Hydrogen Induced Cracking

By: Sukma Suci Friandani (3334131140)

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Outline

Definition

Causes

Mechanism

Prevention

Case Study

Conclusion

References

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What is hydrogen induced cracking ??

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What causes hydrogen induced cracking?

Hydrogen absorbed in metal

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Mechanism

Source of atomic hydrogen H2S 2H+ + S2-

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Corrosive environment

Blister

Thi

ckne

ss

Atmosphere

Hydrogen Induced Cracking

Stepwise crack

Straight crack

Mechanism

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Mechanism

Accumulation in the void

Linking of voids to form cracks

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Diffusion   Fe + 2H + Fe2+ + 2H0

2H0 H2

Prevention

Material Selection

Baking steels at low temperature

(100 °C -150 °C)

Reduce corrosion rate (addition of

inhibitors)

Coating (Zn, Cd)

Alloying

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Case Study

At Saudi Aramco Gas Processing Plant processes wet sour gas streams and produces dry sweet sales gas in addition Natural Gas Liquid (NGL). NGL is Hydrocarbons in natural gas that are separated from the gas as liquids through the process of absorption, condensation, adsorption, or other methods in gas processing or cycling plants. It is not commercially sold, and is generally used to produce petrochemicals and plastics. 

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Case Study

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Condition At Saudi Aramco Gas Processing Plant

Hydrogen sulfide (H2S) concentration is ranging from 2-41 mol% which equivalent to 20,000-410,000 ppm of H2S.

Pipes were fabricated by non HIC resistant material.

Present of element sulfur in the streams. Temperature ranging from 120-280 F.⁰ Present of free water in the fluid stream.

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Conclusion

Hydrogen-Induced Cracking (HIC) is the stepwise internal cracks that connect adjacent hydrogen blisters on different planes in the metal, or to the metal surface. It is also known as stepwise cracking.

The mechanism starts with the atomic hydrogen combines to form molecular hydrogen and forms rows of small blisters. The pressure inside the blisters continues to build up as more H atoms combine to form hydrogen molecules. Blisters are formed at varying depths which link together to form cracks. The cracks formed by bulging of the blisters are parallel to the surface along the original lamination generate in various depths and finally connected together. The cracks may reach the surface and the metal fails

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Conclusion

HIC can be prevented by material selection,

baking steels at low temperature (100-150°C),

minimizing hydrogen content, reduce corrosion

rate , coating (Zn, Cd) and alloying.

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References

Saudi Aramco Engineering EncyclopediaTurnbull, Alan. Hydrogen Transport & Cracking in

Metals. Cambridge, UK. The Institute of Materials, 1995

https://www.corrosionpedia.com/definition/649/hydrogen-induced-cracking-hic

http://www.corrosionclinic.com/types_of_corrosion/hydrogen-induced_cracking_HIC.htm

https://inspectioneering.com/tag/hydrogen+induced+cracking

http://jolisfukyu.tokai-sc.jaea.go.jp/fukyu/mirai en /2013/11_1.html

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Thank you

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The difference between hydrogen and hydrogen induced cracking :Hydrogen damage is encountered in many steel processes, such as pickling, electroplating and welding. One essential contributing feature of hydrogen damage to welds is that mobile hydrogen, by virtue of its very increased solubility and diffusivity through steel at elevated temperatures, is generated at a relatively high concentration in certain regions of the weldment (the heat affected zone). As the weldment cools, the solubility decreases, and so the activity of this mobile hydrogen increases. However, HIC during steel service does not normally involve the cooling of steel after exposure to hydrogen at high temperatures. Usually, active, aqueous acid corrosion by hydrogen promoters, the weak acid hydrides of P, As, Sb, S, Se, Te and F causes atomic hydrogen to enter the steel at extremely high activities. The gaseous hydrogen pressure required to generate the hydrogen in steel concentrations generated by promoters would need to be over one million bar. No wonder steel can be susceptible to hydrogen cracking. The most important hydrogen promoter industrially, and probably the most vigorous are H2S and sour gas.

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Question : What is baking process to prevent hydrogen induced

cracking? (Dea Anggraheni Pusparasmi)

Answer : Baking or known as de-embrittlement is used to overcome

the weaknesses of methods such as electroplating which introduce

hydrogen to the metal, but is not always entirely effective. The de-

embrittlement or baking shall commence as soon as possible,

preferably within one hour but not later than three hours after plating

has been performed. The exact time and temperature of the bake is

not specified, but times between 2 and 24 hours at temperatures

between 350°F and 450°F are listed as suitable depending on type,

size of fastener, geometry and other variables.