JOINT EUROPEAN SUMMER SCHOOL FOR FUEL CELL AND HYDROGEN TECHNOLOGY August 22-24, 2011 Hervé Barthélémy
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
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
GENERALITIES 1.1. Compatibility of non-metallic materials 1.2. Compatibility of metallic materials
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)
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)
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
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
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
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
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
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
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
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
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
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
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
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).
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
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
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
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
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
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
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
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
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
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
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)
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
Internal hydrogen embrittlement HYDROGEN EMBRITTLEMENT - GENERALITIES Internal hydrogen embrittlement External hydrogen embrittlement
HYDROGEN EMBRITTLEMENT - GENERALITIES 1 - COMBINED STATE : Hydrogen attack 2 - IN METALLIC SOLUTION : Gaseous hydrogen embrittlement
HYDROGEN EMBRITTLEMENT - GENERALITIES Important parameter : THE TEMPERATURE T 200°C Hydrogen embrittlement T 200°C Hydrogen attack
HYDROGEN EMBRITTLEMENT - GENERALITIES Reversible phenomena Transport of H2 by the dislocations H2 traps CRITICAL CONCENTRATION AND DECOHESION ENERGY
FAILURE OF A HYDROGEN TRANSPORT VESSEL IN 1980 REPORTED ACCIDENTS AND INCIDENTS ON HYDROGEN EMBRITTLEMENT FAILURE OF A HYDROGEN TRANSPORT VESSEL IN 1980
REPORTED ACCIDENTS AND INCIDENTS ON HYDROGEN EMBRITTLEMENT FAILURE OF A HYDROGEN TRANSPORT VESSEL IN 1983. HYDROGEN CRACK INITIATED ON INTERNAL CORROSION PITS
HYDROGEN CYLINDER BURSTS INTERGRANULAR CRACK REPORTED ACCIDENTS AND INCIDENTS ON HYDROGEN EMBRITTLEMENT HYDROGEN CYLINDER BURSTS INTERGRANULAR CRACK
OF A HYDROGEN STORAGE VESSEL REPORTED ACCIDENTS AND INCIDENTS ON HYDROGEN EMBRITTLEMENT VIOLENT RUPTURE OF A HYDROGEN STORAGE VESSEL
H2 VESSEL. HYDROGEN CRACK ON STAINLESS STEEL PIPING REPORTED ACCIDENTS AND INCIDENTS ON HYDROGEN EMBRITTLEMENT H2 VESSEL. HYDROGEN CRACK ON STAINLESS STEEL PIPING
TEST METHODS Static (delayed rupture test) Constant strain rate Fatigue Dynamic
TEST METHODS Fracture mechanic (CT, WOL, …) Tensile test Disk test Other mechanical test (semi-finished products) Test methods to evaluate hydrogen permeation and trapping
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
Specimens for compact tension test TEST METHODS Specimens for compact tension test
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
TEST METHODS Influence of hydrogen pressure by British Steel K, MPa Vm X 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
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)
TEST METHODS I = (% RAN - % RAH) / % RAN I = Embrittlement index RAN = Reduction of area without H2 RAH = Reduction of area with H2
Cell for delayed rupture test with Pseudo Elliptic Specimen TEST METHODS Cell for delayed rupture test with Pseudo Elliptic Specimen Pseudo Elliptic Specimen
Tubular specimen for hydrogen assisted fatigue tests TEST METHODS Tubular specimen for hydrogen assisted fatigue tests Inner notches with elongation measurement strip
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
Example of a disk rupture test curve TEST METHODS Example of a disk rupture test curve
TEST METHODS Hydrogen embrittlement indexes (I) of reference materials versus maximum wall stresses (m) of the corresponding pressure vessels m (MPa) I
Fatigue test - Principle TEST METHODS Fatigue test - Principle
Fatigue test - Pressure cycle TEST METHODS Fatigue test - Pressure cycle
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 H2 + 300 ppm O2 F 0.07 Hertz
Principle to detect fatigue crack initiation TEST METHODS Fatigue test Principle to detect fatigue crack initiation
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
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)
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
PARAMETERS AFFECTING HYDROGEN EMBRITTLEMENT OF STEELS 5.1. Environment 5.2. Design and surface conditions 5.3. Material
5.1. Environment or “operating conditions” Hydrogen purity Hydrogen pressure Temperature Stresses and strains Time of exposure
Influence of oxygen contamination 5.1. Environment or “operating conditions” Hydrogen purity Influence of oxygen contamination
Influence of H2S contamination 5.1. Environment or “operating conditions” Hydrogen purity Influence of H2S contamination
Influence of H2S partial pressure 5.1. Environment or “operating conditions” Hydrogen pressure Influence of H2S partial pressure for AISI 321 steel
Influence of temperature - Principle 5.1. Environment or “operating conditions” Temperature Influence of temperature - Principle
Influence of temperature for 5.1. Environment or “operating conditions” Temperature Influence of temperature for some stainless steels
5.1. Environment or “operating conditions” Hydrogen purity Hydrogen pressure Temperature Stresses and strains Time of exposure
5.2. Design and surface conditions Stress level Stress concentration Surface defects
Crack initiation on a geometrical discontinuity 5.2. Design and surface conditions Stress concentration Crack initiation on a geometrical discontinuity
Crack initiation on a geometrical discontinuity 5.2. Design and surface conditions Stress concentration Crack initiation on a geometrical discontinuity
5.2. Design and surface conditions Surface defects FAILURE OF A HYDROGEN TRANSPORT VESSEL IN 1983. HYDROGEN CRACK INITIATED ON INTERNAL CORROSION PITS
5.3. Material Microstructure Chemical composition Heat treatment and mechanical properties Welding Cold working Inclusion
5.3. Material Heat treatment and mechanical properties
5.3. Material Welding 4.2 2.0 1.9 Embrittlement index 25 % 8 % 2.5 % 0 % (No weld) Ferrite content
5.3. Material Microstructure Chemical composition Heat treatment and mechanical properties Welding Cold working Inclusion
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
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
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
HYDROGEN ATTACK Nelson curves Legend : Surface decarburization Internal decarburization (Hydrogen attack)
CONCLUSION - RECOMMENDATION The influence of the different parameters shall be addressed.
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 :
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
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
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
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
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