JPS59104498A - Valve body structure of control valve - Google Patents

Abstract

PURPOSE:To contrive the improvement in crevice corrosion resistance and leakage, proof by pad-welding a self-melting Ni or Co-based alloy onto the slided or sealed part of a valve made of an alloy, and then coating said part with hard Cr. CONSTITUTION:A self-smelting Ni or Co-based alloy is formed on the slided or sealed part of a valve made of stainless steel or an Ni-based alloy by spraying or pad-welding. A hard Cr coating layer excellent in crevice corrosion resistance is further formed thereon. Hence, crevice corrosion resistance and leakage proof are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a valve body structure of a control valve used for controlling steam or water for thermal power generation and nuclear power generation.

[Technical background of the invention and its problems]

In general, the surface of the valve body is coated with stellite, a Co-based self-fluxing alloy, or thermal spraying is used to coat the surface of the valve body.
When the base material is used as a valve body, CO powder generated by wear is irradiated in the reactor core and becomes Co60, which has a long half-life.
It is thought that this could lead to increased radiation exposure for workers during periodic inspections of nuclear reactors.

In addition, when the surface of the valve body is coated with a Ni-based self-fusing alloy, Colmonoy, by spraying or overlaying, its corrosion resistance is inferior to that of Stellite, so the sealing performance between the valve and the valve seat is poor, There is a risk that On the other hand, the hard chrome-plated valve body provides a uniform hardened layer and has the same corrosion resistance as Stellite.

Although it is superior to Colmonoy, there is a risk of cracking if it is covered thickly, and there are still problems such as the construction time being longer and the cost being higher, so it is usually 5~
It is used around 50μ. However, since this level of plating layer is thin, if the valve seat is made of austenitic stainless steel or Ni-based alloy, and the contact area between the valve and the valve seat is narrow, plasticity may occur when the valve collides with the valve seat. There were problems such as deformation and a high possibility that fluid sealing performance would be impaired.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and its object is to provide a valve body structure for a control valve that is excellent in crevice corrosion resistance and leakage resistance.

[Summary of the invention]

In order to solve the above-mentioned conventional problems, the present invention has been tested and investigated regarding the following 3' points.

First, when the pitting potential of the valve material was measured, the measurement results shown in FIG. 1 were obtained. In Figure 1, the horizontal axis represents the potential v (vo, It), and the vertical axis represents the current density d (μM
侃). The dotted line is hard chrome plating, the solid line is Stellite, and the two-dot chain line is Colmonoy measurement curves. From these measurement curves, it can be seen that the hard facings with strong pitting corrosion resistance are hard chrome plating, Stellite, and Colmonoy in that order. I understand.

The second point is that as a result of conducting a crevice corrosion test assuming crevice corrosion between the valve and the valve seat, it was found that the hard facings that are most resistant to crevice corrosion are hard chrome plating, stellite, and colmonoy, in that order. Here, an example of the configuration of the test material used in the crevice corrosion test mentioned above will be explained with reference to Fig. 2.
Reference numeral 1 assumes a valve, and numeral 2 is a plate-shaped base material for a heart facing, and 2 is a notebook facing layer formed on the base material 1 by thermal spraying or overlay. Numeral 8 is a plate-shaped mating member assuming a valve seat, 4 is an insulating spacer, and 5 is a fastener consisting of bolts and nuts. An example of the structure of the test material used in the crevice corrosion test is as shown in Figure 2.
Insert the insulating spacer 4 between the plate-shaped mating member 8, and lightly tighten the two plates 1°8 with the fastener 5, and add pure water or NaCl.
After being immersed in a solution for a certain period of time, it was disassembled and crevice corrosion was evaluated based on the number of pits that occurred in the hard facing coating layer.

The third point is the activation of Co in the reactor.As mentioned above, if the valve body is made of Co-based material, the CO powder generated by wear will be irradiated in the reactor core. It is known that 0060 has a long half-life.

In consideration of the above points and in order to achieve the above object, the present invention has been made by thermal spraying or overlay welding on the surface of at least the sliding part or the sealed part of a valve body made of stainless steel or Ni-based alloy. The present invention provides a valve body structure for a control valve in which a Ni-based or Co-based self-fusing alloy is formed, and a hard chromium plating layer resistant to crevice corrosion is further formed on the self-fusing alloy.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to the drawings.

FIG. 8 is a layout diagram of a valve body and a valve seat according to the present invention, and FIG. 4 is a partially detailed view of the sectional view of FIG. 3. In Figure 3, 6
is a valve body, and 7 and 8 are valve seats.Since crevice corrosion is likely to occur at the contact area between the valve body 6 and the valve seats 7 and 8, they are used in nuclear reactors as shown in Figure 4. In some cases, a hard facing coating layer 10 of a Ni-based coating material such as Colmonoy is used as the valve body material 9.
A hard chrome plating 11 is further applied on the surface of this coating layer 10 by thermal spraying or overlay welding. In addition, when used in a place other than a nuclear reactor, in FIG. 4, a hard facing coating layer 10 is provided by thermal spraying or overlay welding Stellite, which is an example of a Co-based coating material, on the valve body material 9. A hard chrome plating 11 is applied on the surface of the plate.

〔Effect of the invention〕

According to the present invention, a valve body can be obtained that has excellent corrosion resistance, does not introduce Co groups into the nuclear reactor, and is highly effective in sealing against water vapor. Furthermore, it is effective to apply hard chrome plating to valve bodies other than nuclear reactors as a sealing treatment for the pores that are unavoidable when spraying stellite or colmonoy, for example. Even if the hard chrome plating is damaged, the very corrosion-resistant stellite or colmonoy matrix appears, so a valve body with double stability in terms of corrosion resistance and leakage resistance can be obtained.

[Brief explanation of drawings]

Fig. 1 is a measurement diagram of the pitting corrosion potential of valve materials, Fig. s2 is a side view of an example of the configuration of the material to be tested used in the crevice corrosion test according to the present invention, and Fig. 8 is a diagram showing the pitting corrosion potential of valve materials according to the present invention. Layout of body and valve seat,
FIG. 4 is a partially detailed view of the cross-sectional view of FIG. 8. 6... Valve body, 7, 8... Valve seat, 9... Valve body material, 1
0...Hard facing coating layer, 11...Hard chrome plating. (8738) Agent Patent attorney Yoshiaki Inomata (and 1 other person) Figure 1 VθIt (VsSζE) Figure 2 Figure 4

Claims (1)

[Claims] (1) Thermal spray patterns are formed on the surface of at least the sliding or sealed parts of a stainless steel or Ni-based alloy valve body by forming a Ni-based or Co-based self-fusing alloy by overlay welding, and then forming a self-fusing alloy of Ni or Co based on this alloy. The valve body structure of the control valve is further characterized by forming a hard chrome plating layer that is resistant to crevice corrosion.