Effect of Bending, Pressure, and Tensile Loads on SG Tube ...

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


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


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


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.


Test Equipment

OTSG tube support plate

Camera viewing tube locked into

split block


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


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







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


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


⎟⎟⎠

⎞⎜⎜⎝

⎛+⎟⎟⎠

⎞⎜⎜⎝

⎛+=

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



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



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





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




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


> 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


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



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



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





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



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)


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


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


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


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.


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


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


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

Effect of Bending, Pressure, and Tensile Loads on SG Tube ...

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