Hydrogen-containing system

Strict quality control is applied to materials, and hydrogen-resistant alloy materials are used to prevent hydrogen embrittlement. Operate strictly in accordance with the temperature and pressure rise curves provided by the equipment.

Pay attention to the following points: 1. The speed of heating/cooling and increasing/decreasing pressure should be slow, generally 10-15 degrees per hour, 1.0 MPa； 2. Pay attention to the critical points: Before the bed temperature reaches 135 degrees and the reactor wall temperature reaches 95 degrees, the system pressure must not exceed 1/3 of the designed operating pressure ； 3. Nitrogen dehydrogenation treatment during shutdown: Nitrogen-based isothermal dehydrogenation at 275, 250, and 225 degrees for 24 hours. 4. Prevent water from entering the reactor; ensure that chloride levels remain below 25 mg/L during pressurization.

(1) Characteristics of hydrogen embrittlement Hydrogen embrittlement is a phenomenon of embrittlement caused by the retention of hydrogen in steel. Steel that has suffered from hydrogen embrittlement exhibits a significant decrease in elongation and reduction of area. Hydrogen embrittlement is reversible and is also known as primary embrittlement. The temperature at which hydrogen embrittlement occurs ranges from room temperature to about 150°C. As the temperature rises, the hydrogen embrittlement effect decreases, and it is less likely to occur when the temperature exceeds 71°C to 82°C. Therefore, in actual installations, hydrogen embrittlement damage usually occurs during the low-temperature phases of startup and shutdown processes. (2) Key points for preventing hydrogen embrittlement: The sensitivity to hydrogen embrittlement generally increases as the strength of the steel increases. Microstructure also has an impact on hydrogen embrittlement; for example, untempered materials and pearlitic microstructures are more sensitive to hydrogen embrittlement. The degree of hydrogen embrittlement in steel is closely related to the hydrogen content in the steel. At temperatures where hydrogen embrittlement may occur, there exists a hydrogen concentration that does not cause subcritical crack propagation; this is known as the safe hydrogen concentration. It is related to the strength level of the steel, the magnitude of the tensile stress at the crack tip, and the geometric dimensions of the crack). For reactors operating in a high-temperature and high-pressure hydrogen environment, a certain amount of hydrogen is absorbed into the reactor walls during operation. During the shutdown process, if the cooling rate is too fast, the hydrogen that has been absorbed does not have enough time to diffuse out, resulting in supersaturated hydrogen remaining within the vessel walls. This can lead to the propagation of subcritical cracks, posing a threat to the safe operation of the equipment. If the material also develops temper embrittlement, the impact is even greater. To prevent hydrogen embrittlement, the following points should be noted: the strength of the steel should not exceed the values specified in the design. PWHT should be carried out properly, and the hardness of the weld heat-affected zone must be controlled (for 2¼Cr-1Mo steel, this value should be ≤220HB). Macroscopic defects should be eliminated through non-destructive testing, and residual stresses should be reduced in order to lower the applied stresses. There is also a phenomenon of hydrogen embrittlement in stainless steels in hydrogen-containing equipment such as hydrogenation reactors; in some cases, σ-phase embrittlement occurs as well. Such defects typically appear at the fillet welds of the reactor’s catalyst support rings and at the corners of the flange’s stepped groove sealing surfaces. To prevent such damage, the following measures should be taken in terms of structural design, manufacturing processes, and production operations: minimize the strain amplitude, reduce thermal stress, and avoid stress concentration ； Try to maintain high ductility in the Tp.347 surfacing metal or weld metal. When the plant is shut down, try to release the hydrogen absorbed in the steel. Try to avoid unplanned emergency shutdowns.