Proceedings of the ASME 2023
Pressure Vessels & Piping Conference
PVP2023
July 16-21, 2023, Atlanta, Georgia
PVP2023-105725
EFFECT OF HIGH PRESSURE HYDROGEN GAS ON FATIGUE AND FRACTURE
PROPERTIES OF API X65 LINEPIPE STEELS
Yoshihiro Nishihara, Hiroshi Okano
JFE Steel Corporation
Kawasaki, Kanagawa, Japan
ABSTRACT
Hydrogen is one of the promising energy carriers for
achieving a carbon neutral society. The pipeline system is
positioned as a major type of infrastructure which will be
indispensable for mass transportation of gaseous hydrogen. It is
acknowledged that existing natural gas pipelines can be used
safely to transport hydrogen blends up to 10 or 20 %. However,
it is also known that the mechanical properties of steels are
significantly degraded by hydrogen embrittlement, even under
small partial pressures of hydrogen. Material degradation is
considered in the hydrogen pipeline code ASME B31.12. This
code requires evaluation of the fracture and fatigue properties of
linepipe materials used under hydrogen, and a critical assessment
is conducted so that fracture of the pipeline can be avoided
during its service life. In the present study, the hydrogen
absorption properties, fracture toughness and fatigue crack
growth properties under a 25 MPa hydrogen gas environment
were investigated by using 3 kinds of linepipe steels
manufactured by different methods. The materials were API X65
linepipe steel, which were manufactured as ERW, LSAW and
seamless (SMLS) linepipes. Although all the materials showed a
bainitic ferrite generally called, each microstructure had
distinctive characteristics attributable to the manufacturing
process. While all the linepipe steels showed better fracture
toughness and fatigue crack growth rates than the ASME B.
31.12 design curve, their hydrogen absorption properties,
fracture toughness in hydrogen gas and fatigue crack growth
properties in hydrogen gas differed due to their crystal structures,
even though the strength grade of the materials. In the steels used
in this study, the fracture toughness and fatigue crack growth
characteristics under a hydrogen atmosphere were insensitive to
the influence of absorbed hydrogen, and were considered to be
influenced by the material factors that determine the fracture
toughness and fatigue crack growth characteristics in the
atmosphere.
1. INTRODUCTION
To realize a carbon neutral society, the infrastructures for
hydrogen storage and transportation must be used safely. One of
the most important issues for the integrity of hydrogen systems
is material degradation caused by hydrogen. It is well understood
that solute hydrogen in steel causes degradation of material
properties, or so-called hydrogen embrittlement. The effects of
hydrogen on the mechanical properties of linepipe steels have
been extensively investigated in recent decades. The slow strain
rate tensile test with a smooth round bar specimen under gaseous
hydrogen showed a modest loss of ductility, while yield and
tensile strength did not show large effects by hydrogen (Hoover,
1981; Cialone, 1985; Stalheim, 2010). The effect of hydrogen
becomes significant in notched specimens, which show a large
drop in reduction of area due to quasi-cleavage fracture at the
surface. (Hoover, 1981; Zhou, 2021). Fracture toughness is also
reduced in high pressure gaseous hydrogen (Hoover, 1981;
Cialone, 1985; Gutierrez-Solana, 1982; Stalheim, 2010). It
seems that low grade linepipe steels such as X42 or X52 tend to
show a lower fracture toughness value in hydrogen (KIH) than
more recent high grade steels. But further higher grade linepipe
such as X100 exhibits a lower KIH value (Ronevich and San
Marchi, 2021). Abnormal fracture such as separations was
reported in the fracture surface of a specimen tested in hydrogen
(Stalheim, 2010). The fracture toughness of linepipe welds is
also reduced in hydrogen (Ronevich, 2021). However, the most
significant effect of hydrogen is seen in fatigue crack growth
behavior. The fatigue crack growth rate (FCGR) is greatly
accelerated in gaseous hydrogen, as demonstrated in many
experimental investigations of linepipe steels (Cialone, 1985;
San Marchi, 2010; Slifka, 2013, 2018). The effect of hydrogen
is modest in the low K region, which is around the threshold
stress intensity for fatigue crack growth, but the ratio of FCGR
in hydrogen to that in the air increases with increasing K.
Linepipe welds show fatigue crack growth behavior similar to
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The fatigue crack growth rate in hydrogen also needs to be
evaluated for consideration of the structural integrity assessment.
ASME B31.12 provides an equation for the fatigue crack growth
rate that was given from the upper bound data among many kinds
of linepipe steels (Slifka, 2018).
Regarding the material selection for hydrogen pipelines, the
Nonmandatory Appendix G of ASME B31.12 recommends a
low carbon Nb microalloyed thermo-mechanical controlled
processing (TMCP) steel with a fine grained polygonal and
acicular ferrite microstructure. The aim of this recommendation
is to apply material with a higher fracture toughness and improve
the structural integrity for hydrogen pressures up to 21 MPa. A
variety of linepipe steels are used in actual pipeline systems.
Even though many kinds of linepipe steels were evaluated
previously, no comparison of the properties in hydrogen of
different types of linepipe steels of comparable strength has been
reported. In the present study, hydrogen absorption properties,
fracture toughness in hydrogen gas and fatigue crack growth
characteristics in hydrogen gas were evaluated using grade X65
linepipe steels with slightly different bainite structures due to
differences in the production methods.
that of the base material (Slifka, 2015), which may indicate that
fatigue crack growth in hydrogen is not largely affected by the
steel microstructure. However, it has been reported that steel
with a finer microstructure obtained by applying optimized plate
rolling conditions exhibits slower FCGR (Stalheim, 2020). The
effect of mixing hydrogen in natural gas on fracture and fatigue
properties was investigated to consider hydrogen transportation
by blending in an existing natural gas pipeline (Meng, 2017;
Nguyen, 2020; Ronevich, 2021). Those studies demonstrated
that even a small mixture of hydrogen deteriorates the fracture
and fatigue properties of linepipe steels exhibiting lower KIH
values and faster FCGR.
The degradation of the mechanical properties of steels under
high pressure gaseous hydrogen described above is considered
to be caused by hydrogen embrittlement. Once hydrogen atoms
uptake into steel, they can easily diffuse in the steel lattice and
accumulate in regions where mechanical discontinuities exist,
such as crack tips and defects, driven by the hydrostatic stress
gradient (Sofronis, 1989; Krom, 1999; Ishikawa, 2015). The
accumulated hydrogen activates the process of hydrogen
mechanisms such as (i) the hydrogen enhanced decohesion
mechanism, HEDE (Oriani, 1987; Yamaguchi, 2012), (ii)
hydrogen enhanced localized plasticity, HELP (Birnbaum, 1994;
Sofronis, 1996; Robertson, 2001) and (iii) the hydrogen
enhanced strain-induced vacancy model, HESIV (Nagumo,
2001, 2004; Neeraj, 2012), and then enhances brittle and/or
ductile fracture, leading to a reduction in fracture toughness and
acceleration of fatigue crack growth.
The standard used in the design of high pressure hydrogen
systems is Article KD-10 of the ASME Boiler and Pressure
Vessel Code, Section VIII, Division 3 (BPVC VIII-3), “Special
requirements for vessels in high-pressure gaseous hydrogen
transport and storage service,” which requires a material
evaluation and integrity assessment. Recently, high pressure
hydrogen storage tanks used in a hydrogen refilling station
applicable up to 100 MPa have been developed and qualified
under Article KD-10 (Okano, 2019). The fatigue crack growth
calculation base of KD-10 can accurately estimate the fatigue life
with the hydrogen pressure cycle, and has been validated by an
experimental pressure cycle test using high pressure hydrogen.
Similar design concepts are adopted in the hydrogen pipeline
design code ASME B31.12, “Hydrogen Piping and Pipelines.”
When choosing Option A in ASME B31.12 (prescribed design
method) for fracture control and arrest design, the basic design
factor is limited to not more than 0.5 and additional safety factors
must be imposed, resulting in a reduced design pressure,
although there are no other strict requirements. For high pressure
design, Option B (performance-based design method) allows the
use of a design factor up to 0.72. However, the pipes and welds
must be qualified for adequate resistance to fracture in hydrogen
gas using the applicable rules provided in Article KD-10.
Fracture toughness testing under a hydrogen environment must
be conducted for the base material and welds, including the heat
affected zone (HAZ) and the weld metal, in order to evaluate KIH,
which must be higher than KIA, the applied stress intensity factor
for the critical condition, and shall not be less than 55 MPa m1/2.
2. Experimental Method
2.1 Materials
The materials used in this study were three kinds of API
grade X65 pipeline steels produced by different manufacturing
methods, namely, ERW, LSAW and SMLS. The ERW and
LSAW linpipes were manufactured by applying low carbon Nb
microalloyed TMCP steel with homogeneous grains. The ERW
linepipe was used a hot rolled steel sheet and manufactured by
high frequency welding. The UOE linpipe was used steel plate
and manufactured through the processes of U-ing press, O-ing
press, submerged arc welding and mechanical expansion. The
SMLS linepipe steel was manufactured by a seamless rolling
process, followed by heat treatment for material structure
control. The heat treatment condition was quenching in water
from austenitization treatment at 920 °C for 10min, then
tempering at 640 °C for 20 min. Scanning Electron Microscope
(SEM) images of the material structures are shown in Figure 1.
ERW consists of quasi-polygonal ferrite, as shown in Figure 1
(a), LSAW consists of quasi-polygonal ferrite and acicular
ferrite, as shown in Figure 1 (b), and SMLS consists of a lathtype bainite structure, as shown in Figure 1 (c). The chemical
compositions, material strength and outer diameter of the
linepipes are shown in Table 1.
Table 1: Chemical compositions (mass%), mechanical
properties and outer diameter of tested materials.
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2.2 Hydrogen Exposure Test
To investigate the hydrogen absorption behavior of the
linepipe steels, a hydrogen exposure test was conducted using a
high pressure hydrogen autoclave. The materials used in the
hydrogen exposure test were API Grade X65 ERW, LSAW and
SMLS linepipe steels, which are the same materials as those used
for the fracture toughness test and fatigue crack growth test
described in the following sections. A rectangular specimen with
a size of 10 mm x 10 mm x 20mmL was taken from the pipe in
the longitudinal direction, and Pd plating was applied after
polishing the surface. All specimens were then put into the
autoclave and pressurized with 100 % hydrogen at 25 MPa. After
exposure for 96 h, the specimens were removed from the
autoclave and stored in liquid nitrogen. The hydrogen
concentration in the specimens was measured by a thermal
desorption analysis using gas chromatography. The heating rate
in hydrogen desorption was 200 °C/h.
2.3 Fracture Toughness Test
The fracture toughness test was conducted following the
basic procedures of ASTM E1820. ASME B31.12 requires an
integrity assessment based on Article KD-10 of ASME BPVC
VIII-3, which specifies the method for KIH determination by
ASTM E1681. While a constant load or constant displacement
test is required for the KIH determination, the rising load fracture
toughness measurement method was used. This was the same
method for KIH determination as in many previous studies (San
Marchi, 2010, 2011; Ronevich, 2021), in which it was used
because the basic plain strain validity criterion is difficult to
achieve with ductile materials and an extremely thick specimen
is needed. The geometry of the specimen for the fracture
toughness test in high pressure gaseous hydrogen is shown in
Figure 2. A sub-size CT specimen with a thickness of 10 mm was
used. The specimens were taken from the base material in the TL direction. All specimens were fatigue pre-cracked and sidegrooved. The fracture toughness test was conducted under pure
hydrogen with a pressure of 25 MPa. The unloading compliance
method in ASTM E1820 was applied for the evaluation of crack
extension, and a clip gauge (KYOWA, DTC-A-5) was used to
evaluate the crack length. Displacement rate was controlled to be
2.0×10-3 mm/sec (Matsuoka, 2018). the plain strain fracture
toughness JIC was determined from the J-R curve, after which the
stress intensity factor K was calculated by the equation below:
KJ=√JE/(1-ν2)
(1)
FIGURE 1: SEM images of (a) ERW, (b) LSAW and (c)
SMLS linepipe steels used for test.
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2.4 Fatigue Crack Growth Test
The fatigue crack growth test was conducted following the
basic procedures of ASTM E647. Figure 3 shows the specimen
geometry. The specimen was taken from the pipe wall close to
the inner surface in the T-L direction. While ASME B31.12
requires a fatigue crack growth test of a specimen from the base
material as well as the HAZ and weld metal, only the base
material was used here, since both girth and seam welds exhibit
fatigue crack growth behavior similar to that of the base material
(Slifka, 2015). The fatigue crack growth test was conducted
under pure hydrogen with a pressure of 25 MPa. The stress ratio
and frequency of the fatigue test were 0.1 and 1 Hz, respectively.
After testing, the fracture surfaces were observed by SEM.
3. RESULTS
3.1 Hydrogen Exposure Test
Figure 4 shows the results of a hydrogen desorption analysis
after the hydrogen exposure test of the API grade linepipes. The
diffusible hydrogen absorbed from the hydrogen atmosphere was
obtained as the sum of the hydrogen desorption curve to 400 °C
and is also shown in the graph. The desorption curves of LSAW
and SMLS have one peak at around 120 °C, and almost no
desorption was seen at temperatures over 300 °C. In contrast,
ERW has two peaks at around 120 °C and 180 °C. LSAW and
SMLS absorbed almost the same amount of hydrogen from the
hydrogen atmosphere, while ERW absorbed about 10 times more
hydrogen than the other two materials.
FIGURE 2: Geometry of fracture toughness test specimen.
FIGURE 4: Hydrogen desorption curves and diffusible
hydrogen of linepipes exposed in 25 MPa hydrogen for 96
h.
3.2 Fracture Toughness Test
Examples of the load, P and clip gauge opening
displacement, Vg curves under 25 MPa hydrogen and air are
shown in Figure 5. Even under the high pressure hydrogen
environment, the crack extension could be determined precisely
by the unloading compliance method. The compliance curves
became steeper in the hydrogen environment, which means the
crack extension was larger than under the air condition. Based
on ASTM E1820, the J-integral and crack extension, a, were
evaluated for the J-R curve and plotted. In some samples, a
tunneling region was shown about 1mm longer than the
average stable crack length. So, ASTM E1820 validity criterion
was not met. Therefore, the J-integral measurements were
FIGURE 3: Geometry of fatigue crack growth rate test
specimen.
evaluated as Jq, then the transferred stress intensity factor given
by Eq. (1) was evaluated as KJQ as a reference value. The
inhomogeneity of the crack extension in the thickness direction
may be due to the effect of hydrogen on the weakest mechanical
position and/or metallurgical condition. All the samples showed
very high Jq under the atmospheric condition, and no stable
cracks occurred until the end of the test. The stress intensity
factors under 25 MPa hydrogen obtained from the Jq data are
shown in Table 2, which shows average values from multiple
tests. All samples exhibit comparable or slightly high with
previous studies, and the stress intensity factors in H2 were far
higher than the minimum requirement in ASME B31.12.
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da/dN = a1ΔKb1+[(a2ΔKb2)-1+(a3ΔKb3)-1]-1
ΔK = Kmax-Kmin
(2)
(3)
Here, a1 = 4.0812E-9, b1 = 3.2106, a2 = 4.0862E-11, b2 =
6.4822, a3 = 4.8810E-8, and b3 = 3.6147. This formulation was
developed by the upper bound solution from a fatigue crack
growth database (Slifka et al., 2018), which was mainly obtained
under the stress ratio of R = 0.5, whereas the stress ratio in this
study was R = 0.1.
FIGURE 5: Load-clip gauge opening displacement curves
in fracture toughness test of SMLS under hydrogen and
air.
Table 2: Fracture toughness test results of grade X65
linepipes under 25 MPa hydrogen atmosphere.
FIGURE 4: Fatigue crack growth curves of grade X65
linepipe steels tested with stress ratio R = 0.1.
3.3 Fatigue Crack Growth Test Results
The fatigue crack growth curves of the grade X65 ERW,
LSAW and SMLS linepipes are shown in Figure 4. Under the
atmospheric condition, the crack growth rates of LSAW and
SMLS were almost the same in the region above ΔK =
10 MPa√m, while those of ERW were about 2 to 3 times faster.
The threshold stress intensity factor, ΔKth was almost same for
ERW and LSAW, but was slightly higher for SMLS. In all
samples, the crack growth rate in hydrogen gas was more than
10 times faster than in the atmosphere in the high ΔK region. In
the low ΔK region, the effect of acceleration by hydrogen
embrittlement was reduced in all samples. Figure 5 shows a
graph comparing the crack growth rate at ΔK = 25 MPa√m. The
crack growth rate was faster in the order of ERW, LSAW and
SMLS. The crack growth rate of ERW in hydrogen gas was
about 1.3 times that of LSAW and about 2 times that of SMLS.
Figure 6 shows the fracture surfaces of the samples at ΔK =
25 MPa√m. All samples showed quasi-cleavage (QC) fracture
surfaces affected by hydrogen embrittlement.
The design curve for calculation of fatigue crack growth in
hydrogen is provided by ASME B31.12, as shown in Eq. 2 and
plotted in Figure 4.
FIGURE 5: Fatigue crack rate under hydrogen at ΔK =
25 MPa√m.
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Crack Propagation
Crack Propagation
Crack Propagation
4. DISCUSSON
The hydrogen absorption properties, fracture toughness in
hydrogen gas and fatigue crack growth properties in hydrogen
gas of linepipe steels were investigated using three different
grade X65 linepipes which had different microstructures due to
differences in the manufacturing methods.
The amount of hydrogen absorbed in hydrogen gas
charging was the highest in the ERW pipe, being about 10 times
higher than in the LSAW and SMLS pipes. In the hydrogen
emission curves in Figure 4, the LSAW and SMLS pipes showed
a single peak, while the ERW pipe showed at least two peaks,
suggesting that the ERW pipe has more hydrogen traps than the
other materials and different material structure factors act as
hydrogen traps. These results indicate that the hydrogen
absorption properties of materials of the same strength grade
differ due to their microstructures. In general, materials with
inferior hydrogen absorption properties, that is, with a large
amount of diffusive hydrogen in the material, tend to exhibit
inferior hydrogen embrittlement properties because a large
amount of hydrogen diffuses and accumulates in stressconcentrated areas when subjected to stress.
In the fracture toughness test in hydrogen gas, the ERW
pipe showed the lowest value among all the samples. Since all
the KJQs showed very high values, it would be difficult to say that
there are large differences in the properties of these materials in
hydrogen. Moreover, the results of the fracture toughness test in
hydrogen gas tend to be variable, and it has been reported that
KJQ shows a range of about 20 MPa√m (San Marchi, 2010). This
suggests that the difference in the fracture toughness values in
hydrogen gas among the samples in this experiment does not
reflect the difference in microstructure, but is within the range of
variation.
Next, in the fatigue crack growth rate test in hydrogen gas,
the ERW pipe displayed the worst characteristics in hydrogen.
However, the difference in the crack growth rate between the
samples was about two times at most, which is unlikely to reflect
the hydrogen absorption characteristics. As shown in Figure 6,
all samples showed hydrogen QC fracture surfaces. In addition,
no mixture of grain boundary fracture surfaces was observed
with increasing ΔK, and there was no significant difference in the
facet spacing of the QC fracture surfaces. These facts suggest
that the difference in the crack growth rates in hydrogen between
the ERW and LSAW pipes and the SMLS pipe is not caused by
hydrogen in the material. Focusing on the results of fatigue crack
growth rate test in air, it was found that the crack growth rates of
the LSAW and SMLS pipes were almost the same, but the
characteristics of the ERW pipe were inferior to those of the
other linepipe steels. Therefore, it is considered that the
difference between the materials in the fatigue crack growth rate
test in hydrogen gas in this study reflects their fatigue crack
growth characteristics in the atmosphere. Compared with the
other samples, the ERW pipe absorbs more hydrogen, but shows
a peak on the high temperature side of the hydrogen deposition
curve, suggesting that hydrogen is trapped in Cu or NbC. Certain
precipitates, such as Cu and VC, are known to enhance delayed
fracture properties by trapping hydrogen in steel as non-diffusive
FIGURE 6: SEM images of fracture surfaces of (a) ERW,
(b) LSAW and (c) SMLS linepipe steels under hydrogen
at ΔK = 25 MPa√m.
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and it is speculated that this bainite interface acts as an obstacle
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decrease in its propagation speed. It is also thought that this
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reduced the growth rate.
These results suggest that grade X65 for use in hydrogen
pipelines should be designed to be resistant to crack initiation
and propagation even when used in the atmosphere in order to
improve its properties in hydrogen.
5. CONCLUSION
An investigation of the hydrogen absorption characteristics,
fracture toughness in hydrogen gas and fatigue crack growth in
hydrogen of linepipe steels was carried out using three kinds of
grade X65 linepipe which were manufactured by different
methods (ERW, LSAW and SMLS), and their characteristics
were compared. As a result of the investigation of the hydrogen
absorption properties, ERW absorbed about 10 times more
hydrogen than the other samples, and high hydrogen
embrittlement sensitivity was expected. However, the results of
the fracture toughness test in hydrogen gas and the fatigue crack
propagation test did not show significant differences in these
characteristics like those found in the hydrogen absorption test.
Therefore, it was clarified that steels with a strength
approximately equivalent to grade X65 linepipe steel, such as
those used in this study, are insensitive to the influence of
absorbed hydrogen. In addition, it was implied that material
properties of linepipe steels in hydrogen gas are mainly
influenced by the material factors that determine their fracture
toughness and fatigue crack growth characteristics in the
atmosphere such as grain size and homogeneity.
ACKOWLEDGMENT
In advancing the study, the authors would like to thank Dr.
N. Ishikawa of JFE Steel Corporation for his valuable advice.
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Copyright © 2023 by ASME
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