JPH04367335A - How to connect stainless steel pipe and zirconium alloy pipe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to prevention and maintenance of crevice corrosion of rolled joints of pressure pipes corresponding to the core of an ATR, and prevention of crevice corrosion of BWR nuclear fuel cladding tubes.

0002

[Prior Art] Conventionally, as disclosed in Japanese Unexamined Patent Application Publication No. 64-71582, when a pipe joint of a stainless steel pipe and a zirconium or zirconium alloy pipe is used in a highly corrosive environment such as nitric acid, In order to improve the corrosion resistance of the pipe joint part, tantalum was interposed between stainless steel and zirconium to join them.

However, in the configuration of the metal material of the present invention, the corrosion potential series is tantalum, zirconium, and stainless steel, and since stainless steel has the most base potential electrochemically, stainless steel serves as a sacrificial anode and cannot be corroded. It is feared.

Therefore, in this method, the gap between the dissimilar metal connection between the zirconium alloy and the stainless steel is 200°C.
No measures have been taken to prevent stainless steel from being damaged by crevice corrosion at this dissimilar metal connection when exposed to high temperature water ranging from 300°C to 300°C.

[0005]

As shown in the prior art, there is a technical method in which the stainless steel and the zirconium alloy are not damaged by crevice corrosion in the joint between the zirconium alloy and the stainless steel, where dissimilar metals form a gap. be.

[0006]

[Means for Solving the Problems] In the conventional metal material composition, electrochemically, stainless steel has the most base potential, so there is a concern that stainless steel may melt into the sacrificial anode and cause corrosion damage. was there.

[0007] In order to achieve the above object, the present invention:
A dissimilar metal connection between zirconium or zirconium alloy and stainless steel, which is formed by joining the ends of a tubular member made of zirconium or zirconium alloy and a tubular member made of stainless steel, is exposed to high-temperature water of 200°C to 300°C. In this case, in order to prevent the tubular member made of zirconium or zirconium alloy and the tubular member made of stainless steel from being damaged by crevice corrosion, a metal member made of iron or carbon steel is interposed at the dissimilar metal connection end as a sacrificial anode. It is a feature. This makes it possible to prevent the tubular member made of stainless steel and zirconium alloy from being damaged by crevice corrosion when the dissimilar metal joint of stainless steel and zirconium alloy is exposed to high-temperature water of 200°C to 300°C.

[0008]

[Operation] In order to achieve the above object, a connection or joint structure is adopted in which a metal member made of iron or carbon steel is interposed between a tubular member made of zirconium or zirconium alloy and a tubular member made of stainless steel. It is characterized by

[0009] As a result, when the metal material is used, the corrosion potential series becomes zirconium alloy, stainless steel, iron, or carbon steel. Currently, these joint structures are heated from 200℃ to 40℃.
When filled with high-temperature water at 0℃, the electrode potential of iron or carbon steel is electrochemically the most base potential, so it dissolves as an anode for zirconium alloy and stainless steel as a sacrificial anode, thereby dissolving the zirconium alloy and stainless steel. is cathodically protected. Here, if the zirconium alloy and stainless steel are subjected to surface oxidation treatment in advance, the effect of cathodic corrosion protection can be maintained for a longer period of time.

Further, as a function of the present invention, iron or carbon steel melted at the anode becomes an oxide such as Fe3O4 as shown in the following formula and is deposited in the cathode area around the anode area.

[0011]

[Formula 1] 3Fe+4H2O=Fe3O4+4H2 Since mass transfer is difficult to occur in such a gap, high-temperature water is difficult to penetrate into the gap. Generally, water is 10
Since it becomes water vapor at temperatures above 0°C, pressure is applied to maintain it in an aqueous solution state. This water-steam equilibrium vapor pressure is proportional to temperature, and increases as the temperature increases, and this relationship is determined physically. Now, based on the present invention, iron or carbon steel within the gap generates fine oxides by anode melting, and when these are deposited on the cathode area around the anode area, mass transfer becomes difficult in the gap area. This makes it difficult for high-temperature water to penetrate into the gaps. In this way, when the crevice is closed by these corrosion products, the aqueous solution in the crevice is consumed as the corrosion progresses as shown in this equation, but as a result of no supply from outside the crevice, it is added to the aqueous solution in the crevice. The pressure at that temperature is lower than the water-steam pressure at that temperature. As a result, steam is generated in the gap, and the inner surface of the gap is repassivated by the steam as shown in the following equation. the result,
Crevice corrosion effects will be reduced.

0012

[Chemical formula 2] Stainless steel surface: 3Fe
+4H2O=Fe3O4+4H2

[0013]

[Chemical formula 3] Surface of zirconium alloy: Z
r+2H2O=ZrO2+2H2 The corrosion reaction of stainless steel shown in the above formula is represented by iron (Fe) for convenience of explanation.

In addition, sacrificial anode materials include aluminum and zinc, but since the electrode potential of these metal materials is significantly lower than that of zirconium alloy, stainless steel, or carbon steel, the hydrogen of zirconium alloy or stainless steel is Unfavorable for promoting absorption.

[0015]

[Embodiment] An embodiment of the present invention will be described above using the corrosion test piece shown in FIG. 1 and the test container shown in FIG. 2.

First, regarding the corrosion test piece shown in FIG. 1, cylindrical test pieces machined from stainless steel with different lengths were placed on both ends of a cylindrical test piece 1 machined from a zirconium alloy to change the gap surface area. 2 to a thickness of 50μ
The stainless steel is processed and assembled as shown in the figure by applying high pressure from the inner diameter side of the stainless steel with an ultra-low carbon steel foil 3 of 300 m thick interposed therebetween. On the other hand, for comparison, a cylindrical specimen 1 was machined from a zirconium alloy without an ultra-low carbon steel foil 3, and a cylindrical specimen 5 was machined from stainless steel 2. Assembled types.

The test container shown in FIG. 2 is for carrying out a corrosion test on a corrosion test piece 5 in high temperature water. Regarding its structure, first, since the corrosion test piece 5 must be electrochemically independent, it is housed in a Teflon insulated tube 6 with water holes provided at both ends, and then installed in a fixture 7. Next, the fixture 9 is placed over the fixture 7 with a shim 8 made of stainless steel interposed therebetween, and the fixtures 9 and 7 are fastened and fixed with bolts 10.

As shown in the figure, the assembled test container was connected to a loop supplying high-temperature, high-pressure water at 80 atm and 288° C., and a long-term corrosion test was conducted. As a result, ultra-low carbon steel foil 3 is placed between the zirconium alloy tube and the stainless steel tube.
Corrosion damage was not observed in both pipes in corrosion test piece 5 in which the pipes were interposed. In addition, there was no significant difference in the corrosion damage of ultra-low carbon steel foil 3 in relatively short-term and long-term corrosion tests.
It is presumed that crevice corrosion was suppressed in this respect. On the other hand, in the corrosion test piece 5 in which the ultra-low carbon steel foil 3 was not interposed between the zirconium alloy tube and the stainless steel tube, corrosion damage was observed on the surface of the stainless steel gap. In this respect, the effect of the present invention was recognized.

[0019]

According to the present invention, when the gap between a dissimilar metal connection between a zirconium alloy and stainless steel is exposed to high-temperature water of 200 to 300 degrees Celsius, the stainless steel at the dissimilar metal connection will suffer from crevice corrosion. damage can be prevented.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a corrosion test piece and its assembled state.

FIG. 2 is an explanatory diagram of the components of the test container and their assembled state.

[Explanation of symbols]

1... Cylindrical test piece made of zirconium alloy, 2... Cylindrical test piece made of stainless steel, 3... Cylindrical test piece made of stainless steel.

Claims (2)

[Claims] Claim 1: A dissimilar metal connection between zirconium or zirconium alloy and stainless steel in which the ends of a tubular member made of zirconium or a zirconium alloy and a tubular member made of stainless steel are joined at a temperature of 200°C to 30°C.
In order to prevent this dissimilar metal connection from being damaged by crevice corrosion when exposed to high temperature water at 0°C, a metal member made of iron or carbon steel is interposed at the dissimilar metal connection end and anodically melted stainless steel is used. A method for connecting stainless steel pipes and zirconium and zirconium alloy pipes, characterized by subjecting the steel pipes and zirconium and zirconium alloy pipes to cathodic corrosion protection. [Claim 2] In Claim 1, the metal member made of iron or carbon steel interposed between the stainless steel pipe and the zirconium or zirconium alloy pipe becomes a stable fine oxide by anode melting within the gap, and A method for connecting stainless steel pipes and zirconium and zirconium alloy pipes, which suppresses crevice corrosion by making it difficult for high-temperature water to accumulate and infiltrate.