Principles for determining design pressure and design service life

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1. When the process system specifications or engineering design documents provide specific requirements for the design pressure of the vessel, the design pressure shall be determined in accordance with those specific requirements, but it shall not be lower than the values specified in the table. 2. The design pressure, together with the corresponding design temperature, shall be used as the design load conditions. Various operating conditions that the vessel may experience during operation must be taken into account, and the design pressure for the vessel under each such condition shall be determined accordingly. 3. The design pressure of containers holding liquefied gases shall comply with the following requirements: (1) In the absence of a safety relief device, the design pressure shall not be lower than 1.05 times the operating pressure; (2) When equipped with a safety valve, the design pressure shall not be lower than the set pressure of the safety valve (the set pressure is generally taken as 1.05 to 1.10 times the operating pressure); (3) The operating pressure refers to the saturated vapor pressure at the highest operating temperature that the container holding liquefied gases may reach. The working pressure of pressure vessels for storing liquefied gases or mixed liquefied petroleum gas at room temperature is determined in accordance with the current regulations, namely the \"Safety Technical Inspection Regulations for Fixed Pressure Vessels\" TSG21--2016. 4. For internal-pressure tower vessels that comply with the current industry standard \"Tower Vessels\" NB/T 47041, when the operating pressure is less than 0.1 MPa, the design pressure shall be set at not less than 0.1 MPa. 5. For vacuum vessels with an integral jacket, the calculated external pressure on the vessel shell shall equal the design external pressure plus the design internal pressure within the jacket, and the stability of the vessel shell under the jacket test pressure (external pressure) shall be verified. II. Principles for determining the design service life 1. The design service life is determined by the design agency based on the expected service life of the container. The expected service life of the container is specified in writing by the client who commissioned the design to the design firm. The design service life of pressure vessels shall be specified in the design drawings. 2. The design service life of pressure vessels is not identical to their actual service life. Users of pressure vessels shall conduct regular inspections and grading of the vessels in accordance with the requirements of the current regulations, namely the \"Safety Technical Inspection Regulations for Fixed Pressure Vessels\" TSG21-2016. When the operating conditions of the vessel change, the corrosion rate should be re-estimated based on actual measurement data to determine the vessel’s new service life. 3. When determining the design service life of a vessel, the following factors should be taken into account: (1) selection of appropriate materials and structural design; (2) reasonable corrosion allowance; (3) appropriate manufacturing and inspection requirements; (4) measures to limit creep (under high-temperature conditions) or fatigue; (5) cost of vessel construction; (6) role of the vessel in the plant; (7) operating cycle of the plant. 4. The design service life of containers shall comply with the following requirements: (1) For thick-walled hydrogenation reactors made of chromium-molybdenum steel or high-alloy steel with a nominal thickness of ≥50 mm: not less than 30 years; (2) For other reactors, columns with a diameter of ≥4 m, or a weight of ≥100 t, or a total height of ≥60 m, high-pressure heat exchanger shells, and containers with a nominal thickness of ≥50 mm, as well as spherical storage tanks: not less than 20 years; (3) For other columns, containers, heat exchanger shells, and tube banks: not less than 15 years. 5. For vessels with periodic variations in operating temperature or pressure, the number of cycles of such temperature or pressure changes during the design service life shall be specified in the design drawings.