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Fatigue Performance of High Strength Riser Materials
RPSEA Project No. DW 1403
PWC Web MeetingNovember 6, 2009
Prepared byStephen J. Hudak, Jr. and James H. Feiger
Materials Engineering DepartmentSouthwest Research Institute
Research Partnership to Secure Energy for America
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Meeting Objective Review variable frequency test data Select test protocol for future testing
• Fatigue Crack Growth Rates (FCGR)• Classical S-N fatigue life
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MaterialsMaterial YS: min/meas Sour Status
1 110/123 ksi yes frequency-scan complete;Fatigue testing underway
2 125/137 ksi yes frequency-scan completeFatigue testing underway
3 125/134 ksi yes Received material this quarter;Specimen machining completeFrequency-scan complete
4 125/132 ksi no frequency-scan complete;Fatigue testing underway.
5 125/163 ksi no Frequency-scan complete;Fatigue testing underway
6 114 ksi yes S-N specs. MachinedFreq-Scan tests underway
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Environments Lab air (baseline): 70-75°F, 40-60% RH
Seawater: ASTM D1141 substitute ocean water open to the air with cathodic protection: - 1050mv vs. Saturated Calomel Electrode
Sour Brine: Production brine with oxygen below 10 ppb and 35% H2S + 65% CO2
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Background: Freq. Dependence Complex at Low DK
Region IIClassicalFreq. Effect
Region IInverseFreq Effect
Mod 4130 Steel: YS=98ksiSour Environment
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Inverse Freq. Effect at Low DK Due to Corrosion-Product Wedging
d=1/p (Kmax/E sys)2
DK, ksiin1 10 100
da/d
N, i
n./c
ycle
10-9
10-8
10-7
10-6
10-5
10-4
10-3
SeawaterLab Air (2 Tests)
YS = 114 ksiSeawater and Lab AirKmax = 44 ksiinC = -6 in-1 0.01 Hz
0.17 Hz
1 Hz
123 ksi Steel in SW+CP vs. Lab AirFrequency Schedule 1
DK, ksiin1 10 100
da/d
N, i
n./c
ycle
10-9
10-8
10-7
10-6
10-5
10-4
10-3
SeawaterLab Air (2 Tests)
YS = 114 ksiSeawater and Lab AirKmax = 44 ksiinC = -6 in-1
0.01 Hz
0.17 Hz
1 Hz
123 ksi Steel in SW+CP vs. Lab AirFrequency Schedule 2
DK, ksiin1 10 100
da/d
N, i
n./c
ycle
10-9
10-8
10-7
10-6
10-5
10-4
10-3
SeawaterSeawaterLab Air (2 Tests)
YS = 114 ksiSeawater and Lab AirKmax = 44 ksiinC = -6 in-1 0.01 Hz
0.17 Hz
1 Hz
0.01 Hz
0.17 Hz
1 Hz
123 ksi Steel in SW+CP vs. Lab AirSchedule 1 vs Schedule 2
DK, ksiin1 10 100
da/d
N, i
n./c
ycle
10-9
10-8
10-7
10-6
10-5
10-4
10-3
Sour BrineLab Air (2 tests)
YS = 114 ksiSour Brine and Lab AirKmax = 44 ksiinC = -6 in-1 0.01 Hz
0.17 Hz
1 Hz
123 ksi Steel in Sour Brine vs. Lab AirFrequency Schedule 1
DK, ksiin1 10 100
da/d
N, i
n./c
ycle
10-9
10-8
10-7
10-6
10-5
10-4
10-3
Sour BrineLab Air (2 tests)
YS = 114 ksiSour Brine and Lab AirKmax = 44 ksiinC = -6 in-1
0.01 Hz
0.17 Hz
1 Hz
123 ksi Steel in Sour Brine vs. Lab AirFrequency Schedule 2
DK, ksiin1 10 100
da/d
N, i
n./c
ycle
10-9
10-8
10-7
10-6
10-5
10-4
10-3
Sour BrineSour BrineLab Air (2 tests)
YS = 114 ksiSour Brine and Lab AirKmax = 44 ksiinC = -6 in-1 0.01 Hz
0.17 Hz
1 Hz
0.01 Hz
0.17 Hz
1 Hz
123 ksi Steel in Sour Brine vs. Lab Air
Schedule 1 vs Schedule 2
123 ksi Steel in Sour Brine vs. Lab Air
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Test Frequency Options Replicate tests using Frequency Schedule 1
• Advantage: closest to service conditions• Disadvantage: may be non-conservative, and increases
test duration Replicate tests using Frequency Schedule 2
• Advantage: provides conservative results, and decreases test duration
• Disadvantage: may not be best representation of riser loading frequency – i.e. damage may be too conservative
One test each at Frequency Schedules 1 and 2• Advantage: Defines effect of frequency on fatigue damage• Disadvantage: no test replication
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Project Schedule Complete FCGR testing: 4-6 months
Complete S-N testing: 12-14 months• Total Material-Envirs. 9 (including added sour tests• Completed Mat-Envirs. 1• Remaining Mat-Envirs. 8• Remaining machine time: 48 Months• Remaining calendar time: 12-14 months (4 test machines)
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Other Issues1. Higher strength materials exhibiting signs of
SCC in both sour brine and SW+CP• Recommend adding selected SCC tests• Formulating Workscope and cost estimate for SCC
testing2. Need to add funding for additional sour
brine testing identified at kick-off meeting• Total cost = testing cost – savings on air tests being
conducted at NETL• Formulating workscope and cost estimate for these addition
sour brine tests.• Source of cost sharing: donated materials?
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Seawater vs. Sour Brine
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YS = 132 ksi
Crack Length, in.0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
da/d
N, i
n./c
ycle
10-6
10-5
10-4
10-3
10-2
10 Hz - air10 Hz - seawater1Hz - seawater0.33 Hz - seawater0.1 Hz - seawater0.01 Hz - seawater
YS = 131 ksiSeawaterDK=20 ksiinR=0.5
Seawater
15X
Crack Length, in.0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
da/d
N, i
n./c
ycle
10-6
10-5
10-4
10-3
10-2
10 Hz - air10 Hz - sour brine1Hz - sour brine0.33 Hz - sour brine0.1 Hz - sour brine0.01 Hz - sour brine
YS = 131 ksiSour BrineDK=20 ksiinR=0.5
250X
Sour Brine
Backup Slides
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FCGR Specimen
Crack Length, in.0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
da/d
N, i
n./c
ycle
10-6
10-5
10-4
10-3
10-2
10 Hz - air10 Hz - seawater1Hz - seawater0.33 Hz - seawater0.1 Hz - seawater0.01 Hz - seawater
YS = 132 ksiSeawaterDK=20 ksiinR=0.5
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Frequency Scan Testing
Corrosion fatigue performance sensitive to loading frequency
Fatigue crack growth rates at constant-DK used to characterize frequency effect in frequency scan (FS) tests
13x
Seawater
Seawater vs. Sour Brine
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Crack Length, in.0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
da/d
N, i
n./c
ycle
10-6
10-5
10-4
10-3
10-2
10 Hz - air10 Hz - seawater1Hz - seawater0.33 Hz - seawater0.1 Hz - seawater0.01 Hz - seawater
YS = 114 ksiSeawaterDK=20 ksiinR=0.5
6X
Seawater
Crack Length, in.0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
da/d
N, i
n./c
ycle
10-6
10-5
10-4
10-3
10-2
10 Hz - air10 Hz - sour brine1Hz - sour brine0.33 Hz - sour brine0.1 Hz - sour brine0.01 Hz - sour brine
YS = 114 ksiSour BrineDK=20 ksiinR=0.5
24X
Sour Brine
YS = 114 ksi
Frequency Response vs. YS
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Cyclic Frequency, Hz0.01 0.1 1 10
Aver
age
da/d
N, i
n./c
ycle
10-6
10-5
10-4
10-3
10-2
Sour BrineDK = 20 ksiinR=0.5
green: YS = 131 ksiblue: YS = 114 ksi
Sour Brine
Air Baseline
Cyclic Frequency, Hz0.01 0.1 1 10
Aver
age
da/d
N, i
n./c
ycle
10-6
10-5
10-4
10-3
10-2
SeawaterDK = 20 ksiinR=0.5
green: YS = 131 ksiblue: YS = 114 ksi
Seawater
Air Baseline
Yield Strength, ksi
114 131 132
Material-Environment Interactions
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Environment:
Sour Brine
Seawater
24X 250X --- 6X 15X 15X
Corrosion-Fatigue Acceleration* vs. Air Baseline
* At DK= 20 ksi√in. R=0.5 and Frequency = 0.01 Hz
