Hydrogen damage
Encyclopedia
Hydrogen damage is the generic name given to a large number of metal
degradation processes due to interaction with hydrogen
.
Hydrogen is present practically everywhere, in the atmosphere, several kilometres above the earth and inside the earth. Engineering materials are exposed to hydrogen and they may interact with it resulting in various kinds of structural damage. Damaging effects of hydrogen in metallic materials have been known since 1875 when W. H. Johnson reported “some remarkable changes produced in iron
by the action of hydrogen and acid
s”. During the intervening years many similar effects have been observed in different structural materials, such as steel
, aluminium
, titanium
, and zirconium
. Because of the technological importance of hydrogen damage, many people explored the nature, causes and control measures of hydrogen related degradation of metals. Hardening
, embrittlement
and internal damage are the main hydrogen damage processes in metals. This article consists of a classification of hydrogen damage, brief description of the various processes and their mechanisms, and some guidelines for the control of hydrogen damage.
s and the search for other sources of energy is a current activity of mankind. Hydrogen is believed to be a possible future source of energy (Engineering note: Hydrogen could not be used as a "source" of energy but only as a means to transport energy from one place to another) and a “hydrogen economy
” is a strong possibility within the next 50 years. In such a scenario, large scale production, storage, transportation and use of hydrogen becomes necessary. Materials’ problems caused by hydrogen damage could limit the progress of such an economy.
Hydrogen may be picked up by metals during melting, casting, shaping and fabrication. They are also exposed to hydrogen during their service life. Materials susceptible to hydrogen damage have ample opportunities to be degraded during all these stages.
and tantalum
dissolve hydrogen and experience hardening and embrittlement at concentrations much below their solid solubility limit. The hardening and embrittlement are enhanced by increased rate of straining.
forming metals like titanium, zirconium and vanadium
, hydrogen absorption causes severe embrittlement. At low concentration
s of hydrogen, below the solid solubility limit, stress-assisted hydride formation causes the embrittlement which is enhanced by slow straining. At hydrogen concentrations above the solubility limit, brittle hydrides are precipitated on slip planes and cause severe embrittlement. This latter kind of embrittlement is encouraged by increased strain-rates, decreased temperature and by the presence of notches in the material.
, flakes, fish-eyes and porosity
. Carbon steels exposed to hydrogen at high temperatures experience hydrogen attack which leads to internal decarburization and weakening.
.
, velocity ratio, creeping waves/time-of-flight measurement, pitch-catch mode shear wave velocity, advanced ultrasonic backscatter techniques (AUBT), time of flight diffraction (TOFD)
, thickness mapping and in-situ metallography – replicas.
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
degradation processes due to interaction with hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
.
Hydrogen is present practically everywhere, in the atmosphere, several kilometres above the earth and inside the earth. Engineering materials are exposed to hydrogen and they may interact with it resulting in various kinds of structural damage. Damaging effects of hydrogen in metallic materials have been known since 1875 when W. H. Johnson reported “some remarkable changes produced in iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
by the action of hydrogen and acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
s”. During the intervening years many similar effects have been observed in different structural materials, such as steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
, aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
, titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
, and zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
. Because of the technological importance of hydrogen damage, many people explored the nature, causes and control measures of hydrogen related degradation of metals. Hardening
Hardening (metallurgy)
Hardening is a metallurgical and metalworking process used to increase the hardness of a metal. The hardness of a metal is directly proportional to the uniaxial yield stress at the location of the imposed strain...
, embrittlement
Embrittlement
Embrittlement is a loss of ductility of a material, making it brittle. Various materials have different mechanisms of embrittlement.* Hydrogen embrittlement is the effect of hydrogen absorption on some metals and alloys....
and internal damage are the main hydrogen damage processes in metals. This article consists of a classification of hydrogen damage, brief description of the various processes and their mechanisms, and some guidelines for the control of hydrogen damage.
Importance
With advancing technology, use of high strength structural materials becomes a necessity. Depletion of fossil fuelFossil fuel
Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...
s and the search for other sources of energy is a current activity of mankind. Hydrogen is believed to be a possible future source of energy (Engineering note: Hydrogen could not be used as a "source" of energy but only as a means to transport energy from one place to another) and a “hydrogen economy
Hydrogen economy
The hydrogen economy is a proposed system of delivering energy using hydrogen. The term hydrogen economy was coined by John Bockris during a talk he gave in 1970 at General Motors Technical Center....
” is a strong possibility within the next 50 years. In such a scenario, large scale production, storage, transportation and use of hydrogen becomes necessary. Materials’ problems caused by hydrogen damage could limit the progress of such an economy.
Hydrogen may be picked up by metals during melting, casting, shaping and fabrication. They are also exposed to hydrogen during their service life. Materials susceptible to hydrogen damage have ample opportunities to be degraded during all these stages.
Classifications
Hydrogen damage may be of four types: solid solution hardening, creation of internal defects, hydride embrittlement, and hydrogen embrittlement. Each of these may further be classified into the various damaging processes.Solid solution hardening
Metals like niobiumNiobium
Niobium or columbium , is a chemical element with the symbol Nb and atomic number 41. It's a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite...
and tantalum
Tantalum
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as tantalium, the name comes from Tantalus, a character in Greek mythology. Tantalum is a rare, hard, blue-gray, lustrous transition metal that is highly corrosion resistant. It is part of the refractory...
dissolve hydrogen and experience hardening and embrittlement at concentrations much below their solid solubility limit. The hardening and embrittlement are enhanced by increased rate of straining.
Hydride embrittlement
In hydrideHydride
In chemistry, a hydride is the anion of hydrogen, H−, or, more commonly, a compound in which one or more hydrogen centres have nucleophilic, reducing, or basic properties. In compounds that are regarded as hydrides, hydrogen is bonded to a more electropositive element or group...
forming metals like titanium, zirconium and vanadium
Vanadium
Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery gray, ductile and malleable transition metal. The formation of an oxide layer stabilizes the metal against oxidation. The element is found only in chemically combined form in nature...
, hydrogen absorption causes severe embrittlement. At low concentration
Concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
s of hydrogen, below the solid solubility limit, stress-assisted hydride formation causes the embrittlement which is enhanced by slow straining. At hydrogen concentrations above the solubility limit, brittle hydrides are precipitated on slip planes and cause severe embrittlement. This latter kind of embrittlement is encouraged by increased strain-rates, decreased temperature and by the presence of notches in the material.
Creation of internal defects
Hydrogen present in metals can produce several kinds of internal defects like blisters, shatter fractureFracture
A fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...
, flakes, fish-eyes and porosity
Porosity
Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0–1, or as a percentage between 0–100%...
. Carbon steels exposed to hydrogen at high temperatures experience hydrogen attack which leads to internal decarburization and weakening.
Blistering
Atomic hydrogen diffusing through metals may collect at internal defects like inclusions and laminations and form molecular hydrogen. High pressures may be built up at such locations due to continued absorption of hydrogen leading to blister formation, growth and eventual bursting of the blister. Such hydrogen induced blister cracking has been observed in steels, aluminium alloys, titanium alloys and nuclear structural materials.Shatter cracks, flakes, fish-eyes and micro perforations
Flakes and shatter cracks are internal fissures seen in large forgings. Hydrogen picked up during melting and casting segregates at internal voids and discontinuities and produces these defects during forging. Fish-eyes are bright patches named for their appearance seen on fracture surfaces, generally of weldments. Hydrogen enters the metal during fusion-welding and produces this defect during subsequent stressing. Steel containment vessels exposed to extremely high hydrogen pressures develop small fissures or micro perforations through which fluids may leak.Porosity
In metals like iron and steel, aluminium and magnesium whose hydrogen solubilities decrease with decreasing temperature, liberation of excess hydrogen during cooling from the melt, (in ingots and castings) produces gas porosityGas porosity
Gas porosity is the fraction of a rock or sediment filled with a gas.Determining the true porosity of a gas filled formation has always been a problem in the oil industry. While natural gas is a hydrocarbon, similar to oil, the physical properties of the fluids are very different, making it very...
.
Hydrogen embrittlement
By far, the most damaging effect of hydrogen in structural materials is hydrogen embrittlement. Materials susceptible to this process exhibit a marked decrease in their energy absorption ability before fracture in the presence of hydrogen. This phenomenon is also known as hydrogen-assisted cracking, hydrogen-induced blister cracking. The embrittlement is enhanced by slow strain rates and low temperatures, near room temperature.Hydrogen stress cracking
Brittle delayed failure of normally ductile materials when hydrogen is present within is called hydrogen stress cracking or internal hydrogen embrittlement. This effect is seen in high strength structural steels, titanium alloys and aluminium alloys.Hydrogen environment embrittlement
Embrittlement of materials when tensile loaded in contact with gaseous hydrogen is known as hydrogen environment embrittlement or external hydrogen embrittlement. It has been observed in alloy steels and alloys of nickel, titanium, uranium and niobium.Loss in tensile ductility
Hydrogen lowers tensile ductility in many materials. In ductile materials, like austenitic stainless steels and aluminium alloys, no marked embrittlement may occur, but may exhibit significant lowering in tensile ductility (% elongation or % reduction in area) in tensile tests.Degradation of other mechanical properties
Hydrogen may also affect the plastic flow behaviour of metals. Increased or decreased yield strengths, serrated yielding, altered work hardening rates as well as lowered fatigue and creep properties have been reported.Control of hydrogen damage
The best method of controlling hydrogen damage is to control contact between the metal and hydrogen. Many steps can be taken to reduce the entry of hydrogen into metals during critical operations like melting, casting, working (rolling, forging, etc.), welding, surface preparation, like chemical cleaning, electroplating, and corrosion during their service life. Control of the environment and metallurgical control of the material to decrease its susceptibility to hydrogen are the two major approaches to reduce hydrogen damage.Detection of hydrogen damage
There are various methods of adequately identifying and monitoring hydrogen damage, including ultrasonic echo attenuation method, amplitude-based backscatterBackscatter
In physics, backscatter is the reflection of waves, particles, or signals back to the direction they came from. It is a diffuse reflection due to scattering, as opposed to specular reflection like a mirror...
, velocity ratio, creeping waves/time-of-flight measurement, pitch-catch mode shear wave velocity, advanced ultrasonic backscatter techniques (AUBT), time of flight diffraction (TOFD)
Time of flight diffraction ultrasonics
Time of Flight Diffraction method of Ultrasonic inspection is a very sensitive and accurate method for nondestructive testing of welds for defects. TOFD originated from tip diffraction techniques which were first published by Silk and Liddington in 1975 which paved the way for TOFD. Later works...
, thickness mapping and in-situ metallography – replicas.
External links
- A 39-page paper on hydrogen damage of metals by M.R. Louthan, "Hydrogen Embrittlement of Metals: A Primer for the Failure Analyst", 2008, from U.S. DOE OSTI, 3.4MB available here.