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transcript
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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