hydrogen-assisted fracture: materials testing and ......• wol and dcb specimens displacement...
TRANSCRIPT
![Page 1: Hydrogen-Assisted Fracture: Materials Testing and ......• WOL and DCB specimens displacement loaded in air –Nelson, ASTM STP 543, 1974 →H 2 dissociation may govern crack extension](https://reader035.vdocument.in/reader035/viewer/2022081601/61199536236ef61b444ee4dc/html5/thumbnails/1.jpg)
Hydrogen-Assisted Fracture: Materials Testing and Variables Governing Fracture
Brian Somerday, Chris San Marchi, and Dorian BalchSandia National Laboratories
Livermore, CA
Hydrogen Pipeline Working Group WorkshopAugusta, GA
August 30-31, 2005
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SNL has 40+ years experience with effects of high-pressure hydrogen gas on materials
• Design and maintenance of welded stainless steel pressure vessels for containment of high-pressure H2 isotopes– Extensive testing of stainless steels exposed to high-pressure
H2 gas
• Six-year program in 1970s focused on feasibility of using natural gas pipeline network for H2 gas– Materials testing in high-pressure H2 gas using laboratory
specimens and model pipeline– Examined fusion zone and heat affected zones of welds
• Active SNL staff have authored 70+ papers and organized 6 conferences/symposia on H2 effects in materials– Seventh conference on Hydrogen Effects on Material Behavior
scheduled for Sept. 2008 at Jackson Lake Lodge, Wyoming
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SNL/CA has capabilities for producing both strength of materials and fracture mechanics data
HH
HH
HH
dδ/dt > 0
strength of materials:σUTS, σYS, εf, RA
H2H2H2H2
H2
H2
H2
H2
HHH
H H
H H
HH
H
dδ/dt ≥ 0
fracture mechanics:KIH, KTH
δ = constant
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Thermal charging of specimens in H2 gas
• Two high-temperature charging stations– temperatures up to 300 oC (572 oF)– pressures up to 138 MPa (20 ksi)– two to four A286 primary vessels in 304 secondary containment– H concentrations from 7,000 to 15,000 appm in stainless steels
• Specimens – compact tension and 3-pt bend fracture mechanics (KIH)– smooth and notched tensile (σUTS, σYS, εf, RA)
• Dedicated 90 kN (20 kip) servo-hydraulic load frame for rising displacement testing
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Measurement of KTH in high-pressure H2 gas
• Five stations for testing in high-pressure H2 gas– pressures up to 200 MPa (29 ksi)– room temperature– A286 primary vessels in
304/321 containment
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Measurement of KTH in high-pressure H2 gas:instrumented WOL and DCB specimens
• WOL specimens– procedures follow ASTM E1681-99– constant displacement with
instrumented load cell– strain gages yield load vs. time:
crack advance → load drop → K drop– crack arrests when K = KTH (load
constant with time)• DCB specimens
– procedures follow NACE TM0177-96– constant displacement from wedge– strain gage signals crack initiation
and arrest– crack arrests when K = KTH (strain
gage signal constant)
Loading bolt
Load cell
strain gage leads (Excitation and DAQ)
0.5 in
strain gage
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Measurement of KTH in high-pressure H2 gas: test assembly
• Up to 4 WOLs in each cradle– 2 cradles/vessel
• Up to 8 DCBs in each modified cradle– 1 cradle/vessel
• Displacement loading applied in air
Test durations can be 1000+ hours for both stainless steels and ferritic steels
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Measurement of KTH in high-pressure H2 gas: environmental chamber
• Temperatures– +175 oC to -75oC (-347 oF to -103 oF)
• Pressures– 200 MPa (29 ksi) below room
temperature– 138 MPa (20 ksi) above room
temperature
• Capacity– one test vessel (8 WOLs or 8 DCBs)
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Tensile tests with internal hydrogen
0
200
400
600
800
1000
1200
1400
316 SS13.5Ni, 0.3Mn
316 SS12.1Ni, 1.7Mn
316 SS11Ni, 1.3Mn
duplex stainless25Cr, 6.9Ni, 0.5Mn
0
50
100
150
200
Stre
ss, S
y, Su (M
Pa) Elu and R
A (%
)
Elu
RA
Sy
Su
1- tested in air2- H-precharged, tested in air
strain-hardened bar stockH-precharging = 138 MPa H
2, 573 K, 10 days
12
12
12
12
HH
HH
HH
dδ/dt > 0
• Materials– Forged 22Cr-13Ni-5Mn and 21Cr-6Ni-9Mn stainless steels– Cold-worked and annealed 316 stainless steel– Cold-worked and annealed SAF 2507 duplex stainless steel– X-70 and X-80 pipeline steels
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Fracture toughness tests with internal hydrogen
∆a (mm)0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
J (k
J/m
2 )
0
50
100
150
200
250
300
350670 MPa σYS - uncharged780 MPa σYS - uncharged670 MPa σYS - H2 charged780 MPa σYS - H2 charged
22-13-5 forgingsCT specimenslongitudinal25oC
HHHH H
H H
HHH
dδ/dt > 0
• Materials– Forged 22Cr-13Ni-5Mn and 21Cr-6Ni-9Mn stainless steels– Cold-worked 316 stainless steel– Cold-worked SAF 2507 duplex stainless steel– Stainless steel welds
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Calculations involving high-pressure H2must consider fugacity
0
100
200
300
400
500
0 50 100 150 200
ideal gasT = 273 K 298 K 373 K 473 K 573 K 673 K 773 K
Fuga
city
, f
Pressure (MPa)
f = P exp(bP/RT)
b = 15.55 cm3/mol
H concentration diffusional flux
21exp
fl
RTH
Jo ⎟
⎠⎞
⎜⎝⎛ −Φ
=
Φ
∞2/1exp f
RTH
K so ⎟
⎠
⎞⎜⎝
⎛ ∆−=χ
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Crack growth threshold tests in hydrogen gas
Ni Cr Mo C Mn Si S P
VM 4340 1.81 0.84 0.27 0.41 0.82 0.29 0.001 0.004
AM 4340 1.71 0.82 0.21 0.41 0.75 0.22 0.007 0.012
SA 372 Gr. J - 0.96 0.18 0.48 0.92 0.30 0.002 0.010
Quenched and tempered low-alloy steels
Material σYS(MPa)
H2(MPa)
Ko(MPa√m)
KTH(MPa√m)
Initiation time (hrs)
VM 4340 862 100 40-60 29-34 65VM 4340 862 40 40-60 - >500VM 4340 600 100 50-75 - >350VM 4340 600 40 70-80 - >500AM 4340 828 100 40-60 - >5000AM 4340 828 130 40-60 35-37 1800
SA 372 Gr. J 718 80 35-105 - >5000
Summary of tests
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KTH measurements for 4340 compared to literature data
H2 gas pressure (MPa)0 30 60 90 120 150
KTH
(M
Pa√
m)
0
30
60
90
120
150
180
H2 gas pressure (ksi)0 5 10 15 20
KTH
(ks
i√in
)
0
20
40
60
80
100
120
140
160Pressure Vessel Steels4147 steel (σYS=869 MPa [126 ksi])4147 steel (σYS=780 MPa [113 ksi])
vacuum-melted 4340σYS=862 MPa
air-melted 4340σYS=828 MPa
data from Loginow and Phelps, Corrosion, 1975
Initial KTH measurements for modern “clean” steels are similar to data for older steels
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Complications testing pressure vessel steels
• Time for initial crack extension in H2 gas varies widely– 65 hrs for VM 4340 vs >5000 hrs for AM 4340 in same test vessel– H2 gas purity important
• W.T. Chandler and R.J. Walter, ASTM STP 543, 1974
– surface oxides important• WOL and DCB specimens displacement loaded in air
– Nelson, ASTM STP 543, 1974 → H2 dissociation may govern crack extension in 4130 steel
• Long cracks complicate KTH measurement in constant-displacement tests– a/W ≥ 0.8 in VM 4340 WOL specimens
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H2 gas analysis in crack growth system
O2 (ppm) H2O (ppm) N2 (ppm) CO (ppm) CO2 (ppm) THC (ppm)
99.9999% H2 spec.
<0.05 <0.5 <0.2 <0.01 <0.02 <0.01
manifold 0.2 <0.5 2 <0.1 <0.1 <0.1
manifold + mol. sieve
0.5 <0.5 2 <0.1 <0.1 <0.1
Gas sampling after H2 flow through manifold
O2 (ppm) H2O (ppm) N2 (ppm) CO (ppm) CO2 (ppm) THC (ppm)
99.9999% H2 spec.
0.1 0.16 0.32 <0.02 <0.02 <0.01
manifold + vessel
0.3 2 2 <0.1 <0.1 0.8
Gas sampling after H2 flow through manifold + pressure vessel
O2 (ppm) H2O (ppm) N2 (ppm) CO (ppm) CO2 (ppm) THC (ppm)
Loginow & Phelps
<5 50 1000 n/a <10 n/a
Walter & Chandler
<0.2 ~1 0.6-0.9 <0.5 <0.5 <0.5
Gas compositions from other laboratories
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Preclude surface oxide effect with glovebox
Loading crack in air Loading crack in glovebox
Exposure to hydrogen gasExposure to hydrogen gas
H2H2 H2H2 H2
HH HH
H2H2 H2H2 H2
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Long cracks result in elevated KTH measurements
0
1000
2000
3000
4000
5000
6000
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Front face COD (mm)
Load
(N)
BC (a/W = 0.559)BC (a/W = 0.893)BD (a/W = 0.571)BD (a/W = 0.795)
crack closure
Measured load vs. COD for WOL specimens
KTH = Kmeas + Kcl
4340 specimen
Initial K (MPa√m)
KTH (MPa√m)meas. load
61 56
VM (BD) 43 46 29
AM (AC) 40 37 37
AM (AD) 62 47 35
KTH (MPa√m)minus closure
VM (BC) 34
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H2-assisted fracture depends on environment: hydrogen source
HHHH H
H H
HHH
dδ/dt > 0
H2H2H2
H2
δ = constant
HH
IN-903
Data from: N.R. Moody et al., Hydrogen Effects on Material Behavior, 1990
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H2-assisted fracture depends on environment: gas purity
Data from: H.H. Johnson, Fundamental Aspects of Stress Corrosion Cracking, 1967
H-11 steel
H2H2
H2
H2H2H2
H2 HH
Data from: M.O. Speidel, Hydrogen Embrittlementand Stress Corrosion Cracking, 1984
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H2-assisted fracture depends on environment: gas purity
• Impurities such as O2 preferentially adsorb on clean metal surfaces → inhibits adsorption of H2
– limits H uptake at crack tip
• Effect of O2 may depend on absolute partial pressure– effect of O2 may be observed at lower concentrations for
higher H2 pressures
• Other impurities may have same effect as O2
– SO2, CO, CS2, CO2
• Resource: ASTM STP 543, 1974
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H2-assisted fracture depends on material: composition
4340 (σYS = 1450 MPa)
H2H2H2
H2
δ = constant
HH
Data from: N. Bandyopadhyay et al., Metallurgical Transactions A, 1983
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SUMMARY
• SNL can characterize hydrogen effects on materials using strength of materials and fracture mechanics approaches
– thermal charging of test specimens using high-pressure H2
– static loading of test specimens in high-pressure H2
• SNL has active programs testing materials in high-pressure H2
– pressure vessel steels and stainless steels
• Numerous variables impact hydrogen-assisted fracture of structural materials
– environmental variables– material variables– mechanical variables