hydrogen embrittlement


  • Another way to minimize the formation of hydrogen is to use special low-hydrogen electrodes for welding high-strength steels.

  • In high-strength steels, anything above a hardness of HRC 32 may be susceptible to early hydrogen cracking after plating processes that introduce hydrogen.

  • This de-embrittlement process, known as low hydrogen annealing or “baking”, is used to overcome the weaknesses of methods such as electroplating which introduce hydrogen to
    the metal, but is not always entirely effective because a sufficient time and temperature must be reached.

  • [7] Hydrogen embrittlement requires the presence of both atomic (“diffusible”) hydrogen and a mechanical stress to induce crack growth, although that stress may be applied
    or residual.

  • Hydrogen embrittlement as a term can be used to refer specifically to the embrittlement that occurs in steels and similar metals at relatively low hydrogen concentrations,
    or it can be used to encompass all embrittling effects that hydrogen has on metals.

  • [24] Tests such as ASTM F1624 can also be used to rank alloys and coatings during materials selection to ensure (for instance) that the threshold of cracking is below the
    threshold for hydrogen-assisted stress corrosion cracking.

  • If the metal has not yet started to crack, hydrogen embrittlement can be reversed by removing the hydrogen source and causing the hydrogen within the metal to diffuse out
    through heat treatment.

  • Apart from arc welding, the most common problems are from chemical or electrochemical processes which, by reduction of hydrogen ions or water, generate hydrogen atoms at the
    surface, which rapidly dissolve in the metal.

  • In the case of welding, often pre-heating and post-heating the metal is applied to allow the hydrogen to diffuse out before it can cause any damage.

  • [29] Prevention Hydrogen embrittlement can be prevented through several methods, all of which are centered on minimizing contact between the metal and hydrogen, particularly
    during fabrication and the electrolysis of water.

  • [10] However, hydrogen embrittlement is almost always distinguished from high temperature hydrogen attack (HTHA), which occurs in steels at temperatures above 400 °C and involves
    the formation of methane pockets.

  • These broader embrittling effects include hydride formation, which occurs in titanium and vanadium but not in steels, and hydrogen-induced blistering, which only occurs at
    high hydrogen concentrations and does not require the presence of stress.

  • [15] • Internal pressure: At high hydrogen concentrations, absorbed hydrogen species recombine in voids to form hydrogen molecules (H2), creating pressure from within the

  • [22] Austempered iron is also susceptible, though austempered steel (and possibly other austempered metals) displays increased resistance to hydrogen embrittlement.

  • Due to the time needed to re-combine hydrogen atoms into the hydrogen molecules, hydrogen cracking due to welding can occur over 24 hours after the welding operation is completed.

  • [32] After a manufacturing process or treatment which may cause hydrogen ingress, the component should be baked to remove or immobilize the hydrogen.

  • • ASTM G142 is the Standard Test Method for Determination of Susceptibility of Metals to Embrittlement in Hydrogen Containing Environments at High Pressure, High Temperature,
    or Both.

  • This pressure can increase to levels where cracks form, commonly designated hydrogen-induced cracking (HIC), as well as blisters forming on the specimen surface, designated
    hydrogen-induced blistering.

  • These coatings not only provide a barrier against hydrogen diffusion but also enhance the corrosion resistance of the metal.

  • This is a particular issue when looking for non-palladium-based alloys for use in hydrogen separation membranes.

  • Testing the fracture toughness of hydrogen-charged, embrittled specimens is complicated by the need to keep charged specimens very cold, in liquid nitrogen, to prevent the
    hydrogen diffusing away.

  • [14] There is a great variety of mechanisms that have been proposed[14] and investigated as to the cause of brittleness once diffusible hydrogen has been dissolved into the

  • HEDE can only occur when the local concentration of hydrogen is high, such as due to the increased hydrogen solubility in the tensile stress field at a crack tip, at stress
    concentrators, or in the tension field of edge dislocations.

  • The coating materials used in this process are often composed of materials with excellent resistance to hydrogen diffusion, such as ceramics or cermet alloys.

  • This process can cause the grains to literally be forced away from each other, and is known as steam embrittlement (because steam is directly produced inside the copper crystal
    lattice, not because exposure of copper to external steam causes the problem).

  • The test uses the incremental step loading (ISL) or Rising step load testing (RSL) method 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).

  • Hydrogen embrittlement (HE), also known as hydrogen-assisted cracking or hydrogen-induced cracking (HIC), is a reduction in the ductility of a metal due to absorbed hydrogen.

  • One of these chemical reactions involves hydrogen sulfide (H 2S) in sulfide stress cracking (SSC), a significant problem for the oil and gas industries.

  • As an example of severe hydrogen embrittlement, the elongation at failure of 17-4PH precipitation hardened stainless steel was measured to drop from 17% to only 1.7% when
    smooth specimens were exposed to high-pressure hydrogen[2] As the strength of steels increases, the fracture toughness decreases, so the likelihood that hydrogen embrittlement will lead to fracture increases.

  • By applying an electric current, the metal ions are reduced and form a metallic coating on the substrate.

  • • Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments[40] Notable failures from hydrogen embrittlement
    • In 2013, six months prior to opening, the East Span of the Oakland Bay Bridge failed during testing.

  • [24] Environmental embrittlement is also observed to reduce fracture toughness in fast fracture tests, but the severity is much reduced compared with the same effect in fatigue[24]
    Hydrogen embrittlement is the effect where a previously embrittled material has low fracture toughness whatever atmosphere it is tested in.

  • [34] Testing Most analytical methods for hydrogen embrittlement involve evaluating the effects of (1) internal hydrogen from production and/or (2) external sources of hydrogen
    such as cathodic protection.

  • Heat treatment (baking) was used to reduce hydrogen content.

  • [11] Metals can be exposed to hydrogen from two types of sources: gaseous hydrogen and hydrogen chemically generated at the metal surface.

  • Environmental embrittlement[2] is a surface effect where molecules from the atmosphere surrounding the material under test are adsorbed onto the fresh crack surface.

  • Chemical conversion coatings are another effective method for surface protection.

  • That this effect is due to adsorption, which saturates when the crack surface is completely covered, is understood from the weak dependence of the effect on the pressure of

  • [1][13][14] Mechanisms Hydrogen embrittlement is a complex process involving a number of distinct contributing micro-mechanisms, not all of which need to be present.

  • There are many other related standards for hydrogen embrittlement: • NACE TM0284-2003 (NACE International) Resistance to Hydrogen-Induced Cracking • ISO 11114-4:2005 (ISO)Test
    methods for selecting metallic materials resistant to hydrogen embrittlement.

  • [37][38] F1624 provides a rapid, quantitative measure of the effects of hydrogen both from internal sources and external sources (which is accomplished by applying a selected
    voltage in an electrochemical cell).

  • These materials have a low permeability to hydrogen, creating a robust barrier against hydrogen ingress into the metal substrate.

  • [18] Fatigue While most failures in practice have been through fast failure, there is experimental evidence that hydrogen also affects the fatigue properties of steels.


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