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HYDROGEN DAMAGE is a term used to designate a

number of processes in metals by which the loadcarryingcapacity of the metal is reduced due to the presence ofhydrogen.

The detrimental effects of hydrogen on metals are often enhanced

when the hydrogen is present in combination with residual orapplied tensilestresses.

Many types of hydrogen damage are notreally due to corrosion processes at all.

Many metals and alloys are susceptible tohydrogen damage; however, specific formsof hydrogen damage are generally morecommon within particular alloy systems.

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Overview of Hydrogen Damage

ProcessesHydrogen is known to cause various problems in many

metals and is readily available during the production,

processing, and service of metals from operations such

as: Refining (precipitates upon solidification from

supersaturated concentrations)

Acid cleaning (pickling)

Electroplating

Contact with water or other hydrogen-containingliquids or gases

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ManifestationDepending on the type of hydrogen-metal interaction,

hydrogen damage of metal manifests itself in one of

several ways. The types of interactions betweenhydrogen and metals include:

the formation of solid solutions of hydrogen inmetals,

molecular hydrogen, gaseous products from reactionsbetween hydrogen and

alloying or segregated impurity elements, or brittleintermetallic hydride compounds.

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Types of hydrogen damage Specific types of hydrogen damage, some of which

occur only in specific alloys under specific conditions:

Hydrogen embrittlement

Hydrogen-induced blistering

Cracking from precipitation of internal hydrogen

Hydrogen attack

Cracking from hydride formation

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Specific damage

process/mechanism

Most common in Comments

Cracking fromprecipitationof internal gaseoushydrogen

Heavy steel sections Induced by high-temperature exposurefollowed by rapidcooling

Hydrogen attack Steels subject tocombined hightemperature and high-pressure hydrogen. Alsoaffects copper

Irreversible chemicalreactions of hydrogen

with matrix or alloyelements form high-pressure pockets ofgases other thanmolecular hydrogen.

Cracking from hydrideformation

Transition, rare earth,alkaline earth metals,and their alloys(includes titanium,tantalum, zirconium,uranium, and thorium)

Brittle hydrides oftenform preferentially

where the stress ishighest.

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The first three types are usually observed atambienttemperatures and are closely related to one another.Hydrogen damage usually manifests itself ashydrogenembrittlement in high-strength steels and as hydrogeninduced blistering in low-strength steels. The solubility and

diffusivity of hydrogen in steel sharply decrease withlowering temperatures; therefore, when a heavy section ofsteel containing hydrogen at elevated temperature is rapidlycooled to ambient temperature, the hydrogen remaining in

the steel precipitates out in the gaseous state.

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The pressure of the hydrogen gas is often greatenough to produce internal cracks. Hydrogenattack is an elevated-temperature phenomenon, in

which hydrogen reacts with metal substrates oralloy additions. A number of transition and rareearth metals form hydrides, and the formation ofmetal hydrides can result in cracking.