JPH0436638A - Crevice corrosion monitoring method and equipment - Google Patents

Abstract

PURPOSE:To estimate the rupture strength of alloy by brining zirconium alloy which is given 0.01 - 2.5% bending strain into contact with stainless steel across a gap of <=0.5 mm placing the both in running water, and detecting the amount of absorbed hydrogen of the alloy at the time of crevice corrosion. CONSTITUTION:A stainless steel test-piece 22 and a flat plate type zirconium alloy test-piece 23 are put in a stainless steel container 26. The test-piece 22 has a concave surface with a 300 - 2000 mm radius of curvature and a bending jig 28 presses the test-piece 23 against the test-piece 22 by clamping a bolt 27 engaging the screw on the inner peripheral surface of the container through a round rod 24. The maximum value of the gap between the test-piece 23 which is given the bending strain and the test-piece 22 is varied and after the test- pieces are held in 280 deg.C pure water for a 1000h time, a hydrogen analysis is taken. At this time, the test-piece 23 is strained, so the amount of absorbed hydrogen increases as the temperature rises, but when the gap exceeds a con stant value, the absorption is eliminated. Consequently, the hydrogen absorption characteristic of the zirconium alloy by crevice corrosion can be evaluated quantitatively.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method and device for monitoring crevice corrosion, and in particular to monitoring zirconium alloy pressure pipes and stainless steel pipes installed in the core of an ATR (Advanced Converter Reactor). Crevice corrosion at the connected rolled joint (pipe expansion part),
A crevice corrosion monitoring method suitable for detecting the amount of hydrogen absorbed by the zirconium alloy during crevice corrosion at the contact area between the zirconium alloy cladding tube and the stainless steel tube of the fuel rod installed in the core of a BWR (boiling water reactor). and its apparatus.

[Conventional technology]

For example, ArR is equipped with approximately 650 pressure tubes with an inner diameter of 110 m made of zirconium (Zr)-2.5% niobium (N b ) alloy loaded with nuclear fuel in the reactor core, and these pressure tubes have high temperature inside them. Flow high pressure cooling water. Also, this Zr
- 2,5% Nb pressure pipe supplies cooling water to it S
It is connected to a US 403 MOD stainless steel pipe via a tube expansion section.

In the tube expansion section, hydrogen is generated by anode melting of the SUS 403 M o d material, and this hydrogen is transferred to Zr-
2.5%Nb material absorbs Z during the cathode reaction process.
Causes strength deterioration of r-2,5%Nb alloy.

So far, regarding the hydrogen absorption of Zr-2.5%Nb,
For example, the following reports have been made regarding corrosion of stainless steel.

For example, report (1) “Oxidation and
deuterium uptake of Zr-2,
5%Nb pressure tube in CAN
DU-P HW reactors”, International Conference Papers on Zirconium in the Atomic Crab Industry (19-23J
une1988, San Diego, CA, U
As discussed in S.A., hydrogen absorption of zirconium alloy pressure tubes used in the reactor core is evaluated during actual operation time, including neutral irradiation in the reactor core, or in piping outside the reactor. This has been carried out using the retention time by heating high-temperature water as a parameter.

Also report (2) “Corrosion performance
anceofZr-2,5wt%-Nb pressu
re tube in 0ntario Hydro'
soperating CANDU nucleus
r reactors''', Ont, ar
i.

In the Hydro Research Division report, it is reported that Fe and Mo as impurities in the zirconium alloy, which is the material for the pressure tube, enhance hydrogen absorption.

Also, report (3) “High-temperature water stress corrosion cracking susceptibility of stainless steel” (Ishikawajima-Harima Giho, Vol. 17, No. 5, 1977, p.
472-478) discuss a stress corrosion cracking susceptibility test method in which a stainless steel flat specimen is sandwiched between a graphite fiber and an uneven bending jig and bending stress is applied as a crevice corrosion test. According to this method, it is possible to evaluate welding conditions and heat treatment conditions that affect the stress corrosion cracking susceptibility of stainless steel. This method is based on Crevice B ent B ea
It is known as the CBB test, which stands for mTest.

[Problem to be solved by the invention]

The prior art described in reports (1) and (2) above evaluates the hydrogen absorption of zirconium alloys in nuclear reactors simply by using retention time in high-temperature, high-pressure cooling water or impurities in its chemical composition as parameters. However, the effect of stress or strain acting on the zirconium alloy during actual reactor assembly or operation is not mentioned at all.

In contrast, hydrogen uptake in zirconium alloys is much greater due to crevice corrosion in the environment in contact with the stainless steel than to corrosion on the free surface. Furthermore, when stress is applied to the surface and tensile strain is present, hydrogen absorption increases. In the prior art, hydrogen absorption has not been evaluated based on such surface physicochemical parameters.

In addition, the conventional technology described in report (3) above cannot measure the amount of strain applied, and because it involves three-point bending, the test must be conducted with locally yielded parts, and the amount of strain and hydrogen absorption cannot be measured. It is not possible to quantitatively evaluate the relationship between

It is an object of the present invention to provide a crevice corrosion monitoring method and apparatus for evaluating the effect of stress or strain on hydrogen absorption of zirconium alloys in contact with stainless steel in a corrosive environment.

[Means to solve the problem]

In order to achieve the above object, the crevice corrosion monitoring method of the present invention involves applying a bending strain of 0.01 to 2.5% to a zirconium alloy test piece containing 2.5% or less niobium. They are kept in contact with a stainless steel test piece or with a gap of 0.5 mm or less, and installed in a cooling water piping path or in a parallel circuit with this, and the zirconium alloy is absorbed by crevice corrosion. By detecting the amount of hydrogen generated, the fracture strength of the zirconium alloy and the amount of hydrogen generated inside can be estimated.

In the above crevice corrosion monitoring method, if the bending strain applied to the zirconium alloy is 0.01% or less, the effect of strain on the hydrogen absorption amount of the zirconium alloy is not clear, so the amount of strain is limited to 0.01% or more. . In addition, if the strain amount is 2.5% or more, cracks may occur in the zirconium alloy, so the strain amount is 2.5% or more.
Limited to the following.

In the above crevice corrosion monitor, if the gap between the stainless steel test piece and the zirconium alloy test piece is 0.5nwn or more, the gap will not be large because the zirconium alloy will hardly absorb hydrogen due to crevice corrosion. is limited to 0.5 nn or less.

In order to achieve the above object, the corrosion monitoring device of the present invention includes a flat zirconium alloy test piece, a stainless steel test piece having a cylindrical concave surface on which the zirconium alloy test piece is placed, and a surface of the zirconium alloy test piece. It is characterized by consisting of two rods installed in the axial direction of a cylindrical concave surface, and a pressing means for pressing the zirconium alloy test piece through the rods. The pressing means may be a steady pressing device that generates a steady pressing force or a dynamic pressing device that generates a dynamic pressing force depending on the load conditions to be applied to the zirconium alloy test piece.

[Effect]

Generally, when 5 stainless steel and zirconium alloy are brought into contact and penetrated into water, corrosion occurs between the two. Hydrogen is generated by corrosion of the metal, and the generated hydrogen is absorbed by the zirconium alloy. In particular, when tensile strain remains on the surface of the zirconium alloy, hydrogen absorption increases.

Further, the solid solubility limit of hydrogen in a zirconium alloy increases as the temperature rises, and hydrogen that cannot be dissolved in solid form when the temperature falls during the heating and cooling process forms hydrogen compounds such as ZrH2.

In the crevice corrosion monitoring method of the present invention, zero
．． When an arbitrary strain between 0.01% and 2.5% is applied either steadily or dynamically, hydrogen absorption occurs corresponding to the magnitude of the strain in the former case, and in the latter case, the effect of the magnitude of strain as well as the relationship with fatigue strength. is obtained.

In addition, in a corrosive environment, when a zirconium alloy specimen is brought into contact with a stainless steel specimen and a tensile or compressive strain is repeatedly applied by applying a unilateral or double oscillating load, the zirconium alloy absorbs hydrogen in response to the stress amplitude. can be evaluated.

In addition, - When a zirconium alloy is brought into contact with stainless steel and repeatedly slid in a corrosive environment during boat fishing, the zirconium alloy will absorb hydrogen due to fretting corrosion.
It is possible to evaluate the hydrogen absorption of a zirconium alloy corresponding to conditions such as the surface pressure applied to the zirconium alloy, sliding speed, and number of times.

Further, according to the water corrosion monitoring device of the present invention, a zirconium alloy test piece is pressed against the concave surface of a stainless steel test piece by a pressing means via two rods, and a predetermined bending strain is applied to the zirconium alloy test piece. Also, a predetermined gap is formed between the center of the zirconium alloy test piece and the concave surface. The zirconium alloy test piece was supported by concave surfaces at both ends and pressed at two points by two rods. Since it is bent using the so-called four-point support method, uniform bending strain can be applied.

〔Example〕

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

FIG. 1 is an overall configuration diagram of a corrosion testing apparatus suitable for carrying out the crevice corrosion monitoring method according to the embodiment of the present invention.

Using this corrosion test device, simulated water is created by simulating the internal temperature of a nuclear reactor and the pressure of the cooling water inside the reactor, and stainless steel test pieces and zirconium alloy test pieces are tested in the flow of simulated water. Perform crevice corrosion test by contacting.

In Figure 1, the corrosion test equipment is equipped with pure water at 288°C.
A circulation pipe comprising an autoclave 1 filled with a pressure of 0 at+m, a pure tank 2 storing pure water to be supplied to the autoclave 1, and a high-pressure pump 3 circulating pure water between the pure water tank 2 and the autoclave 1. have. Furthermore, a heater 8 is installed in the outgoing pipe from the high-pressure pump 3 to the autoclave 1 to heat the pure water to a predetermined temperature, and in the return pipe from the autoclave 1 to the pure water tank 2, the pure water is heated to room temperature. A cooling device 13 for cooling is installed.

A parallel pipe line is connected in parallel with the pipe line from the heater 8 to the autoclave 1, and a sample setting chamber 4 is provided in the parallel line, and a gap described later is provided in the sample setting chamber 4. Corrosion monitoring equipment is installed. Also, tank 2
The heater 8 is equipped with stop valves 5 and 6 that turn on and off the flow of pure water to the 8-port side piping and the inlet side piping, respectively. 4 are provided with stop valves 9, 10, and the autoclave 1 is provided with stop valves 11, 12.

Further, the pure water tank 2 is provided with a circulation pipe line including a circulation pump 18 and an ion exchange resin 19, and the pure water supplied from the pure water tank 2 by the circulation pump 18 is purified by the ion exchange resin 19. The components and water quality of purified pure water are measured by a water quality sensor 20, and are recorded and managed by a recorder 21. Note that stop valves 15, 16, and 17 are also provided in these pipes, respectively.

Next, FIG. 2 shows the concept of a corrosion sensor that constitutes the crevice corrosion monitoring device installed in the sample chamber 4. The crevice corrosion monitoring device is a stainless steel specimen with a cylindrical concave surface.
2, a flat zirconium alloy test piece 23 pressed against the cylindrical concave surface, a strain gauge 25 attached to the side surface, and two round bars 24 for pressing the zirconium alloy test piece 23. has been done. When the cylindrical concave surface of the stainless steel test piece 22 is pressed against the cylindrical surface and brought into contact with the zirconium alloy test piece 23,
0.01 to 2.5 on the surface of the zirconium alloy test piece 23
It has a radius of curvature such that a tensile strain of % is applied. The two round bars 24 are used when pressing and bending the flat plate 23.
In order to avoid damaging the strain gauge 25 located between the strain gauges 4 and 24, the strain gauges 25 and 24 are spaced apart from each other by Ω. Furthermore, in order to apply bending stress uniformly in a four-point supported state, an appropriate radius of curvature R was added to the corners at both ends of the zirconium alloy test piece 23.

FIG. 3 is a detailed view of the sensor of the crevice corrosion monitoring device according to the embodiment of the present invention, which is constructed based on the above concept.

In the figure, the container 26 is made of stainless steel (SUS) with good corrosion resistance.
316), and sequentially stores a stainless steel test piece 22 made of 5US403, a flat zirconium alloy test piece 23, etc. A screw is machined on the inner circumferential surface of the upper part of the container.
In addition, there are two stainless steel test pieces on the inner peripheral surface in the axial direction of the container.
A guide groove a is machined to prevent rotation of the
Furthermore, two water intake holes are machined symmetrically about the center of the circumference at the circumference where the zirconium alloy test piece 23 is installed.

Stainless steel specimen 22 has a curvature radius of 300 to 2000 m
zirconium alloy test piece 23 on this concave surface.
(5+nmX 13+nmX 2mm) is pressed through the round bar 24 by the bending jig 28. The pressing force by the bending jig 28 is applied via the spacer 29 by tightening the bolt 27 that engages with a thread on the inner peripheral surface of the container 26 .

The bolt 27 is made of SUS 316, and the bending jig 2
8. The spacer 29 was made of 5US403.

Here, a protrusion is added to the spacer 29, and this protrusion is inserted into the guide groove a of the container 26 to prevent the spacer 29 from rotating, and the bending jig uses the rotational force of the bolt 27 as a vertical driving force. 28.

The strain gauge 25 attached to the zirconium test piece 23 is used to determine the tensile strain on the surface side of the gap when stress is applied.

In this example, the zirconium alloy test piece 23 was not brought into complete contact with the concave surface of the stainless steel test piece 22.
It is also possible to configure an arbitrary gap. In this case, a parallel beam of light is applied to the stainless steel test piece 22 and the zirconium alloy test piece from the other end of the water intake hole machined into the container 26.
The maximum width of the gap can be regulated by irradiating the gap 3, measuring the gap by installing a memory scope at the other end, and adjusting the tightening state of the bolt 27.

Experimental results using the apparatus of this embodiment assembled as described above are shown in FIGS. 4, 5, and 6.

Figure 4 shows the bending strain and hydrogen absorption amount obtained by hydrogen analysis of the zirconium alloy test piece 23 after applying various bending strains to the zirconium alloy test piece 23 and holding it in pure water at 280°C for 100 ohms. shows the relationship between From the same figure,
It can be seen that although the amount of hydrogen absorbed by the zirconium alloy test piece 23 increases as the strain increases, the amount of hydrogen absorbed becomes saturated when the amount of strain exceeds a certain value.

Figure 5 shows the state in which the zirconium test piece 23 is strained by applying stress, and the state in which the zirconium test piece 23 is in smooth contact with the stainless steel test piece 22 without applying stress, and is held in pure water at various temperatures for 1000 hours. After that, the zirconium alloy test piece 23 was analyzed for hydrogen, and the relationship between the strain temperature and the amount of hydrogen absorbed is shown below. From the figure, when no strain is applied to the zirconium alloy specimen 23, no effect of temperature is observed on hydrogen absorption, as shown by curve e, but when strain is applied to the zirconium alloy specimen 23, as shown by curve d. It can be seen that the amount of hydrogen absorbed increases as the temperature rises.

Figure 6 shows that the maximum value of the gap between the zirconium alloy test piece 23 and the stainless steel test piece 22 was changed while strain was applied, and the hydrogen in the zirconium alloy test piece 23 was maintained in pure water at 280°C for 1000 hours. The relationship between the maximum gap value obtained through analysis and the amount of hydrogen absorbed by the zirconium alloy test piece 23 is shown. The figure shows that even if strain is applied to the zirconium alloy test piece 23, the zirconium alloy test piece 23 hardly absorbs hydrogen when the gap exceeds a certain value.

〔Effect of the invention〕

According to the present invention, the hydrogen absorption characteristics of the zirconium alloy due to the crevice corrosion effect that occurs between the zirconium alloy and the stainless steel that forms a crevice structure, for example,
The effects of strain, gap distance, temperature, liquid quality, etc. can be quantitatively evaluated.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a corrosion testing device using the crevice corrosion monitoring method of the present invention, Fig. 2 is a conceptual diagram of the crevice corrosion monitoring device of the present invention, and Fig. 3 is a diagram of the crevice corrosion monitoring device of an embodiment of the present invention. Figure 4 is a diagram showing the effect of strain on the hydrogen absorption characteristics of a zirconium alloy placed in contact with stainless steel in water, and Figure 5 is a diagram showing the effect of strain on the hydrogen absorption characteristics of a zirconium alloy placed in contact with stainless steel in water. FIG. 6 is a diagram showing the influence of water temperature on hydrogen absorption. FIG. 6 is a diagram showing the influence of gaps on hydrogen absorption of a zirconium alloy placed in contact with stainless steel in water. 1...Autoclave, 2...Pure water tank, 3...
・High pressure pump, 4...sample installation chamber, 5~12゜14~
17...Stop valve, 13...Cooling device, 18
...Circulation pump, 19...Ion exchange resin, 20.
... Water quality sensor 21 ... Recorder, 22 ... Stainless steel test piece, 23 ... Zirconium alloy test piece,
24... Round bar, 25... Strain gauge, 26...
・Container, 27... Bolt, 28... Bending jig, 29
・・・Spacer diagram 24・Round bar 25・Strength casing 26, 1η 27・Bo'Jreto◇Taste 280°C, 80atm +000h f? :i 5th Figure 6 Pure water + oooh stock general frleJ+ 280'C, 100Oh -I, ni'T'', b 2.5% Theft degree (0C) Maximum gap (um)

Claims (1)

[Claims] 1. Bending the zirconium alloy to apply a strain of 0.01 to 2.5%, bringing it into contact with stainless steel with a gap of 0.5 mm or less, and placing the zirconium alloy and stainless steel in running water. A method for monitoring crevice corrosion, comprising: detecting the amount of hydrogen absorbed by the zirconium alloy during crevice corrosion that occurs in the crevice after a predetermined period of time after installation in the crevice. 2. Bring the zirconium alloy and stainless steel into contact with each other in running water, apply a bending strain of 0.01 to 2.5% to the zirconium alloy, and leave a gap of 0.5 mm between the zirconium alloy and the stainless steel during the bending strain. A crevice corrosion monitoring method comprising: repeatedly applying hydrogen for a predetermined period of time, and detecting the amount of hydrogen absorbed by a zirconium alloy during crevice corrosion occurring in the crevice. 3. The crevice corrosion monitoring method according to claim 1 or 2, characterized in that the fracture strength of the zirconium alloy is estimated from the amount of hydrogen absorbed by the zirconium alloy. 4. The crevice corrosion monitoring method according to claim 1 or 2, characterized in that the amount of hydride generated in the zirconium alloy is estimated from the amount of hydrogen absorbed by the zirconium alloy. 5. A flat zirconium alloy test piece, a stainless steel test piece having a cylindrical concave surface on which the zirconium alloy test piece is placed, and 2 installed on the surface of the zirconium alloy test piece in the axial direction of the cylindrical concave surface. A crevice corrosion monitoring device comprising a real bar and a pressing means for pressing the zirconium alloy test piece through the two bars. 6. The crevice corrosion monitoring device according to claim 5, wherein the pressing means generates a steady pressing force. 7. The crevice corrosion monitoring device according to claim 5, wherein the pressing means generates a dynamic pressing force.