What is hydrogen embrittlement? What is hydrogen corrosion, and what is hydrogen bubbling? Please explain in detail regarding the corrosion caused by hydrogen

Hydrogen embrittlement occurs when hydrogen dissolved in steel combines to form hydrogen molecules, resulting in stress concentration that exceeds the steel’s strength limit and leads to the formation of tiny cracks within the steel, also known as white spots. Hydrogen embrittlement can only be prevented, not cured. Once hydrogen embrittlement occurs, it cannot be eliminated. Trace amounts of hydrogen (on the order of 10–6) that enter the steel during its smelting process and during the manufacturing and assembly of parts (such as electroplating and welding) can cause the material to become brittle or even crack under the effect of internal residual stresses or external stresses. The properties of the steel can be restored through dehydrogenation treatment (for example, by heating to over 200°C for several hours to reduce internal hydrogen) before cracking occurs. Therefore, internal hydrogen embrittlement is reversible. Hydrogen blistering is caused by hydrogen entering the interior of the metal. It is common in steel during electrochemical corrosion, electrolysis, or electroplating; due to the high hydrogen activity, there is always a certain concentration of hydrogen atoms on the metal surface. Some of these highly active hydrogen atoms, which have not formed hydrogen molecules, diffuse into the interior of the metal before eventually combining to form hydrogen molecules. Since hydrogen molecules cannot diffuse, the hydrogen concentration and pressure inside the metal increase, causing the metal to expand and deform locally; blistering can be observed on the surface of the steel. Hydrogen corrosion is a type of high-temperature corrosion. It mainly occurs in steel-based units such as oil hydrogenation and cracking. Under high temperature and pressure, hydrogen in the gas phase penetrates into the steel in the form of hydrogen atoms, where it combines with carbon in the steel to form methane. This leads to decarburization of the steel’s surface, reducing its strength and ductility; in severe cases, it can cause bubbling or cracking on the surface. The resistance of carbon steel to hydrogen corrosion decreases as the carbon content in the steel increases ； Low-alloy steels containing small amounts of elements such as titanium, niobium, vanadium, and molybdenum, which have a strong affinity for carbon, possess good resistance to hydrogen corrosion. 　　The hydrogen dissolved in the molten steel during the smelting process remains in the steel because it was not able to escape immediately during crystallization and cooling ； During welding, hydrogen generated by the decomposition of moisture or oil under the high temperature of the arc dissolves into the steel ； During the operation of the equipment, hydrogen in the working medium enters the steel. When hydrogen is present in steel and the stress exceeds a certain critical value, hydrogen-induced cracking occurs. The embrittlement of steel by hydrogen is a process in which microcracks propagate under high stress. The brittle fracture stress can be as low as 20% of the yield limit. The higher the strength of the steel (the greater the stress it can withstand), the more sensitive it is to hydrogen embrittlement. The stress levels in the container, including service stress and residual stress, are important factors contributing to hydrogen embrittlement. Hydrogen embrittlement is a type of delayed fracture; the delay before failure can be as short as a few minutes or as long as several days.

Are there any other types of corrosion caused by hydrogen? Please be as comprehensive as possible. Thank you

There should be four types of hydrogen damage: Hydrogen corrosion: At high temperatures (205–595°C), hydrogen reacts chemically with the components of the alloy. 　　 Decarburization: A special case of hydrogen corrosion that occurs at high temperatures (205–595°C). At these high temperatures, hydrogen atoms penetrate into the steel and combine with carbon to form methane, thereby causing decarburization of the steel. When the temperature drops, bubbling also occurs on the surface of the steel. Decarburization can also occur on the surface of steel when the medium contains hydrogen. 　　 Hydrogen bubbling: If atomic hydrogen is absorbed into the steel, it then forms molecular hydrogen which accumulates in microscopic voids, creating a high internal pressure sufficient to cause small bubbles to appear on the metal surface. The temperature at which bubbling occurs most easily is 0–150℃ ； 　　 Hydrogen embrittlement: Hydrogen embrittlement occurs in steel when it contains hydrogen at levels of (0.1–10)×10⁻⁶; under tensile stress and slow strain, the steel becomes more brittle, and cracks may even form. Hydrogen embrittlement occurs very easily in the temperature range of –100 to 100°C. Internal hydrogen embrittlement is a type of hydrogen embrittlement and represents a classic issue related to hydrogen embrittlement. Trace amounts of hydrogen (on the order of 10–6) that enter the steel during its smelting process and during the manufacturing and assembly of parts (such as electroplating and welding) can cause the material to become brittle or even crack under the effect of internal residual stresses or external stresses. The properties of the steel can be restored through dehydrogenation treatment (for example, by heating to over 200°C for several hours to reduce internal hydrogen) before cracking occurs. Therefore, internal hydrogen embrittlement is reversible.

Is there one with a finer division? Thank you

Does hydrogen exist in steel in atomic form or as a compound? Is hydrogen gas formed when hydrogen escapes from the matrix after heating? Or hydrogen compounds? Which specific compound is it?

This post was last edited by realben on 2010-11-11 17:37. There are various opinions on this issue, and the slightest carelessness can lead to confusion. Firstly, the damage caused by H can be divided into two main types: high-temperature hydrogen damage (HTHA) that occurs at high temperatures (above 200 degrees), and wet hydrogen sulfide damage that occurs at low temperatures (up to 120 degrees). High-temperature hydrogen damage results from the combination of H with cementite in the steel, leading to the formation of methane and ferrite. Wet hydrogen sulfide damage is further divided into four types: hydrogen-induced cracking, stress-guided hydrogen-induced cracking, sulfide stress corrosion cracking, and hydrogen blistering. I won’t go into detail regarding the specific mechanisms; please refer to API571 at http://bbs.hcbbs.com/viewthread...highlight=API%2B571