Standard and Vanadium-alloyed, chromium, and molybdenum 2,25Cr–1Mo steel grades (EN 10028-2 12CrMo9-10/ASTM A387 gr. 22 and 13CrMoV9-10/ASTM A542 tp. D) is commonly used for the fabrication of heavy pressure vessels for applications in petroleum refining plants.
These reactors are made of heavy plates, forged shells, forged nozzles, and fittings. They are subjected to thermal cycles (stop and go) and to severe service conditions (high temperatures and high hydrogen partial pressures).
MPT (Minimum pressurization temperature) is the lowest temperature at which the vessel can be repressurized after shutdown and ensures no risk of brittle failure of the containment body. The MPT is defined by fracture mechanics and calculations.
It is very important to establish minimum pressurization temperature, in order to ensure the safety of the reactors during start-ups and reactor cool down. A reasonable threshold value of the reactor’s skin temperatures is recommended by the vendor for pressurization. The establishment of minimum pressurization temperature accommodates the potential of temperature embrittlement and hydrogen embrittlement.