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NDE Based Finite Element Modeling & Analysis of

Wall Thinning in CANDU Feeders

Usama Abdelsalam & Dk Vijay

AMEC NSS Ltd. - Power and Process Americas

Toronto, Ontario, Canada

usama.abdelsalam@amec.com

Presented at the CANDU In-service Inspection and NDT in Canada 2010 National Conference

June 14-17, 2010

Hilton Markham/Toronto

ISI-2010

ABSTRACT

During operation under flow accelerated corrosion (FAC) favourable conditions, CANDUoutlet feeder pipes experience general and local wall thinning. The wall thickness of suchfeeders is monitored as part of the life cycle management plans developed and used by theutilities. Thickness measurements of CANDU feeder bends are performed using a bracelettool that has 14 probes equally spaced along the circumference covering a 140o angleproducing 4 sets of thickness data (Extrados, Intrados, Left Cheek, and Right Cheek).Close to the Grayloc hub weld, a 6-probe tool is used producing two sets of thickness datafor the extrados and intrados. These thickness measurements are used to assess thefitness for service of feeders at the end of a projected operating period.

The Design by Analysis rules of the ASME B&PV Code SEC III Division 1 NB-3200 criteriaare used to perform fitness for service assessments of CANDU outlet feeders consideringthe primary loadings. The tight radius pipe bends with local thin areas (LTA) located on theinner surface and super imposed on general thinning region are considered using detailedFEA models implementing idealized smooth axial and circumferential thickness profiles. Alocation dependent thinning rate function is developed (based on the smoothed profiles andthe assumed original thickness distribution) to predict the wall thickness distribution at theend of an arbitrary evaluation period. Internal pressure and dead weight loads are staticallyapplied. Linear elastic analysis is performed and the results are checked against the ASMECode criteria for the primary Stresses. It is demonstrated that a “local” wall thicknessconsiderably below the pressure based thickness for the corresponding straight pipesegment meets the requirements of the ASME Code SEC III for the primary Stresses. Theeffects of the extent of the local thin area in the axial and circumferential directions areexplored.

The Objective is to Demonstrate the Effectiveness of NDE based FEA in the Life

Extension of CANDU Outlet Feeders

CANDU Feeder Pipes Experiencing Local Wall Thinning:

– Nominal Thickness, tnom = 7.01 mm = 2.23 tmin

– Measured Local Minimum Thickness, tmeasured,local = 2.55 mm = 0.81 tmin

tmeasured,local < MAWT (3.15(1) mm for 2 ½ Inch Straight Segments of Feeders as per

ASME SEC III NB-3600) Feeder Repair or Replacement?

Detailed FEA Extends the Life of the Thinned Feeder Pipes:

– NB-3200: Design By Analysis

– Axial & Circumferential Wall Thickness Profiles Based on Thickness Scans

– Introducing Location Dependent Wall Thinning Rate

– MAWT = 1.99 mm (0.63 tmin) ~2.15 EFPY Life Extension (0.26 mm/EFPY)

(1) MAWT > 3.15 mm for pressure loading on the Intrados.

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Objective

Typical CANDU Reactor Face

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Introduction

• 480 Fuel Channels

• 480 Outlet Feeders (SA106-

Gr.B)

• PHT Class 1

• ASME SEC III NB-3600 (Piping

Design)

• FAC Wall Thinning (Tight

Radius Bends)

• Pressure, Dead Weight,

Thermal & Seismic Loadings

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Introduction

Typical CANDU Reactor Horizontal Feeders Row

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Introduction

Typical Horizontal Feeders’ Row – Tight Radius Bends

NDE Axial & Circumferential Thickness Data

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NDE: Thickness Measurements

14-probe Tool*

6-probe Tool*

* Courtesy of the Inspection, Maintenance & Commercial

Services Division of Ontario Power Generation

Intrados Scan Extrados Scan

ISI-2010

NDE: Thickness Measurements

140◦

114

EXTRADOS

INTRADOS

RIGHT

CHEEK

LEFT

CHEEK 20

140◦

1 14

EXTRADOS

INTRADOS

RIGHT

CHEEK

LEFT

CHEEK

2020

ISI-2010

NDE: Thickness Measurements

140◦

1

14

EXTRADOS

INTRADOS

RIGHT

CHEEK

LEFT

CHEEK

20

20

140◦

1

14

INTRADOS

RIGHT

CHEEK

LEFT

CHEEK

EXTRADOS

20

Left Cheek Scan Right Cheek Scan

Overlapped Scans

ISI-2010

NDE: Thickness Measurements

INTRADOS

RIGHT

CHEEK

LEFT

CHEEK

EXTRADOS

I

E

RCLC

E+RCE+LC

I+RCI+LC

20◦

70◦110◦

160◦

200◦

250◦ 290◦

340◦

ASME SEC III NB-3640: Piping Desing NB-3640: Pressure Design

NB-3642.1: Pipe BendsFor R/Do = 6

t’min > 1.06 tmin (2.59 mm)

For R/Do = 3

t’min > 1.25 tmin (3.06 mm)

t’min Min Allowable Thickness at the Intrados before Bending

ISI-2010

Code Compliance

APyS

PDt

m

o

)(2

min 3.15 mm

NB-3641.1: Straight Pipe Under Internal Pressure

• Bend Angle, θ = 73o

• Bend Radius, R = 4.5 in (114.3 mm)

• Do = 3.03 in (76.96 mm)

• tnom = 0.276 in (7.01 mm)

• tmin = 3.15 mm (Straight Pipe)

• tmeasured = 2.55 mm (0.81 tmin)

• Bend R/Do = 1.48

t’min > 1.45 tmin (4.57 mm) ?

1

1.1

1.2

1.3

1.4

1.5

1.6

0 1 2 3 4 5 6 7R/Do

t'm

in/t

min

ASME

Fitted?

ISI-2010

Code Compliance

Typical CANDU Feeder Tight Radius

Bend Configuration

Allowable Thickness for Pipe Bends

Applying the Criteria of D.A. Osage, et al, “Technologies for the Evaluation of Non-Crack-Like Flaws in Pressurized Components-Erosion/Corrosion, Pitting, Blisters, Shell Out-of-Roundness, Weld Misalignment, Bulges and Dents”, WRC Bulletin 465, September 2001.

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

0 15 30 45 60 75 90 105 120 135 150 165 180

θ L

t alo

c/t

min

2" Feeders

2.5" Feeders

CheekExtrados Intrados

2" Extrados:

t aloc /t min = 0.863

2" Intrados:

t aloc /t min = 1.303

2.5" Extrados:

t aloc /t min = 0.878

2.5" Intrados:

t aloc /t min = 1.238

L

b

aloc

CosR

Rt

t

minmin 1

5.05.0

ISI-2010

Code Compliance

Intrados (2 ½ Inch Pipe):

taloc = 1.238 tmin (3.90 mm)

Extrados (2 ½ Inch Pipe):

taloc = 0.878 tmin (2.77 mm)

Uniform Wall Thinning? Too Conservative

ISI-2010

Modelling

Axial & Circumferential Thickness Profiles Life Extension Potential

Measured & Idealized Axial & Circumferential Thickness Profiles

ISI-2010

Modelling

Idealized Profile

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0 30 60 90 120 150 180 210 240 270 300 330 360

Circumferencial Angle (Deg)

Wall T

hic

kn

ess (

mm

)

E,1 E,2 E,3 E,4 E,5 E,6

I,1 I,2 I,3 I,4 I,5 I,6

tmintmin

0

1

2

3

4

5

6

7

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

Axial Distance Along Bend Centerline (mm)

Wall T

hic

kn

ess (

mm

)

14-probe Extrados 14-probe Intrados

14-probe Left Cheek 14-probe Right Cheek

6-Probe Extrados 6-Probe Intrados

Idealized Profile

Location Dependent Thinning Rate Life Extension Potential

Intrados is 7% Thicker than Nominal

Extrados is 7% Thinner than Nominal

Extrados Thinning Rate = (0.93tnom-tmeasured)/Time

Intrados Thinning Rate = (1.07tnom-tmeasured)/Time

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Finite Element Model

Location Dependent Thinning Rate

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Finite Element Model

0

1

2

3

4

5

6

7

8

9

0 15 30 45 60 75

Axial Distance (Deg.)

t p (

mm

)

tmin

Original Thickness

Idealized Thickness

0

1

2

3

4

5

6

7

8

9

0 90 180 270 360

Circumferential Distance (Deg.)

t p (

mm

)

tmin

Intrados LCRC

Original Thickness

Idealized Thickness

0

0.05

0.1

0.15

0.2

0.25

0.3

0 15 30 45 60 75

Axial Distance (Deg.)

Th

inn

ing

Rate

, t R

(m

m/E

FP

Y)

0

0.05

0.1

0.15

0.2

0.25

0.3

0 90 180 270 360

Circumferential Distance (Deg.)

Th

inn

ing

Rate

, t R

(m

m/E

FP

Y)

Intrados LCRC

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FE Model & Thinning Cases

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0 30 60 90 120 150 180 210 240

Circumferential Distance (mm)

Th

ick

ne

ss

(m

m)

tmin

taloc

Lm(t)

tnom

oc

tloc,min=2.55 mm

tloc,min=1.99 mm

tloc,min=1.53 mm0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

-15.0 -10.0 -5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0

Axial Distance (mm)

Th

ick

ne

ss

(m

m)

tmin

taloc

tnom

Lm(a)

tloc,min=2.55 mm

tloc,min=1.99 mm

tloc,min=1.53 mm

ASME SEC III NB-3221 Design Loadings (Linear Elastic Criteria)

NB-3221.1 General Primary Membrane Stress Intensity

Pm ≤ Sm

NB-3221.2 Local Membrane Stress Intensity

PL ≤ 1.5 Sm (Sint > 1.1 Sm within √Rt)

NB-3221.3 Primary Membrane (General or Local) Plus Primary Bending Stress Intensity

(Pm or PL) + Pb ≤ 1.5 Sm

Design Stress Intensity values Sm are given by NB-3229 SEC II Part D

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Acceptance Criteria

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FE Results & Code Qualifications

0

5

10

15

20

25

30

0 15 30 45 60 75

Axial Distance (Deg.)

Pm

(K

si)

0

2

4

6

8

10

12

14

16

18

20

Th

ickn

ess (

mm

)

Sm

tminThickness

1.1 Sm

1.5 Sm

0

5

10

15

20

25

30

0 90 180 270 360

Circumferential Distance (Deg.)

Pm

(K

si)

0

2

4

6

8

10

12

14

16

18

20

Th

ickn

ess (

mm

)

Sm

tmin Thickness

Intrados LCRC

1.1 Sm

1.5 Sm

0

5

10

15

20

25

30

0 15 30 45 60 75

Axial Distance (Deg.)

Pm

(K

si)

Sm

1.1 Sm

1.5 Sm

0

5

10

15

20

25

30

0 90 180 270 360

Circumferential Distance (Deg.)

Pm

(K

si)

Sm

Intrados LCRC

1.1 Sm

1.5 Sm

Primary Membrane Stress Intensity (Nominal Thickness)

Primary Membrane Stress Intensity (tloc,min = 2.55 mm = 0.810 tmin)

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FE Results & Code Qualifications

0

5

10

15

20

25

30

0 15 30 45 60 75

Axial Distance (Deg.)

Pm

(K

si)

0

2

4

6

8

10

12

14

16

18

20

Th

ickn

ess (

mm

)

Sm

tminThickness

1.1 Sm

1.5 Sm

0

5

10

15

20

25

30

0 90 180 270 360

Circumferential Distance (Deg.)

Pm

(K

si)

0

2

4

6

8

10

12

14

16

18

20

Th

ickn

ess (

mm

)

Sm

tmin Thickness

Intrados LCRC

1.1 Sm

1.5 Sm

0

5

10

15

20

25

30

0 15 30 45 60 75

Axial Distance (Deg.)

Pm

(K

si)

0

2

4

6

8

10

12

14

16

18

20

Th

ickn

ess (

mm

)

Sm

tminThickness

1.1 Sm

1.5 Sm

0

5

10

15

20

25

30

0 90 180 270 360

Circumferential Distance (Deg.)

Pm

(K

si)

0

2

4

6

8

10

12

14

16

18

20

Th

ickn

ess (

mm

)

Sm

tmin Thickness

Intrados LCRC

1.1 Sm

1.5 Sm

Primary Membrane Stress Intensity (tloc,min = 1.99 mm = 0.631 tmin)

Primary Membrane Stress Intensity (tloc,min = 1.53 mm = 0.486 tmin)

ISI-2010

FE Results

0.5

0.8

1.0

1.3

1.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5Lm(a)/√(rt)

Pall/P

D

Lm(a)1 Lm(a)2

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

-15 -10 -5 0 5 10 15 20 25 30 35 40 45 50

Axial Distance (mm)

Th

ick

ne

ss

(m

m)

tmin

taloc

Lm(a)2

Lm(a)1

0.0

0.5

1.0

1.5

2.0

2.5

0.0 0.5 1.0 1.5 2.0 2.5

tloc,min / tmin

Pall/P

D

tloc,min/tmin = 0.631

AcceptableNot Acceptable0.0

0.5

1.0

1.5

2.0

2.5

0.0 0.5 1.0 1.5 2.0 2.5

tuniform / tmin

Pa

ll/P

D

tuniform/tmin = 1.215

AcceptableNot Acceptable

Liner Elastic Allowable Pressure for Uniform & Local Thickness

LTA Axial Extent & Allowable Pressure (tloc,min = 1.99 mm = 0.631 tmin)

ISI-2010

SUMMARY

NDE of CANDU Feeder Pipes Tight Radius Bends Thickness Data

• Idealized Axial & Circumferential Wall Thickness Profiles are Developed based on the Measured Thickness Data

• The Idealized Wall Thickness Profiles with Local Thin Areas (LTA) Located on the Inner Surface and Super Imposed on General Thinning are Implemented in Detailed FEA Models.

• Location Dependent Thinning Rate Function is Developed to Predict the Wall Thickness Distribution at the End of an Arbitrary Evaluation Period.

• The Design by Analysis Rules of the ASME B&PV Code SEC III Division 1 NB-3200 Criteria are Used to Perform Fitness for Service Assessments of CANDU Outlet Feeders Considering the Pressure & Dead Weight Loading Conditions.

• Linear Elastic Analysis is Performed and the Results are Checked Against the ASME Code Criteria for the Primary Stress (SEC III NB-3221).

• It is Demonstrated that a “Local” Wall Thickness Considerably below the Pressure Based Thickness of the Corresponding Straight Pipe Segment Meets the Requirements of the ASME Code SEC III for the Primary Stresses.

• The Effects of the Extent of the Local Thin Area in the Axial and Circumferential Directions are Explored.

NDE based Detailed FEA Feeder Life Extension

ISI-2010

NDE Based FEA Procedure

NDE Thickness DataIdealized Axial & Circumferential

Wall Thickness Profiles, cEFPY

Detailed FEA Models

Location Dependent Thinning Rate

LE FEA (Pressure & Dead Weight)

ASME

NB-3221?

pEFPY = cEFPY + ΔEFPY

Predicted Axial & Circumferential

Wall Thickness Profiles

Feeder Life ExtensionYes No

ISI-2010

REFERENCES

1. ASME Boiler and Pressure Vessel Code, Section III, “Rules for Construction of Nuclear Power Plants”, 2004.

2. Usama Abdelsalam and Dk Vijay, “Finite Element Modelling of Locally Thinned Short Radius Pipe Bends”, Presented at the 8th International Conference on CANDU Maintenance (CMC2008), Toronto, Ontario, November 16-18, 2008.

3. Usama Abdelsalam and Dk Vijay, “Detailed FEA of Locally Thinned Pipe Bends”, 20th International Conference on Structural Mechanics in Reactor Technology (SMiRT 20), SMiRT20-Division 3, Paper 2575, Espoo, Finland, August 9-14, 2009.

4. Usama Abdelsalam and Dk Vijay, “ASME CODE QUALIFICATION OF PIPE BENDS WITH LOCALIZED WALL THINNING “, Proceedings of the ASME 2010 Pressure Vessels and Piping Division Conference, Paper No PVP2010-25178, July 18-22, 2010, Bellevue, Washington, USA.

5. Usama Abdelsalam, “Application of the ASME Code SEC III Pressure Design Requirements on Locally Thinned Tight Radius Pipe Bends”, Proceedings of the ASME 2010 Pressure Vessels and Piping Division Conference, Paper No PVP2010-25271, July 18-22, 2010, Bellevue, Washington, USA.

Thank YouQuestions?

ISI-2010

The End