Effect of temperature on cavitation erosion of 9Cr steel in liquid metal

　　　 University of Fukui, Japan　　　　　○ Akihiro Nimura　　　　　　　 Shuji Hattori　　　　　　　 Hiroki Yada

Research background• Research on cavitation erosion in

liquid metal is very important to confirm the safety of the “Monju”.

• But, research on cavitation erosion on liquid metal has been hardly done compared with research in water.

• Cavitation erosion rate at a temperature of 260 in sodium ℃was 9 times higher than that in water.

• We are afraid that cavitation erosion rate increases at 500 .℃• Cavitation erosion in a fast breeder reactor environment has

hardly been studied.

Fast breeder reactor “Monju”.

2

Previous research

• In the previous research, we clarified that erosion rates in PbBi at relative temperature of 14° is 10 - 12 times higher than that in deionized water.

• We carried out the cavitation erosion tests in three kinds of lead bismuth ( PbBi ) alloy.

• Effect of test temperature is larger than that of metal composition on cavitation erosion.

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※ Hattori et al. Wear 267 (2009) 2033-2038

Objectives

• Test temperature range is very limited for 75 to 150 ℃ (1.4 - 16° of relative temperature ranges)

• Erosion rate at high temperatures remains uncertain.

• Cavitation erosion tests were carried out at various temperatures.• Effect of the test temperature on the cavitation erosion rates is

clarified. • A method for predicting the erosion rate in sodium is proposed

using the test results of deionized water and PbBi alloy obtained in this study.

Problems

　　　　　　　　　　　　

Present test region

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Chemical composition and physical properties of test materials

• Test specimen is 9Cr steel which is proposed to be used for pipes in the next-generation fast breeder reactor and stainless steel SUS304 which is used for pipes in the present fast breeder reactor “Monju”.

• Liquid metal is a low melting-point PbBi alloy which consists of the elements Bi, Pb, Sn, and Cd. Melting temperature is 68 .℃

Material C Si Mn P S Ni Cr Mo V Nb Al HV

9Cr steel 0.09 0.23 0.37 0.02 0.001 0.18 8.82 0.97 0.20 0.07 0.004 180

SUS304 0.05 0.33 1.76 0.036 0.022 8.49 18.2 ― ― ― ― 189

　 Bi Pb Sn Cd

PbBi-68 50 26.7 13.3 10　 PbBi-68

Freezing point [℃] 68

Boiling point [℃] 575

Density 20℃ [g/cm3] 9.38 5

100 mmPbBi

Test apparatus and test conditions

• Cavitation erosion tests were carried out with the vibratory specimen method specified in ASTM G32.

• Cavitation erosion was evaluated in terms of mass loss and instantaneous MDER (Mean Depth of Erosion Rate) of the test specimen.

Piezo-electric oscillation apparatus (according to ASTM G32)

Test temperature available : 50 - 400℃Vibrational frequency : 20kHzPeak-to-peak displacement amplitude : 40μmCovering gas : Ar

( for the tests at 250 to 400 )℃Test method

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Specimen

Mantle 　heater

Cooling coil

Thermocouple

Piezo converter Amplifying horn

Fig. Whole test apparatus

Fig. Cooling coil

8.2 /min℃

5.6

Performance of test apparatus

• Test temperature increased and deceased in a short time.

• Test temperature was controlled with cooling air with a tolerance ±3℃.

Variation in temperature for heatingTemperature decrease for cooling

Variation in temperature during test

7.9

3.5

7

Melting

Mass loss curves in liquid metal

• For 9Cr steel, incubation period were 1 hour at 100 , 0.3 hour at ℃250 and 300 , and 0.2 hour at 350 and 400 .℃ ℃ ℃ ℃

• Mass loss rate in the maximum rate stage were about 3 times higher at 100℃, 12 times at 250 and 300℃ ℃, and 23 times at 350 and ℃400 ℃ compare with that in deionized water.

• Mass loss rates increased with the temperature.• Incubation period of SUS304 is similar to that of 9Cr steel.

9Cr steel SUS304

8

69

515490

250

22 mg/h50

266

267488

553265

Incubation period

Eroded specimen surfaces

In PbBi of 400℃

In deionized water of 25℃

9Cr steel 9Cr steel In water In PbBi

Uneroded regionIn deionized water at 400 9Cr steel after 5 hours℃

Specimen surface of before test15.6mm

μm

In PbBi at 400 9Cr steel after 2 hours℃

5mm

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• In deionized water, the test surface has an uneroded ring region.

• In PbBi, the test surface is eroded over the whole surface.

• The difference in surface profile is due to the difference in the mobility of vapor bubbles.

Mean depth of erosion rate and temperature

• MDERmax of 9Cr steel and SUS304 changes similarly.• In deionized water, each increase of 1 increases the erosion rate by ℃ 1 to 2 %

at near 25℃.• In PbBi, each increases 1°in relative temperature increased the erosion rate in

PbBi by 3 - 4 % at 10 - 40°and by 6 - 7 % at 40 - 50°. • The increasing ratio in PbBi was almost 3 times higher.

( )

6.6 ％

3.3 ％4.3％

6.1 ％

1 – 2 %

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Prediction method of erosion rate in sodium : Basic idea

※ Hattori et al.　Wear 265 (2008) 1649-1654

𝑎=1

( 1𝜌𝐿𝐶𝐿

+ 1𝜌𝑆𝐶𝑆 )√𝜌𝐿

𝑀𝐷𝐸𝑅𝑚𝑎𝑥=𝑘𝑎𝑛ρ: Density, C: Sound velocity, S: Solid, L: Liquid

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• MDERmax can be evaluated in various liquids and liquid metals by using the this parameter.

• MDERmax can be expressed with a power law as a function of . The lower equation can be obtained.

• We predicted the erosion rate by using this equation.

Liquid

PbBi 120,000Deionized water 45,000

Sodium 69,000

[ √𝑘𝑔√𝑚𝑠

]

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Prediction method of erosion rate in sodium: Procedure

• Prediction erosion rate curve in sodium is located halfway from the rates between PbBi and deionized water.

① Select a temperature to obtain the MDERmax in deionized water and in PbBi.

② k and n are obtained.

③ MDERmax in sodium is obtained using the value of sodium.

④ Prediction curve of MDERmax is obtained as a function of relative temperature.

⑤ Young’s test results in sodium (green points) agree with the prediction curve.

𝑴𝑫𝑬𝑹𝒎𝒂𝒙=𝒌𝒂𝒏

①

②

③④

Conclusions1. Performance test of newly developed apparatus showed

that test temperature increased and deceased in a short time and test temperature was controlled with a tolerance of ± 3℃.

2. Each increase of 1°relative temperature increased the erosion rate in PbBi by 3 - 7 % and the increasing ratio in PbBi is almost 3 times higher than that in deionized water

3. Erosion rate in sodium was estimated to be located halfway from the rates between lead bismuth and deionized water.

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AcknowledgementThe present study includes the FY2010 result of the “Core R&D program for commercialization of the fast breeder reactor by utilizing Monju” entrusted to the University of Fukui by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT).