Patent Description:
Solid particle erosion is a common problem affecting steam power production components in the power generation industry. Many parts of the steam path between the power boiler and steam turbine are subject to material erosion problems due to entrained magnetite particles exfoliated from boiler tubes into the steam transport system. Over time, erosion damage can accumulate and impact steam piping integrity, valve operation, steam turbine blades, etc. resulting in a loss of plant efficiency, as well as lower reliability and availability due to increase forced outages to repair damaged components. Ultimately, the plant owner will recognize an increasing loss in revenues and profitability.

Steam valves can experience extreme erosion conditions, particularly when the steam valve opens and closes. As shown in <FIG>, a known steam valve, generally designated <NUM>, has a steam valve body <NUM> having an internal cavity <NUM>, a steam inlet <NUM>, a steam outlet <NUM>, a control valve <NUM> including a control valve head <NUM>, and a stop valve <NUM> including a stop valve head <NUM>. Above the control valve <NUM>, a control valve actuator (not shown) is coupled to a stem <NUM> for raising and lowering the control valve head <NUM> to selectively engage a valve seat <NUM> for controlling the steam flow through the valve <NUM>. It will be appreciated that the position of the flow control head <NUM> relative to the valve seat <NUM> can be controlled in response to load changes on a turbine.

The control head <NUM> is annular in configuration, having a hollow or recess <NUM> along its underside. The annular lower edge of control valve head <NUM> in a closed position, as shown in <FIG>, engages and seals against the valve seat <NUM>. The stop valve head <NUM> is configured for reception within the recess <NUM> and also includes an annular surface <NUM> about its underside for sealing and engaging against the valve seat <NUM> in a stop valve closed position. The stop valve head <NUM> is mounted on a shaft or stem <NUM> which extends through a pressure seal head <NUM> to a hydraulic cylinder (not shown). The stop valve head <NUM> follows the movement of the control valve head <NUM> through a control system (not shown). By following the movement of the control valve <NUM>, the combination of the control valve head <NUM> and stop valve head <NUM> provide a smooth, laminar flow of steam past those heads and through the valve to the outlet <NUM>.

<FIG> illustrates both the control valve head <NUM> and stop valve head <NUM> of <FIG> in an open position. Below the control valve head <NUM> and the stop valve head <NUM>, an outlet passage <NUM> is provided which directs the flow of steam passing through the valve to the outlet <NUM>. The outlet passage <NUM> and the valve seat <NUM> have walls substantially forming a smooth, continuous transition therebetween without any abrupt changes in flow direction. In this manner, the steam flowing through the valve <NUM> past the valve seat <NUM> and through the outlet passage <NUM> to the outlet <NUM> is substantially without vortices and affords optimum steam flow characteristics, with minimum losses. Moreover, the outlet passage <NUM> has a cross-sectional area which is not substantially larger than the cross-sectional area of the valve seat <NUM> and the outlet <NUM>. Thus, the pattern of steam flow in the valve-open condition tends toward a laminar flow without substantial vortices and, consequently, with minimum head losses. This laminar flow may include entrained solid particles that when passing through the outlet passage, impinge upon the upper tip of the pressure seal head <NUM> resulting in severe erosion.

Referring to <FIG>, a schematic view of the steam valve <NUM> in a partially open position shows a high velocity annular steam flow <NUM> passing between the control valve head <NUM> and the valve seat <NUM>, particularly when the spacing therebetween is narrow such as during the transition period when the control valve seat <NUM> or stop valve head <NUM> is lifting from or engaging the valve seat <NUM>. During this transition time or valve position, the high velocity steam <NUM> annularly impacts the tip of the pressure seal head <NUM>, for example, at area <NUM>. One will appreciate any particle entrained in the steam flow <NUM> will increase erosion of the pressure seal head <NUM> at this area <NUM>. <CIT>, <CIT> and <CIT> teach valves in which valve heads of the valve are more erosion resistant than the respective valve stems. <CIT> teaches to provide a wall section of a valve assembly with a flow channel underneath the wall, and discloses the technical features of the preamble of claim <NUM>. Erosion of the wall may then be detected as a fluid flow in said passage.

As such, it is desirable to provide a means to reduce the erosion of the pressure seal head of a steam valve. <CIT> discloses a pressure seal head for a valve, wherein the pressure seal head is a monobloc device. A valve stem with a proximally arranged valve body extending through the pressure seal head. Proximal facing steps of the pressure seal head have a wear coating disposed thereon, which, in some instances, is of greater hardness, and thus erosion resistance, than the valve stem and the valve body. <CIT> is, however, silent about the hardness of the wear coating relative to the body of the pressure seal head.

Aspects and advantages will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. The herein claimed invention resides in the subject matter set forth in the claims.

These features, aspects and advantages will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain certain principles of the invention.

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended Figs. , in which:.

Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the presently claimed invention.

Reference now will be made in detail to embodiments of the herein claimed invention, one or more examples of which are illustrated in the drawings. Features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the presently claimed invention covers such modifications and variations as come within the scope of the appended claims.

The terms "upper", "lower", "upward", and "downward" refer to the relative position of features of a component or direction with respect to its orientation in the illustration of the component and are not intended to signify orientation of the features or direction during the use of the components.

The terms "integral" and "unitary" refer to at least two components which are metallurgically joined or formed together, such that the separation of the components is not easily performed without damaging a component.

The terms "coupled", "fixed", "attached to", "secure", and the like refer to both direct coupling, fixing, or attaching, as well as indirect coupling, fixing, or attaching through one or more intermediate components or features, unless otherwise specified herein.

<FIG> shows an exemplary embodiment of a pressure seal head <NUM> of the present invention for use in the steam valve <NUM> of <FIG>. The pressure seal head <NUM> includes a body <NUM> and a nose piece <NUM> attached to the body to enable the nose piece to be removed and replaced without damaging the body. The nose piece <NUM> is formed of high erosion resistant material such as cobalt based alloy, cobalt/chromium alloy, tungsten alloy, titanium alloy or any other high erosion resistant material. For example, the nose piece <NUM> may be formed of Stellite 6B. The body <NUM> is formed of a material having less erosion resistant characteristics than the material of the nose piece.

The body <NUM> may be generally cylindrical in shape having a first through bore <NUM> passing longitudinally or axially through the body for slidably receiving the stem <NUM> of the stop valve <NUM> of <FIG>. The first through bore <NUM> defines an inner surface <NUM> of the body <NUM> having a recess <NUM> to accommodate a sleeve bushing (not shown) to provide a bearing surface for the stem <NUM>. The body <NUM> includes an annular ridge <NUM> extending from the outer surface <NUM> for engaging the housing <NUM> (as best shown in <FIG>) to provide support and a stop to ensure the body extends within the internal cavity <NUM> of the steam valve <NUM> at a desired height. A lower end <NUM> of the body <NUM> is configured to extend into and/or through a bore in the housing <NUM>. The upper end <NUM> of the body <NUM> has an outer diameter less than the outer diameter of the outer surface <NUM> to provide an annular step <NUM>, which may provide a seat for the nose piece <NUM>. At the step <NUM>, the upper end <NUM> of the body <NUM> may include an annular groove <NUM> for engaging the nose piece <NUM>.

The nose piece <NUM> may be shaped to include a lower portion <NUM> having a generally cylindrical shape and a generally tapered end portion <NUM>. The outer diameter or shape of the lower portion <NUM> may be substantially the same as the outer surface <NUM> of the body <NUM> to provide a relatively smooth transition therebetween. The outer surface <NUM> of the tapered end portion <NUM> of the nose piece <NUM> may be arcuate, rounded, flat or any other characteristic to provide the desired aerodynamic profile for engaging the steam flow <NUM> (<FIG>) passing over the pressure seal head <NUM>. As shown in <FIG>, the tapered end portion <NUM> of the nose piece <NUM> may have a rounded, convex surface <NUM>. The nose piece <NUM> includes a second through bore <NUM> defines an inner surface <NUM> of the nose piece and passes longitudinally or axially therethrough for slidably receiving the stem <NUM> of the stop valve <NUM>. The second through bore <NUM> of the nose piece <NUM> includes a recess <NUM> to accommodate a sleeve bushing (not shown) to provide a bearing surface for the stem <NUM>. The lower portion <NUM> of the nose piece <NUM> includes a counterbore <NUM> having a diameter that is substantially equal to or less than the outer diameter of the upper end <NUM> of the body <NUM> for receiving the body therein. The lower end <NUM> within the counterbore <NUM> may include an annular ridge <NUM> extending inwardly having a complimentary shape as the groove <NUM> in the body.

As best shown in <FIG>, the nose piece <NUM> may be attached to the body <NUM> by shrink fitting the nose piece to the body whereby the nose piece fits over the upper end <NUM> of the body and the annular ridge <NUM> of the noise piece locks into the groove <NUM> of the body to form the pressure seal head <NUM>. To further secure the nose piece <NUM> to the body <NUM>, at least one pin may extend through a through hole in the nose piece into a hole in the upper end <NUM> of the body <NUM>. The invention also contemplates the nose piece <NUM> providing no annular ridge <NUM> nor the body <NUM> providing a groove <NUM>, whereby the nose piece <NUM> is simply secured to the body <NUM> by the at least one pin, which is removable. The invention further contemplates that one to four pins <NUM> may be used to secure the nose piece <NUM> to the body <NUM> to form the pressure seal head <NUM>.

In another exemplary embodiment in <FIG>, a pressure seal head <NUM> is shown, which is similar to the pressure seal head <NUM> of <FIG>, and therefore, the common features will have the same reference number and characteristics. The primary difference between the pressure seal head <NUM> and the pressure seal head <NUM> is the means to attach the nose piece to the body to enable removal and/or replacement of the nose piece. In this embodiment, both the outer surface of the upper portion <NUM> of the body <NUM> and the inner surface of the counterbore <NUM> of the lower portion <NUM> of the nose piece <NUM> are threaded. The nose piece <NUM> and the body <NUM> are threaded together to secure these components together. These attachment means shown in <FIG> enable the nose piece <NUM>, <NUM> to be removed from the body <NUM>, <NUM> and replaced with a new nose piece without damaging the body of the pressure seal valve <NUM>, <NUM>.

While the attachment means shown in <FIG> provide features to insert and attach the body <NUM>, <NUM> into the nose piece <NUM>, <NUM>, the present invention contemplates these attachment features may be reversed whereby the nose piece <NUM>, <NUM> and the body <NUM>, <NUM> are attached together by inserting the nose piece into the body, such that the nosepiece <NUM>, <NUM> includes the male portion of the attachment and the body <NUM>, <NUM> includes the female portion. For example, the upper portion <NUM> of the bodies <NUM>, <NUM> may include a counterbore similar to the counterbore <NUM> of the respective nose piece <NUM>, <NUM> of <FIG>, while the lower portion <NUM> of the nose pieces <NUM>, <NUM> may include a lower end with an outer diameter less than the outer diameter of the outer surface of the nose piece <NUM>, <NUM> to provide an annular step similar to the upper end <NUM> of the respective bodies <NUM>, <NUM> of <FIG>. This alternative embodiment for the pressure seal head <NUM> of <FIG> may include a complementary annular ridge and groove to attach the nose piece into the body. Similarly, this alternative embodiment for the pressure seal head <NUM> of <FIG> may include threaded surfaces on the lower end of the nose piece and the counterbore of the body to thread and secure the nose piece into the body. Furthermore, while the noise piece <NUM>, <NUM> and body <NUM>, <NUM> are described as having a generally cylindrical shape or circular cross-section, one will appreciate the shape or cross-section may include any shape or cross-section, for example any hexagonal shape.

Referring to <FIG>, another embodiment of a pressure seal head <NUM> according to the present invention is shown, which is similar to the pressure seal heads <NUM>, <NUM> of <FIG>, respectively, and therefore, the common features will have the same reference number and characteristics. The pressure seal head <NUM> includes a body <NUM> and a nose piece <NUM> fixedly attached together. Similar to the pressure seal heads <NUM>, <NUM>, the nose piece <NUM> is formed of high erosion resistant material, while the body may be formed of a material having less erosion resistant characteristics than the material of the nose piece.

The primary difference between the pressure seal head <NUM> and the pressure seal heads <NUM>, <NUM> is the means to attach the body <NUM> and nose piece <NUM> together. The body <NUM> and the nose piece <NUM> may be formed or joined together to form an integral or unitary component by various attachment methods or means, such as conventional brazing or welding (e.g., inertia welding) attachment methods. Alternatively, the nose piece <NUM> and body <NUM> may be formed as a unitary component by molding or additive manufacturing methods, including dissimilar additive manufacturing methods. As shown, the nose piece <NUM> and body <NUM> provide complementary flat engagement surfaces <NUM>, <NUM> respectively, to provide a planar transition between the components. While the engagement surfaces are flat, one will appreciate the engagement surfaces by provide complementary interlocking features. For example, the upper end of the body <NUM> may extend into a complementary bore within the nose piece <NUM>, or vice versa. In this embodiment, the non-destructive removal and replacement of the nose piece <NUM> from the body <NUM> is not simple nor economical, and therefore, replacement of entire pressure seal head <NUM> is the most practicable.

In another exemplary embodiment, <FIG> illustrate a nose piece <NUM> similar to the nose piece <NUM> of the pressure seal head <NUM> of <FIG> modified to include a wear indicator <NUM> to provide a means to notify an operator that the outer surface of the nose piece <NUM> has excessive erosion. The common features, therefore, will have the same reference number. The nose piece <NUM> may include at least one cavity <NUM> disposed within the tapered end portion <NUM> where the nose piece may experience the greatest amount of erosion at area <NUM>, as illustrated in <FIG>. The cavity <NUM> may extend from the tip of the nose piece <NUM> to at least the bottom of the tapered end portion <NUM> of the nose piece <NUM>. The cavity <NUM> is in fluid communication with an opening or slot <NUM> disposed in the inner surface of the lower portion <NUM> of the nose piece <NUM>. The cavity <NUM> is spaced from the outer surface of the nose piece <NUM> to provide an inner wall <NUM> and an outer wall <NUM> having a desired outer wall thickness ti, as best shown in <FIG>. The thickness ti of the outer wall <NUM> is indicative of the amount of acceptable erosion for the specific area <NUM> (see <FIG> and <FIG>) on the nose piece <NUM>. As shown, the thickness of the outer wall <NUM> of the nose piece <NUM> may be increasing greater as the cavity <NUM> extends downward. The invention further contemplates the thickness of the outer wall to remain constant over the tapered end portion <NUM> of the nose piece <NUM>, or the thickness of the outer wall over the tapered end portion <NUM> decreasingly as the cavity <NUM> extends downward. Further, the thickness of the outer wall may vary depending on the erosion pattern on the nose piece <NUM>. For example, the wall thickness may be greatest at the area <NUM> experiencing the most erosion. As best shown in <FIG>, the cavity <NUM> further extends circumferentially about a portion of the nose piece <NUM>, as shown, or completely around the entire circumference of the nose piece. In the embodiment shown in <FIG>, the nose piece <NUM> includes four cavities <NUM> evenly spaced, circumferentially around the nose piece <NUM>, with each cavity in fluid communication with a respective slot <NUM>. One will appreciate any number of cavities <NUM> may be disposed circumferentially within the nose piece <NUM>. In one embodiment the spacing <NUM> between the cavities <NUM> is minimal to minimize the circumferential area void of the wear indicator. The cavities <NUM> may have different varying circumferential widths or the same circumferential widths. The wear indicator system <NUM> further includes a sensor (not shown) for measuring the pressure within the second through bore <NUM> and the first through bore <NUM> and outside of surface <NUM> and <NUM> of the pressure seal head <NUM>. When the outer wall <NUM> of the nose piece <NUM> erodes to the point of breaching any one of the cavities <NUM>, the steam in the steam valve <NUM> flows into the cavity <NUM> to the second through bore <NUM> and the first through bore <NUM> via the respective slot <NUM> in the fluid communication with a respective cavity <NUM>. In response to the pressure change, a control system (not shown) provides an alarm or indicator to an operator that the nose piece <NUM> indicating the excessive erosion, and therefore, replacement of the nose piece <NUM> may be needed.

While the nose piece <NUM> may be modified to include the wear indicator <NUM>, as shown in <FIG>, one will appreciate each of the nose pieces <NUM>, <NUM> provided here before may include a similar excessive wear indicator <NUM> to determine the need to replace the nose piece <NUM> or the pressure seal head <NUM>.

This invention will provide customers with added levels of protection from the long-term effects of solid particle erosion. The pressure seal head with this applied feature will have increased resistance to erosion and help prevent forced outages due to equipment failure.

Claim 1:
A pressure seal head (<NUM>, <NUM>, <NUM>) for a steam valve, the pressure seal head comprising an elongated body (<NUM>, <NUM>, <NUM>) and a nose piece (<NUM>, <NUM>, <NUM>, <NUM>) comprising a tapered end portion (<NUM>),
the pressure seal head having a through opening, wherein the through opening of the pressure seal head is comprised of a first through bore (<NUM>) extending longitudinally through the elongated body and a second through bore (<NUM>) extending longitudinally through the nose piece,
wherein
the nose piece (<NUM>, <NUM>. <NUM>, <NUM>) includes a wear indicator (<NUM>) having at least one cavity (<NUM>) therein extending circumferentially about at least a portion of the nose piece, the at least one cavity (<NUM>) defining an inner wall radially inward of the at least one cavity and an outer wall radially outward of the at least one cavity; and a slot (<NUM>) providing fluid communication between the at least one cavity (<NUM>) and the second through bore (<NUM>) of the nose piece; wherein the at least one cavity extends below a portion of the outer wall exposed to erosion,
characterised in that the nose piece (<NUM>, <NUM>, <NUM>, <NUM>) is formed of a first material and the elongated body (<NUM>, <NUM>, <NUM>) is formed of a second material, wherein the first material is a higher erosion resistance material than the second material, and in that the nose piece (<NUM>, <NUM>, <NUM>, <NUM>) is configured to removably and replaceably attach the elongated body (<NUM>, <NUM>, <NUM>) of the pressure seal head.