del2fatiguecapacityjipodaugust2004

8/19/2019 del2fatiguecapacityjipodaugust2004

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Fatigue lives for the ballast condition

0 100000 200000 300000 400000 500000 600000 700000 800000 900000 1E+06

1

2

3

4

5

T e s t s p e c i m e n n o

Fatigue life (Number of cycles)


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Loaded and ballast for the same load range

0 1000000 2000000 3000000 4000000 5000000 6000000 7000000

1

2

S p e c i m e n n o

Fatigue life (Number of cycles)


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Reduction factor from test and design curve

0

0.2

0.4

0.6

0.8

1

1.2

-1 -0.5 0 0.5 1

Mean stress per stress range

R e d u c t i o n f a c t o r o n

s t r e s s r a n g e

Curve for design used by one

Classification Company

Compressive stress

at hot spot

Full scale fatigue

test result


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Geometry of ISSC specimen

Investigated

hot spot area


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Specimens tested by HHI

1

54

32

1

54

32


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Description of accuracy of FE analyses

• Good: Within +10 and –

5% of target value

• Acceptable: Within +20

and –10 %

• Conservative: More than+ 20% ( C)

• Non-conservative: Less

than –10 % (NC).

(A lower S-N curve may beconsidered used)

NC

Good

Acceptable

C


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Hot spot stress by 0.5t/1.5t using 4 node shell elements

S-N curve: FAT90

Specimen Company 0.5t x 0.5t t x t 2t x 2t 4t x 4tISSC NTNU Good Good NC (-17%)

ISSC LR Good

ISSC ABS Acceptable-

ISSC BV(2) Good

HHI 1 HHI Acceptable+

HHI 1 DNV C C Acceptable+

HHI 2 LR Good

HHI 2 HHI Good

HHI 2 BV(2) Good

HHI 2 DNV Good Good NC (-15.2%)HHI 3 HHI Good

HHI 3 DNV (1) Good Good Good

HHI 3 DNV (2) Good Good Good

HHI 4 LR C

HHI 4 HHI C

HHI 4 ABS C

HHI 4 BV (2) C

HHI 4 DNV C C C Good

HHI 5 LR C

HHI 5 HHI CHHI 5 BV (2) C

HHI 5 DNV C C Good

GL DP LR Good

GL DP BV (2) Good

DNV SND DNV C C C

Mesh Size


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Hot spot stress by 0.5t/1.5t using 8 node shell elements

S-N curve: FAT90

Specimen Company 0.5t x 0.5t t x t 2t x 2t 4t x 4tISSC NTNU NC (-18%) Acceptable- Acceptable- NC (-17%)

ISSC GL Good

ISSC AMT NC (-10.5%)

ISSC BV Acceptable-

ISSC BLU Acceptable-

HHI 1 DNV C C Good

HHI 2 GL Good

HHI 2 BV Good

HHI 2 DNV Good Good NC (-15.7%)

HHI 3 DNV (1) Good Good GoodHHI 3 DNV (2) Good Good Good

HHI 4 GL C

HHI 4 BV C

HHI 4 UM C

HHI 4 DNV C C C Good

HHI 4 NUS C C C

HHI 5 GL Good

HHI 5 BV C

HHI 5 BLU GoodHHI 5 DNV Acceptable+ C Good

GL DP BV Acceptable+

GL DP BLU Good

GL DP NUS Acceptable+ Acceptable+ Acceptable+

DNV SND DNV C C C

Mesh Size


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Hot spot stress by 0.5t/1.5t using 3D elements

S-N curve: FAT90

Specimen Company 0.5t x 0.5t t x t 2t x 2t 4t x 4t

ISSC NTNU Acceptable+

ISSC GL Good

ISSC NUS Good

HHI 2 GL Good

HHI 2 ABS Good

HHI 2 HHI Acceptable-

HHI 2 UM (1) Good

HHI 2 UM (2) Good

HHI 2 NUS NC (-12.2%)HHI 3 DNV Acceptable- Acceptable-

HHI 4 GL Acceptable+

HHI 4 HHI Acceptable+

HHI 4 UM C

HHI 4 NUS Good

HHI 4 DNV Acceptable+ C Good

HHI 5 GL Good

HHI 5 AMT Good

HHI 5 HHI Good

HHI 5 DNV Good Acceptable+GL DP GL Good

GL DP AMT Good

GL DP ABS Good

GL DP NUS Acceptable+ Acceptable+ Good

DNV SND DNV Acceptable- NC (-11.5%)

Mesh Size


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Different hot spot positions

c

c

b

a


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Stress extrapolation in a three-dimensional FE model


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Stress extrapolation in a three-dimensional FE model


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Conclusions fatigue crack growth from weld toes

The project has provided:

• Small scale and full scale S-N data for a large

number of typical welded connections in ships and

FPSOs.

• Improved information on the important link

between finite element analyses and S-N data.

• Recommendations on finite element modeling and

derivation of hot spot stress.


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Sketch of fillet weld connection with symbols

Tht

a

L

PTh

t

a

L

P σ ττ

Throatsection


16/30

Fillet welded tubular test specimen

Test fillet weld

Fixture plate

Full pen. weld

Test pipe (Ø7")

40

40

180

Ø

2 6 0 ± 0 . 5

Fixture plate

5

FULL PEN.

Ø32

Ø7" (177.8mm)

Ø350

12.5

+0-1

4 5 ° T Y P .

4Test fillet weld

Fixture plate

Full pen. weld

Test pipe (Ø7")

40

40

180

Ø

2 6 0 ± 0 . 5

Fixture plate

5

FULL PEN.

Ø32

Ø7" (177.8mm)

Ø350

12.5

+0-1

4 5 ° T Y P .

4


17/30

Sketch of the rig used to test tubular specimens

Front view:

100 t

actuator

Specimen

Top view

600 600 600

6 0 0

600600600

25 t

actuator

25 t

actuator

600

600

1

2

3

5

4

Test

weld

5 2 SUPORT ASSEMBLY

4 1 SUPORT PLATE, 25t 350x350x100 ST52-3N or equivalent

3 1 MOMENT ARM 950x400x100 ST52-3N or equivalent

2 1 PIPE OD=177.8, WT=12.5, L=110 ST52-3N or equivalent

7 5 0

Fmax ≈ 500kN∆ ≈ 2 mm

Fmax

≈ 150kN∆ ≈ 2 mm

Front view:

100 t

actuator

Specimen

Top view

600 600 600

6 0 0

600600600

25 t

actuator

25 t

actuator

600

600

1

2

3

5

4

Test

weld

5 2 SUPORT ASSEMBLY

4 1 SUPORT PLATE, 25t 350x350x100 ST52-3N or equivalent

3 1 MOMENT ARM 950x400x100 ST52-3N or equivalent

2 1 PIPE OD=177.8, WT=12.5, L=110 ST52-3N or equivalent

7 5 0

Fmax ≈ 500kN∆ ≈ 2 mm

Fmax

≈ 150kN∆ ≈ 2 mm


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Test rig


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Test specimen in the test rig


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DNV-RP-C203 and NS 3472

0

50

100

150

200

250

0 50 100 150 200 250 300 350

Parallel shear stress (MPa)

E n g i n e e r i n g s h e

a r s t r e s s ( M P a )

DNV Mean

DNV Design

R = -1

R = 0

R = 0.4

R = -1 x2 (24)


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Background

Alexander Kielland

Brace Hydrophone holder


22/30

Publication of results for fillet welds

• Lotsberg, I. (2004), “Fatigue Design of Welded Pipe

Penetrations in Plated Structures”.

Marine Structures, Vol 17/1 pp. 29-51.

• Maddox, S. “Status Review of the Fatigue

Assessment of Fillet Welds”.To be published in International Journal of Fatigue.

• Lotsberg, I. “Fatigue Capacity of Fillet Welded

Connections subjected to Axial and Shear Loading”.

To be published in International Journal of Fatigue.


23/30

Fatigue testing performed at TUHH


24/30

Potential fatigue cracks at cope holes at block welds

B

B

B - B

Potential

crack areas

Longitudinal

Plate


25/30

Fatigue analysis methodology


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Loading andanalysis nominal

stress:

CoV = 15 - 20 %

Hot spot stress:CoV = 5 - 10 %

S-N data

Log s = 0.20

Miner sum

CoV = 0.30

11 %

41 %

39 %

9 %

Contributing parameters to fatigue failure


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Accumulated probability of fatigue crack

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0 50 100 150 200

Time in service (years)

A c c

u m u l a t e d p r o b a b i l i t y o f f a t i g u e f a i l u r e

Uncertainty in S-N-Curve only

Uncertainty in S-N, Miner,CoVnom = 0.15, CoVhs = 0.05

Uncertainty in S-N, Miner,CoVnom = 0.20, CoVhs = 0.05

Uncertainty in S-N, Miner,

CoVnom = 0.15, CoVhs = 0.10Uncertainty in S-N, Miner,CoVnom = 0.20, CoVhs = 0.10


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Accumulated probability of fatigue crack

0.0000001

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

0 2 4 6 8 10 12 14 16 18 20

Time in service (years)

A

c c u m u l a t e d p r o b a b i l i t y o f f a t i g u e f a i l u r

Unc. in S-N curveonly

Unc. in S-N, Miner,CoVnom = 0.15,CoVhs = 0.05





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Conclusions fatigue crack growth from weld root

• Design criteria have been established for fatigue

crack growth from the root of fillet welds in

typical details in FPSOs:

Ø fillet welds around attachments

Ø fillet welds around pipes penetrating deck plates.


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Closure

• This JIP has been strongly supported by the industry

• More than 30 papers from Phase I and II published atinternational conferences and in journals.

• The design recommendations from the project is

being included in revised guidelines.• Revision of DNV-RP-C203 ”Fatigue Strength

Analysis of Offshore Steel Structures”dated November 2004.

• Use the technology and perform fatigueassessment of important detai ls!

Documents

del2fatiguecapacityjipodaugust2004