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HIC – SSC

Hydrogen Induced Cracking (HIC)

The HIC (Hydrogen Induced Cracking) test in accordance to the NACE TM 0284, is executed sinking the specimen in solution which are saturated with hydrogen sulfide (H2S). Once the corrosion is finished, the specimens are polished and examined by micrography.
The hydrogen induced cracking is related to the isolated hydrogen atoms diffusivity inside the metal, generally under pressure tubes and vessels that are built of low alloys or nickel and titanium alloys. During the machining and the fabrication, the formation process and the high hydrogen concentration gradient change the hydrogen diffusivity coefficient that could penetrate with an isolated state. Once the atomic hydrogen in penetrated, these atoms unify to generate gaseous hydrogen and a series of small gas pockets that generate various localized stresses and eventual cracks along the working direction.

 

Sulphide Stress Corrosion Cracking

The SSCC (Sulphide Stress Corrosion Cracking) test verifies the cracking resistance under a uniaxial tensile stress in conjunction with a solution of hydrogen sulfide (H2S).

Generally, many alloys are sensible to hydrogen sulfide and they form metal sulfides and atomic hydrogen as corrosion byproduct. Successively, the atomic hydrogen diffuses in the metal alloy and it recombines in order to form gaseous pockets and localized pressure that reduces the material ductility. In particular, the sulfur presence highly reduces the chance of hydrogen combination on the metal surface, inducing an higher atomic hydrogen diffusivity.

 

 

References:

Hydrogen Induced Cracking – https://en.wikipedia.org/wiki/Hydrogen_embrittlement

NACE TM 0284 – https://www.nace.org/cstm/Store/Product.aspx?id=56061ccc-a50b-4e56-84ba-ad689a9fb03b

Hydrogen Sulfide (H2S) – https://en.wikipedia.org/wiki/Hydrogen_sulfide

Nickel alloys – https://en.wikipedia.org/wiki/Category:Nickel_alloys

Sulphide Stress Corrosion Cracking – https://www.nace.org/cstm/Store/Product.aspx?id=56061ccc-a50b-4e56-84ba-ad689a9fb03b

NACE TM 0177 – https://www.nace.org/cstm/Store/Product.aspx?id=9c03e61f-b2ab-494a-bf74-5ab687c570bd