2> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Effect of Bending, Pressure and Tensile Loads on SG Tube Leakage Integrity
Jim Begley
NRC – Washington, DCJuly 12, 2006
3> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Determine the effect bending loads have on the ligament pop-through and crack opening area (leakage) of once-through (straight) and recirculating (U-bend) steam generator tubes with circumferential degradation.
Purpose
4> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Test geometry and parameters simulates actual SG configurations• Similar to those used previously for structural integrity test
program
0.625” OD by 0.037” wall Alloy 600 tubing used
U-bend radius of 36” with 3” straight leg extensions selected to represent RSG outer rows• 36” radius 0.625”OD tube = ~ 50” radius 0.875” OD tube
Straight tube of 45.5” used to represent OTSG upper span
Test boundary conditions (tubesheet, tube support plate) simulate actual plant conditions
Test Parameters
5> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Various magnitudes of circumferential degradation considered• Circumferential extents from 60 to 180 degrees
• Flaw depths from 40% to 90% through-wall
A complete range of potential tube loads were tested• Bending loads equivalent to the limiting design values for the
RSG and OTSG (bending stress < 50 ksi).
• Axial tensile loads up to and exceeding the yield strength of the tubing.
• Pressure loads in excess of the maximum MSLB pressure (2560 psi).
Test Parameters, cont.
6> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Test Equipment
OTSG tube support plate
Camera viewing tube locked into
split block
7> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Test Results
Typical tensile test load-displacement plot (90 degree, 50% tw flaw)
load vs displacement (90/50-1)
0
500
1000
1500
2000
2500
3000
3500
4000
4500
0.00 0.10 0.20 0.30 0.40
displacement (in)
load
(lbs
)
small LVDT
large LVDT
ligament pop-thru
Ligament Pop-Through
8> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Test Results, cont.
Crack Opening vs Load (U-bend 180 deg EDM notch)
COD
No load
2566 psi internal pressure
2566 psi + 12 ksi bending
2566 psi + 19 ksi bending
2566 psi + 27 ksi bending
2566 psi + 34 ksi bending
2566 psi + 41 ksi bending
2566 psi + 49 ksi bending
9> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Test Results, cont
Summary:
> Approximately 50 tests performed for pop-through> Approximately 20 tests performed for COD> Tests performed for straight and u-bend geometries> Tests considered pressure, tensile, and moment
loads> Results show very good trending of all data> Results used to develop analytical models for
ligament pop-through and crack opening displacement
10> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Ligament Pop-Through Analysis
Ligament Pop-Through Modelσσ flowMnom =Generic pop-through equation =
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛−
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛−
=
t
d
tF
d
M
1
1
where:
d/t is the fractional crack depth
σflow = α(σyield + σultimate)
α = 0.6 for pressure and tensile loading
α = 0.72 for bending
11> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
⎟⎟⎠
⎞⎜⎜⎝
⎛+⎟⎟⎠
⎞⎜⎜⎝
⎛+=
tRatR
aF p
m
m 2exp
1125.021312.08875.0
⎟⎠⎞
⎜⎝⎛
⎟⎠⎞
⎜⎝⎛
⎟⎠⎞
⎜⎝⎛
+−+=πθ
πθ
πθ 2
725
23
0.330.155.70.1F f
⎟⎠⎞
⎜⎝⎛
⎟⎠⎞
⎜⎝⎛
⎟⎠⎞
⎜⎝⎛
+−+=πθ
πθ
πθ 2
725
23
0.206.138.60.1Fb
and F = for pressure
for tension
for bending
Ligament Pop-Through Analysis, cont.
Rm = mean radiust = wall thicknessa = one-half crack lengthΘ = one-half crack angle
12> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Ligament Pop-Through Analysis, cont.
Straight Legs, 90 Degree, Uniform Depth Flaws Pop Thru Test Results
0102030405060708090
100
0 10 20 30 40 50 60 70Axial Stress (ksi)
Dep
th (%
tw)
Pressure Loading
Tensile Loading
MSLB Pressure + Bending
Equation Results vs Test Data
13> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Ligament Pop-Through Analysis, cont.
Straight Legs, 180 Degree, Uniform Depth Flaws
Pop Thru Test Results
0102030405060708090
100
0 10 20 30 40 50 60 70 Axial Stress (ksi)
Dep
th (%
tw)
Pressure LoadingTensile Loading
MSLB Pressure + Bending
Equation Results vs Test Data
14> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Ligament Pop-Through Analysis, cont.
Equation Results vs Test Data
Straight Legs and Extrados U-Bends, 90 Degree,
Uniform Depth Flaws, Pop Thru Test Results
010
2030
405060
7080
90100
0 10 20 30 40 50 60 70Axial Stress (ksi)
Dep
th (%
tw)
Straight Legs
Large Radius U-Bends
15> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Ligament Pop-Through Analysis, cont.
Equation Results vs Test Data
Straight Legs and Extrados U-Bends, 180 Degree,
Uniform Depth Flaws, Pop Thru Test Results
0102030405060708090
100
0 10 20 30 40 50 60 70 80 Axial Stress (ksi)
Dep
th (%
tw)
Straight Legs
Large Radius U-Bends
16> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
> Crack Opening Area, COA, and Crack Mouth Opening
Displacement, CMOD, are directly related.
> COA equation for pressure loading can be used for tension and bending loads.
> For bending loads a limiting value of must be applied.
Crack Opening Area Analysis
4LCMODCOA ••= π
( )λλλσπ 432 03.030.081.002.02effeffeff
axm
EtRCOA +++=
σ B
CMOD∆
∆
tR
KL
m
ypeff
2
)/)(/1( 2σπλ
+=
⎟⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜⎜
⎝
⎛
++=)exp(
1125.01312.08875.02
tRLtR
LLK
m
max πσ
17> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Crack Opening Area Analysis cont.
> For straight sections the limiting slope is:
> For large radius U-bends the limiting slope is:
> The angle Φ is the elastic bend angle when a pin connection replaces the crack.
σσ B
m
B
RCMOD Φ=∆
∆ •
σσ B
m
B
RCMOD Φ=∆
∆ •2
18> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Crack Opening Area Analysis cont.
Straight Leg Flaw
0
5
10
15
20
25
30
35
40
0 10 20 30 40 50 60 70
Axial Stress, ksi
CO
D, m
ils
Strraight Leg Flaw, 168 Degree Circumferential Extent
19> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Crack Opening Area Analysis cont.
Large Radius U-Bend and Straight Leg Flaws
0
5
10
15
20
25
30
35
40
0 10 20 30 40 50 60 70
Axial Stress, ksi
CO
D, m
ils
U-Bend Flaw, 179 Degree Circumferential Extent
Strraight Leg Flaw, 168 Degree Circumferential Extent
Equation Results vs Test Data
20> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Crack Opening Area Analysis cont.
Equation Results vs Test Data
Straight Leg Flaw, 95 Degree Circumferential Extent
0
5
10
15
20
25
0 10 20 30 40 50 60 70
Axial Stress. ksi
CO
D, m
ils
21> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Crack Opening Area Analysis cont.
OTSG 180 COA 1 (load cycling, no pressure)
0
5
10
15
20
25
30
35
40
-70 -50 -30 -10 10 30 50 70
stress (ksi)
CO
D (m
ils)
22> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Straight Sections and Small Radius U-Bends, Uniform Depth Flaws, Pressure and Bending
0
10
20
30
40
50
60
70
80
90
100
0 30 60 90 120 150 180 210 240
Total Circumferential Angle, degrees
Deg
rada
tion
Dep
th, %
TW
48,000 psi
28,000 psi
14,000 psi
0 psi
Outer Fiber Bending Stress
23> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Large Radius U-Bends, Uniform Depth Flaws, Pressure and Bending
0
10
20
30
40
50
60
70
80
90
100
0 30 60 90 120 150 180 210 240
Total Circumferential Angle, degrees
Deg
rada
tion
Dep
th, %
TW 28,000 psi
0 psi
14,000 psi
48,000 psi
Outer Fiber Bending Stress
24> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
OTSG Tube Ligament Pop-Through
OTSG Ligament Pop-Through Critical Depths
OTSG Top Span - 90 deg Flaw Pop-Thru Depth(MSLB + SSE)
50
60
70
80
90
100
0 10 20 30 40 50
Elev ation From Upper TSP
Pop-
Thru
Dep
th, %
R<58" R<52" R<48" R<42"
R<33" R<24" R<16"
Secondary face of UTS
25> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Conclusions
> Both ligament pop-through and crack opening displacement test results provide good trending and are acceptable for developing analytical models.
> An analytical approach to address the effects of non-pressure loads on the ligament pop-through of tubing with circumferential degradation has been extended to include tension and bending loads.
> Simplified analytical methods to address the effects of bending loads on crack opening displacement and therefore leakage for tubing containing circumferential degradation have been developed.
> The results of the program and analytical methods are applicable to all sizes and types of domestic steam generator tubing.
26> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Conclusions cont.
Results for bending loads with circumferential degradation• RSGs are affected in high row U-bends
– Only a concern for significant circ cracks on extrados and intrados of tube
• Original design OTSGs are affected in the upper span
• Impact on leakage has been quantified
27> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Conclusions cont.
> Study found, as with SIPC, not a safety issue
Limited to circumferential flawsIndustry has not experienced circumferential degradation capable of leaking in high bending stress areas
> Experimental results to be published in a technical report
> Interim guidance under development based on study results
28> Effect of bending load on leakage integrity of SG tubesAREVA NP Inc.
Conclusions cont.
> Consideration of bending loads does not lead to additional leakage sites.
> The conclusions of current leakage assessment methodologies dealing with pressure and axial force loading remain valid.
> At present there have been no observed circumferential degradation sites that are both capable of leaking and located in high bending stress regions