Fluid handling – With casing – support – protector or static constructional... – Jacketed
Reexamination Certificate
2001-02-05
2004-01-06
Mancene, Gene (Department: 3754)
Fluid handling
With casing, support, protector or static constructional...
Jacketed
C251S368000, C376S352000, C252S06230C, C148S648000, C228S193000
Reexamination Certificate
active
06672330
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a valve having a corrosion and wear proof alloy bonded to the sliding portion, and to apparatuses using said valve.
In recent years, chemicals, such as hydrogen peroxide and hydrazine, have come to be injected into the recirculation system of turbine generation facilities in order to adjust the quality of recirculating water. This increases the volume of dissolved oxygen on the downstream side of the inlet where said chemicals are introduced, resulting in damage to the valve seat, etc. due to erosion and scoring.
Official Gazette of Japanese Patent Laid-Open NO. 179283/1984 discloses a valve wherein a valve seat comprising 30 to 45 wt % of Cr, 3.0 to 8.0 wt % of Ti, 0 to 10 wt % of Mo and remaining Ni is diffusion-bonded to the valve disc and valve body.
In such valves as a globe valve, a gate valve and a butterfly valve, alloys of high hardness characterized by excellent corrosion and wear resistance, such as a cobalt (Co) base alloy, a nickel (Ni) base alloy, and an iron (Fe) base alloy, are padded onto the sliding portion of the valve and valve seat in order to avoid damage due to erosion caused by fluid close to the valve seat during operation, or to prevent scoring at the time of valve operation.
However, an eutectic carbide of cobalt (Co) base, nickel (Ni)base or iron (Fe) base alloy and others padded onto the sliding portion and valve seat of the valve, when subjected to steam or hot water, is selectively corroded and damaged. Fluid in the recirculating water system has a high temperature and high speed. After the said damage due to corrosion, the base metal of the cast structure may be separated to cause erosion. (Thermal nuclear power generation, Vol. 30, No.5, P.67 and “Machine damage”: 1982 No.2 P.90)
This will lead to reduced leakage resistance of the valve, resulting in failures, such as changes in the controllability and in the operating characteristics. This is accompanied by more frequent inspection and disassembling of the valve, hence leading to poorer plant maintainability.
If the above-described failure occurs to the sliding portion in contact with reactor water and to the valve of the facilities in the system to supply coolant into the reactor in the nuclear power generation facilities, cobalt, nickel or iron alloy of high hardness padded to these positions may be separated and dissolve into the system due to corrosion and erosion.
In the welded overlay alloy comprising a conventional cast structure base metal and eutectic carbide of a network structure, the resistance to corrosion and erosion is not sufficient. To solve these problems, in accordance with the present invention, a corrosion and wear proof alloy with non-continuously distributed eutectic carbide is bonded to the sliding portions of the valve and other parts by diffusion bonding, thereby providing a valve characterized by excellent resistance to corrosion and erosion and superb maintainability.
SUMMARY OF THE INVENTION
The object of the present invention is to improve the corrosion and erosion resistance of the sliding portions and valve seat of valves used in a thermal and nuclear power plant or the like.
The present invention relates to a valve comprising a valve disc and valve body with a valve seat installed on each of the sliding portions of said valve disc and box; said valve being characterized in that the surface of said valve seat is made of a material selected from one of a cobalt base alloy, a nickel base alloy and an iron base alloy, and said alloys have a granular or lumpy eutectic carbide in the matrix having a metallic micro-structure, wherein the particle size of said eutectic carbide does not exceed 30 microns or more preferably 10 microns. The alloy selected from one of a cobalt base alloy, a nickel base alloy and an iron base alloy is preferably bonded to the surface of the valve seat by diffusion bonding, especially by transient liquid phase diffusion bonding.
Resistance to corrosion can be improved by as much as about 300 times by changing the eutectic carbide from a continuous network form to a non-continuous granular or lumpy form having a particle size not exceeding 30 microns. The particle size of the eutectic carbide is preferred to be smaller, and this improves the mechanical characteristics thereof, including ductility, toughness and resistance to impact.
In accordance with this invention, a member comprising a cobalt, nickel or iron base alloy having said granular or lumpy eutectic carbide is bonded on the sliding surface of a valve seat composed of stainless steel, made of carbon steel, low alloy steel or stainless steel.
The cobalt base alloy preferably contains 0.6 to 3 wt %, or more preferably 1.0 to 3 wt %, of C; 2 wt % or less of Si; 25 to 32 wt % of Cr; 15 wt % or less, or more preferably 4 to 15 wt %, of W; 0 to 3 wt % of Fe; 0 to 3 wt % or less of Ni; and 0 to 6 wt % of Mo. The nickel base alloy preferably contains 1 wt % or less, or more preferably 0.2 to 0.5 wt %, of C; 7% wt % or less of Si; 7 to 20 wt % of Cr; 5 wt %, or more preferably 0.5 to 2 wt %, of W; and 3.5 wt % or less of B. The iron base alloy preferably to contain 1.5 wt % or less, or 0.3 to 1.0 wt %, of C; 4 wt % or less, or 0.5 to 5 wt %, of S; 15 to 27 wt % of Cr; and 8 wt % or less, or more preferably 0.5 to 2 wt %, of Mo.
A corrosion and wear proof alloy used in accordance with the invention is typically made by plastic deformation of a base alloy containing an eutectic carbide in a continuous network structure, for example, in order to make the eutectic carbide non-continuous or granular. Preferably, the corrosion and wear proof alloy is bonded to the valve seat by diffusion bonding.
Furthermore, said diffusion bonding is preferred to be transient liquid phase diffusion bonding wherein the insert material having a melting point lower than that of the base metal is inserted into the boundary of bonding, and the melting point lowering element is diffused in the base metal, thereby promoting coagulation and bonding. Said insert material is preferably a nickel base alloy containing 1 to 8 wt % of Si and 1 to 5 wt % of B, or this nickel alloy further containing 5 to 20 wt % of Cr in addition. Particularly, said insert material is preferably a nickel base alloy containing 3 to 6 wt % of Si and 2 to 4 wt % of B, or this nickel base alloy further containing 5 to 10 wt % of Cr in addition. Said base metal is preferably a cobalt base corrosion and wear proof alloy.
The present invention provides a nuclear power plant comprising piping equipment having water feed valves in the recirculating system carrying nuclear reactor coolant water, characterized in that the valve seat of said valve is formed so as to be bonded with the corrosion and wear proof alloy, wherein said eutectic carbide contained in the alloy comprising the cast structure base metal and eutectic carbide is formed into granules and lumps, and said eutectic carbide is non-continuously distributed. It also provides a power plant characterized in that piping equipment using the valve according to the present invention is installed in the recirculating system where coolant water or very hot water recirculates.
As discussed above, the apparatus and valve according to the present invention provides a reliable method of reducing the damage to the sliding portion of the valve or valve seat resulting from damage due to corrosion of the eutectic carbide caused by dissolved oxygen in the fluid, and of avoiding an increase in the frictional resistance on the sliding portion and valve seat and leakage from the valve seat.
Furthermore, the nuclear power plant according to the present invention prolongs the service life of apparatuses and valves in said plant.
The present invention is characterized in that the alloy is composed of Co base alloy, Ni base alloy or Fe base alloy, and a cast structure base metal and eutectic carbide continuously distributed in a network form is subjected to plastic processing by forging or rolling; and, thereby, a eutectic carbide continuously distributed
Chiba Yoshiteru
Chigasaki Mitsuo
Kato Takahiko
Kiyotoki Yoshihisa
Kuniya Jiro
Keasel Eric
Mancene Gene
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