24P099-P
Fatigue behavior on welded joint for JT-60SA Vacuum Vessel
JT-60SA真空容器の連続プラグ継手の疲労強度

柳Yutaka Yanagi1, Masanao Shibui1, Toshio Kanahara1,Tsutomu Mochida1, Mitsuru Ejiri1, Shiro Asano1,Yusuke K.Shibama2, Kei Masaki2 and Akira Sakasai21
寛 , 澁井正直1，金原利雄1，持田 務1，江尻 満1，浅野史朗1
芝間祐介2，正木 圭2，逆井 章2
1Toshiba Corporation,2-4, Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
株式会社東芝 〒230-0045 横浜市鶴見区末広町2-42
Japan Atomic Energy Agency, Naka Fusion Institute,801-1, Mukoyama, Naka, Ibaraki 311-0193, Japan
独立行政法人 日本原子力研究開発機構 那珂核融合研究所 〒311-0193 那珂市向山801-1
JT-60SA Vacuum Vessel (VV) has D-shaped cross section and double-walled structure. It consists of theinner and outer wall reinforced by poloidal ribs and is made of SUS316L (Co<0.05wt%) [1-2]. The
welding outer wall on rib (so called continuous plug) is performed from the outside of double-wall. Since itis difficult to confirm the penetration bead from the inside of double-wall, an incomplete penetration isassumed to be included in this welded joint. In this study, the fatigue test of continuous plug welded joint
with an artificial incomplete penetration was performed to investigate the effect of the incomplete
penetration on fatigue behavior and fatigue strength.

9.95m

6.6m

Outer wall

Poloidal rib
Inner wall

effect of artificially introduced incomplete
penetration on the fatigue behavior and strength.
2. Experiment2.1. Welded joint and welding conditions
The cross-sectional view of the welded joint isshown in Fig.2. The thickness of the outer wall andrib were selected as 18mm and 22mm, respectivelyin accordance with the actual VV. The material of
the specimen was SUS316L without control ofcobalt content. The welding conditions arepresented in Table I. The welding condition ofGTAW was adjusted to produce incomplete
penetrations on both sides of the rib.
25°

Outer wall18

1. Introduction
The VV of JT-60SA has D-shaped cross section
and double-walled structure to circulate
boric-acid water between the walls for neutron
shielding. It consists of the inner and outer wall
reinforced by poloidal ribs as shown in Fig.1 andis made of SUS316L ( Co<0.05wt%).

Fig.1. JT-60SA Vacuum Vessel andcross section (Inboard R segment )The welding of the outer wall on the rib isperformed by GTAW(TIG) followed byGMAW(MAG) from the outside of double-wall.
Since it is difficult to confirm the penetration
bead from the inside of double-wall, an
incomplete penetration is assumed to be includedin this welded joint (so called continuous plug)that is not qualified in the conventional design
standards for a light water nuclear reactor.
In this study, the fatigue test of continuous plugwelded joint was performed to investigate theRib22

Fig.2. Groove of continuous plug
Table I. Welding conditions (Flat position)
Process

Pass

GTAW
GMAW

12-lastCurrent[A]
200-300
140-200

Voltage
[V]
10-15
24-30

Consumable
Y316L
TS316L-FC1

As the results of PT and RT, defects were notdetected in the weld metal.

2.2. Fatigue test
Test configuration and the specimen are shown inFig.3. The length of the incomplete penetration,
which is shown as “a” in the Fig.3, is ~ 3.0mm at
the most because of its maximum wrap length
between outer wall and rib.

5050

181822aOuter wall

2mm

M20

Fatigue crack
Fig.4. Macroscopic cross-section (Case1)“a”: Length of incomplete penetration

10000

Fig.3. Configuration of fatigue test
Both sides of the outer wall was supported
symmetrically and cyclic load was applied to the ribat the frequency of 5Hz by the triangular wave form.
Produced shear stress near the tip of the incomplete
penetration was estimated by introducing Tresca
stress at the state of plane stress to evaluate fatigue
strength. Crack growths were measured in amicroscope.
Table II. Fatigue test conditions
Case1
Case2
Case3

Applied Stressσmax [MPa]
453.5
340.1
226.7

Eq.amplitude

Saeq [MPa]
222.2
166.6
111.1

Stress amplitude, Sa [MPa]Equivalent stress amplitude, Saeq [MPa]Rib#Length of incomplete penetration

15

Cyclic load

Outer wallquoted from JSME S NC1, all data are above thefatigue curve which relates one fourth of the stressamplitude with the number of cycles. Therefore thefatigue strength reduction factor Kf is evaluatedabout 4.

1000

JSME S NC1 Design fatigue curve [Sa - Nf]( Smooth specimen)
Nc-0.5mm，Case1(σmax=453.5MPa)
Nc-0.5mm，Case2(σmax=340.1MPa)
Nc-0.5mm，Case3(σmax=226.7MPa)

100(JSME)/4 [Sa - Nf]

10
1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

Number of cycles, Nc or Nf [c]Stress ratio
R
0.02
0.02
0.02

As is shown in Table II, three combinations ofapplied stress and equivalent stress amplitude wereselected as the test conditions. As crevice-likeincomplete penetration was closed by the residual
stress of welding, a crack initiation life wasevaluated, instead of a fracture life, as fatigue
strength. The cycle when a crack observed in a
microscope reached to 0.5mm was defined as crack
initiation.
3. Results
The crack propagation through the weld metal ispresented in Fig.4. In this case, “a” is ~ 2.5mm. As
the crack propagates in mixed mode, curving
appears and the bending stress mainly contributes tothe crack propagation in this test configuration.
Obtained data of crack initiation lives from six
specimens for each test condition are plotted inFig.5. Compared with the design fatigue curve

Fig.5. Comparison of experimental data withdesign fatigue curve (JSME S NC1)
4. Summary
The fatigue test of continuous plug welded joint
was performed to investigate the effect of
artificially introduced incomplete penetration on
the fatigue behavior and strength.
The fatigue strength reduction factor Kf wasevaluated about 4.
Acknowledgements
The authors would like to thank Dr.H.Takano, Dr.
S.Mizumaki, Dr.T.Okuyama and Dr.M.Ushijima ofToshiba Corporation for their support of this study.
References[1] S.Sakurai, K.Masaki, Y.K.Shibama, et al.; FusionEng. and Des. 84 (2009) 1684-1688.
[2] S.Asano, T.Okuyama, T.Oonawa, Y. Yanagi et al.;Fusion Eng. and Des. 86 (2011) 1816-1820.