Comprehensive Guide to Low-Temperature Pressure Vessel Design: From Temperature Calculations to Quality Inspection

Thread Content

Three rules for determining temperature parameters Theoretical calculation method: When the container is under conditions of two-way heat transfer, it is necessary to use the heat conduction equation to accurately calculate the average temperature of the metal wall surface. By establishing a three-dimensional thermodynamic model and substituting parameters such as ambient temperature, medium temperature, and material thermal conductivity into the formulas, accurate design reference temperature values can be obtained. For containers equipped with a complete insulation system, the empirical value method recommends using the actual measured temperature of the medium as a reference. Through multi-point temperature monitoring at the site, 90%-95% of the peak temperature of the medium during operation is taken as the reference value for design temperatures; this method exhibits high reliability in engineering practice. To handle extreme operating conditions for outdoor equipment without insulation measures, an environmental compensation factor must be introduced. It is recommended to add a safety margin of 10–15°C to the conventional calculated values, while taking into account dynamic factors such as day-night temperature differences and seasonal changes, in order to establish a multi-dimensional temperature compensation model. Selection Criteria for Key Materials: The toughness assurance system prioritizes the use of ASTM A333 Gr.6 low-temperature steel series. Materials must pass ultra-low temperature impact tests at -196°C; sheets with a thickness exceeding 30 mm require detection of delamination defects. Quality control requirements specify that each batch of materials must be accompanied by a third-party test report, and V-notched three-point bend tests shall be conducted. Ultrasonic testing must comply with ASME Section V standards.

Key Points of Structural Design: Stress optimization strategies involve the use of ring-shaped reinforcement ribs to reduce local stress. The radius of curvature in transition areas must be at least 3 times the wall thickness, and flexible compensation structures should be installed at support points. Manufacturing process specifications require full penetration butt joints as the preferred option; cross-weld patterns are prohibited. Fillet welds must undergo 100% magnetic particle inspection.

Welding Quality Control System: Process qualification requires that each container be equipped with an independent welding test plate. The GTAW method is used for root welding, followed by SMAW for filling; inter-layer temperatures must be strictly controlled between 100–150°C. Defect prevention measures include the use of argon back shielding before welding, with weld height kept within the range of 0–1.5 mm, and undercut depth not exceeding 0.5 mm.

Key Indicators for Quality Inspection: Non-destructive testing standards require that radiographic testing meet NB/T 47013 Class II requirements, while fillet weld magnetic particle testing must achieve sensitivity equivalent to Type A1 test pieces. TOFD testing is used for butt joints with a thickness greater than 50 mm. Overall acceptance criteria include a hydrostatic test pressure of 1.3 times the design pressure, with a pressure retention time of at least 30 minutes. After stress-relief heat treatment, the hardness value must be ≤225 HB. Through systematic design specifications and strict quality control, modern low-temperature pressure vessels can be reliably used in key applications such as LNG storage and transportation, as well as air separation equipment. The concept of continuously optimized design and detection technologies provide a solid guarantee for the safe operation of low-temperature equipment.