DNV GL © 2014 27. august 2014 SAFER, SMARTER, GREENER DNV GL © 2014 Utmatting av buttsveiser i rør – utfordringer og status

27. august 2014

Agnes Marie Horn

Joint Industry Project buttsveis (Girth Weld JIP) - problemstillingen og status

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DNV GL © 2014 27. august 2014

Challenges for deep water

Harsh environment

– severe fatigue loading from waves

– high-cycle fatigue damage due to Vortex Induced

Vibrations (VIV) from water currents at free spans

Large floater motions

Metallic risers for deep Water riser applications

Special concerns: Interface to floater, seafloor

interaction

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DNV GL © 2014 27. august 2014 3

Todays challenge

Riser solutions

Design standards for risers, tendons and pipelines

Overview of JIP FATIGUE OF GIRTH WELDS (PHASE 1)

Summing up

Content

DNV GL © 2014 27. august 2014 4

Steel Catenary Riser (SCR) - Deep water riser concept

Steel pipes can be arranged in free-

hanging configuration for deep water.

Denoted Steel Catenary Risers

Special joints may be applied in touch-

down area to improve fatigue

performance.

Optimization of weight distribution along

riser pipe may be considered to improve

fatigue performance.

Well suited for benign conditions

TLP, Spar or DDF required for large

diameter SCR in harsh environmental

conditions

Fatigue life in

Touch-down

critical design

issue

Flex-joint/

titanium stress-

joint to limit

bending stress

DNV GL © 2014 27. august 2014

Todays challenge; S-N fatigue versus weld acceptance criteria derived from engineering critical assessment (ECA)

.

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Need for high S-N fatigue life: e.g. high quality welds

recent fatigue test results of full scale pipes, seem to indicate that the common S-N curve classification may be unnecessary conservative for some modern high quality weldments

Weld defect acceptance criteria for girth welds are today often determined based on Fracture Mechanics assessment (ECA);

height of the order of 2-4 mm with 25-100 mm in length

predicted fatigue life is usually much shorter than predicted by standard S-N curves, and this is generally believed to be unnecessarily conservative

DNV GL © 2014 27. august 2014

Comparison of S-N and Paris from a case study

01/09

/2014

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DNV GL © 2014 27. august 2014

Objective of the Girth Weld JIP

There is a definite need to better align S-N type analyses, weld

quality/defect acceptance criteria and ECA’s in order to have a

consistent and reliable way of assessing the fatigue life of girth

welded tubulars both at the design stage, when determining

inspection programs and after inspection.

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DNV GL © 2014 27. august 2014

FATIGUE OF RISERS, TENDONS and PIPELINES

Design standards

– DNV-OS-F201 (2010) ‘Dynamic Risers’,

– DNV-RP-F204 (2010) ‘Riser Fatigue’ with ref. to DNV RP-C203

– DNV-OS-F101 (2010) ‘Submarine Pipelines’ 2012

– API RP2RD ‘Design of Risers for Floating Production Systems (FPSs)

and Tension-Leg Platforms (TLPs) ’ (to be harmonized with ISO13628-

12).

– Fatigue lives can either be estimated by S-N or fracture mechanics

approaches

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DNV GL © 2014 27. august 2014

Influencing fatigue factors

Uncertainties occur from both the loading and the resistance assessments.

Weld quality: effect of workmanship, complete joint penetration, internal defects

and welding procedure.

Depending on the welding procedure and quality, S-N curves ranging from F3 up

to C are used in design of girth welds.

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DNV GL © 2014 27. august 2014

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Fatigue of Girth Welds Phase 1

RELATION BETWEEN WELD QUALITY / DEFECT ACCEPTANCE CRITERIA AND

FATIGUE LIFE IN TENDONS, RISERS AND PIPELINES

Cooperation between DNV, Sintef/ NTNU and Stress Engineering Services

Started in 2011 ended in 2012

Phase 1a; Chevron, ExxonMobil, Total, Petrobras, Subsea 7, Tenaris, Woodside, JFE

Steel and Sumitomo

Phase 1b; Chevron, ExxonMobil, Total, Petrobras, Tenaris, Woodside, Statoil and Ptil

DNV GL © 2014 27. august 2014

Fatigue of Girth Welds Phase 1a

To identify the features of girth welds in pipes that on the one hand

influence the fatigue performance and on the other hand can be

controlled and checked to ensure that they are consistent with the

required fatigue performance.

To develop a consistent and reliable methodology for ECAs of girth

welds, quantitatively including the significant fatigue critical features,

with the particular aim of achieving better alignment of the ECA and S-N

curve based approaches for assessing the fatigue performance.

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RE-ASSESSMENT OF

FATIGUE DATA

METHODS FOR CONTROL AND

INSPECTION OF FATIGUE CRITICAL

FEATURES OF GIRTH WELDS.

FATIGUE ASSESSMENT METHODS INCLUDING

INITIATION AND EARLY GROWTH

To develop Design Guidelines for Fatigue Design of Girth Welds,

including calibrated Safety Factors.

DNV GL © 2014 27. august 2014 27. august 2014

01/09/2014 12

0

50

100

150

200

250

300

350

6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 23 24 28 29 32 35

OD/WT

Co

un

t

e.g. 4.5x0.65 inch, 6-5/8x0.9 inch,

8-5/8x1.3 inch

e.g. 6-5/8x0.72 inch, 8-5/8x0.95

inch, 10.75x1.2 inch

Phase 1a Data from just under 1200 weld tests.

1084 full scale tests 109 strip sample tests

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Fatigue Girth weld database phase 1a

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Phase 1a: OD crack failure

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1,20

1,30

1,40

1,50

1,60

1,70

1,80

1,90

2,00

2,10

2,20

2,30

2,40

2,50

2,60

2,70

4,0E+00 4,5E+00 5,0E+00 5,5E+00 6,0E+00 6,5E+00 7,0E+00 7,5E+00

Lo

g(S

)

Log(N)

S-N data

S-N Mean curve

S-N DesigncurveD curve air

E curve air

F1 curve air

m = 3

E[Log10(a)] =12,636

StD[Log10(N)] =0,424

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Phase 1a: ID crack failure

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1,20

1,30

1,40

1,50

1,60

1,70

1,80

1,90

2,00

2,10

2,20

2,30

2,40

2,50

2,60

2,70

5,0E+00 5,5E+00 6,0E+00 6,5E+00 7,0E+00 7,5E+00 8,0E+00

Lo

g(S

)

Log(N)

S-N data

S-N Mean curve

D curve air

F1 curve air

E curve air

S-N design

m =

E[Log10(a)] =

StD[Log10(N)] =

3,000

12,524

0,274

DNV GL © 2014 27. august 2014

OD failure ID failure

ID failure CASE-1 CASE-2

m = 3,000 2,583

E(log10(a)) 12,524 11,698

F curve

E(log10(a))

11,855

StD(log10(N)) 0,274 0,270

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Od failure CASE-1 CASE-2

m = 3,000 3,039

E(log10(a)) 12,636 12,724

D curve

E(log10(a))

12,164

StD(log10(N)) 0,424 0,424

Most of the OD ‘s were ground

Several were reeled

~½ of OD ground

ID/OD ground As-welded

Several were reeled

DNV GL © 2014 27. august 2014

Failed X-70 specimen

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0

5

10

15

20

25

30

35

0 0,2 0,4 0,6 0,8 1 1,2

cra

ck

de

pth

(m

m)

cycles 1=2193704 cycles

surface flaw, X-70

ai=0,09 mm(mean +2stv air)

ai=0.16mm(mean curve air)

Final flaw size from fatigue test measured; 33mmx81,3 mm after 2,19x10^6 cycles Crack growth curve for air according to BS7910 in order to assess the initiation life

Fracture mechanics evaluation

DNV GL © 2014 27. august 2014

Phase 1 b: Quantitative and qualitative safety studies

Alignment and mismatch

Weld quality, weld process, and

backing information

Base and weld metal material

strength

Weld cap and root profiles

Base and weld material chemistry

Residual stresses

Presence of flaws

Effect of reeling

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Status of phase 1b

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Phase 1b Data from just under 1869 weld tests.

1760 full scale tests 109 strip sample tests 250 ID failure 70 OD failure 130 reeled samples

0

50

100

150

200

250

300

350

400

1,00E+05 1,00E+06 1,00E+07 1,00E+08

Str

ess r

an

ge (

Mp

a)

Cycles (N)

Database phase 1b

All fullscale

OD Crack-DNV SCF OD

Stress

ID Crack-Nominal ID Stress

DNV GL © 2014 27. august 2014

Summery

Need for high quality welds in order to meet design

fatigue requirements.

It is necessary to assure that weld quality/defect

acceptance criteria and process control, inspection and

NDT match such that it is possible to reliably assure the

weld features, e.g. weld toe geometry, weld defect

distribution, etc, that will control the fatigue performance.

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