Hydrogen Embrittlement

Definition - What does Hydrogen Embrittlement mean?

Hydrogen embrittlement (HE) is a process resulting in a decrease of the toughness or ductility of a metal due to the presence of atomic hydrogen.

Corrosionpedia explains Hydrogen Embrittlement

Hydrogen embrittlement starts with lone hydrogen atoms diffusing 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, a process known as hydrogen-induced cracking (HIC). High-strength and low-alloy steels, nickel and titanium alloys are most susceptible.

Hydrogen embrittlement has been recognized classically as being of two types:

· Internal hydrogen embrittlement: This occurs when the hydrogen enters molten metal which becomes supersaturated with hydrogen immediately after solidification.

· Environmental hydrogen embrittlement: This results from hydrogen being absorbed by solid metals. It can occur during elevated-temperature thermal treatments and in service during electroplating, contact with maintenance chemicals, corrosion reactions, cathodic protection, and operating in high-pressure hydrogen.

Hydrogen embrittlement can be prevented through:

· Control of stress level (residual or load) and hardness

· Avoiding the hydrogen source

· Baking to remove hydrogen

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