The key difference between hydrogen embrittlement and stress corrosion cracking is that hydrogen embrittlement occurs due to corrosion caused by acids such as wet hydrogen sulfide and hydrofluoric acid, whereas stress corrosion cracking occurs due to the influence of tensile stress and a corrosive environment.
Hydrogen embrittlement is also known as hydrogen-assisted cracking or hydrogen-induced cracking. This process is very important in alloys as well as in pure metals; however, stress corrosion cracking is applicable only for alloys, not for pure metals.
CONTENTS
1. Overview and Key Difference
2. What is Hydrogen Embrittlement
3. What is Stress Corrosion Cracking
4. Hydrogen Embrittlement vs Stress Corrosion Cracking in Tabular Form
5. Summary – Hydrogen Embrittlement vs Stress Corrosion Cracking
What is Hydrogen Embrittlement?
Hydrogen embrittlement is a reduction in the ductility of a metal due to the absorbed hydrogen. It is also known as hydrogen-assisted cracking or hydrogen-induced cracking. Hydrogen atoms are very small. Therefore, these atoms can permeate solid metals. When it is absorbed, hydrogen can lower the stress that is required to form cracks in the metal, which results in embrittlement. Moreover, hydrogen embrittlement takes place most notably in steel, iron, nickel, titanium, cobalt, and the alloys of these metals. Furthermore, copper, aluminum, and stainless steel are metals that are susceptible to hydrogen embrittlement.
Important facts about the nature of hydrogen embrittlement have been known since the 19th century. It can be maximized at a temperature that is around room temperature in steel, and most metals are relatively immune to the hydrogen embrittlement process at a temperature that is above 150 degrees Celsius. This process also requires the presence of both atomic hydrogen and mechanical stress to induce crack growth. However, this stress can be applied or residual. Generally, higher-strength materials are highly susceptible to hydrogen embrittlement. Moreover, it can increase at a lower strain rate.
Hydrogen embrittlement is a complex process that involves a number of distinct contributing micro-mechanisms, but all these processes are not required at once. The mechanism of hydrogen embrittlement involves the formation of brittle hydrides, the creation of voids that lead to high-pressure bubbles, enhanced decohesion at internal surfaces, and localized plasticity at crack tips that can assist the propagation of cracks.
What is Stress Corrosion Cracking?
Stress corrosion cracking involves the growth of crack formation in a corrosive environment. This type of cracking can lead to unexpected and sudden failure of normally ductile metal alloys that are subject to tensile stress. This can specifically happen at elevated temperatures.
Moreover, stress corrosion cracking is highly chemically specific, as certain alloys can undergo stress corrosion cracking only upon exposure to a small number of chemical environments. This chemical environment that causes stress corrosion cracking for a specific alloy is often one that is only mildly corrosive to the metal. Metal parts undergoing severe stress corrosion cracking can appear bright and shiny. This is because they are filled up with microscopic cracks. This can make stress corrosion cracking hard to detect.
Stress corrosion cracking mainly affects metals and metallic alloys. Environmental stress cracking is a comparable effect that also affects other materials, including polymers, ceramics, and glass.
What is the Difference Between Hydrogen Embrittlement and Stress Corrosion Cracking?
Hydrogen embrittlement and stress corrosion cracking are two important industrial processes. The key difference between hydrogen embrittlement and stress corrosion cracking is that hydrogen embrittlement occurs due to corrosion from acids such as wet hydrogen sulfide and hydrofluoric acid, whereas stress corrosion cracking occurs due to the influence of tensile stress and a corrosive environment.
The below infographic presents the differences between hydrogen embrittlement and stress corrosion cracking in tabular form for side-by-side comparison.
Summary – Hydrogen Embrittlement vs Stress Corrosion Cracking
Hydrogen embrittlement is a reduction in the ductility of a metal due to the absorbed hydrogen, while stress corrosion cracking is the growth of crack formation in a corrosive environment. The key difference between hydrogen embrittlement and stress corrosion cracking is that hydrogen embrittlement occurs due to corrosion caused by acids such as wet hydrogen sulfide and hydrofluoric acid, whereas stress corrosion cracking occurs due to the influence of tensile stress and a corrosive environment.
Reference:
1. “What Is Hydrogen Embrittlement? – Causes, Effects and Prevention.” TWI.
Image Courtesy:
1. “Steel-with-Hydrogen-Induced-Cracks-01” By © CEphoto, Uwe Aranas (CC BY-SA 4.0) via Commons Wikimedia
2. “Stress-Corrosion-Cracking-caused-by-weld-stress-01” By © CEphoto, Uwe Aranas (CC BY-SA 3.0) via Commons Wikimedia