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Flaw Tolerance Assessments for ISI Relief

Request on Weldment of Main Steam Line

Branch Connection Weldolets

Jun-Seog Yang (Korea Hydro & Nuclear Power Co., Ltd)

Nam-Su Huh (SEOULTECH)

Yun-Jae Kim (Korea University)

1st KEPIC/ASME Joint Seminar on

In-service Inspection (ASME BPV XI / KEPIC-MI)

September 5, 2017

ISI Relief Request for Weldolet Welds

[Source] www.google.com & Bonney Forge [ Weldolet ]

Implementation of augmented ISI to MSL branch connection weldolets

- Weldolet as branch connecting fitting of main steam line

- RT: Unusual difficulties due to the interference by the surrounding structures

- UT: The problems associated with the weldolet configuration

- Limitation of essentially 100% examination coverage of weld volume

Final Safety Analysis Report (FSAR) & Technical Specification (T/S)

- FSAR 3.6.2 (Postulated Pipe Rupture): Break exclusion with augmented ISI

- Volumetric ISI with 100% coverage in every 10 years

2

Objectives

Alternative approaches for the ISI relief request for weldolet welds

- UT with various transducers as for non-destructive examination

- Probabilistic safety analysis

- Flaw tolerance assessment based on the deterministic fracture mechanics

(This presentation)

3

General Procedure

Deterministic Flaw Tolerance Assessment

Material Testing (Base/Weld, -/J-R curve)

Fatigue Crack Growth of Weldolet Welds

Geometry: Three MSL weldolets Flaw type: 360 internal surface flaw (a/t) Initial flaw depth: Prescribed ISI depth Outcome II: SIF solutions for 360 internal surface flaw Outcome III: Time to critical flaw length (Effects of WRS on Paris’ constants)

FE J based Critical Flaw Length of Weldolet Welds

Geometry: Three MSL weldolets Flaw location: Upper fusion line Type I: Through-wall flaw (Crotch, Flank, Between C&F) Type II: 360 internal surface flaw Loading: Normal and Faulted (+ pressure) Outcome I: Critical flaw length/depth

FCG Testing / Code Properties

Effect of WRS

SIF solutions (360 internal surface flaw)

4

Geometries of Weldolet Welds

[6” SCH 120, SA105] [8” SCH 160, SA105] [12” SCH 160, SA105]

■ Sinkori Units 1 and 2

- Korean advanced nuclear power plants

- 1400 MWe

- Three types of weldolets

Flank side

Crotch side

Crotch side Flank side

5

1

2

3

Locations for Postulated Flaw I

■ Examples of summary of UT coverage

6

Not examined region (Upper fusion line) Run Pipe

Branch Pipe

Weldment

Crotch side

Flank side

Upper fusion line

Lower fusion line

Run pipe

Branch pipe

- Circumferential through-wall and 360 internal surface flaws (Based on the ISI results, Conservative) - Upper fusion line - 0 (crotch), 45, 90 (flank): The effects of flaw locations

Crotch side

Locations for Postulated Flaw II

■ Postulated flaws (Locations, Orientations)

7

Flaw Location

Weld Zone

Upper fusion

line flaw

Projected flaw

Main Pipe

Main Pipe

Maximum K

■ Upper fusion line flaw vs. Run pipe OD surface flaw (Branch weldolet)

- Comparisons of stress intensity factors according to the flaw locations

Flaw is postulated along the upper fusion line

Locations for Postulated Flaw III

Projected flaw

Upper fusion line flaw

8

Ro

Rm Ri

t

① 50°

②

Ri

Ro

K, Stress Intensity Factor

Direction

Loads

① ②

KI KII Diff.

Internal Pressure

206.2 164.0 71.1 178.8 13.3%

Bending Moment

1254 785 570 970 18.5%

MPa mm

.1caseeffK

■ cf.] Straight pipe: Stress intensity factors of 360 internal surface flaw

- Projected flaws: Higher stress intensity factors than inclined flaws

9

Critical Flaw Length Determination

Determination of critical flaw length

- Crack driving force diagram (CDFD) based on elastic-plastic FE J-integral

J-in

tegra

l

a ac (Critical flaw length)

J-R

Japp.(PNOP or PFaulted)

a1 a2

a3

a4

a5

Lower bound - (Base metal) (Operating Temp.)

Lower bound J-R (Weld metal) (Operating Temp.)

10

Upper fusion line

CDFD based Critical Flaw Length Determination I: Through-Wall Flaw

Example

Circumferential through-wall flaw, Crotch side

Korean NPP 8 inch weldolet

11

FE model for through-wall flaws along the upper fusion line in crotch side

(Half model)

- Flaw angle (/)=0.15, 0.3, 0.5, 0.55, 0.6, 0.75

Upper fusion line

Flaw surface

/=0.15

/=0.3 /=0.5

12

FE J analyses

- Deformation plasticity

- Lower bound stress-strain data of base metal at operating temperature

- Loading conditions

+ Normal and faulted conditions (+ Pressure)

+ Directions of moments: To produce maximum J-integral

13

FE results

- Path independence of J-integral

0 1 2 3 4 5 6 7 8 90

4

8

12

16

At inner point

J (i

n-l

b/i

n2)

Contour number

0 1 2 3 4 5 6 7 8 90

10

20

30

40

50

60

At middle point

J (i

n-l

b/i

n2)

Contour number

0 1 2 3 4 5 6 7 8 90

4

8

12

16

At inner point

J (i

n-l

b/i

n2)

Contour number

14

FE results

- Variations of J-integral along the thickness

+ The use of maximum J and averaged J for CDFD assessments

J max. : 60

J avg. : 52 J max. : 95

J avg. : 79

J max. : 159

J avg. : 124

J max. : 2,331

J avg. : 1,558

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00

500

1000

1500

2000

2500

3000

8in., /=0.75, through-wall flaw

crotch side(0), LEVEL A

J (i

n-l

b/i

n2)

Normalized distance(x)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00

50

100

150

200

250



J (i

n-l

b/i

n2)


0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00

20

40

60

80

100

120

140



J (i

n-l

b/i

n2)


0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00

10

20

30

40

50

60

70

80



J (i

n-l

b/i

n2)


15

0 1 2 3 4 5 6 7 8 9 10 11 120

2000

4000

6000

8000

10000

/=0.60

8in., through-wall flaw

crotch side(0), LEVEL D, Javg

J (i

n-l

b/i

n2)

a, flaw length (in)

/=0.55

/=0.15

/=0.5

/=0.3

JR

Javg

Critical flaw length

a0=6.66 in

Tangent instability point

a=6.869 in

0 1 2 3 4 5 6 7 8 9 10 11 120

2000

4000

6000

8000

10000


crotch side(0), LEVEL D, Jmax

J (i

n-l

b/i

n2)

a, flaw length (in)

/=0.55

/=0.5

/=0.3/=0.15

Jmax

JR


a0=6.53 in


a=6.742 in

Resulting CDFD and critical flaw length for unstable fast fracture (faulted condition)

- ac=6.66 inch (52.5% of circumference, Using averaged J)

- ac=6.53 inch (51.4% of circumference, Using maximum J)

2321)( amamm

applied eaJ

2)()(*

01

CR

a

aaCaJ

[Using Javg.] [Using Jmax.] 16

A

A’

A A’

Upper fusion line

Flaw Surface

Example

360 internal surface flaw

Korean NPP 8 inch weldolet

CDFD based Critical Flaw Length Determination II: 360 Internal Surface Flaw

17

a/t=0.5 a/t=0.65 a/t=0.75

a/t=0.9 a/t=0.8

FE model (8 inch)

- Flaw depth (a/t) = 0.5, 0.65, 0.75, 0.8, 0.9

18

Effect of contact due to crack closure on J

19

1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.00

500

1000

1500

2000

2500

3000

3500

4000

J (i

n-l

b/i

n2)

a, flaw depth (in)

8in., 360 fully circumferential surface flaw

Jmax


a=3.01 in

a/t=0.50 a/t=0.65 a/t=0.75 a/t=0.80

a/t=0.90J

R

Critical flaw depth

a0=2.97 in

3.11 inch

Resulting CDFD and critical flaw depth for unstable fast fracture (faulted condition)

- ac=2.97 inch (a/t=0.954, Using maximum J along the crack front)

[Crack-tip mesh for a/t=0.9]

20

Through-wall flaws (percentage of the circumference)

- 6 & 8 inch: about 50% (faulted) ~ 70% (normal)

- 12 inch: about 45% (faulted) ~ 55% (normal)

- The effects of flaw locations (crotch, flank, middle): Not significant

360 internal surface flaws

- 6, 8, & 12 inch: over a/t=0.9 (both normal and faulted)

Summary of Critical Flaw Length Determinations

21

Example: 8 inch, crotch side, faulted condition

Simply applied as uniform primary tension to branch pipe (conservative)

WRS: 30% of yield strength of the base metal

ac=4.81 inch (37.9% of circumference, reduced by 25%)

- Detailed analyses using pre-defined uniform secondary stress field are in progress

0 1 2 3 4 5 6 7 8 9 10 11 120

4000

8000

12000

16000

20000

J (i

n-l

b/i

n2)

a, flaw length (in)

Jmax

/=0.5

/=0.4

/=0.3

JR


a=5.089 in


a0=4.81 in

8in., through-wall flaw, crotch side(0)

LEVEL D+Residual, Jmax

Effect of Weld Residual Stress

0 1 2 3 4 5 6 7 8 9 10 11 120

2000

4000

6000

8000

10000


crotch side(0), LEVEL D, Jmax

J (i

n-l

b/i

n2)

a, flaw length (in)

/=0.55

/=0.5

/=0.3/=0.15

Jmax

JR


a0=6.53 in


a=6.742 in

w/o WRS w/ WRS (Primary tension)

22

Initial depth

Time to critical flaw depth (a/t=0.9)

For fatigue crack growth of 360 internal surface flaws in upper fusion line

Stress intensity factor solutions for MSL branch connection weldolets

Stress Intensity Factors for FCG

,

,

1 0.45

0.8880 1.3996 0.45 0.80

Branch FE

I

Straight Pipe ASME

I

for a tK

afor a tK

t

- KI

23

,

,

0.3593 0.2418 6

0.9425 0.0885 8

1 12

Branch FE

eff

Straight Pipe ASME

eff

afor inch

t

K afor inch

tK

for inch

- Keff

Fatigue crack growth calculations of 360 internal surface flaw (in progress)

- Only in-plane crack growth along the upper fusion line

- Uniform crack growth along the crack front using Keff,max (conservative)

- The effects of WRS on Paris’ constants (30% of yield strength)

24