J. Plasma Fusion Res. SERIES, Vol. 11 (2015)

Corrosion Properties of F82H in Flowing High Temperature Pressurized
Water
Motoki NAKAJIMA, Takanori HIROSE, Hisashi TANIGAWA, Mikio ENOEDA
Japan Atomic Energy Agency, Rokkasho, Aomori, Japan(Received: 30 September 2014 / Accepted: 19 January 2015)

This work reports the effects of water flow and dissolved oxygen (DO) on corrosion behavior of reduced
activation ferritic/martensitic steel, F82H. The corrosion tests were performed in high temperature pressurizedwater by using a test apparatus for rotated disk sample. All of specimens showed weight gains after static corrosion
tests up to 500 h. However, the rotated disk showed weight losses except for test in the water with DO=8 ppm, andthe weight loss was significant with lowering DO concentration.
Keywords: Reduced activation ferritic/martensitic steel, Corrosion, High temperature pressurized water, Flowaccelerated corrosion, Test blanket module, Dissolved oxygen

structural material for the blanket. Moreover, the effectsof water flow and dissolved oxygen (DO) in the test
water on corrosion properties were investigated usingrotating disk specimen in autoclave.

1. Introduction

Water-cooled blanket is an attractive concept for its
compactness and its compatibility with the conventional
technologies for pressurized water reactor (PWR) [1-3].
For blanket application, the structural material is required
to be as thin as possible for tritium breeding. On the otherhand, the pressure tightness is required to withstand 15
MPa of internal pressure. Therefore it is necessary tounderstand the corrosion mechanism in high temperaturepressurized water. However, the corrosion data of
reduced activation ferritic/martensitic steel (RAFM),
F82H is limited in high temperature pressurized watercondition. Shiba et al. reported the weight change of
F82H located in autoclave with dissolved oxygen of 1
ppm at temperatures ranging from 493 K to 563 K in thepressure of 10 MPa [4]. The results demonstrated that thespecimen lost weight at temperatures below 533 K but
gained weight at temperatures over 533 K. And they also
reported that corrosion properties of F82H were almost
same as that of 12% chromium steel, HT-9. Hirose et al.
measured the weight change behavior of F82H in super
critical pressurized water up to 1000 h [5]. The weight
simply increased with surface oxidation and the weightchange of F82H was almost same as commercial 9%chromium steels. In either case, they reported thecorrosion properties in static water condition. However,
the maximum flow rate of ITER-TBM is planning to 6m/s [6]. Therefore, it is essential to understand thecorrosion properties in flowing high temperature watercondition.
This work reports results of corrosion tests on a
reduced activation ferritic/martensitic steel, F82H as a2. Experimental procedure

The material used in this study was a RAFM steel,
F82H (Fe-8Cr-2W-0.2V-0.04Ta-0.1C). The corrosion test
using a rotated disk specimen (I100 mm x 5 mm) was
performed in the autoclave with rotation speed of 1000rpm. The circumferential velocity on the specimen edge
was 5 m/s. The coupon type specimen (20 x 20 x 1.0mm3) was used for static corrosion test. All specimens
were mirror finished by a buff polishing. The DOconcentrations in the inlet water were 20 ppb, 1 ppm, 3ppm and 8 ppm. The corrosion tests were conducted at573 K with the pressure of 15 MPa. The corrosion tests
were performed under testing time ranging from 28 h to
500 h. Before and after the corrosion test, the specimen
weight was measured by using a precision balance.
Corrosion products were examined on the specimen
surface and cross-section using scanning electron
microscopy(SEM),
X-raydiffraction(XRD)
spectrometry, and electron probe micro-analyzer(EPMA).

3. Results and Discussion

Figure 1 shows the weight change of coupon typespecimen plotted as a function of testing time. All of thespecimens gained weight after static corrosion tests up to500 h. It seems that their increases follow the paraboliclaw. As shown in this figure, the DO concentration has no

author’s e-mail:nakajima.motoki@jaea.go.jp

69©2015 by The Japan Society of Plasma
Science and Nuclear Fusion ResearchM. Nakajima et al., Corrosion Properties of F82H in Flowing High Temperature Pressurized Water

significant influence on the corrosion rate. On thecontrary, as shown in figure 2, rotated disks lost weight
except for the test with DO 8 ppm, and the weight loss
became significant with lowering DO concentration.
Additionally, there were no significant difference
between the weight change of coupon type specimen andthat of disk type specimen at DO 8 ppm condition.
Figure 3 shows the SEM micrographs of thespecimen surface after corrosion test. All of thespecimens tested in the static water, the block like oxides
are observed on each sample. The particle size of 20 ppb
sample was significantly enlarged. The oxide morphologyof the rotated disk tested in the water with 20 ppb DO
was quite different from the others. Although the oxide
particles were not observed on the surface of DO 20 ppb,
the block like oxide particles were formed in DO contents
greater than 1 ppm. These results suggested that the oxide
which was formed on the coupon specimen of 20 ppb waslost by the water flow. It can be speculated that the oxide
was lost as a results of dissolution and/or exfoliation.
Figure 4 shows the results of XRD spectrometry onspecimen tested in static water. The results indicated thatthe surface oxide of 20 ppb specimen was identified as
Magnetite (Fe3O4). With increasing DO concentration, thedominant surface oxide was changed from Fe3O4 toHematite (Fe2O3). This change of surface oxide wasseemed to be attributable to increase the corrosion potential
which caused by the increase of DO concentration. XRD
patterns of rotated disk sample were shown in Fig. 5. It canbe seen that the Fe2O3 peak disappeared under the waterflow condition. Since it has been well known that thesolubility of Fe2O3 was quite smaller than that of Fe3O4,
the surface oxide of higher DO concentration could beregarded as Fe2O3 [7].
Figure 6 shows the EPMA mapping of cross sectionof rotated disk specimen. The observation was performedon the edge of the disk specimen (r=50 mm). The
elemental mappings of 1 ppm, 3 ppm and 8 ppm showed

Figure 1 Weight change of coupon type specimenplotted as a function of time.

Figure 2 Weight change of rotated disk specimenplotted as a function of time. The result of coupon
type specimen measured on DO 8 ppm was alsoplotted in this figure.

Figure 3 SEM micrographs of the specimen surface after corrosion test for 250 h.
70M. Nakajima et al., Corrosion Properties of F82H in Flowing High Temperature Pressurized Water

Figure 4 XRD patterns measured on DO 20 ppb, 1ppm and 8 ppm of coupon type specimen.

Figure 6 EPMA element map (O, Cr, Fe) measured on
the cross section of rotated disk specimen (r=50 mm)
after corrosion test for 250 h.
Fe2O3 by that of Fe3O4. DO dependency of Fe2O3/Fe3O4
ratio was shown in figure 7. Fe2O3/Fe3O4 ratio has atendency to increase with increasing the DO concentration.
It was considered that the increase of Fe2O3/Fe3O4 ratio
was caused by increase of corrosion potential as a result ofincrease in DO concentration. These results are consistent
with the fact that the stable oxide is changed from Fe3O4 toFe2O3 in higher corrosion potential on Pourbaix diagram ofFe-H2O at 573 K [8].
Figure 8 shows the weight changes of coupon typespecimen and rotated disk specimen plotted as a functionof the Fe2O3/Fe3O4 ratio. The weight change of coupon
type specimen shows almost constant, while that of rotateddisk specimen decrease with increasing the Fe2O3/Fe3O4ratio. Additionally, the weight changes of coupon typespecimen and rotated disk specimen showed no significant
difference when Fe2O3/Fe3O4 ratio reached 2.

Figure 5 XRD patterns measured on DO 20 ppb, 1ppm and 8 ppm of rotated disk specimen.
the outer block oxide was Fe oxide and the inner oxide(iron-poor layer) was chromium rich oxide. According to
the XRD results of rotated disk samples, the inner oxide
was identified as the FeCr2O4. Comparing the thickness ofiron-poor layer, the thickness was increased withdecreasing the DO concentration. This iron-poor layer
should be formed as a result of dissolution of Fe ions.
Therefore, it can be concluded that the weight loss of thedisk specimen was caused by the Fe ion dissolution frombase metal. Considering the results of SEM observationand EPMA mapping, relatively smaller iron-poor layer wasobserved on the specimen which was formed Fe2O3 on thesurface. These results suggest that the Fe2O3 may act as theprotective oxide for Fe ion transport. Therefore, Fe2O3 ratio
in the oxide was estimated from the results of XRD spectrameasured on the coupon type specimen. The Fe2O3/Fe3O4
ratio was determined by dividing the peak value of XRD ofFigure 7 Hematite/Magnetite ratio plotted as afunction of DO concentration.

71

M. Nakajima et al., Corrosion Properties of F82H in Flowing High Temperature Pressurized Water[8]

Figure 8 Relationship between the weight changes ofcoupon type specimen and rotated disk specimen andHematite/Magnetite ratio.

That is to say, the formation of Fe2O3 is effective forthe corrosion in flowing high temperature pressurizedwater, and the effect of water flow is negligible when
Fe2O3/Fe3O4 ratio reached about 2.

4. Conclusion
1.

2.

3.

The significant weight loss by water flow wasobserved except for the test in the water with DO 8
ppm. It becomes significant with lowering DO
concentration.
The weight loss of rotated disk specimen wasseemed to be attributable to dissolution of Fe ion,
which caused by dissolution and/or exfoliation ofFe3O4.
Fe2O3 may acts as a diffusion barrier of Fe iontransport. Therefore, it seemed that the formation ofFe2O3 was effective for the suppression of weight
loss, and it is considered that the effect of water flowis negligible when Fe2O3/Fe3O4 ratio reached about 2.

References
[1]

[2]
[3]
[4]
[5]
[6]
[7]

M. Akiba et al., Fusion Engineering and Design 85,
1766-1771 (2010).
T. Hirose et al., Fusion Engineering and Design 86,
2265-2268 (2011).
Y. Nomoto et al., Fusion Engineering and Design 81,719-724 (2006).
K. Shiba et al., JAERI-Tech 97-038 (1997).
T. Hirose et al., Journal of Nuclear Materials 367-370,1185-1189 (2007).
A. Suzuki et al., J. Plasma Fusion Res. 86, 390-392 (2010).
H. Abe et al., Journal of the Surface Finishing Society ofJapan 63, 290-295 (2012).

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B. Beverskog et al., Corrosion Science. 38, 2121-2135(1996).