Solving corrosion problems in hydrogenation units

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Equipment corrosion: Hydrogenation units operate under high temperature and pressure in an environment with hydrogen, and the systems contain H2S and NH3. Therefore, the corrosion problem in hydrogenation units also requires attention. The main ways to address this issue are to select appropriate materials and to strengthen monitoring and testing during operation. 1. High-temperature hydrogen corrosion: Hydrogen does not cause corrosion in ordinary carbon steel at room temperature, but it does lead to corrosion under high temperature and pressure, resulting in a decrease in the mechanical strength and ductility of the material. The mechanism of high-temperature hydrogen corrosion is the reaction of hydrogen with carbon in the material to form methane, which reduces the mechanical strength and ductility of the material. The methane formed accumulates between the grains of the steel, causing significant internal stresses or the formation of bubbles and cracks. As for the conditions under which corrosion occurs, it depends on Nels. The n-curve is determined. To avoid high-temperature hydrogen corrosion, equipment and pipelines in the high-temperature, high-pressure, and hydrogen-exposed sections of hydrogenation units are often made of alloy steel or stainless steel. 2. Hydrogen embrittlement: When hydrogen atoms penetrate steel, they reduce the bonding force between atoms within the steel’s grains, resulting in a decrease in the material’s ductility and toughness; this phenomenon is known as hydrogen embrittlement. This type of hydrogen embrittlement is reversible; once the hydrogen escapes from the material, its mechanical properties can be restored. The hazards of hydrogen embrittlement mainly occur during the shutdown phase of hydrogenation units. During this phase, the system temperature and pressure drop, resulting in a decrease in the solubility of hydrogen in the materials. Since hydrogen escapes from the materials at a slow rate, hydrogen remains in a supersaturated state within these materials. When the temperature drops to 150°C, large amounts of this supersaturated hydrogen accumulate at defects in the materials, such as the tips of cracks, thereby causing the cracks to propagate. Therefore, when the hydrogenation unit is shut down, the rate of temperature and pressure reduction should be appropriately controlled to carry out dehydrogenation treatment. 3. High-temperature H2S corrosion: High-temperature H2S corrosion occurs primarily in the high-temperature sections of the reaction system. This type of corrosion takes place in conjunction with H2; the presence of hydrogen enhances the corrosive effect of H2S, while at the same time, the presence of H2S also intensifies the corrosive effect of hydrogen. The method to prevent this type of corrosion is to use materials resistant to H2S corrosion.