JP2009174324A - Steam valve - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve erosion resistance of a valve stem of a steam valve. <P>SOLUTION: The steam valve is constructed containing, in a casing 1, a valve seat 3 having an opening 2, a valve element 5 disposed opposed to the opening 2, the valve stem 7 for moving the valve element 5 toward and away from the valve seat 3, and a gland casing 9, a cylindrical support member, slidably supporting the valve stem 7. Even when the valve element 5 opens or closes, the collision of solid particles entrained in steam flow with the valve stem 7 is avoided by inserting a cylindrical part 17 of the gland casing 9 into an annular groove part 25 disposed in the valve element 5, and setting an axial distance D1 of a hole 23 and an axial distance D2 of the cylindrical part 17 to more than a stroke D3 of the valve stem. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a steam valve, and more particularly to a technique for improving the erosion resistance of a valve stem.

  The main steam valves installed in the steam turbine power generation facility of the thermal power plant are composed of a main steam stop valve and a steam control valve of the main steam system, a reheat steam stop valve of the reheat steam system, an intercept valve, and the like. The main steam stop valve and reheat steam stop valve are arranged for the purpose of shutting off the steam flowing into the turbine in an emergency, and the steam control valve and intercept valve are for the purpose of adjusting the amount of steam flowing into the turbine and controlling the turbine. Has been placed.

  The steam valve is composed of a valve seat having an opening, a valve body provided opposite to the opening of the valve seat, a valve rod that moves the valve body in a direction to contact and separate from the valve seat, and a valve rod that can freely slide. And a cylindrical support member to be supported.

  By the way, with the high efficiency and low cost of thermal power plants, high-temperature and high-pressure steam conditions, and longer maintenance intervals, it is required to improve the reliability of steam valves. In particular, it is required to improve the reliability of a valve stem that is exposed to a high-temperature and high-pressure steam flow.

  In response to these requirements, in order to improve the reliability of the valve stem, by using a Ni-based alloy having a highly protective oxide film as the material of the valve stem, the oxide scale that causes the valve stem stick A technique for improving wear resistance by suppressing generation and further nitriding the surface of the valve stem has been proposed (for example, Patent Document 1).

2004-183051 gazette

  However, Patent Document 1 does not take into consideration that the surface of the valve stem is damaged by oxide solid particulates flying along with the steam flow.

  In other words, the valve stem of a steam valve is a valve that is eroded or worn by erosion when powder particles such as oxide solid particulates flying along with the steam flow from the boiler collide with the surface of the valve stem. There is a problem that the movement of the rod is affected, the valve rod sticks and cannot be opened or closed, and the smoothness of the opening and closing operation of the steam valve is impaired.

  An object of the present invention is to improve the erosion resistance of a valve stem of a steam valve.

  In order to solve the above-described problems, a steam valve according to the present invention moves a valve seat having an opening, a valve body provided to face the opening of the valve seat, and a direction in which the valve body comes into contact with and separates from the valve seat. In a steam valve including a valve stem and a cylindrical support member that slidably supports the valve stem, the valve body and the support member are formed in a shape in which opposing ends overlap each other in the movable range of the valve body. It is characterized by.

  As a result, even when the valve body is opened and closed, the valve stem is not exposed to the steam flow, so that solid particles accompanying the steam flow can be blocked from hitting the valve stem, and erosion due to the solid particles can be suppressed. can do. As a result, the erosion resistance of the valve stem of the steam valve can be improved.

  In this case, an annular groove into which the cylindrical end of the support member is inserted is provided at the end facing the support member of the valve body, and the annular groove and the support member when the valve body comes into contact with the valve seat It is preferable that the length in the axial direction of the overlapping portion be greater than or equal to the stroke of the valve body. In general, since the support member is disposed on the downstream side of the steam flow with respect to the valve seat, the steam flow having a high flow rate between the valve seat and the valve body can be prevented from directly colliding with the valve stem. It is possible to suppress the inflow of steam between the annular groove and the support member.

  Further, the end of the valve body facing the support member is formed to extend in a cylindrical shape, and the end of the support member facing the valve body is provided with an annular groove into which the end of the cylindrical valve body is inserted. The axial length of the portion where the annular groove and the valve body overlap when the valve body is brought into contact with the valve seat can be made longer than the stroke of the valve body.

  According to the present invention, the erosion resistance of the valve stem of the steam valve can be improved.

  Hereinafter, the present invention will be described based on embodiments. FIG. 1 is a structural cross-sectional view showing a main part of a steam valve according to an embodiment of the present invention, and FIG. 2 is a structural cross-sectional view for explaining the operation of the steam valve of the present embodiment. As shown in the figure, the steam valve of the present embodiment is moved in a direction in which the valve seat 3 having the opening 2, the valve body 5 provided to face the opening 2, and the valve body 5 are in contact with and away from the valve seat 3. The casing 1 is configured to accommodate a valve stem 7 to be moved and a sanitary casing 9 that is a cylindrical support member that freely supports the valve stem 7. 1 shows a state in which the valve body 5 is at the upper end position, that is, when the valve is fully opened, and FIG. 2 shows a state in which the valve body 5 is in the lower end position, that is, when the valve is fully closed.

  Inside the casing 1, a valve chamber partitioned up and down by a valve seat 3 is formed. An inlet 11 through which steam flows is provided at the upper part of the valve chamber partitioned by the valve seat 3. A steam outlet (not shown) is provided below the valve chamber partitioned by the valve seat 3.

  The guard casing 9 is fixed to the bottom of the valve chamber partitioned by the valve seat 3, and is provided with a hole 13 through which the valve rod 7 is inserted in the vertical direction. A valve body 5 is fixed to the upper end portion of the valve stem 7, and the valve body 5 is disposed above and above the valve seat 3 so as to be able to contact and separate. Below the valve stem 7, a valve stem drive means (not shown) for driving the valve stem 7 in the vertical direction is provided.

  Further, an enlarged diameter portion 13 a is formed at the lower portion of the hole 13, and a reduced diameter portion 13 b is formed at the upper portion of the hole 13. Further, the enlarged diameter portion 7a and the reduced diameter portion 7b are also formed in the valve stem 7 so as to correspond to the enlarged diameter portion 13a and the reduced diameter portion 13b. The stepped portion formed between the enlarged diameter portion 13a and the reduced diameter portion 13b of the hole 13 is engaged with the stepped portion of the enlarged diameter portion 7a and the reduced diameter portion 7b of the valve rod 7 so that the upper end position of the valve body 5 is set. I try to regulate it. A cylindrical bush 19 into which the enlarged diameter portion 7a of the valve rod 7 is inserted is fitted into the enlarged diameter portion 13a of the hole 13, and the inner diameter of the bush 19 is slidably movable by the enlarged diameter portion 7a. The diameter is set. The stepped portion of the valve stem 7 and the stepped portion of the hole 13 are formed in a taper shape, and when the valve body 5 is at the upper end position, the stepped portions are in close contact with each other so that steam flows into the sliding portion of the valve stem 7. I try to suppress it.

  Next, a protection structure for a valve stem, which is a characteristic part of the present embodiment, will be described. A hole 23 having a diameter larger than that of the reduced diameter portion 7 b of the valve body 7 is provided at an end portion of the valve body 5 facing the guard casing 9, and an annular groove portion 25 is formed between the hole 23 and the valve stem 7. Has been. The cylindrical portion 17 at the end facing the valve body 5 of the guard casing 9 is formed so as to be able to enter the groove portion 25. A distance D1 in the axial direction of the hole 23 and a distance D2 in the axial direction of the cylindrical portion 17 are set to be not less than the stroke D3 of the valve stem. In other words, the axial length of the portion where the annular groove 25 and the cylindrical portion 17 of the guard casing 9 overlap when the valve body 5 is in contact with the valve seat 3 is longer than the stroke D3 of the valve body 5. It is said. Here, the stroke D3 is defined as a difference in the distance that the valve stem 7 moves in the axial direction when the valve is fully opened and when the valve is fully closed. D1 and D2 are set to a distance at which the valve body 5 and the valve stem 7 do not collide with each other.

  Further, the clearance between the outer surface of the cylindrical portion 17 and the inner surface of the hole 23 and the clearance between the inner surface of the reduced diameter portion 13b of the hole 13 and the outer surface of the reduced diameter portion 7b of the valve stem 7 when the valve is fully closed are as follows. In consideration of the coefficient of linear expansion of the material that changes depending on the steam conditions and the amount of oxide scale generated on the metal surface, it is set to a level that does not affect the operability of the valve stem (for example, 5 mm).

  Next, operation | movement of the steam valve comprised in this way is demonstrated. First, as shown in FIG. 2, when the valve is fully closed, the valve body 5 and the valve seat 3 are in close contact with each other, so that the steam does not flow to the outlet side. Next, as shown in FIG. 1, when the valve rod 7 is driven by the valve rod driving means to raise the valve body 5, the steam that has flowed in through the inlet 11 from a boiler (not shown) or the like is indicated by an arrow. As shown in the figure, a part of the steam flow that has flowed through the gap between the valve body 5 and the valve seat 3 and increased in speed collides with the valve body 5 and the guard housing 9 and flows to the outlet. At this time, the tubular portion 17 that has entered the valve body 5 is exposed to the steam flow as the valve rod 7 rises, but the steam flow collides with the tubular portion 17 and flows to the outlet, and the valve rod 7 There is no direct vapor flow. When the valve stem 7 is further raised, the stepped portion of the valve stem 7 is locked to the stepped portion of the guard casing 9 so that the valve body 5 reaches the upper end position, and the flow rate of the steam becomes maximum. At this time, since the axial distance D1 of the hole 23 and the axial distance D2 of the cylindrical portion 17 are set to be equal to or greater than the stroke D3 of the valve rod, the valve rod 7 is covered with the cylindrical portion 17, The steam flow collides with the cylindrical portion 17 and flows to the outlet, and the steam flow does not directly hit the valve stem 7 in the entire stroke range of the valve stem 7.

  Thus, even when the valve body 5 is opened and closed, the valve stem 7 is not exposed to the steam flow, so that the solid particles accompanying the steam flow can be prevented from hitting the valve stem 7 and erosion due to the solid particles can be suppressed. can do. As a result, the erosion resistance of the valve stem of the steam valve can be improved.

  In the above-described embodiment, the tubular portion 17 of the guard casing 9 is caused to enter the annular groove portion 25 provided in the valve body 5, but the present invention is not limited to this embodiment. An annular groove portion in which an end portion facing the guard casing 9 extends in a cylindrical shape, and an end portion of the cylindrical valve body 5 is inserted into an end portion facing the valve body 5 of the guard casing 9 The axial length of the portion where the annular groove and the valve body 5 overlap when the valve body 5 is brought into contact with the valve seat 3 may be equal to or longer than the stroke of the valve body 5.

  In the present embodiment, 12% chrome steel can be used for the casing 1, and 9% chrome steel can be used for the valve seat 3, the valve body 5, and the guard casing 9. However, the material of the casing 1, the valve seat 3, the valve body 5, and the guard casing 9 is not limited to this, and any material having corrosion resistance and heat resistance may be used. For example, chromium-molybdenum-vanadium steel, 9% Chrome steel, 12% chromium steel, or the like can be used.

  The bush 19 is made of, for example, a Co-based alloy (Stellite), and the valve stem 7 is made of, for example, an incoloy having high oxidation resistance (suppression of oxide scale generation) and wear resistance (improvement of high temperature hardness). (The main component is nickel-chromium-iron). Further, nitriding treatment can be performed on the valve stem surface in order to improve wear resistance. However, the bush 19 and the valve stem 7 are not limited to these, and may have any corrosion resistance, heat resistance, and wear resistance.

  Further, the valve stem is preferably subjected to nitriding treatment on the surface. In this nitriding treatment, nitrogen is infiltrated into the base material surface under a temperature condition of 500 to 600 ° C. to form a hardened layer of iron nitride.

It is a composition sectional view showing the important section of the steam valve of one embodiment of the present invention. It is a structure sectional view for explaining operation of a steam valve of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Casing 2 Opening 3 Valve seat 5 Valve body 7 Valve rod 9 Guard casing 11 Inlet 13, 23 Hole 17 Cylindrical part 19 Bush 25 Groove part

Claims (3)

A valve seat having an opening, a valve body provided to face the opening of the valve seat, a valve stem for moving the valve body in a direction to contact and separate from the valve seat, and the valve stem to be freely slidable In a steam valve provided with a cylindrical support member to support,
The said valve body and the said supporting member are formed in the shape in which the edge part which opposes mutually overlaps in the movable range of the said valve body. The steam valve according to claim 1,
An annular groove into which the end of the support member is inserted is provided at an end of the valve body facing the support member, and the annular groove when the valve body is in contact with the valve seat and the The length of the axial direction of the part which a support member overlaps is more than the stroke of the said valve body, The steam valve characterized by the above-mentioned. The steam valve according to claim 1,
The valve body is formed such that an end portion facing the support member extends in a cylindrical shape, and an end portion of the valve body is inserted into an end portion of the support member facing the valve body. The length of the axial direction of the portion where the annular groove and the valve body overlap when the valve body is in contact with the valve seat is equal to or longer than the stroke of the valve body. Features a steam valve.

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