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Hydrogen embrittlement

 

 
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Hydrogen embrittlement
 
 
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Hydrogen embrittlement (or hydrogen grooving) is the process by which various metals, most importantly high-strength steel
Steel

Steel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.14% by weight , depending on grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten....
, become brittle and crack following exposure to hydrogen
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
. Hydrogen cracking can pose an engineering problem especially in the context of a hydrogen economy
Hydrogen economy

The hydrogen economy is a proposed system of meeting energy needs by using hydrogen as a fuel source that could be generated from alternative fuels or other energy sources that don't give off greenhouse gases....
. However, commercially workable and safe technology exists globally in the hydrogen industry, which produces some 50 million metric tons per year.

Hydrogen embrittlement is also used to describe the formation of zircaloy
Zircaloy

Zircaloy, also incorrectly called zircalloy, is a group of high-zirconium alloys. One of the main uses of zircaloys is in nuclear technology, as zirconium has very low absorption cross section of thermal neutrons and therefore it is frequently used as cladding of fuel rods in nuclear reactors....
 hydride.






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Hydrogen embrittlement (or hydrogen grooving) is the process by which various metals, most importantly high-strength steel
Steel

Steel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.14% by weight , depending on grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten....
, become brittle and crack following exposure to hydrogen
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
. Hydrogen cracking can pose an engineering problem especially in the context of a hydrogen economy
Hydrogen economy

The hydrogen economy is a proposed system of meeting energy needs by using hydrogen as a fuel source that could be generated from alternative fuels or other energy sources that don't give off greenhouse gases....
. However, commercially workable and safe technology exists globally in the hydrogen industry, which produces some 50 million metric tons per year.

Hydrogen embrittlement is also used to describe the formation of zircaloy
Zircaloy

Zircaloy, also incorrectly called zircalloy, is a group of high-zirconium alloys. One of the main uses of zircaloys is in nuclear technology, as zirconium has very low absorption cross section of thermal neutrons and therefore it is frequently used as cladding of fuel rods in nuclear reactors....
 hydride. This use of the term in this context is common in the nuclear industry.

Process

The mechanism starts with lone hydrogen atoms diffusing
Diffusion

Molecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion....
 through the metal. At high temperatures, the elevated solubility of hydrogen allows hydrogen to diffuse into the metal (or the hydrogen can diffuse in at a low temperature, assisted by a concentration gradient). When these hydrogen atoms re-combine in minuscule voids of the metal matrix to form hydrogen molecules, they create pressure from inside the cavity they are in. This pressure can increase to levels where the metal has reduced ductility and tensile strength, up to the point where it cracks open (hydrogen induced cracking, or HIC). High-strength and low-alloy steels, nickel
Nickel

Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge....
 and titanium
Titanium

Titanium is a chemical element with the symbol Ti and atomic number 22. Sometimes called the ?space age metal?, it has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver colour....
 alloys are most susceptible. Steel with an ultimate tensile strength
Tensile strength

Tensile strength , or is the Stress at which a material breaks or permanently deforms. Tensile strength is an Intensive and extensive properties and, consequently, does not depend on the size of the test specimen....
 of less than 1000 MPa or hardness of less than 30 HRC
Hardness comparison

There are a large number of hardness testing methods available . Although it is impossible in many cases to give an exact conversion it is possible to give a comparison table....
 are not generally considered susceptible to hydrogen embrittlement. Jewett et al. reports the results of tensile tests carried out on several structural metals under high-pressure molecular hydrogen environment. These tests have shown that aluminium
Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
 and beryllium copper
Beryllium copper

Beryllium copper, also known as copper beryllium, BeCu or beryllium bronze, is a metal alloy of copper and 0.5 to 3% beryllium, and sometimes with other alloying elements, and has significant metalworking and operating performance qualities....
 alloys are some of the least susceptible to hydrogen embrittlement along with few other metals.

Hydrogen embrittlement can happen during various manufacturing operations or operational use, anywhere where the metal comes in contact with atomic or molecular hydrogen. Processes which can lead to this include cathodic protection
Cathodic protection

Cathodic protection is a technique to control the corrosion of a metal surface by making it work as a cathode of an electrochemical cell. This is achieved by placing in contact with the metal to be protected another more easily corroded metal to act as the anode of the electrochemical cell....
, phosphating, pickling
Pickling (metal)

Pickling is a treatment of metallic surfaces in order to remove impurities, stains, rust or Fouling with a solution called pickle liquor, containing strong acids, before subsequent processing, such as extrusion, rolling, painting, galvanization or plating with tin or chromium....
, and electroplating
Electroplating

Electroplating is a plating process that uses electrical direct current to redox cations of a desired material from a solution and coat a electrical conductivity object with a thin layer of the material, such as a metal....
. A special case is arc welding
Arc welding

Arc welding uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point....
, in which the hydrogen is released from moisture (for example in the coating of the welding electrodes; to minimize this, special low-hydrogen electrodes are used for welding high-strength steels). Other mechanisms of introduction of hydrogen into metal are galvanic corrosion, chemical reactions of metal with acids, or with other chemicals (notably hydrogen sulfide
Hydrogen sulfide

Hydrogen sulfide is the chemical compound with the chemical formula Hydrogen2Sulfur. This colorless, toxic and flammable gas is partially responsible for the foul odor of egg and flatulence....
 in sulfide stress cracking, or SSC, a process of importance for the oil and gas industries).

Counteractions

If the metal has not yet started to crack, the condition can be reversed by removing the hydrogen source and causing the hydrogen within the metal to diffuse out, possibly at elevated temperatures. Susceptible alloys, after chemical or electrochemical treatments where hydrogen is produced, are often subjected to heat treatment in order to remove absorbed hydrogen. There is a 4-hour time limit for baking out entrapped hydrogen after acid treating the parts. This is the time between the end of acid exposure and the beginning of the heating cycle in the baking furnace. This per SAE AMS 2759/9 Section 3.3.3.1 which calls out the correct procedure for eliminating entrapped hydrogen.

In the case of welding, often pre- and post-heating the metal is applied to allow the hydrogen to diffuse out before it can cause any damage. This is specifically done with high-strength steels and low alloy steel
Low alloy steel

Alloy steel is steel alloyed with other Chemical element in amounts of between 1 and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups: low alloy steels and high alloy steels....
 such as the chrome/molybdenum/vanadium alloys. Due to the time needed to re-combine hydrogen atoms into the harmful hydrogen molecules, hydrogen cracking due to welding can occur over 24 hours after the welding operation is completed.

Related phenomena

If steel is exposed to hydrogen at high temperatures, hydrogen will diffuse into the alloy
Alloy

An alloy is a partial or complete solid solution of one or more chemical element in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history....
 and combine with carbon
Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
 to form tiny pockets of methane
Methane

Methane is a chemical compound with the molecular formula . It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.5 degrees....
 at internal surfaces like grain boundaries and voids. This methane does not diffuse out of the metal, and collects in the voids at high pressure and initiates cracks in the steel. This process is known as hydrogen attack
Hydrogen damage

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....
 and leads to decarburization
Decarburization

Decarburization is the process opposite to carburization, namely aimed at decreasing the content of carbon in metals . Higher grade steel is achieved when carbon content of a steel melt is increased....
 of the steel and loss of strength.

Copper alloys which contain oxygen can be embrittled if exposed to hot hydrogen. The hydrogen diffuses through the copper and reacts with inclusions of Cu2O, forming H2O (water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
), which then forms pressurized bubbles at the grain boundaries. This process can cause the grains to literally be forced away from each other, and is known as Steam Embrittlement (because steam is produced, not because exposure to steam causes the problem).

Test

There are two ASTM standards for testing embrittlement due to hydrogen gas. The standard] uses a diaphragm loaded with a differential pressure. The test uses a cylindrical tensile specimen tested into a enclosure pressurized with hydrogen or helium.

Another ASTM standard exists for quantitatively testing for the Hydrogen Embrittlement threshold stress for the onset of Hydrogen-Induced Cracking due to platings and coatings from Internal Hydrogen Embrittlement (IHE) and Environmental Hydrogen Embrittlement (EHE) - F1624-06 Standard Test Method for Measurement of Hydrogen Embrittlement Threshold in Steel by the Incremental Step Loading Technique. References: ASTM STP 543,"Hydrogen Embrittlement Testing" and ASTM STP 962,"Hydrogen Embrittlement: Prevention and Control."

  • NACE TM0284-2003 (NACE International
    NACE International

    NACE International is a professional organization for the corrosion control industry established in 1943. As of 2008, there are approximately 20,312 NACE members world wide....
    ) Resistance to Hydrogen-Induced Cracking
  • ISO 11114-4:2005 (ISO
    International Organization for Standardization

    The International Organization for Standardization , widely known as ISO , is an international standard-setting body composed of representatives from various national standards organizations....
    )Test methods for selecting metallic materials resistant to hydrogen embrittlement .
  • - Standard Test Method for Process Control Verification to Prevent Hydrogen Embrittlement in Plated or Coated Fasteners
  • -Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments


See also

  • Hydrogen analyzer
    Hydrogen analyzer

    A Hydrogen Analyzer is a device used to measure the amount of hydrogen concentration in steels and has industrial applications for corrosion monitoring....
  • Hydrogen damage
    Hydrogen damage

    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....
  • Hydrogen fuel enhancement
  • Hydrogen piping
    Hydrogen piping

    Within installations, hydrogen piping is a system of pipes used to convey hydrogen from one location to another.For low pressure <275 psig and high pressure high purity hydrogen piping stainless steel 303, 304, 316 tubing, piping, fittings and components are preferred....
  • Hydrogen safety
    Hydrogen safety

    Hydrogen safety covers the safe use and handling of hydrogen. Hydrogen poses unique challenges due to its ease of leaking, low-energy ignition, wide range of combustible fuel-air mixtures, buoyancy, and its ability to embrittle metals that must be accounted for to ensure safe operation....
  • Low hydrogen annealing
    Low hydrogen annealing

    Low hydrogen annealing is a heat treatment in metallurgy for the reduction or elimination of hydrogen in a material to prevent hydrogen embrittlement....
  • Nascent hydrogen
    Nascent hydrogen

    H atoms, also called nascent hydrogen or atomic hydrogen, are claimed to exist transiently but long enough to effect chemical reactions. According to one claim, nascent hydrogen is generated in situ usually by the reaction of zinc with an acid, or by electrolysis at the cathode....


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