What is hydrogen embrittlement?

Simple to understand: Materials break below the allowable stress in a hydrogen environment. For example, if heat-treated parts are not dehydrogenated during the pickling process, hydrogen embrittlement will easily occur. This post was last edited by lxzzl on 2009-3-27 11:36 ]

Hydrogen embrittlement is a phenomenon in which steel is exposed to high temperature and high pressure hydrogen, causing chemical changes in the metal structure of the steel. As a result, the strength and plasticity of the steel decrease, and the fracture surface becomes brittle fracture, which is called hydrogen embrittlement. The cause is that hydrogen enters the interior of the steel under high temperature and high pressure conditions and interacts with cementite to generate methane, which greatly reduces the decarburization strength of the steel. The generated methane cannot dissolve the ferrite and escapes in gaseous state, accumulating at the grain boundaries of the steel, generating a large internal pressure and causing the steel to crack along the grain boundaries. Hydrogen will not cause obvious corrosion to steel at normal temperatures and pressures, but when the temperature exceeds 300°C and the pressure is higher than 30MPa, corrosion defects such as hydrogen embrittlement will occur, especially under high temperature conditions. Such as desulfurization tower, shift tower and ammonia synthesis tower in the production process of ammonia synthesis ； Some hydrogenation reaction units in the oil refining process ； Methanol synthesis tower in petrochemical production process, etc. This post was last edited by lxzzl on 2009-3-27 11:38 ]

I heard an old professor say that it is because hydrogen reacts with steel at a certain temperature, causing the carbon in the steel to precipitate, changing the composition of the steel, and also changing the stress of the steel, which can be regarded as a kind of corrosion. This post was last edited by lxzzl on 2009-3-27 11:38 ]

Molecular hydrogen is partially decomposed into atomic hydrogen under high temperature and pressure, or hydrogen is electrochemically reacted in wet corrosive gases to generate hydrogen atoms. After these hydrogen atoms penetrate into the steel, the atomic bonding force between the steel grains is reduced, resulting in a reduction in the elongation and area shrinkage of the steel, and a change in strength. This phenomenon is called hydrogen embrittlement. After the steel has been in contact with high-temperature and high-pressure hydrogen for a long time, hydrogen atoms or hydrogen molecules diffuse inward through the crystal lattice and between the crystals. These hydrogen react chemically with the carbides in the steel to generate methane, resulting in internal decarburization of the steel. Methane gas cannot diffuse out of the steel and accumulates in the steel. Local high pressure is formed between the crystals, resulting in stress concentration and widening of the crystals, resulting in micro cracks or blistering. At first, the cracks are small, but over time, numerous cracks are connected, causing the strength and toughness of the steel to decrease, lose its original plasticity and become brittle. This is called hydrogen corrosion. This post was last edited by lxzzl on 2009-3-27 11:40 ]

Hydrogen embrittlement is a one-time embrittlement, which is a reversible phenomenon, while hydrogen corrosion is a permanent embrittlement, which is irreversible. There is an essential difference between the two.

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Hydrogen atoms invade the lattice gap of the material, causing stress and causing hydrogen embrittlement.

As we all know, hydrogen has the smallest atomic weight and can easily enter the crystal lattice of other materials, causing other materials to change their mechanical properties and become brittle.

The principle of hydrogen embrittlement is already very clear. Preventing the occurrence of hydrogen embrittlement depends on material selection and operating conditions. The hydrogen embrittlement conditions mentioned on the third floor: But when the temperature exceeds 300°C and the pressure is higher than 30MPa, corrosion defects such as hydrogen embrittlement will occur, especially under high temperature conditions. There is also information that the conditions for hydrogen embrittlement are 100~150℃. Therefore, I think we should talk about the conditions for hydrogen embrittlement occurrence for a specific material.

Hydrogen embrittlement (or hydrogen damage) of a pressure vessel means that its wall is eroded by hydrogen, resulting in a reduction in the plasticity and strength of the material, which may lead to cracking or delayed brittle failure. The damage caused by hydrogen at high temperature and high pressure to steel is mainly because hydrogen penetrates into the metal in an atomic state and recombines into molecules inside the metal, generating high pressure. In severe cases, it can cause bulges or wrinkles on the surface. ； Hydrogen combines with the carbon in the steel to decarburize the steel or reduce the sulfides and oxides in the steel. The hydrogen that causes hydrogen embrittlement damage of pressure vessels can be originally present in the equipment. For example, moisture during steelmaking and welding processes is reduced at high temperatures to generate hydrogen, which is dissolved in the liquid metal. Or when the equipment is electroplated or pickled, the steel surface is supersaturated with adsorbed hydrogen atoms, causing hydrogen to penetrate into the steel. ； It can also be absorbed from the medium after use. For example, in petroleum and chemical containers, there are many impurities containing hydrogen or hydrogen sulfide in the medium. The characteristics of hydrogen embrittlement in steel are mainly manifested in the microstructure. Decarburized ferrite of steel can often be seen on its corrosion surface, and the hydrogen embrittlement layer has corrosion cracks extending along the grain boundaries. For containers that are particularly corroded, bulges caused by hydrogen embrittlement can be seen macroscopically. Whether a container containing hydrogen (or hydrogen sulfide) in the medium will suffer from hydrogen embrittlement mainly depends on the operating temperature, partial pressure of hydrogen, action time and chemical composition of the steel. The higher the temperature and the more severe the hydrogen partial pressure, the deeper the hydrogen embrittlement layer of carbon steel and the shorter the time for hydrogen embrittlement rupture to occur. Temperature is especially an important factor. The higher the carbon content of the steel, the more serious the tendency of hydrogen embrittlement will be under the same temperature and pressure conditions. Elements such as chromium, titanium, and vanadium are added to steel to prevent hydrogen embrittlement.

Hydrogen embrittlement (or hydrogen damage) of a pressure vessel means that its wall is eroded by hydrogen, resulting in a reduction in the plasticity and strength of the material, which may lead to cracking or delayed brittle failure. The damage caused by hydrogen at high temperature and high pressure to steel is mainly because hydrogen penetrates into the metal in an atomic state and recombines into molecules inside the metal, generating high pressure. In severe cases, it can cause bulges or wrinkles on the surface. ； Hydrogen combines with the carbon in the steel to decarburize the steel or reduce the sulfides and oxides in the steel. The hydrogen that causes hydrogen embrittlement damage of pressure vessels can be originally present in the equipment. For example, moisture during steelmaking and welding processes is reduced at high temperatures to generate hydrogen, which is dissolved in the liquid metal. Or when the equipment is electroplated or pickled, the steel surface is supersaturated with adsorbed hydrogen atoms, causing hydrogen to penetrate into the steel. ； It can also be absorbed from the medium after use. For example, in petroleum and chemical containers, there are many impurities containing hydrogen or hydrogen sulfide in the medium. The characteristics of hydrogen embrittlement in steel are mainly manifested in the microstructure. Decarburized ferrite of steel can often be seen on its corrosion surface, and the hydrogen embrittlement layer has corrosion cracks extending along the grain boundaries. For containers that are particularly corroded, bulges caused by hydrogen embrittlement can be seen macroscopically. Whether a container containing hydrogen (or hydrogen sulfide) in the medium will suffer from hydrogen embrittlement mainly depends on the operating temperature, partial pressure of hydrogen, action time and chemical composition of the steel. The higher the temperature and the more severe the hydrogen partial pressure, the deeper the hydrogen embrittlement layer of carbon steel and the shorter the time for hydrogen embrittlement rupture to occur. Temperature is especially an important factor. The higher the carbon content of the steel, the more serious the tendency of hydrogen embrittlement will be under the same temperature and pressure conditions. Elements such as chromium, titanium, and vanadium are added to steel to prevent hydrogen embrittlement. 　　Workpieces with hydrogen embrittlement can also be eliminated by hydrogen removal treatment (such as heating, etc.). Hydrogen embrittlement can be avoided by heating in a vacuum, low hydrogen atmosphere or inert atmosphere. For example, electroplated parts are dehydrogenated at a temperature of 200 to 240 degrees, and most of the hydrogen can be removed by heating for 2 to 4 hours. 　　Hydrogen will not cause obvious corrosion to steel at normal temperatures and pressures, but when the temperature exceeds 300°C and the pressure is higher than 30MPa, corrosion defects such as hydrogen embrittlement will occur, especially under high temperature conditions. Such as desulfurization tower, shift tower and ammonia synthesis tower in the production process of ammonia synthesis ； Some hydrogenation reaction units in the oil refining process ； Methanol synthesis tower in petrochemical production process, etc.

1. Hydrogen embrittlement phenomenon and characteristics: The so-called hydrogen embrittlement is the embrittlement phenomenon caused by hydrogen remaining in steel. The elongation and area shrinkage of steel materials that have suffered from hydrogen embrittlement are significantly reduced. This is because the atomic hydrogen that invades the steel weakens the atomic bonding force of the crystal or precipitates as molecules at the grain boundaries or around inclusions. However, under certain conditions, if the hydrogen can be released more completely, the mechanical properties of the steel can still be restored. This characteristic is completely different from hydrogen corrosion (hydrogen corrosion is caused by chemical reactions and is irreversible, called permanent embrittlement), so hydrogen embrittlement is reversible, called primary embrittlement. The susceptibility to hydrogen embrittlement generally increases as the strength of the steel increases, and the microstructure of the steel also has a certain impact on hydrogen embrittlement. The degree of hydrogen embrittlement of steel is also closely related to the hydrogen content in the steel. The higher the strength, the inhalation of a small amount of hydrogen can cause severe embrittlement. The relationship curve between the critical stress intensity factor of hydrogen-induced crack propagation and the tensile strength of the steel and the hydrogen content in the steel shows that as the hydrogen concentration in the steel increases, the critical stress intensity factor will decrease. For equipment operating in a high-temperature and high-pressure hydrogen environment, a certain amount of hydrogen will be absorbed into the device wall during operation. During the shutdown process, if the cooling rate is too fast, the absorbed hydrogen will not have time to diffuse out, resulting in supersaturated hydrogen remaining in the vessel wall, which may cause subcritical cracks to expand when the temperature is lower than 150 degrees, posing a threat to the safe use of the equipment. 2. Hydrogen embrittlement damage in hydrogenation equipment: In high-temperature and high-pressure hydrogen equipment, especially hydrogenation reactors with austenitic stainless steel surfacing layers on the inner surface, some hydrogen embrittlement damage has occurred. 3. Several countermeasures to prevent hydrogen embrittlement: a. Minimizing the strain amplitude is very helpful for improving the service life. Measures such as reducing thermal stress and avoiding stress concentration are effective ； b. Try to keep the TP374 cladding metal or welding metal with high ductility, and control the ferrite content in TP374. The maximum value in the welded state is 3% to 10%. ； c. The cooling rate should not be too fast when the device is shut down, and there should be a process to release the hydrogen absorbed in the steel as much as possible during the shutdown process to reduce the residual hydrogen content in the wall. (Reactor dehydrogenation) In addition, it is also very important to try to avoid unplanned emergency shutdowns (emergency venting). Because the residual hydrogen concentration in the wall will be very high under this condition.