Material Testing and Analysis of Metals
in Hydrogen Gas Environments
In response to global climate change, efforts toward decarbonization and carbon neutrality have significantly accelerated. Manycountries have set their goals to achieve carbon neutrality, such as by the year 2050. Hydrogen energy is considered apromising solution due to minimal environmental impact and zero carbon dioxide emissions during combustion.
Hydrogen has exceptional capabilities in energy conversion, making it a valuable resource for electricity generation. Kobe
Material Testing Laboratory Co., Ltd. has actively developed various material testing technologies in hydrogen environments. This
document highlights our testing achievements and prospects for further technological advancements.

Aiming to realize hydrogen energy society
Transport
Store

Hydrogen energy

Produce

Use

The demand for using structural materials in hydrogen environments is increasing,but challenges remain.

Challenge 1
Can existing designs be used as they are?
■ Is fundamental improvement necessary?
■Electrochemical
reaction

Concerns in Strength Design

Hydrogen Embrittlement
Hydrogen atoms infiltrate and diffuse within
metallic materials, reducing their strength.

H2H2H

H
H

Hydrogen diffusion and trap

H2HH
H

H
H

Deformation Hbands

Inclusion

Precipitates

Initiation andpropagation of crack■

Delayed Fracture■

Decrease in tensile properties such as elongation at break andreduction of area■

Reduction in fatigue life and fatigue limit■

Acceleration of fatigue crack growth rate■

Decrease in fracture toughness

Material testing in hydrogen environments is essential to evaluate
the hydrogen compatibility of intended metallic materials.

Challenge 2 | Current situation■

Handling hydrogen gas requires specialized knowledge and rigorous safety measures due to its flammability.

■

Testing in hydrogen environments requires expensive, explosion-proof equipment.

■

The high cost of testing services in hydrogen environments hinders the development of a hydrogenenergy society.

Please refer to the next pages for our proposed solutions.
1Solution

Various strength tests usinghydrogen gas-sealed hollow specimens
Load cellRealizes strength testing while exposing
the material's surface to hydrogen gas

Benefit1

Pressure gageValve

2

Integration with KMTL's core testing technology
Responds to diverse testing needs at an appropriate cost

Benefit3Vacuumpump

Hollow specimen

Our hydrogen material testing lineup
4H[LYPHS:[YLUN[O;LZ[Z3V^LY <WWLY 3V^LY <WWLY::9;:SV^Z[YHPUYH[L[LUZPSL[LZ[ë*YLLW[LZ[ë/VSSV^

3V^J`JSLMH[PN\L[LZ[/PNOJ`JSLMH[PN\L[LZ[*YLLW[LZ[::9;[LZ[/PNOJ`JSLMH[PN\L[LZ[:VSPK-H[PN\LJYHJRNYV^[O[LZ[1407YLZZ\YL47H ;LTWLYH[\YLá*

Solid SSRT test
High cycle fatigue test
Fatigue crack growth test
Fracture toughness test
4 points bending fatigue crack growth test

120

Hydrogen gas pressure (MPa):WLJPTLU

Hydrogen gas cylinder

Minimal amount of hydrogen gas
Ensures safety even if hydrogen gas diffuses outside
the specimen

Benefit100
80

Hollow Low cycle fatigue test
High cycle fatigue test

60

Hollow SSRT test
Creep test

Solid Creep test

40

Under development

20-YHJ[\YL[V\NOULZZ[LZ[0-200WVPU[ZILUKPUN
MH[PN\LJYHJRNYV^[O[LZ[-1000100200300

400500600700800900

Hydrogen gas temperature (˚C )EBSD analysis of fractured hollow specimens
IPF map

Phase map

Cross-sectional SEM image near fracture

Color Coded Map Type : Inverse Pole Figure [001]
CrystaI direction

AnalysisSecondary crack

FaceCenteredCubic

111001

101

Color Coded Map Type : Phase
Phase
Face Centered Cubic (γ phase)
Body Centered Cubic (α phase)

KAM map

GROD map

Material : Type304 austenite
stainless steel
In 13.3 MPa H2 at RT
CHS : 0.002 mm/sec

Magnified view of secondary crackColor Coded Map Type : KerneI Average Misorientation
TotalPartition
Min Max Fraction Fraction
051.000
1.000

Color Coded Map Type : Grain Reference Orientation Deviation - Angle
TotalPartition
Min Max Fraction Fraction
050
0.782
0.782

▶Fracture surface observation of a hollow specimen confirmed crack initiationfrom the inner surface exposed to hydrogen.

Scope▶Phase transformation from austenite to martensite was observed along the crack path.
▶Type304, with relatively low austenite stability, exhibited lower ductility due tohydrogen exposure.

2Continuous electrolytic H-charging for SSRT test
Electrolytic hydrogen charging is a method used to add hydrogen to metallic materials. The specimen is polarized in an aqueoussolution, allowing hydrogen to penetrate the material from its surface and diffuse. It has been primarily used to study hydrogen
embrittlement and delayed fracture of steels under corrosive environments. Hydrogen embrittlement tends to increase with thehydrogen concentration in the steel. Electrolytic hydrogen charging allows us to simulate hydrogen effects in actualenvironments to evaluate the hydrogen resistance of steel.
Kobe Material Testing Laboratory Co., Ltd. faced the challenge of hydrogen desorption during tensile tests in the atmosphereconducted after hydrogen charging. This document introduces our developed method for maintaining hydrogen charging during
tensile tests, effectively solving this issue.

Experimental setup of the continuous electrolytic charging SSRT testing method■■

Optimal for evaluating hydrogen embrittlement, including delayed
fracture in corrosive environments, with a wide range of parametersettings such as electrolyte composition, current value, and test
speed.

Galvano stat
Platinum electrodeTensile specimen (Cathode)
Thermocouple

Hydrogen concentration analysis is conducted by immersing thefractured specimen in liquid nitrogen and store it without hydrogen
desorption.

Electrolyte
Rubber heater

Custom design and fabrication of experimental equipment areavailable.
Test vessel

Stress-stroke curves

Thermal Desorption Analysis (TDA) of hydrogen

1600

0.40
Material : JIS-SCM435
Test temperature : 50˚C
CHS : 0.0012 mm/sec
Electrolyte : 3 mass %NaCl + 3 g/L NH4SCN

1400
1200

CM03
0.1 mA/cm2
pre charge : 0.5h

1000

CM04
0.01 mA/cm2
pre charge : 0.5h800600

CM05
1 mA/cm2
pre charge : 48.5h

400CM02
1 mA/cm2
pre charge : 0.5h

200000.5

11.522.53.544.5

0.30
CM05
CH= 5.1 mass ppm
1mA/cm2
pre-charge : 48.5 h

0.25
0.20

CM02
CH= 2.0 mass ppm
1mA/cm2
pre-charge : 0.5 h

0.15
0.10

CM01 : CH= 0.1 mass ppm
CM03 : CH= 0.1 mass ppm

0.05

CM01
Non-charged in air

3Material : JIS-SCM435
Heating rate : 200 K/h

0.35

Desorption rate (mass ppm/min)■SSRT testing is performed with a specimen hydrogen-charged using
electrochemical reactions during the process.

Nominal stress (MPa)■5Stroke displacement (mm)CM04 : CH= 0.2 mass ppm

0.00
050

100

150200250300

350

400

Temperature (˚C)

〜 Key discussions in this experiment 〜▶Significant ductility reduction occurred due tohydrogen under high current densityconditions.
▶ Longer pre - charging time caused more
pronounced hydrogen embrittlement.
▶ Diffusible hydrogen was detected from thefractured specimen.

▶Correlation exists between ductility reduction

and hydrogen concentration.

▶ Evaluating concentration distribution in thetest section requires the hydrogen diffusion
coefficient.

3SSRT, fatigue life and fatigue crack growth tests under
100 MPa class high pressure hydrogen gas environment
High pressure hydrogen gas vessels and piping are essential for hydrogen-energy related products and infrastructure,including FCV fuel tanks, hydrogen station refueling equipment, and large-scale hydrogen transportation and storage facilities.
While these components enhance energy density and efficiency, they require specialized technologies and materials to handle
the pressure safety. Strict safety standards and regulations necessitate extensive material testing in an high pressure hydrogen gasenvironment.
Kobe Material Testing Laboratory Co., Ltd. has established SSRT, fatigue life, and fatigue crack growth tests under high pressurehydrogen gas environments. This was achieved by mounting a specially structured small pressure vessel on a general-purpose
hydraulic servo-type fatigue testing machine. This document introduces the technology.

New test method for small-sized specimens under high-pressure gaseous hydrogen

System for SSRT and fatigue life tests

System for fatigue crack growthand fracture toughness tests

Our dedicated explosion-proof test room has been registered as a High-Pressure Gas Production Facility in Hyogo Prefecture.
Tests are conducted in full compliance with safety regulation by Japanese law, including gas detectors, forced exhaust fans, explosion-proof
fluorescent lights, and regular voluntary inspections.

Test procedures
Install the specimen in the pressure vessel

Evacuate the pressure vessel

Conduct the test

Replace the gas in the pressure vessel

Release the gas

Adjust gas pressure using a booster pump

Remove the specimen4

Testing performance in high pressure hydrogen gas environment
SSRT test result
JIS-SCM435
In air or 120 MPa H2 at RTCHS : 0.0005 mm/sec

900800Fatigue life test result
800Type304
In air or 100 MPa H2 at RT600
500
4003001.0E-07

1.0E-08200
120 MPa H2Air

100100 MPa H2Air
1.0E-09
10000.5

11.52

2.5

2030

40

JIS-SCM435
In air or 60 MPa H2 at RT
R=-1, f=1〜5 Hz

700

1.0E-06

700

da/dN [m/cycles]

Nominal stress (MPa)Fatigue crack growth test result
1.0E-05

Stress amplitude, σa [MPa]

1000

600
500
40030020060 MPa H2Air

10001.0E+0350

1.0E+04

1.0E+05

1.0E+06

1.0E+07

Stroke displacement (mm)∆K [MPa m1/2]

Number of cycles to failure, N f [cycles]

Ductility loss
Relative reduction of area, RRA : 0.6
Relative elongation, REL : 0.6

Accelerated crack growth rate
10 times fasterthan that in air!

Impact in low cycle life regime
Minimal impact in high cycle life regime

Our standard test specimens in KMTL
CT specimen forfatigue crack growth test

SSRT test specimen

8M6

9.6

3

2.2

φ2R3

1.6

10(10.7)
2.2(10.7)372-φ2(unit : mm)

410(unit : mm)

CT specimen forfracture toughness test
C1

φ62.2
3
9.6.5

7R0R05.5

φ10φ283φ10φ6C1R8Fatigue life test specimen

52.247(unit : mm)

2-φ2104(unit : mm)

Core technology of KMTL miniature testing method
In all industrial fields, there is a need to take samples
from actual products or components and conductvarious material tests while simulating similare n v i r o n m e n t s . H o w e v e r, l i m i t a t i o n s o n t h edimensions of materials that can be taken from
actual machines often result in specimens that do notm e e t t h e s i z e r e c o m m e n d e d by g e n e ra l t e s t
standards.
We specialize in miniature testing technology, wheresmall samples taken from actual components aremachined into specimens and subjected to a range oftesting methods. This technology has been adapted
for high-pressure hydrogen gas environment,
resulting in our original test method described in thisdocument. Please view our miniature testing services
using the QR code.

Electrode

Setting frame

Body of device

Discharge sampling device fortaking miniature specimens

For more information5Measurement and analysis of hydrogen diffusivity, D
Hydrogen atoms in metals diffuse significantly faster than other solute atoms such as carbon. Many researchers identify hydrogen
diffusion as a primary cause of hydrogen embrittlement.
Kobe Material Testing Laboratory Co., Ltd. studied for a method of experimentally obtaining the hydrogen diffusivity, D.
Hydrogen concentration distribution analysis using FEM, based on this hydrogen diffusivity is shown as follows.

Procedure for hydrogen diffusivity by thermal desorption analysis (TDA)
Electrolytichydrogen charging

StepⅠⅡ

H2H2H

H

H

H

H

H2H2H2H2H2H2H2H

H2H2HH

H●Solution temperature : T = 50˚C
● Charging time : t = 48 h
●Fitting analysis

H2HH

Ⅲ

H

H2HH
H

H

H2

H2

H2t

Pre-measurement tasks

Charging conditions

Diffusion equation

Mass measurement after sample thawing●Reference : Acta Metallurgica,
Vol.2, 2, 1954, 214-223

Measurement conditions●Fitting : Least squares method●Numerical calculation code : Python●Equipment : JEOL GC-MS●Holding temperature : T = 24, 50, 80 ˚CFitting analysis results

Diffusion simulation by FEM analysis

Temperature, T (K)Time history change of hydrogen concentration distribution inthe cross-section of round bar specimens

440 420 400 380

360

340

320

300

280

1E-6KMTL

Hydrogen diffusivity, D (m2/sec)

H

H

3% NaCl + 3g/L NH4SCN

10-6

H

HElectrolyte
●HH

H2HH

H2H2H

H

H2StepC

H2H2H

H

H

H2

Hydrogen desorption
curve acquisition by TDA
H2H2H2StepBeck et al
Asano et al
OrianiSuzuki et al

10-7

Pure iron

1E-7

Analysis conducted using the hydrogen diffusion coefficient
D50˚C = 2.315×10 -10m2/s for Cr-Mo steel at 50˚C

High hydrogenconcentration
1.0
0.8
0.7
0.6

1E-8

10-8

0.5
0.4
0.3
0.2
0.1

10-9

1E-9

7.141E-10
2.315E-10
8.832E-11

10-10

Low-alloy
steel

10-11
2.2

2.4

2.6

2.8

3.0

3.2

0.0

Low hydrogenconcentration

3.4

Reciprocal temperature, T (K )-1

For more information* This is an animation of the analysis results using FEM analysis software Abaqus 2021.
1E-10

1E-11
3.6

▶ Hydrogen concentration saturation isreached in approximately 10 hours.
▶Hydrogen charging of 0.5 hour results in
a concentration gradient.

HPTEL

https://en.kmtl.co.jp/+81-79-435-5010

Contact6