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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
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.
ISI-2010
Objective
Typical CANDU Reactor Face
ISI-2010
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
ISI-2010
Introduction
Typical CANDU Reactor Horizontal Feeders Row
ISI-2010
Introduction
Typical Horizontal Feeders’ Row – Tight Radius Bends
NDE Axial & Circumferential Thickness Data
ISI-2010
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
ISI-2010
Finite Element Model
Location Dependent Thinning Rate
ISI-2010
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
ISI-2010
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
ISI-2010
Acceptance Criteria
ISI-2010
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)
ISI-2010
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