NUM> in second direction SD. First working fluid flow path <NUM> and second working fluid flow path <NUM> in lower casing half shell <NUM> may also be created, in part, by a circumferentially-extending channel <NUM> that runs parallel to diaphragm mounting elements <NUM> and is in fluid communication with inlets <NUM>, <NUM> (<FIG>). Relative to upper casing half shell <NUM> (<FIG>), first working fluid flow path <NUM> and second working fluid flow path <NUM> may be created by a circumferentially-extending channel <NUM> running parallel to diaphragm mounting elements <NUM> and in fluid communication with circumferentially extending channel <NUM> in lower casing half shell <NUM>, i.e., body <NUM>. Flow paths <NUM>, <NUM> direct first working fluid flow <NUM> in first direction FD, and second working fluid flow <NUM> in second direction SD. As observed, second direction SD is tangentially opposed to first direction FD regardless of casing <NUM>, <NUM> and regardless of whether at a lowermost point of lower casing half shell <NUM> or an uppermost point of upper casing half shell <NUM>. In any event, working fluid flows <NUM>, <NUM> travel in opposite directions in casing <NUM>. It will be appreciated that each inlet <NUM>, <NUM> (<FIG> and <FIG>) in lower casing half shell <NUM> (<FIG>) may include any now known close-coupled valve (not shown) on an outer end thereof to control working fluid flows <NUM>, <NUM> for lower casing half shell <NUM>. It will be appreciated that working fluid flows <NUM>, <NUM> have a similar flow arrangement in HP steam turbine <NUM>.

Referring to <FIG>, in operation, working fluid flows <NUM>, <NUM>, i.e., steam, initially follow first and second working fluid flow paths <NUM>, <NUM> of HP steam turbine <NUM> and are channeled into a collective steam path (see CFD) of HP steam turbine <NUM>, i.e., stationary vanes and rotating blades thereof. Working fluid flows <NUM>, <NUM> may be sourced from any now known or later developed steam source, e.g., a heat recovery steam generator (HRSG), a boiler, etc., and delivered to inlet(s) <NUM> of HP steam turbine <NUM>. As working fluid flows <NUM>, <NUM> are directed by the stationary vanes and impact rotating blades <NUM> in HP steam turbine <NUM>, they impart a force on the blades, causing rotor <NUM> to rotate. Subsequently, working fluid flows <NUM>, <NUM> exit HP steam turbine <NUM> at an exit <NUM> and are redirected to one or more inlets <NUM>, <NUM> for IP steam turbine <NUM>. As understood in the art, the working fluid for IP steam turbine <NUM> may be reheated and/or combined with other working fluid flows prior to introduction into IP steam turbine <NUM>. As working fluid flows into IP steam turbine <NUM>, it is directed by the stationary vanes and impacts rotating blades <NUM> in IP steam turbine <NUM>, causing rotor <NUM> to rotate. The working fluid flow may exit IP steam turbine <NUM> at an exit <NUM>. Each turbine <NUM>, <NUM> may include any number of stages of vanes and blades. At least one end of rotor <NUM> may be attached to a load or machinery (not shown) such as, but not limited to, a generator, and/or another turbine.

Referring to <FIG> and <FIG>, as working fluid flows <NUM>, <NUM> travel in open interior <NUM> of casing <NUM> in opposite tangential directions, the working fluid must be directed axially into the relevant steam turbine, i.e., HP steam turbine <NUM> or IP steam turbine <NUM> (<FIG>) - see arrows denoting combined flow direction (CFD) in each turbine. <FIG> shows an enlarged, cross-sectional and perspective view of a conventional casing half shell <NUM>, <NUM> where working fluid flows <NUM>, <NUM> meet in casing <NUM> - typically at an uppermost point of upper casing half shell <NUM> or a lowermost point of lower casing half shell <NUM>. As illustrated in <FIG>, conventional casing half shells include a working fluid (steam) dam <NUM> where working fluid flows <NUM>, <NUM> meet. Dam <NUM> assists in redirecting working fluid flows <NUM>, <NUM> with curvature of inlets <NUM>, <NUM> (for lower casing half shell <NUM>), and casing flow guide <NUM>, axially into the relevant steam turbine <NUM>, <NUM> (<FIG>) and prevents flow oscillations. More particularly, working fluid flows <NUM>, <NUM> impact dam <NUM> and are redirected into steam turbine <NUM>, <NUM> (<FIG>) to the right as shown in the <FIG> example - see arrow CFD. Dam <NUM> is typically cast with casing half shell <NUM> or <NUM>. Dam <NUM>, however, creates a high local stress (see shaded area) that can require additional maintenance, and thus can reduce the availability of the system.

<FIG> show various embodiments of a stress reducing arrangement for a working fluid dam in a turbine system in accordance with embodiments of the disclosure. Generally, as shown in <FIG>, embodiments of the disclosure provide a working fluid dam <NUM> that extends radially and axially in body <NUM> between first working fluid flow path <NUM> and second working fluid flow path <NUM>. (Note, in <FIG>, working fluid flow paths <NUM>, <NUM> are shown at inlets <NUM>, <NUM> of lower casing half shell <NUM>. Similar flow paths exist for upper casing half shell <NUM>). Working fluid dam <NUM> extends radially and axially in body <NUM>, <NUM> at a location where tangentially opposing working fluid flow paths <NUM>, <NUM> meet, typically, at a lowermost point of lower casing half shell <NUM> or an uppermost point of upper casing half shell <NUM>. In contrast to conventional working fluid dams, working fluid dam <NUM> includes a stress-mitigating slot <NUM> extending radially therein. That is, stress-mitigating slot <NUM> is defined radially within working fluid dam <NUM>. Stress-mitigating slot <NUM> causes any high local stress to be located radially outward in casing half shell <NUM>, and more particularly, into a thicker metal <NUM> of casing half shell <NUM> or <NUM>. Thicker metal <NUM> is more capable of absorbing any high stress experienced during operation. Hence, stress-mitigating slot <NUM> reduces stress in a high stress-prone area that may form in the dam and forces stresses radially outward in the casing half shell to either maintain current stress or relieve the high stress from the working fluid dam. As illustrated, body <NUM> (and <NUM>) includes packing head main fit <NUM> with casing flow guide <NUM> extending axially therefrom upstream of working fluid dam <NUM> and diaphragm mounting element(s) <NUM> downstream of working fluid dam <NUM>, i.e., relative to steam turbine <NUM>, <NUM> (<FIG>). It is understood the diaphragm mounting elements <NUM> are configured to receive diaphragms (not shown) that aerodynamically interact with rotating blades <NUM> (<FIG>) to receive the kinetic energy of working fluid flows <NUM>, <NUM>. In order to continue to provide the full functionality of working fluid dam <NUM>, and as will be further described herein, casing half shell <NUM> further includes a fill member <NUM> mounted in stress-mitigating slot <NUM>.

Stress-mitigating slot <NUM> is formed to extend radially in working fluid dam <NUM>. Stress-mitigating slot <NUM> can be formed using any now known technique such as but not limited to: milling, electric discharge machining, laser cutting, water jetting, grinding, etc. As used herein, "extend radially" as it applies to stress-mitigating slot <NUM> indicates the slot extends generally radially but that some axial angling is allowable. For example, as shown in <FIG>, stress-mitigating slot <NUM> has an angle α relative to an axis A' (parallel to rotor axis A in <FIG>). Angle α may be, for example, between approximately <NUM>° and <NUM>°. Stress-mitigating slot <NUM> may be positioned in any axial location in working fluid dam <NUM> desired to, e.g., relieve a high local stress. As shown in <FIG> and in particular in <FIG>, stress-mitigating slot <NUM> extends adjacent an axially facing surface <NUM> of packing head main fit <NUM>, leaving a remaining portion of working fluid dam <NUM> as is. Here, a portion of casing <NUM> may be removed, e.g., by milling, to form an opening <NUM> (<FIG> and <FIG>) therein, i.e., as part of stress-mitigating slot <NUM> therein. As part of the removal, a part of casing flow guide <NUM> may be removed. In addition, stress-mitigating slot <NUM> may have any shape, axial width and/or radial depth desired to reduce and/or relieve stress. In terms of shape, as shown best in <FIG>, although not necessary in all cases, stress-mitigating slot <NUM> may have a radial outer end <NUM> including a curved shape <NUM>, i.e., a stress-mitigating contour or radius. The radius may include, for example, a single radius or a compound radius. In addition, while shown as a generally linear slot, the slot may curve. Stress-mitigating slot <NUM> may extend to any radial depth. In one example, shown in <FIG> and <FIG>, stress-mitigating slot <NUM> extends to be coplanar or nearly coplanar with a surface of inlet(s) <NUM>, <NUM> and/or a bottom of working fluid dam <NUM>. Alternatively, as shown in one example in <FIG>, stress-mitigating slot <NUM> may extend deeper into body <NUM> (or <NUM>), e.g., deeper than a surface of flow paths <NUM>, <NUM> and/or a bottom of working fluid dam <NUM>. Stress-mitigating slot <NUM> may extend to any axial length L and use any required axial extent of working fluid dam <NUM> necessary to address the expected stress. The shape (e.g., radius), axial length and radial depth used can each vary depending on a number of factors such as but not limited to: a width of dam <NUM>, the material used, operational parameter such as temperature, expected thermal cycling, desired stress to be removed, the location to which the stress is to be directed, etc..

Fill member <NUM> is fixedly coupled in stress-mitigating slot <NUM> in any now known fashion. Fill member <NUM> may be used, for example, to provide full functioning of working fluid dam <NUM>, despite the presence of stress-mitigating slot <NUM>. Fill member <NUM> may not be necessary in all cases. As shown in <FIG> and <FIG>, in this embodiment, fill member <NUM> is fixedly coupled to packing head main fit <NUM>. In this example, fill member <NUM> is at least partially positioned in opening <NUM> (<FIG> and <FIG>) in casing <NUM>, e.g., in casing flow guide <NUM>. Fill member <NUM> may be fixedly coupled, for example, by welding (<FIG>), or using fasteners <NUM> (<FIG>), e.g., screws, bolts, etc. In the <FIG> embodiment, fixedly coupling fill member <NUM> includes positioning the fill member in the stress-mitigating slot <NUM> and opening <NUM>, e.g., sliding it in, and coupling it to working fluid dam <NUM>, packing head main fit <NUM>, casing <NUM> and/or other structure.

Fill member <NUM> may have any shape and size desired to fill stress-mitigating slot <NUM>, and be fixedly coupled in place. In <FIG> and <FIG>, fill member <NUM> includes a planar plate. In addition, although not necessary in all cases, where stress-mitigating slot <NUM> includes radial outer end <NUM> including curved shape <NUM> (<FIG>), as shown in <FIG> and <FIG>, fill member <NUM> may have a complementary curved shape <NUM>. As shown in one example in <FIG>, fill member <NUM> may also have a radially inner end <NUM> that is shaped to match a radially inner end <NUM> of working fluid dam <NUM>. Alternatively, fill member <NUM> may have a radially inner end <NUM> that does not match a radially inner end <NUM> of working fluid dam <NUM> (see e.g., <FIG>). Where stress-mitigating slot <NUM> is curved, fill member <NUM> may be similarly curved.

<FIG> show additional alternative examples, outside of the scope of the claims, of fill member <NUM> and stress-mitigating slot <NUM> arrangements. <FIG> shows a perspective view of working fluid dam <NUM> and fill member <NUM> according to certain embodiments, and <FIG> shows a schematic cross-sectional view of a similar arrangement to that of <FIG>. In <FIG> and <FIG>, diaphragm mounting element <NUM> includes an opening <NUM> therein, e.g., a slot, and fill member <NUM> is at least partially positioned in opening <NUM>. Here, opening <NUM> may be formed into diaphragm mounting element <NUM>, e.g., using any technique listed herein for forming slot <NUM>, and fill member <NUM> is positioned in stress-mitigating slot <NUM> and opening <NUM>, and fixedly coupled therein. In certain embodiments such as those shown in <FIG> and <FIG>, fill member <NUM> has two angled portions <NUM>, <NUM> (<FIG>). In one example, fill member <NUM> has an L-shape with a slot portion <NUM> in stress-mitigating slot <NUM> and an axial portion <NUM> extending into opening <NUM>. Fill member <NUM> may be fixedly coupled in the slot in any manner, e.g., by fasteners <NUM> (<FIG>) or welding, to working fluid dam <NUM> and/or diaphragm mounting element <NUM>. While portions <NUM>, <NUM> are shown as perpendicular to one another that is not necessary in all instances, i.e., they can be set at other angles.

As shown in the schematic cross-sectional view of <FIG>, stress-mitigating slot <NUM> may extend radially in working fluid dam <NUM>, but may also include an additional axially extending portion <NUM> in working fluid dam <NUM> alone (not in packing head main fit <NUM> or diaphragm mount element <NUM>). Here, fill member <NUM> has an L-shape with slot portion <NUM> in stress-mitigating slot <NUM> and axial portion <NUM> extending into axially extending portion <NUM> of slot <NUM>. Here, fill member <NUM> is just fixedly coupled to working fluid dam <NUM>. Fill member <NUM> may be fixedly coupled in the slot in any manner, e.g., by fasteners <NUM> (<FIG>) or welding, to working fluid dam <NUM>. While shown with axial portion <NUM> of fill member <NUM> extending in a direction towards IP steam turbine <NUM> (<FIG>) in <FIG>, it is recognized that axial portion <NUM> may extend towards space <NUM> for HP steam turbine <NUM> (<FIG>). Further, while the L-shapes of fill member <NUM> in the examples shown have slot portion <NUM> and axial portion <NUM> at perpendicular angles, portions <NUM>, <NUM> may be at a non-perpendicular angle, e.g., for situations where slot is axially angled as in <FIG>.

As shown in the schematic cross-sectional view of <FIG>, in another example falling outside of the scope of the claims, stress-mitigating slot <NUM> may extend radially in working fluid dam <NUM>, but may include an additional two axially extending portions <NUM>, <NUM> in working fluid dam <NUM> alone (not in packing head main fit <NUM> or diaphragm mount element <NUM>). Here, fill member <NUM> has a T-shape with a slot portion <NUM> in stress-mitigating slot <NUM>, a first axial portion <NUM> extending into a first axially extending portion <NUM> of slot <NUM>, and a second axial portion <NUM> extending into a second axially extending portion <NUM> of slot <NUM>. Fill member <NUM> may be just fixedly coupled to working fluid dam <NUM>. Fill member <NUM> may be fixedly coupled in the slot in any manner, e.g., by fasteners or welding, to working fluid dam <NUM>. Here, fill member <NUM> may have a T-shape, which can be symmetrical or non-symmetrical. Although not shown, in other embodiments, fill member <NUM> may also have axial portions <NUM> and/or <NUM> extend into packing head main fit <NUM> and/or diaphragm mounting element <NUM>, similar to <FIG> and <FIG>.

While shown fixedly coupled to particular structure in the examples shown, it is emphasized that fill member <NUM> may be fixedly coupled to any of working fluid dam <NUM>, packing head main fit <NUM>, diaphragm mounting element <NUM> and/or other structure, depending on its shape and size.

While embodiments of the disclosure have been mainly illustrated and described relative to use in IP steam turbine <NUM> (<FIG>) and/or lower casing half shell <NUM> thereof, it is emphasized that the teachings are applicable to HP steam turbine <NUM> (<FIG>) and the lower and/or upper casing half shells thereof.

Stress-mitigating slot <NUM> provides a mechanism to implement a low cost working fluid dam <NUM> where necessary to reduce stress, such as in a double-shell opposed flow configuration. Fill member <NUM> may be employed, where desired, to retain the functioning of the working fluid dam, e.g., with little to no leakage thereacross. The manufacturing process can be carried out via conventional casing <NUM> formation processes, e.g., casting, with working fluid dam <NUM>, and then removing a section of material using to create stress-mitigating slot <NUM> with, for example, any desired stress-mitigating contour. Fill member <NUM> can then be optionally fixedly coupled in the slot to block the working fluid cross-flow area. The arrangement and process enable a significant cost reduction of the opposed flow configuration versus the separate HP and IP shell configurations, and may provide similar savings in other applications. The teachings of the disclosure can be applied to any type of turbine, and in either casing half shell thereof.

Accordingly, a value modified by a term or terms, such as "about," "approximately" and "substantially," are not to be limited to the precise value specified. "Approximately" as applied to a particular value of a range applies to both values, and unless otherwise dependent on the precision of the instrument measuring the value, may indicate +/- <NUM>% of the stated value(s).

Claim 1:
A casing half shell (<NUM>, <NUM>) for a turbine system (<NUM>, <NUM>), wherein the casing half shell (<NUM>, <NUM>) comprises:
• a body (<NUM>, <NUM>) having an open interior (<NUM>) for enclosing parts of the turbine system (<NUM>, <NUM>),
• a first working fluid flow path (<NUM>) defined in the body (<NUM>, <NUM>) for directing a first working fluid flow (<NUM>) in the open interior (<NUM>) in a first direction (FD),
• a second working fluid flow path (<NUM>) defined in the body (<NUM>, <NUM>) for directing a second working fluid flow (<NUM>) in the open interior (<NUM>) in a second direction (SD) that is opposed to the first direction (FD),
• a working fluid dam (<NUM>) extending radially and axially in the body (<NUM>, <NUM>) between the first working fluid flow path (<NUM>) and the second working fluid flow path (<NUM>), the working fluid dam (<NUM>) including a stress-mitigating slot (<NUM>) extending radially therein, and
• a fill member (<NUM>) mounted in the stress-mitigating slot (<NUM>), and wherein the body (<NUM>, <NUM>) further includes a packing head main fit (<NUM>) upstream of the working fluid dam (<NUM>) and a diaphragm mounting element (<NUM>) downstream of the working fluid dam (<NUM>), and
characterised in that the stress-mitigating slot (<NUM>) extends adjacent an axially facing surface (<NUM>) of the packing head main fit (<NUM>), and the fill member (<NUM>) is fixedly coupled to the packing head main fit (<NUM>).