Mechanical Properties of

Structural Steels in Hydrogen

B.P. Somerday, K.A. Nibur, C. San Marchi, and M. Yip Sandia National Laboratories

Livermore, CA

DOE Hydrogen Pipeline Working Group Meeting Aiken, SC

September 25-26, 2007

HHH

d/dt 0

H2H2

Methods for measuring mechanical properties

of structural steels in hydrogen

d/dt > 0 d/dt > 0 strength of materials: UTS, YS, f, RA

H2HH H H2H H2H H2H HH2H H2

fracture mechanics: KIH, KTH

HH H

H H

H H

H

H H

d/dt 0

H

H H

H

H

H HH

H

H

HH H

H

H2H2 H2 H2 H2

H2

Tensile Testing Carbon Steel in H2

Extrusion Direction/ L-C Orientation

T

T

Base HA

Z

Weld

Wel

d

Alloys: 106 Grade B Multi-pass SMAW w/out stress

relief Specimens machined in 3

conditions: Base metal, Weldand HAZ

Orientation: L-C Atmosphere: 10.3 MPa H2,

ambient pressure Air Strain Rate: 10-4 /sec # of samples per matrix point:

6 Argon purge followed by H2

pressurization Soak (30 min.) at pressure Test to failure

Tensile Properties

Mechanical Properties Average Properties

0.2%Yield (MPa)

Dev. UTS (MPa)

Dev. Elong. at

failure

Dev. Reduction of

Area (%) Dev.

Air 355.3 15.8 484.6 8.6 0.29 0.04 68.6 1.5

Bas

e

H2 357.1 32.9 486.4 17.8 0.19 0.04 30.8 5.0

Air 343.0 20.0 490.4 9.0 0.28 0.01 74.9 2.2

Wel

d

H2 350.0 16.1 480.9 12.0 0.21 0.02 30.5 6.4

Air 349.3 20.8 482.3 7.6 0.27 0.04 71.0 1.7

HA

Z

H2 338.2 18.5 475.5 9.6 0.19 0.04 30.4 6.8

Fractography

Fracture Surface

Area

Air Hydrogen HAZ Samples

Reduction of Area reduced when tested in hydrogen

Crack propagation resistance of X100 steel

Alloy composition C Mn Si P S Ti V Ni Cu Mo Cr

0.073 1.86 0.11 0.009

Measurement of sustained-load cracking thresholds

wedge opening load (WOL) cracking threshold specimen

Loading bolt

Load cell

13 mm

strain gage leads (Excitation and DAQ)

Load

(P)

Po Ko

PTH KTH

incubation time= f(environment, Ko)

Time in H2

Specimen loaded to Ko>KTH using bolt while contained in glove box (Ar with ~1 ppm O2)

Loaded specimen exposed to H2, crack extends after incubation time

Crack arrests at K=KTH

High-pressure H2 gas severely degrades crack

propagation resistance of X100 steel

Stre

ss in

tens

ity fa

ctor

, K (

ksii

n1/2)

X100 in air H2 gas pressure (MPa)

0 25 50 75 100 125 150 400

150

KJIc Ko KTH

X100 Steel C-L orientation 25 oC

no crack extension after >1000 hrs

150

100 100

50 50

0 0

1/2 )

Stre

ss in

tens

ity fa

ctor

, K (

MP

am400 350

350 300

300 250

250 200

200

X100 in 15 kpsi H2 gas

0 5 10 15 20 25 H2 gas pressure (kpsi)

Images of fracture surfaces from X100 tested in

H2 show long crack lengths and delaminations

H2-assisted crack extension from precrack

a/W=0.94

http:a/W=0.94

FEM calculations verify K solution and demonstrate

K dominance for long cracks in WOL specimen

a / W = 0.941 KI

VmE / W1/ 2

0.18

0.16

0.14

0.12

0.1

0.08

0.06

0.04

0.02

0 0.5 0.6 0.7 0.8 0.9 1

a / W ASTM E1681: KI = 57.5 MPa m FEM elastic: KI = 63.8 MPa m FEM plastic: J = 16.0 kJ/m2

Calculations by M. Dadfarnia and P. Sofronis JEKIJ = 2 KIJ = 62.2 MPa m1

ASTM E1681

FEM

Incubation time for crack extension depends on Ko

Initial stress intensity factor, Ko (MPam1/2)

0 30 60 90 120 150 2700

0 30 60 90 120 150

cracking in H2 no cracking in H2

X100 Steel WOL specimens 15 kpsi H2 gas 25 oC

no crack extension after >2500 hr

KTH In

cuba

tion

time

(hr)

2400

2100

1800

1500

1200

900

600

Load

(P)

Po Ko

PTH KTH

incubation time

Time in H2 300 0

Initial stress intensity factor, Ko (ksi in1/2)

Measurement of sustained-load cracking threshold in H2 cannot be assured unless crack propagates

Crack branching may account for no crack extension

in specimens with Ko>KTH

Incu

batio

n tim

e (h

r)

SA 372 Gr. J in 15 kpsi H2

Initial stress intensity factor, Ko (MPam1/2)

0 30 60 90 120 150 2700

2400

2100

1800

1500

1200

900 X100 in 15 kpsi H2 600

300

0 0 30 60 90 120 150

Initial stress intensity factor, Ko (ksi in1/2)

precrack

cracks propagated in H2

cracking in H2 no cracking in H2

X100 Steel WOL specimens 15 kpsi H2 gas 25 oC

no crack extension after >2500 hr

KTH

Low-alloy steels for pressure vessels:

sustained-load cracking thresholds in H2 gas

Yield strength, Sy (ksi) 87 92 97 102 107 112 117 122 127 132 137

160

600 650 700 750 800 850 900 950

Cr-Mo Steels WOL specimens

4130 steel

100 MPa H2 gas

25 oC DOT 3AAX

Loginow and Phelps, Corrosion, 1975

4145 steel 4147 steel

SA 372 Grade J

DOT 3T

80 80

60

60

140

140 120

120

1/2 )

(M

Pa

mK

TH

100 100

(ksi

in1/

2 )K

TH

4040

2020

0 0

Yield strength, Sy (MPa)

Thresholds in modern Cr-Mo steels are higher than thresholds in older steels

Stainless steels for piping: tensile fracture results

for specimens precharged in hydrogen gas

316 stainless steels with ~140 wppm hydrogen

Tensile fracture resistance of H-precharged specimens is sensitive to nickel content but not strain hardening

Stainless steels tested in hydrogen gas vs precharged show different tensile fracture behavior

H2 H2

H2

H2 H2

H2

H

H H H

HH

H H

0

20

40

60

80

100R

educ

tion

of A

rea,

RA

(%)

1 1 2

2 3

4

3

4

3

4

Internal Hydrogen 3 - air 4 - H-precharged

External Hydrogen 1 - 69 MPa He 2 - 69 MPa H 2

A-286 San Marchi et al., SAE World Congress, 2007

S (MPa) = 720 850 790 810 810 y

Stable stainless steels may not exhibit loss in RA when strained in H2 due to limited H uptake

System for measuring fatigue crack growth

in high-pressure H2 nearly complete

vessel on mechanical test frame

gas manifold

Pressure vessel can contain H2 gas up to 20 kpsi (138 MPa)

What is metric for qualifying steels for H2 pipelines?

Tech. Ref. Hydrogen Compatibility of Materials, www.ca.sandia.gov/matlsTechRef

10-1

10-2

10-3 X70 (6.9 MPa H2) X42 (6.9 MPa H2) X60 (6.9 MPa H2) A516 (6.9 MPa H2)

10-4 1020 (7.0 MPa H2) SA 105 (6.9 MPa H2) X70 (6.9 MPa N2)

10-5 X42 (6.9 MPa N2) X60 (air) A516 (air) 1020 (air)

10-6 SA 105 (34.5 MPa He)

10-7

Stress intensity factor range, K (MPam1/2) 1 10 100

Fatig

ue c

rack

gro

wth

rate

, da/

dN (

mm

/cyc

le)

Carbon Steels frequency = 0.1 to 1 Hz load ratio = 0.1 to 0.15 Fatigue crack growth rates in

H2 greater than growth rates in air or inert gas

Fatigue crack growth rates in H2 vary by factor of 10

What is acceptable fatigue crack growth rate?

Assess fatigue crack growth data by conducting

fracture mechanics analysis of pipeline

Assume pipeline subjected to pressure cycling

p

Ri Ro

aot

p pR=pmin/pmax~0.1 R=pmin/pmax~0.8 pmax pmax

pmin

pmin time time

Calculate number of pressure cycles for crack to reach critical depth

calculated from threshold for sustained-load cracking, KTH, or fracture toughness, KIH ac

a

ao number of pressure cycles, N Nc

X

calculated from da/dN vs K relationship

Assume steel, dimensions, and maximum

pressure are similar to current H2 pipelines

p

Ri Ro

aot

Data for Air Products H2 pipelines (ASME, Hydrogen Standardization Interim Report, 2005)

API 5L X42 steel, manufactured with ERW Inner radius, Ri = 6.0 in Wall thickness, t, from 0.219 to 0.500 in

Maximum operating pressure, p = 1500 psi

Assume existing defect with depth ao and length parallel to pipeline axis Simulates defect along manufacturing

(seam) weld

Select appropriate material property data Fa

tigue

cra

ck g

row

th ra

te, d

a/dN

(in

/cyc

le)

10-2

Cialone et al., Met Trans A, 1985

10-3

10-4

10-6

10-5 1000 psi H2, R=0.1 1000 psi N2, R=0.1 1000 psi H2, R=0.8 1000 psi N2, R=0.8

10-7

Stress intensity factor range, K (ksiin1/2)

10-8

1 10 100

API 5L X42 Steel frequency = 1 Hz

da/dN=(3.55x10-11)K3.83

da/dN=(2.51x10-12)K6.56

Need da/dN vs K for X42 ERW in 1500 psi H2 gas assume data for 1000 psi H2

gas representative assume data for weld and base

metal are similar Need da/dN vs K at relevant

R ratio and frequency pressure cycling parameters

for pipeline unknown use data at R=0.1 and

frequency=1 Hz Need fracture toughness for

X42 ERW in 1500 psi H2 gas KIH=44 ksiin1/2 for weld HAZ in

1000 psi H2 (Cialone et al., ASTM STP 962, 1988)

Fatigue crack growth rates similar in base

metal, fusion zone, and HAZ for X60 steel

Fatig

ue c

rack

gro

wth

rate

, da/

dN (

mm

/cyc

le)

Wachob, NASA-CR-166334, 1981

10-2

10-3 base metal (6.9 MPa H2) SA weld FZ (6.9 MPa H2) SA weld HAZ (6.9 MPa H2) base metal (air) SA weld FZ (air) SA weld HAZ (air)

10-4

10-5

1/2)Stress intensity factor range, K (MPam

X60 Steel frequency = 1 Hz load ratio = 0.15

1 10 100

Calculate number of pressure cycles to reach

critical crack depth for three cases

cycle 1 cycle 2

p

Ri Ro

aot

K1=f(ao,p,Ro,Ri,t) K2=f(a1,p,Ro,Ri,t) p

1500 psi

150 psi cycles

a=(2.51x10-12)K1 6.56 a1=ao+a

a=(2.51x10-12)K2 6.56 a2=a1+a

ao a1 a2

Case 1: t=0.330 in (h=65% SMYS) and ao/t=0.10

Case 2: t=0.500 in (h=43% SMYS) and ao/t=0.10

Case 3: t=0.500 in (h=43% SMYS) and ao/t=0.05

http:ao/t=0.05http:ao/t=0.10http:ao/t=0.10

0.3

0.7

0.8

Number of pressure cycles vs crack depth

relationships: H2 compared to inert gas

crac

k de

pth

/ wal

l thi

ckne

ss, a

/t

0.6

0.5

0.4

0.2

0.1

0.0 0 50000 100000 150000 200000 250000

hydrogen t=0.50 in h=43% SMYS

nitrogen t=0.50 in h=43% SMYS

X42 Pipeline hydrogen or nitrogen gas pressure cycle = 150 - 1500 psi inner diameter = 12 in

X

X critical crack depth calculated from KIc

critical crack depth calculated from KIH

10-2

Fatig

ue c

rack

gro

wth

rate

, da/

dN (

in/c

ycle

)

10-3

10-4

10-5

10-6

10-7

1 10 100

API 5L X42 Steel frequency = 1 Hz

da/dN=(3.55x10-11)K3.83

da/dN=(2.51x10-12)K6.56

1000 psi H2, R=0.1 1000 psi N2, R=0.1

10-8

number of pressure cycles Stress intensity factor range, K (ksiin1/2)

Number of cycles to critical crack depth reduced

by about factor of 40 in H2 compared to inert gas

0.3

0.7

0.8

Number of pressure cycles vs crack depth

relationships in H2 for varying dimensions

crac

k de

pth

/ wal

l thi

ckne

ss, a

/t

0.6

0.5

0.4

0.2

0.1

0.0 0 5000 10000 15000 20000 25000 30000 35000 40000 45000

case 1 t=0.33 in h=65% SMYS

case 2 t=0.50 in h=43% SMYS

case 3 t=0.50 in h=43% SMYS

X42 Pipeline hydrogen gas pressure cycle = 150 - 1500 psi inner diameter = 12 in

X

X X

critical crack depths calculated from KIH

10-2 API 5L X42 Steel frequency = 1 Hz

1000 psi H2, R=0.1

case 1 initial K

case 2 initial K

case 3 initial K

da/dN=(2.51x10-12)K6.56

10-8

1 10 100 Stress intensity factor range, K (ksiin1/2)number of pressure cycles

Fatig

ue c

rack

gro

wth

rate

, da/

dN (

in/c

ycle

)

10-3

10-4

10-5

10-6

10-7

Number of cycles to critical crack depth is sensitive to applied stress and initial crack depth

http:da/dN=(2.51x10-12)K6.56

ASME applies safety factors on critical crack depth

and number of cycles to critical crack depth

a/ac

1.0

0.25

critical crack depth critical crack depth

M.D. Rana et al., ASME PVP, 2007 cycles to

Safety factors: a/ac = 0.25 N/Nc = 0.5

0.5 1.0 N/Nc

0.500

0.500

0.500

0.330

t (in)

43% SMYS

43% SMYS

43% SMYS

65% SMYS

h

112,545125,2600.10inert

20,69038,7900.05H2

2,6602,7350.10H2

5351700.10H2

0.5 x Nccycles to 0.25 x ac

ao/tEnvironment

Lifetime of steel hydrogen pipeline depends on

both material properties and structural design

Fatigue crack growth law da/dN=CKn in stage II

Fracture toughness or threshold for sustained-load cracking does not significantly affect cycles to critical crack depth

Wall thickness affects stress (K)

Initial crack depth depends on detection limit of NDE

Operating pressure affects stress (K) and material properties

Fatigue crack growth rates depend on

load cycle profile

da/d

N (

mm

/cyc

le)

Walter and Chandler, Effect of Hydrogen on Behavior of Materials, 1976

0.04 SA 105 Steel H2 pressure = 100 MPa K = 44 MPam

0.03 load ratio = 0.1

0.02

0.00 0 200 400 600 800 1000 1200 1400

Seconds Per Cycle

0.01

0.5 sec ramp 100 sec ramp

Mechanical Properties ofStructural Steels in HydrogenMethods for measuring mechanical propertiesof structural steels in hydrogenTensile Testing Carbon Steel in H2Tensile PropertiesFractographyCrack propagation resistance of X100 steelMeasurement of sustained-load cracking thresholdsHigh-pressure H2 gas severely degrades crackpropagation resistance of X100 steelImages of fracture surfaces from X100 tested inH2 show long crack lengths and delaminationsFEM calculations verify K solution and demonstrateK dominance for long cracks in WOL specimenIncubation time for crack extension depends on KoCrack branching may account for no crack extensionin specimens with Ko>KTHLow-alloy steels for pressure vessels:sustained-load cracking thresholds in H2 gasStainless steels for piping: tensile fracture resultsfor specimens precharged in hydrogen gasStainless steels tested in hydrogen gas vs prechargedshow different tensile fracture behaviorSystem for measuring fatigue crack growthin high-pressure H2 nearly completeWhat is metric for qualifying steels for H2 pipelines?Assess fatigue crack growth data by conductingfracture mechanics analysis of pipelineAssume steel, dimensions, and maximumpressure are similar to current H2 pipelSelect appropriate material property dataFatigue crack growth rates similar in basemetal, fusion zone, and HAZ for X60 steelCalculate number of pressure cycles to reachcritical crack depth for three casesNumber of pressure cycles vs crack depthrelationships: H2 compared to inert gasNumber of pressure cycles vs crack depthrelationships in H2 for varying dimensionsASME applies safety factors on critical crack depthand number of cycles to critical crack depthLifetime of steel hydrogen pipeline depends onboth material properties and structural designFatigue crack growth rates depend onload cycle profileFatigue crack growth rates depend onload cycle profile

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