How should the design service life be determined?
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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 \"Technical Regulations for Safety Inspection of Fixed Pressure Vessels\" TSG21-2016. When the operating conditions of the container change, the corrosion rate should be re-evaluated based on actual measurement data to determine the new service life of the container. 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 margin; (3) suitable 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 vessels shall comply with the following requirements: (1) 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) 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, vessels with a nominal thickness of ≥50 mm, and spherical storage tanks: not less than 20 years; (3) Other columns, vessels, 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.
The determination of the design service life is based on the following factors: First, it is determined by the design firm according to the expected service life provided by the client, and this is clearly specified in the design drawings. Secondly, the designed service life differs from the actual service life, and users are required to conduct regular inspections and evaluations in accordance with the law. Furthermore, when determining the design service life, factors such as material selection, corrosion margin, manufacturing inspection standards, and the control of creep or fatigue risks must be considered. Certain types of containers, such as hydrogenation reactors and some large-scale equipment, also have specific minimum service life requirements. For equipment with frequent operating condition changes, the design drawings must also specify the number of temperature or pressure cycles. .