1. JOINT EUROPEAN SUMMER SCHOOL FOR FUEL CELL AND HYDROGEN TECHNOLOGY
August 22-24, 2011
Hervé Barthélémy

2. 1.1. Compatibility of non-metallic materials
HYDROGEN STORAGE TECHNOLOGIES: COMPATIBILITY OF MATERIALS WITH HYDROGEN
GENERALITIES
1.1. Compatibility of non-metallic materials
1.2. Compatibility of metallic materials
HYDROGEN EMBRITTLEMENT - GENERALITIES
REPORTED ACCIDENTS AND INCIDENTS ON HYDROGEN EMBRITTLEMENT
TEST METHODS

3. PARAMETERS AFFECTING HYDROGEN EMBRITTLEMENT OF STEELS
HYDROGEN STORAGE TECHNOLOGIES: COMPATIBILITY OF MATERIALS WITH HYDROGEN
PARAMETERS AFFECTING HYDROGEN EMBRITTLEMENT OF STEELS
5.1. Environmental parameters
5.2. Design and surface conditions
5.3. Materials
HYDROGEN EMBRITTLEMENT OF OTHER MATERIALS
HYDROGEN ATTACK
CONCLUSION - RECOMMENDATION

4. GENERALITIES
1.1. Compatibility of non-metallic materials
1.2. Compatibility of metallic materials

5. 1.1. Gas compatibility of non-metallic materials
Explosion and fire (oxidation/burning)
Weight loss (W)
B.1. Extraction
B.2. Chemical attack
Swelling of material (S)
Change in chemical properties (M)

6. 1.1. Gas compatibility of non-metallic materials
Other compatibility considerations
E.1. Impurities in the gas (I)
E.2. Contamination of the material (C)
E.3. Release of dangerous products (D)
E.4. Ageing (G)
E.5. Permeation (P)

7. Explosion and fire (oxidation/burning)
Compatibility depends mainly on the operating conditions (pressure, temperature, gas velocity, particles, equipment design and application)
The risk should particularly be considered with gases such as oxygen, fluorine and chlorine
Most of the non-metallic materials can be ignited relatively easily when in contact with highly oxidizing gases

8. Explosion and fire (oxidation/burning)
HYDROGEN IS FLAMMABLE consequently
risk of violent reactions which flammable
solid non-metallic materials cannot occur.
However, for liquid hydrogen vessels, if
there is a leak of the outer jacket, air will
penetrate in the interspace under vacuum,
the air will condensate into a liquid mixture
composed of about 50 % O2 and 50 % N2.
Such an oxygen mixture is very oxidizing
and can react with non-metallic (or even thin
metallic) materials

9. Weight loss (W) B.1. Extraction
Solvent extraction of plasticizers from elastomers can cause shrinkage, especially in highly plasticized products
Some solvents, e.g. acetone or DMF (Dimethylformamide) used for dissolved
gases such as acetylene, can damage non-metallic materials
Liquefied gases can act as solvents but there are no known materials which can dissolve into liquid hydrogen

10. Weight loss (W) B.2. Chemical attack
Some non-metallic materials can be chemically attacked by gases. This attack can sometimes lead to the complete destruction of the material, e.g. the chemical attack of silicone elastomer by ammonia
There is no known reaction of “chemical attack” of commonly used materials with hydrogen

11. Swelling of material (S)
Elastomers are subject to swelling due to gas (or liquid) absorption. This can lead to an unacceptable increase of dimensions (especially for O-rings) or the cracking due to sudden out­gassing when the partial pressure is decreased, e.g. carbon dioxide and chlorofluorocarbons

12. Swelling of material (S)
In standards a swelling of more than
approximately 15 % in normal service conditions is marked NR (not recommended);
a swelling less than this is marked A (acceptable) provided other risks are acceptable
Hydrogen gas under pressure may lead to swelling of several elastomer

13. Change in chemical properties (M)
Gases can lead to an unacceptable change of mechanical properties in some non-metallic materials. This can result, for example, in an increase in hardness or a decrease in elasticity
Hydrogen does not create this phenomenon at room temperature

14. Other compatibility considerations
E.1. Impurities in the gas (I)
Some gases contain typical impurities which may not be compatible with the candidate materials (e.g. acetone in acetylene, H2S in methane)
This risk shall be addressed depending on the hydrogen source (electrolytic hydrogen is not likely to contain such contamination except if it is a by-product from chlorine production

15. Other compatibility considerations
E.2. Contamination of the material (C)
Some materials become contaminated in toxic gas usage by the toxic gas and
become hazardous themselves (e.g. during maintenance of equipment)
No case known with hydrogen

16. Other compatibility considerations
E.3. Release of dangerous products (D)
Many materials when subjected to extreme conditions (such as elevated temperature) can release dangerous products. This risk shall be considered in particular for breathing gases
No case known with hydrogen

17. Other compatibility considerations
E.4. Ageing (G)
Ageing is a gradual change in the mechanical and physical properties of the material due to the environment in which it is used or stored. Many elastomer and plastics materials are particularly subject to ageing; some gases like oxygen can accelerate the ageing process, leading sometimes to brittleness
No case known with hydrogen at room temperature

18. Other compatibility considerations
E.5. Permeation (P)
Permeation is a slow process by which gas passes through materials
Permeation of some gases (e.g. helium, hydrogen, carbon dioxide) through non-metallic material can be significant. For a given material, the permeation rate mainly depends on temperature, pressure, thickness, and surface area of the material in contact with the gas. The molecular weight and the specific formulation of plasticizers and other additives can cause a wide range of permeation rates for a particular type of plastics or elastomers
The risk shall be considered for hydrogen due to the effects to surroundings (e.g. fire potential).

19. 1.2. Gas compatibility of metallic materials
General
Corrosion
B.1. Dry corrosion
B.2. Wet corrosion
B.3. Corrosion by impurities
Hydrogen embrittlement
Generation of dangerous products
Violent reactions (e.g. ignition)
Embrittlement at low temperature

20. General
Compatibilty between a gas and metallic materials is affected by chemical reactions and physical influences classified into five categories:
Corrosion (the most frequent type of expected reaction)
Hydrogen embrittlement
Generation of dangerous products through chemical reaction
Violent reactions (like ignition)
Embrittlement at low temperature

21. Corrosion B.1. Dry corrosion
Is the chemical attack by a dry gas on the cylinder material. The result is a reduction of the cylinder wall thickness. This type of corrosion is not very common, because the rate of dry corrosion is very low at ambient temperature
At high temperature, hydrogen can react with some materials and can form for example hydrides

22. Corrosion B.2. Wet corrosion Most common sources of water ingress:
By the customer (retro-diffusion/backfilling or when the cylinder is empty, by air entry, if the valve is not closed)
During hydraulic testing
During filling

23. Corrosion B.2. Wet corrosion
Different types of “wet corrosion” in alloys:
General corrosion: e.g. by acid gases (CO2, SO2) or oxidizing gases (O2, Cl2). Additionally some gases, even inert ones, when hydrolysed could lead to the production of corrosive products (e.g. SiH2Cl2)
Localised corrosion: e.g. pitting corrosion by wet HCl in aluminium alloys or stress corrosion cracking of highly stressed steels by wet CO/CO2 mixtures
H2 cannot even in wet conditions create such types of corrosion

24. B.3. Corrosion by impurities
Most common polluants:
Atmospheric air, in this case the harmful impurities can be moisture and oxygen (e.g. in liquefied ammonia)
Agressive products contained in some gases, e.g. H2S in natural gas

25. B.3. Corrosion by impurities
Agressive traces (acid, mercury, etc.) remaining from the manufacturing process of some gases
For example, some electrolytic hydrogen
can contain traces of mercury (from the
diaphragm). Mercury reacts with many
metals at room temperature especially aluminium

26. Hydrogen embrittlement
Embrittlement by dry gas can occur at ambient temperature in the case of certain gases and under service conditions with stresses the cylinder material. The best know example is embrittlement caused by hydrogen
The type of stress cracking phenomenon can, under certain conditions, lead to the failure of gas cylinders (or other metallic components) containing hydrogen, hydrogen mixtures and hydrogen bearing compounds including hydrides

27. Hydrogen embrittlement
The risk of hydrogen embrittlement only occurs if the partial pressure of the gas and the stress level of the cylinder material is high enough
This compatibility issue is one of the most important and well described in details in the following

28. Generation of dangerous products
In some cases, reactions of a gas with a metallic material can lead to the generation of dangerous products. Examples are the possible reaction of C2H2 with copper alloys containing more than 70 % copper and of CH3Cl in aluminium cylinders
No case known with hydrogen

29. Violent reactions (e.g. ignition)
In principle, such types of gas/metallic material reactions are not very common at ambient temperatures, because high activation energies are necessary to initiate such reactions. In the case of some non-metallic materials, this type of reaction can occur with some gases (e.g. O2, Cl2)

30. Embrittlement at low temperature
Ferritic steels are known to be sensitive to this phenomenon
Liquid hydrogen is very cold (20 K). In such cases, materials having good impact behaviour at low temperature (aluminium alloys, austenitic stainless steels) shall be used and carbon or low alloyed steels shall be rejected

31. Internal hydrogen embrittlement
HYDROGEN EMBRITTLEMENT - GENERALITIES
Internal hydrogen embrittlement
External hydrogen embrittlement

32. HYDROGEN EMBRITTLEMENT - GENERALITIES
1 - COMBINED STATE :
Hydrogen attack
2 - IN METALLIC SOLUTION :
Gaseous hydrogen embrittlement

33. HYDROGEN EMBRITTLEMENT - GENERALITIES
Important parameter : THE TEMPERATURE
T  200°C Hydrogen embrittlement
T  200°C Hydrogen attack

34. HYDROGEN EMBRITTLEMENT - GENERALITIES
Reversible phenomena
Transport of H2 by the dislocations
H2 traps
CRITICAL
CONCENTRATION AND
DECOHESION ENERGY

35. FAILURE OF A HYDROGEN TRANSPORT VESSEL IN 1980
REPORTED ACCIDENTS AND INCIDENTS
ON HYDROGEN EMBRITTLEMENT
FAILURE OF A HYDROGEN TRANSPORT VESSEL IN 1980

36. REPORTED ACCIDENTS AND INCIDENTS ON HYDROGEN EMBRITTLEMENT
FAILURE OF A HYDROGEN TRANSPORT VESSEL IN HYDROGEN CRACK INITIATED ON INTERNAL CORROSION PITS

37. HYDROGEN CYLINDER BURSTS INTERGRANULAR CRACK
REPORTED ACCIDENTS AND INCIDENTS
ON HYDROGEN EMBRITTLEMENT
HYDROGEN CYLINDER BURSTS INTERGRANULAR CRACK

38. OF A HYDROGEN STORAGE VESSEL
REPORTED ACCIDENTS AND INCIDENTS
ON HYDROGEN EMBRITTLEMENT
VIOLENT RUPTURE
OF A HYDROGEN STORAGE VESSEL

39. H2 VESSEL. HYDROGEN CRACK ON STAINLESS STEEL PIPING
REPORTED ACCIDENTS AND INCIDENTS
ON HYDROGEN EMBRITTLEMENT
H2 VESSEL. HYDROGEN CRACK ON STAINLESS STEEL PIPING

40. TEST METHODS
Static (delayed rupture test)
Constant strain rate
Fatigue
Dynamic

41. TEST METHODS
Fracture mechanic (CT, WOL, …)
Tensile test
Disk test
Other mechanical test (semi-finished products)
Test methods to evaluate hydrogen
permeation and trapping

42. Fracture mechanics test with WOL type specimen
TEST METHODS
Fracture mechanics test with WOL type specimen
Vessel head
Specimen
O-rings
Vessel bottom
Gas inlet – Gas outlet
Torque shaft
Load cell
Instrumentation feed through
Crack opening displacement
gauge
Knife
Axis
Load application

43. Specimens for compact tension test
TEST METHODS
Specimens for compact tension test

44. TEST METHODS
Influence of hydrogen pressure (300, 150, 100 and 50 bar) - Crack growth rate versus K curves
10-4
10-5
10-6
10-7
10-8 20 25 30

45. TEST METHODS Influence of hydrogen pressure by British Steel K, MPa VmX
152 bar
41 bar
1 bar
165 bar H2 N2
K, MPa Vm
Influence of
hydrogen pressure
by British Steel
10-2
10-3
10-4
10-5 10 20 30 40 60 80
100 da dN
mm/cycle

46. TEST METHODS
Tensile specimen for hydrogen tests (hollow tensile specimen) (can also be performed with specimens cathodically charged or with tensile spencimens in a high pressure cell)

47. TEST METHODS I = (% RAN - % RAH) / % RAN I = Embrittlement index
RAN = Reduction of area without H2
RAH = Reduction of area with H2

48. Cell for delayed rupture test with Pseudo Elliptic Specimen
TEST METHODS
Cell for delayed rupture test
with Pseudo Elliptic Specimen
Pseudo Elliptic
Specimen

49. Tubular specimen for hydrogen assisted fatigue tests
TEST METHODS
Tubular specimen for hydrogen assisted fatigue tests
Inner notches
with elongation
measurement
strip

50. Disk testing method – Rupture cell for embedded disk-specimen
TEST METHODS
Disk testing method – Rupture cell for embedded disk-specimen
Upper flange
Bolt Hole
High-strength steel ring
Disk
O-ring seal
Lower flange
Gas inlet

51. Example of a disk rupture test curve
TEST METHODS
Example of a disk rupture test curve

52. TEST METHODS
Hydrogen embrittlement indexes (I) of reference materials versus maximum wall stresses (m) of the corresponding pressure vessels
m (MPa) I

53. Fatigue test - Principle
TEST METHODS
Fatigue test - Principle

54. Fatigue test - Pressure cycle
TEST METHODS
Fatigue test - Pressure cycle

55. Fatigue tests, versus  P curves
TEST METHODS
Fatigue tests, versus  P curves
nN2
nH2 1 2 3 4 5 6 7 8 9 10 11 12 13
Delta P (MPa)
Cr-Mo STEEL
Pure H2
H ppm O2
F 0.07 Hertz

56. Principle to detect fatigue crack initiation
TEST METHODS
Fatigue test
Principle to detect fatigue crack initiation

57. TESTS CHARACTERISTICS
Type of hydrogen embrittlement and transport mode
TESTS
LOCATION OF HYDROGEN
TRANSPORT MODE
Disk rupture test
External
Dislocations
F % test
External + Internal
Diffusion + Dislocation
Hollow tensile specimen test
Fracture mechanics tests
P.E.S. test
Tubular specimen test
Cathodic charging test
Diffusion

58. Practical point of view Electrochemical equipment (potentiostat)
TESTS CHARACTERISTICS
Practical point of view
TESTS
SPECIMEN
(Size-complexity)
CELL
COMPLEMENTARY
EQUIPMENT NEEDED
Disk rupture test
Small size and very simple
Hydrogen compressor and high pressure vessel
Tensile test
Relatively small size
Large size
Tensile machine
Fracture mechanics test
Relatively large size and complex
Very large size and complex
Fatigue tensile machine for fatigue test only
P.E.S. test
Average size and very easy to take from a pipeline
Average size --
Tubular specimen test
Large size and complex
No cell necessary
Large hydrogen source at high pressure
Cathodic charging test
Small size and simple
Electrochemical equipment (potentiostat)

59. TESTS CHARACTERISTICS
Interpretation of results
TESTS
TESTS SENSIBILITY
POSSIBILITY OF RANKING MATERIALS
SELECTION OF MATERIALS – EXISTING CRITERIA
PRACTICAL DATA TO PREDICT IN SERVICE PERFORMANCE
Disk rupture
High sensitivity
Possible
Yes
PHe/PH2
Fatigue life
Tensile test
Good/Poor sensitivity
Possible/Difficult
Yes/No
Treshold stress
Fracture mechanics
Good sensitivity
No, but maximum allowable KIH could be defined
- KIH
- Crack growth rate
P.E.S. test
Poor sensitivity
Difficult No
Tubular
specimen test
Cathodic
charging
Possible but difficult in practice
Critical hydrogen concentration

60. PARAMETERS AFFECTING
HYDROGEN EMBRITTLEMENT OF STEELS
5.1. Environment
5.2. Design and surface conditions
5.3. Material

61. 5.1. Environment or “operating conditions”
Hydrogen purity
Hydrogen pressure
Temperature
Stresses and strains
Time of exposure

62. Influence of oxygen contamination
5.1. Environment or “operating
conditions”
Hydrogen purity
Influence of oxygen contamination

63. Influence of H2S contamination
5.1. Environment or “operating
conditions”
Hydrogen purity
Influence of H2S contamination

64. Influence of H2S partial pressure
5.1. Environment or “operating
conditions”
Hydrogen pressure
Influence of H2S partial pressure
for AISI 321 steel

65. Influence of temperature - Principle
5.1. Environment or “operating
conditions”
Temperature
Influence of temperature - Principle

66. Influence of temperature for
5.1. Environment or “operating
conditions”
Temperature
Influence of temperature for
some stainless steels

67. 5.1. Environment or “operating conditions”
Hydrogen purity
Hydrogen pressure
Temperature
Stresses and strains
Time of exposure

68. 5.2. Design and surface conditions
Stress level
Stress concentration
Surface defects

69. Crack initiation on a geometrical discontinuity
5.2. Design and surface conditions
Stress concentration
Crack initiation on a geometrical discontinuity

70. Crack initiation on a geometrical discontinuity
5.2. Design and surface conditions
Stress concentration
Crack initiation on a geometrical discontinuity

71. 5.2. Design and surface conditions
Surface defects
FAILURE OF A HYDROGEN TRANSPORT VESSEL IN HYDROGEN CRACK INITIATED ON INTERNAL CORROSION PITS

72. 5.3. Material Microstructure Chemical composition
Heat treatment and mechanical properties
Welding
Cold working
Inclusion

73. 5.3. Material
Heat treatment and mechanical properties

74. 5.3. Material Welding 4.2 2.0 1.9 Embrittlement index 25 % 8 % 2.5 %
0 %
(No weld)
Ferrite content

75. 5.3. Material Microstructure Chemical composition
Heat treatment and mechanical properties
Welding
Cold working
Inclusion

76. HYDROGEN EMBRITTLEMENT OF OTHER MATERIALS
All metallic materials present a certain
degree of sensitive to HE
Materials which can be used
Brass and copper alloys
Aluminium and aluminium alloys
Cu-Be

77. HYDROGEN EMBRITTLEMENT OF OTHER MATERIALS
Materials known to be very sensitive to HE :
Ni and high Ni alloys
Ti and Ti alloys
Steels : HE sensitivity depend on exact
chemical composition, heat or mechanical
treatment, microstructure, impurities
and strength
Non compatible material can be used at
limited stress level

78. HYDROGEN ATTACK Main parameters summarized on the « Nelson curves » :
Influence of P, T, Cr and Mo
Ti and W have also a beneficial effect
C, Al, Ni and Mn (excess) have a
detrimental effect
Other parameters :
Heat treatment
Stress level, welding procedure

79. HYDROGEN ATTACK Nelson curves Legend : Surface decarburization
Internal decarburization
(Hydrogen attack)

80. CONCLUSION - RECOMMENDATION
The influence of the different parameters shall
be addressed.

81. CONCLUSION - RECOMMENDATION
The influence of the different parameters shall
be addressed.
To safely use materials in presence of
hydrogen, an internal specification shall
cover the following :

82. CONCLUSION - RECOMMENDATION
The influence of the different parameters shall
be addressed.
To safely use materials in presence of
hydrogen, an internal specification shall
cover the following :
The « scope », i.e. the hydrogen pressure, the temperature and the hydrogen purity

83. CONCLUSION - RECOMMENDATION
The influence of the different parameters shall
be addressed.
To safely use materials in presence of
hydrogen, an internal specification shall
cover the following :
The « scope », i.e. the hydrogen pressure, the temperature and the hydrogen purity
The material, i.e. the mechanical properties,
chemical composition and heat treatment

84. CONCLUSION - RECOMMENDATION
The influence of the different parameters shall
be addressed.
To safely use materials in presence of
hydrogen, an internal specification shall
cover the following :
The « scope », i.e. the hydrogen pressure, the temperature and the hydrogen purity
The material, i.e. the mechanical properties,
chemical composition and heat treatment
The stress level of the equipment

85. CONCLUSION - RECOMMENDATION
The influence of the different parameters shall
be addressed.
To safely use materials in presence of
hydrogen, an internal specification shall
cover the following :
The « scope », i.e. the hydrogen pressure, the temperature and the hydrogen purity
The material, i.e. the mechanical properties,
chemical composition and heat treatment
The stress level of the equipment
The surface defects and quality of finishing

86. CONCLUSION - RECOMMENDATION
The influence of the different parameters shall
be addressed.
To safely use materials in presence of
hydrogen, an internal specification shall
cover the following :
The « scope », i.e. the hydrogen pressure, the temperature and the hydrogen purity
The material, i.e. the mechanical properties,
chemical composition and heat treatment
The stress level of the equipment
The surface defects and quality of finishing
And the welding procedure, if any