Hydrogen Embrittlement

Hydrogen embrittlementFrom Wikipedia, the free encyclopedia

Hydrogen embrittlement is the process by which various metals, most importantlyhigh-strength steel, become brittle and fracture following exposure to hydrogen. Hydrogenembrittlement is often the result of unintentional introduction of hydrogen into susceptiblemetals during forming or finishing operations and increases cracking in the material. Thisphenomenon was first described in 1875.[1]

Hydrogen embrittlement is also used to describe the formation of zirconium hydride anddelayed hydride cracking. Use of the term in this context is common in the nuclearindustry.

Contents

1 Process1.1 Counteractions1.2 Decision support tool

2 Related phenomena3 Testing4 See also5 References6 Further reading7 External links

ProcessThe mechanism starts with lone hydrogen atoms diffusing through the metal. At hightemperatures, 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 formhydrogen molecules, they create pressure from inside the cavity they are in. This pressurecan increase to levels where the metal has reduced ductility and tensile strength up to thepoint where it cracks open (hydrogen induced cracking, or HIC). High-strength andlow-alloy steels, nickel and titanium alloys are most susceptible. Austempered iron is alsosusceptible. Steel with an ultimate tensile strength of less than 1000 MPa (~145,000 psi) orhardness of less than 30 HRC are not generally considered susceptible to hydrogenembrittlement. Jewett et al.[2] reports the results of tensile tests carried out on severalstructural metals under high-pressure molecular hydrogen environment. These tests haveshown that austenitic stainless steels, aluminum (including alloys), copper (includingalloys, e.g. beryllium copper) are not susceptible to hydrogen embrittlement along with fewother metals.[3] For example of a severe embrittlement measured by Jewett, the elongation

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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.

Hydrogen embrittlement can occur during various manufacturing operations or operationaluse - anywhere that the metal comes into contact with atomic or molecular hydrogen.Processes that can lead to this include cathodic protection, phosphating, pickling, andelectroplating. A special case is arc welding, in which the hydrogen is released frommoisture (for example in the coating of the welding electrodes; to minimize this, speciallow-hydrogen electrodes are used for welding high-strength steels). Other mechanisms ofintroduction of hydrogen into metal are galvanic corrosion, chemical reactions of metal withacids, or with other chemicals (notably hydrogen sulfide in sulfide stress cracking, or SSC,a process of importance for the oil and gas industries).[4]

Counteractions

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

In the case of welding, often pre- and post-heating the metal is applied to allow thehydrogen to diffuse out before it can cause any damage. This is specifically done withhigh-strength steels and low alloy steel such as the chrome/molybdenum/vanadium alloys.Due to the time needed to re-combine hydrogen atoms into the harmful hydrogenmolecules, hydrogen cracking due to welding can occur over 24 hours after the weldingoperation is completed.

Products such as ferrosilicates can be used to treat surfaces normally subject to hydrogenembrittlement in order to prevent it from taking place.

Decision support tool

To handle the frequency of occurrence of embrittlement in steel, decision support tools areused[5] depending on the field of application.[6]

Related phenomenaIf steel is exposed to hydrogen at high temperatures, hydrogen will diffuse into the alloyand combine with carbon to form tiny pockets of methane at internal surfaces like grainboundaries and voids. This methane does not diffuse out of the metal, and collects in thevoids at high pressure and initiates cracks in the steel. This selective leaching process isknown as hydrogen attack, or high temperature hydrogen attack and leads todecarburization of the steel and loss of strength and ductility.

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





(water), which then forms pressurized bubbles at the grain boundaries. This process cancause the grains to literally be forced away from each other, and is known as steamembrittlement (because steam is produced, not because exposure to steam causes theproblem).

TestingThere are two ASTM standards for testing embrittlement due to hydrogen gas. Thestandard ASTM F1459-06 Standard Test Method for Determination of the Susceptibility ofMetallic Materials to Hydrogen Gas Embrittlement (HGE) Test (http://www.astm.org/Standards/F1459.htm) uses a diaphragm loaded with a differential pressure. The testASTM G142-98(2004) Standard Test Method for Determination of Susceptibility of Metals toEmbrittlement in Hydrogen Containing Environments at High Pressure, High Temperature,or Both (http://www.astm.org/Standards/G142.htm) uses a cylindrical tensile specimentested into an enclosure pressurized with hydrogen or helium.

Another ASTM standard exists for quantitatively testing for the Hydrogen Embrittlementthreshold stress for the onset of Hydrogen-Induced Cracking due to platings and coatingsfrom Internal Hydrogen Embrittlement (IHE) and Environmental Hydrogen Embrittlement(EHE) - F1624-06 Standard Test Method for Measurement of Hydrogen EmbrittlementThreshold in Steel by the Incremental Step Loading Technique.[7][8] and ASTM STP962,"Hydrogen Embrittlement: Prevention and Control."

NACE TM0284-2003 (NACE International) Resistance to Hydrogen-Induced CrackingISO 11114-4:2005 (ISO)Test methods for selecting metallic materials resistant tohydrogen embrittlement.ASTM F1940-07a (http://www.astm.org/cgi-bin/SoftCart.exe/DATABASE.CART/REDLINE_PAGES/F1940.htm?L+mystore+yvst4574+1196145312)- Standard TestMethod for Process Control Verification to Prevent Hydrogen Embrittlement in Platedor Coated FastenersASTM F519-06e2 (http://www.astm.org/cgi-bin/SoftCart.exe/STORE/filtrexx40.cgi?U+mystore+yvst4574+-L+F519+/usr6/htdocs/astm.org/DATABASE.CART/REDLINE_PAGES/F519.htm)-Standard Test Method forMechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes andService Environments

See also

Hydrogen analyzerHydrogen damageHydrogen pipingHydrogen safetyLow hydrogen annealing



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Nascent hydrogenOxygen-free copper

References

^ "Study reveals clues to cause of hydrogen embrittlement" (http://www.mcgill.ca/newsroom/channels/news/study-reveals-clues-cause-hydrogen-embrittlement-219051) (Press release).McGill University. November 19, 2012. Retrieved November 20, 2012.

1.

^ Jewett, R.P. (1973). Hydrogen Environment Embrittlement of Metals. NASA CR-2163.2.^ "Overview of interstate hydrogen pipeline systems" (http://corridoreis.anl.gov/documents/docs/technical/APT_61012_EVS_TM_08_2.pdf) (PDF). Retrieved 2013-12-16.

3.

^ ASTM F1940-07a Hydrogen Project (http://www.astm.org/cgi-bin/SoftCart.exe/DATABASE.CART/REDLINE_PAGES/F1940.htm?L+mystore+yvst4574+1196145312)

4.

^ "Decision Support Tool" (http://www.naturalhy.net/docs/final_public_presentation/09.%20WP6%20-%20Decision%20Support%20Tool.pdf) (PDF). Retrieved 2013-12-16.

5.

^ "Using the existing natural gas system for hydrogen" (http://www.naturalhy.net/docs/Naturalhy_Brochure.pdf) (PDF). Retrieved 2013-12-16.

6.

^ ASTM STP 543,"Hydrogen Embrittlement Testing"7.^ Raymond L (1974). Hydrogen Embrittlement Testing. ASTM International.ISBN 978-0-8031-0373-3.

8.

Further reading

ASM international, ASM Handbook #13: Corrosion, ASM International, 1998

External links

Zinc Plating and Hydrogen Embrittlement (http://www.beyondrigging.com/2014/02/hydrogen-embrittlement/)Hydrogen embrittlement (http://www.uni-saarland.de/fak8/wwm/research/phd_barnoush/hydrogen.pdf)Corrosion-Doctors.org Hydrogen embrittlement (http://www.corrosion-doctors.org/Forms-HIC/embrittlement.htm)Hydrogen purity plays a critical role (http://www.hydrogen.energy.gov/pdfs/progress05/v_a_4_adams.pdf)A Sandia National Lab technical reference manual. (http://www.sandia.gov/matlsTechRef/)Hydrogen Embrittlement group (http://www.linkedin.com/groups/Hydrogen-Embrittlement-4991909?trk=myg_ugrp_ovr)The Network of Excellence (NoE) in Hydrogen Embrittlement



http://www.mcgill.ca/newsroom

http://corridoreis.anl.gov/documents

http://www.astm.org/cgi-bin/SoftCart.exe

http://www.naturalhy.net/docs/final_public_presentation

http://www.naturalhy.net

http://www.beyondrigging.com/2014/02

http://www.uni-saarland.de/fak8/wwm/research

http://www.corrosion-doctors.org

http://www.hydrogen.energy.gov

http://www.sandia.gov

http://www.linkedin.com/groups/Hydrogen



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