Professor V.I. Makhnenko, scientist A.S. Milenin

E.O. Paton Electric Welding Institute

of National Academy of Sciences of Ukraine

1

Remaining Time Assessment of the Steam Generator Welding Joint

№111-1 of NPP VVER-1000 with Respect to Detected Cracks.

2

Fig. 1. Scheme of location of the welded joint № 111:

1. body of steam generator;

2. collector;

3. nipple 1200;

4. pipe conduit DU-850;

5. pocket;

A discontinuity (defect).

3

Fig. 2. Defectogram of the welded joint №111-1 of “hot” collector 1PG-1 of Uzhno-Ukrainskaya nuclear power-plant in ~1 year after

first repair.

4

Fig. 3. Defectogram of ultrasonic inspection of the steam generator

№ 3, power unit № 4 of Zaporozhskaya nuclear power-

plant.

5

Fig. 4. Cartogram of discontinuity №3 of the welded joint №111-1 (“hot” collector) PG-3 of power unit №4 Zaporozhskaya nuclear

power-plant according to the data of the Expert's report “UkrTsNIITMASh” of 13.01.2006.

6

Main Problem: permissibility of exploitation of the steam generator 4PG-3 of Zaporozhskaya nuclear power-plant with a detected defect in the region of the welded joint №111-1 until at least the next planned repair (about 1 year).

Questions are to be answered: 1. What is the degree of risk of the generation of the through-wall crack within the mentioned period of the exploitation, i.e. the leakage in the region of the growing defect, that will lead to the emergency stop of the power unit?

2. What is the degree of risk of the spontaneous destruction with the unpredictable consequences?

7

Table 1. Chemical composition and mechanical properties of steel 10GN2MFA.

Chemical composition, weight percent. Mechanical properties.

С Si Mn Cr Ni Mo VσВ, MPa

(200С)

σВ, MPa

(3500С)

σ0.2,

MPa (200С)

σ0.2,

MPa (3800С)

0.134 0.245 0.79 0.25 2.09 0.51 0.02 608 539 500-490 422

8

Fig. 5. Calculation data about the distribution of working stresses zz in the region of the pocket depending on pressure in the steam

generator P=6.4 MPa and in the collector PC=16 MPa.

9

Table 2. Stresses zz in the region of the defect depending on working pressure 6.4 MPa.

10

Table 3. Residual stresses

(MPa) in the region of the

welded joint №111.

597 607 617 627 637 647 657 667 r, mm

z, mm

5 86.85 86.16 79.91 69.22 56.83 45.29 36.04 29.33

15 78.68 73.50 67.96 61.79 55.16 48.58 42.70 38.36

25 68.66 64.57 62.28 60.81 58.88 55.92 52.38 49.80

35 60.43 59.21 60.62 62.98 64.64 64.71 63.52 62.49

45 54.47 56.44 61.17 66.49 70.96 73.82 75.29 76.35

55 50.49 55.20 62.84 70.49 77.27 82.77 87.32 91.32

65 48.13 54.79 65.22 74.84 83.40 91.44 99.35 107.16

75 47.85 55.10 68.98 79.36 89.29 99.98 111.13 123.36

85 49.83 65.62 74.51 84.07 95.50 108.96 122.86 138.84

95 130.20 99.19 86.20 91.58 103.41 119.35 135.39 151.88

105 149.72 130.69 126.18 123.01 125.53 134.43 149.64 165.11

115 186.77 180.50 171.04 165.63 160.97 161.55 170.41 183.02

125 220.56 218.10 212.87 209.39 202.83 197.88 197.18 194.71 Seam №111

135 225.94 224.91 222.37 314.19 210.05 204.41 200.93 196.45

145 168.58 156.43 149.18 153.81 160.58 171.71 182.66 194.74

155 157.85 145.07 145.82 154.03 164.00 175.81 191.44 202.23

165 149.36 139.96 139.98 145.89 158.92 178.75 197.08 212.97

175 140.76 132.79 132.63 141.22 157.36 179.27 203.90 220.17

185 129.27 121.76 123.57 132.08 148.67 173.68 206.78 229.28

195 115.26 108.45 107.98 113.02 126.15 151.31 198.05 249.03

205 100.57 93.09 87.86 85.61 86.63 69.35 86.97 47.65

215 86.60 77.67 69.64 61.95 53.59 40.48 14.86 -48.71

225 73.60 63.97 53.93 42.38 28.19 8.36 -24.61 -63.10

235 62.82 52.91 41.57 28.06 11.29 -10.67 -37.26 -68.46

245 55.26 45.35 33.47 19.13 1.78 -18.47 -41.81 -69.35

255 51.84 41.86 29.84 15.47 -1.39 -20.33 -41.67 -66.95

265 52.50 42.84 30.93 16.66 0.27 -17.83 -38.00 -61.50

275 57.95 48.35 36.39 22.10 5.83 -12.13 -31.81 -54.00

285 68.16 58.42 46.21 31.63 14.85 -3.83 -23.83 -45.07

295 83.11 73.00 60.38 45.24 27.06 6.80 -14.46 -35.42

305 102.56 92.08 79.19 62.15 42.36 20.35 -2.92 -25.70

315 126.93 116.79 103.69 87.15 67.68 46.29 24.70 3.41

11

597 607 617 627 637 647 657 667 r, mm

z, mm

5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

15 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

25 -1.95 -2.22 -1.82 -1.44 -1.13 -0.94 -0.74 1.08

35 -4.00 -4.55 -3.61 -2.82 -2.36 -2.13 -1.65 0.45

45 -5.28 -5.54 -4.11 -3.38 -3.36 -3.60 -3.51 -2.53

55 -4.79 -4.29 -2.67 -2.92 -4.16 -5.59 -6.68 -8.01

65 -0.98 0.10 0.79 -1.75 -5.09 -8.22 -11.22 -15.72

75 9.25 8.48 5.54 -0.74 -6.46 -11.37 -17.05 -25.03

85 32.00 20.30 9.06 -0.62 -8.14 -14.73 -23.57 -35.33

95 77.13 25.73 10.57 -0.15 -9.62 -17.85 -29.56 -46.46

105 77.15 38.92 1674 2.45 -10.52 -21.20 -35.35 -56.82

115 72.34 55.81 24.91 6.80 -14.09 -30.21 -42.14 -60.70

125 75.02 58.64 31.26 7.83 -12.88 -30.98 -44.28 -70.82 Seam №111

135 71.89 59.03 39.01 12.81 -8.29 -30.50 -50.93 -78.54

145 71.18 62.12 34.91 18.29 -4.80 -29.46 -57.14 -80.27

155 73.07 55.38 37.69 19.15 -3.37 -30.38 -56.17 -80.64

165 70.90 51.62 37.78 20.00 -2.80 -28.33 -56.96 -77.92

175 70.13 47.18 31.88 17.42 0.28 -24.37 -53.05 -75.94

185 64.36 41.92 28.38 15.90 2.36 -18.57 -48.92 -73.00

195 54.66 37.11 24.34 13.21 3.03 -10.10 -36.41 -74.85

205 45.79 31.68 19.44 8.44 -0.92 -7.59 -7.82 -79.78

215 38.92 26.40 16.02 7.04 -0.66 -10.18 -32.65 -37.64

225 31.55 20.91 11.88 3.72 -4.71 -15.71 -28.52 -9.33

235 23.90 14.94 7.02 -0.47 -8.05 -15.34 -14.46 2.01

245 16.37 9.09 2.42 -3.70 -8.89 -10.27 -4.54 7.53

255 9.65 4.00 -1.18 -5.41 -7.62 -5.51 1.66 10.68

265 4.36 0.13 -3.49 -5.86 -5.90 -2.12 5.18 12.71

275 0.80 -2.26 -4.58 -5.58 -4.41 -0.18 6.75 13.79

285 -0.86 -3.35 -4.65 -4.79 -3.33 0.42 6.62 13.80

295 -0.97 -3.38 -3.77 -3.57 -2.58 0.04 4.96 12.38

305 -0.25 -2.56 -2.11 -2.30 -1.91 -0.55 2.49 8.50

315 0.30 -0.76 -1.01 -1.10 -1.00 -0.35 1.30 -0.28

Table 4. Residual

stresses zz (MPa) in the region of the welded joint

№111.

12

Fig. 6. Total stresses zz at the plane of crack z=const.

13

Fig. 7. Scheme of the diagram of the static corrosive crack growth resistance of constructional material:

1. diagram lg v – KI according to experimental data;

2. idealized diagram.

14

first stage (KI<KISCC), when the mechanism of the electrochemical corrosion in the growth of crack prevails, here the values of the crack growth rates are rather small and with reference to the case under consideration don't exceed 1-2 mm/year;

second stage (KISCC<KI<KIC), when the mechanism of the hydrogen embrittlement in the growth of the corrosion crack prevails, here the values of crack growth rates are sufficient enough and for constructional steels in the environment of the feedwater they can mount to the values 50 mm/year;

third stage (KI>KIC) corresponds to the state of high risk of the spontaneous growth of crack.

Three main stages of the diagram of the static corrosive crack growth resistance:

15

Table 6. Sizes of defects and equivalent crack, values of KI(G) and KI(D).

Steam generator

Number of defect

Size of defect, mm Equivalent crackScheme of

semi-elliptical crackDepth, H, mm

Width, 2L, mm

а, mm

с, mm

KI(G),

MPam1/2

KI(D),

MPam1/2

1PG-1UUNPP

1 63 65 51.2 51.2 59.24 41.18

2 64 85 59.0 59.0 70.18 45.20

3 50 50 40.0 40.0 45.11 35.50

4 40 15 19.6 19.6 26.75 24.34

5 53 70 48.7 48.7 55.75 39.90

6 3 10 3 5 10.60 12.15

1PG-2UUNPP

1 8 15 8.8 8.8 17.82 16.34

a = H, c = L, if H L;

if H > L;

2 50 25 28.3 28.3 33.90 29.40

3 40 15 19.6 19.6 26.75 24.34

4 35 30 25.9 25.9 31.86 28.07

5 10 25 10.0 12.5 19.29 19.63

6 48 72 47 47 53.45 39.04

,28.0 LHHa

16

Table 5. Total stresses (MPa) in case of T=3000C

and working pressure in the region of the welded joint

№111-1

597 607 617 627 637 647 657 667 r, mm

z, mm

5 86.85 86.16 79.91 69.22 56.83 45.29 36.04 29.33

15 75.50 75.63 69.26 64.49 58.55 52.14 46.05 41.63

25 68.20 68.45 64.91 64.39 63.14 60.68 57.95 56.80

35 62.37 63.09 64.14 67.36 69.84 70.84 71.40 72.87

45 58.23 60.14 64.93 71.25 76.84 81.11 85.30 89.65

55 55.09 58.14 65.85 74.87 83.20 90.84 99.05 107.00

65 52.18 56.35 66.10 77.29 88.64 99.82 112.32 124.65

75 51.57 49.30 62.62 78.52 93.53 108.63 124.87 142.11

85 47.39 40.48 66.29 82.29 98.54 116.13 134.80 165.01

95 117.31 88.58 92.87 98.57 112.42 131.06 151.54 168.18

105 143.70 126.20 126.75 129.24 134.88 146.46 165.17 185.42

115 185.38 180.93 175.51 172.17 169.85 172.52 185.24 198.97

125 221.57 220.81 215.14 214.53 210.43 207.71 208.86 205.93 Seam №111

135 230.44 231.20 227.04 221.01 218.29 213.95 211.89 207.90

145 180.09 170.07 162.40 166.02 172.31 182.80 193.83 205.06

155 172.73 161.81 160.05 167.57 176.30 186.95 200.50 211.66

165 168.01 160.38 159.08 162.07 172.25 189.31 205.42 220.18

175 163.60 157.20 154.44 158.99 171.14 189.31 209.12 227.37

185 157.07 151.07 147.72 151.54 162.86 182.24 208.85 234.07

195 148.68 143.40 136.40 135.45 141.49 158.23 190.94 230.10

205 139.62 133.69 122.10 112.59 105.75 100.36 77.02 54.73

215 131.11 123.77 108.87 93.33 76.20 50.96 10.51 -82.48

225 123.25 115.25 98.03 79.44 57.88 31.75 -23.90 -62.06

235 116.81 108.54 90.09 70.27 47.48 18.45 -21.33 -49.95

245 112.88 104.61 85.88 66.14 43.55 18.15 -13.73 -38.77

255 112.31 104.20 85.90 67.09 46.21 23.71 -3.74 -26.53

265 115.78 107.87 90.44 72.87 53.64 33.22 8.37 -12.58

275 123.55 115.78 99.32 82.86 64.86 45.62 22.24 2.69

285 135.82 128.05 112.48 96.84 79.41 60.43 37.64 19.12

295 152.65 144.70 129.83 114.78 97.09 77.49 54.52 36.55

305 173.98 165.89 151.46 136.02 117.87 97.38 73.43 53.25

315 196.29 186.76 173.96 159.30 141.90 122.15 100.24 87.43

17

Calculation of the coefficient of stress intensity KI(D), KI(G) and ref for the semi-elliptical crack a×2c.

where

Sj is an equivalent stress

Here zz(i) is total stress zz according to the diagram in Fig. 6 at the depth (a/20)·i

(i=0,1,2,…,20); Ci, Di, Ei, Fi are tabulated weighting functions,

If (a/c)<1.0 and (a/)<0.7

GDjmMPaa

YSjK jj ,,,1000

21

5.065.125.3

5.13

464.1157.089.01

c

aa

c

a

Y jj

c

a

c

aaD

09.023.132.01

2

c

aG 09.012.1

20

0

20

0

i

izziD

i

izziiiG

iFS

iEDc

aCS

5.175.1

9.09.10.1c

a

c

aa

18

If (a/c)>1.0 and 0.2<(a/)<1.0

where

; ;

; ;

.,,

464.11

5.065.1

4

3

2

21 DGj

ca

gaM

aMMY j

j

c

aM 09.013.11 ;

c

aM

2.0

89.054.02

; 24

3 11465.0

15.0

c

a

c

aM ;

0.1Ggc

aag D

2

35.01.1

.,, GDjHS вjmj

N

m 2

6

M

в

25.175.0

47.005.155.012.022.11

;11.034.01

a

c

a

c

aa

c

aH

a

c

aaH

G

D

19

, if Lr < Lrmax

Kr=0, if Lr ≥ Lrmax

where

ref is the stress that is determined with external power load without taking into account the residual stresses and that is able at some level of the loading to cause the plastic collapse in

the region of the defect under consideration.

662 65.0exp7.03.014.01 nLnLKn rrr

Cr K

KK

max

2.0 ref

rL

22.0max B

rL

Mathematical formulation of R6 approach.

20

To calculate ref it was used

where

3

95,022

mввref

Z

1

2

222

Z

1212

1221

;

2

;

;

24

;sinarccos

2

A

R

a

R

c

A

cp

cp

21

Fig. 8. Time dependences of a, c (a) and KI(D), KI(G) (b).

(a) (b)

22

Fig. 9. Kinetics of reducing of the safety factor against spontaneous growth of crack a0=40 mm, c0=45 mm in time: KISCC=10 MPa·m1/2, vm=44 mm/year.

23

Conclusions: 1. Numerical analysis of state of the steam generator 4PG-3 of Zaporozhskaya nuclear power-plant showed that the risk of

leakage (through defect) in the course of year of its exploitation (with double time reserve) is obviously absent.

2. The kinetics of the changing of safety factor against the spontaneous propagation of crack showed that during a year of

the exploitation the risk of such a spontaneous growth is minimal.