Sand Numberr 2010-6416C 1

Hydrogen Effects on Materials

for CNG / H2 Blends

Brian Somerday*, David Farese** and

Jay Keller* (Presenting)

*Sandia National Laboratories, USA, **Air Products, USA

Presented at the

International Hydrogen Fuel and Pressure Vessel

Forum 2010

Beijing, China

September 28, 2010

Sand Numberr 2010-6416C 2

Issue: Can existing CNG on-board storage tanks be used for HCNG?

What are considerations for

• Type 1, 2, 3, 4 tanks?

• 20% H2 and less?

• higher than 20% H2?

Type 3 and Type 4 are likely fine

• Comments from manufacturers

Concern is primarily for steel Type 1 and Type 2 tanks

• Commonly designed and manufactured according to

NGV-2 and ISO 9809-1

Sand Numberr 2010-6416C 3

a

Number of pressure cycles, N

crack in H2 or HCNG

crack in CNG

Dp a

H2 H2 H2

H2

What is the concern for steel HCNG storage tanks?

H2-assisted fatigue cracking

Barthélémy, 1st ESSHS, 2006

H2 cylinder

Sand Numberr 2010-6416C 4

No concerns for HCNG in steel storage tanks if material strength is limited

H2 compatibility of Cr-Mo steel cylinders designed to

ISO 9809-1 demonstrated through service experience

• Example: typical duty cycle for steel H2 trailer tubes in USA

H2 pressure ~20 MPa

pressure cycles ~2/week (50 year life)

• Such service conditions bound the H2 partial pressure and

number of pressure cycles for steel HCNG storage tanks

• H2 transport cylinders must have tensile strength < 950 MPa

All HCNG blends expected to be compatible with steel

CNG tanks provided tensile strength < 950 MPa

But CNG tanks designed to ISO 9809-1 allow tensile

strength up to 1100 MPa

Sand Numberr 2010-6416C 5

Issue: H2-assisted fatigue cracking enhanced in higher strength steel

H2

H2

H2

H2H2

H2

H2H

HH

load

aH2

H2

H2

H2H2

H2

H2H

HH

load

a

R. Irani, ISO/TC 58/WG 7 workshop, 2008

950 MPa

strength

Sand Numberr 2010-6416C 6

ISO 11114-4 addresses H2 compatibility of steel cylinders with strength > 950 MPa in two ways

According to ISO 11114-4, cylinders may be designed to ISO 9809-1 (i.e., with strength up to 1100 MPa) “if at least one of the following conditions for intended gas service is fulfilled:

• the working pressure of the filled embrittling gas is less than 20% of the test pressure of the cylinder

• the partial pressure of the filled embrittling gas of a gas mixture is less than 5 MPa (50 bar) in the case of hydrogen…”

Based on ISO 11114-4, CNG tanks are suitable for

HCNG blends with <20% H2

However, guidance apparently not developed from

fatigue cracking data nor service experience

1) Lower H2 partial pressures

Sand Numberr 2010-6416C 7

Issue: steels are susceptible to H2-assisted fatigue cracking at low H2 pressures

Recommend evaluating H2-assisted fatigue cracking in higher strength steels at low H2 pressure

H2

H2

H2

H2H2

H2

H2H

HH

load

aH2

H2

H2

H2H2

H2

H2H

HH

load

a

DK (MPam1/2

)10 100

da

/dN

(m

m/c

ycle

)

10-5

10-4

10-3

10-2

10-1

7 MPa H2

2.2 MPa H2

0.14 MPa H2

0.02 MPa H2

air

1020 Steelfrequency = 1 Hzload ratio = 0.15

Fatigue cracking rates in

H2 pressure < 5 MPa

can be notably higher

than rates in air

Technical Reference on Hydrogen

Compatibility of Materials, Sandia, 2008

Sand Numberr 2010-6416C 8

ISO 11114-4 addresses H2 compatibility of steel cylinders with strength > 950 MPa in two ways

ISO 11114-4 specifies that steels with strength >950 MPa can be qualified based on materials testing in H2 gas

Evolving ISO 11114-4 currently specifies 3 tests:

• Method A (disc rupture test)

• Method B (crack propagation threshold test under step loading)

• Method C (crack propagation threshold test under static load)

Based on ISO 11114-4, CNG tanks suitable for HCNG

blends with >20% H2 if steel passes qualification test

However, qualification tests do not directly evaluate H2-

assisted fatigue cracking

Recommend evaluating H2-assisted fatigue cracking in

higher strength steels at H2 partial pressure in blend

2) Higher H2 partial pressures

Sand Numberr 2010-6416C 9

Limited H2-assisted fatigue cracking data for higher strength steel cylinders are promising

Higher strength cylinders with 400 MPa wall stress did not exhibit cracking in H2 after 17,000 cycles

Dp

H2 H2 H2

H2

strength < 950 MPa

strength ~ 1100 MPa

max. H2 pressure = 20 MPa

Cr-Mo steel cylinders

G. Bayer, Messer,

1999

Sand Numberr 2010-6416C 10

D K (MPa × m 1/2 )

10 100 d

a/d

N (m

m/c

ycle

) 10 -5

10 -4

10 -3

10 -2

0.088 MPa H 2

0.081 MPa H 2 +0.007 MPa CO

2

0.075 MPa H 2 +0.013 MPa nat. gas

0.088 MPa nat. gas 0.101 MPa air

1020 Steel frequency = 1 Hz load ratio = 0.05

H2-assisted

fatigue cracking

rates in HCNG

blend same as

rates in pure H2

Technical Reference on Hydrogen

Compatibility of Materials, Sandia,

2008

Issue: Does CNG modify H2-assisted fatigue cracking of steels in gas blends?

Some data show H2-assisted fatigue cracking

same in HCNG and H2 …

H2

H2

H2

H2H2

H2

H2H

HH

load

aH2

H2

H2

H2H2

H2

H2H

HH

load

a

Sand Numberr 2010-6416C 11

Issue: Does CNG modify H2-assisted fatigue cracking of steels in gas blends?

Why are fatigue cracking data for HCNG blends not consistent?

… but other data show lower cracking

rates in HCNG compared to H2

H2

H2

H2

H2H2

H2

H2H

HH

load

aH2

H2

H2

H2H2

H2

H2H

HH

load

a

I. Alliat, NATURALHY

EC project, 2007

0,01

0,1

1

10

100

1 10 100

Stress intensity factor range DK [MPa√m]

Cra

ck g

row

th r

ate

Da

/ DN

[u

m/c

ycle

] reference curve EGKS, airBS 7910 airBase metal, natural gas, trapeziumBase metal, 50% ng+ 50% hydrogen, trapeziumBase metal, 50% ng+ 50% hydrogen, sinusBase metal, 100% hydrogen, trapeziumBase metal,100% hydrogen, sinus

P = 66 bar

m = 3

X52 base metal

Fatigue cracking

rates in HCNG

notably less than

rates in pure H2

Sand Numberr 2010-6416C 12

Constituents in CNG can inhibit H2-assisted fatigue cracking

Can CNG constituent such as CO ensure resistance to H2-assisted fatigue cracking?

H2

H2

H2

H2H2

H2

H2H

HH

load

aH2

H2

H2

H2H2

H2

H2H

HH

load

a

J. Holbrook et al.,

BNL report, 1986

Gases such as O2 and CO are known

to inhibit H2-assisted cracking

Sand Numberr 2010-6416C 13

Summary

No concerns for HCNG in steel storage tanks if

material strength is < 950 MPa

Recommend evaluating H2-assisted fatigue

cracking in higher strength steels at H2 partial

pressure in blend

• Limited fatigue testing on higher strength steel

cylinders in H2 shows promising results

Impurities in CNG (e.g., CO) may provide

extrinsic mechanism for mitigating H2-assisted

fatigue cracking in steel tanks

14

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