What are the structural characteristics of large spherical tanks? (There are rewards for participating)

The design of large spherical tanks must consider stress concentration in the structure, especially at the columns. At present, domestic steelmaking technology is developing rapidly. The production ship deck is relatively wide, which can reduce the number of welds. It is designed using the stress analysis method. The spherical crown is integrally formed by stamping parts. The equatorial plate and polar plate are made of ship deck. The column section connecting the column and the spherical skin is made of forgings. At present, Lanzhou Chemical Machinery uses elliptical balls in the design of large balls. Not much else is known.

Large spherical tanks have the following structural characteristics: 1. Large gas storage tanks have a large diameter, but their total weight is not large, and their pillar sizes are relatively small, such as a 20,000M3 coal tank with a total weight of 1,400 tons. ； In contrast, the 5000M3 liquefied balloon tank has a total weight of 3500 tons and 13 pillars, each carrying 230 tons. The pillars use steel pipes with an outer diameter of 800mm and a wall thickness of 13MM. Therefore, judging from the thickness of the pillars, the pillars of large gas storage tanks are thin, while the pillars of large liquefied balloon tanks are thick. 2. There is a revolving staircase inside. For the convenience of inspection inside the ball, a straight ladder or a rotary ladder is installed inside the ball. The rotary ladder is an arc-shaped ladder that runs from the top of the ball to the equator or the lower part of the ball. It can rotate all the way around the top of the ball along the guide rails at the equator. 3. There are stairs and platforms outside. For external inspection of large spherical tanks, it is not possible to set up a ladder to go straight up like a small spherical tank. Therefore, a spiral ladder is often set up along the outside of the ball to the top, and a rest platform is set in the middle.

1 Composition characteristics The main composition characteristics of steel plates for large petroleum storage tanks are:: Based on low C-Si-Mn steel, low sulfur and low phosphorus, alloyed, pure steel. Low C-Si-Mn means low carbon equivalent Ceq, which is the fundamental condition to ensure excellent weldability of steel plates ； Low sulfur and low phosphorus (P not greater than 0.015%, S not greater than 0.010%) is beneficial to the improvement of steel plate plasticity, toughness and weldability ； The purpose of alloying is to control the expected transformation of the microstructure and lay the foundation for the strength and toughness of the steel plate. The addition of appropriate amounts of Nb, V, Ti, Mo, and Ni series alloy elements has become the main alloying method. ； Steel purity means that the number of inclusions in the steel should be controlled at a low level to reduce its adverse effects on toughness and plasticity. KST treatment technology (Kobe Super Toughening Treatment), which adds an appropriate amount of Ti to control TiN dispersion distribution, has become a practical technology for developing steel for high thermal energy welding. The low N, high Al and trace Ti alloying treatment method can completely solve the problem of toughness deterioration in the heat affected zone caused by high input energy welding. 2 Production process characteristics The smelting process of steel plates for large petroleum storage tanks is: Pretreatment of molten iron (desulfurization and dephosphorization) - converter smelting - argon blowing and stirring - vacuum treatment (VD or RH) - continuous casting. The rolling process is: Controlled rolling and controlled cooling (TMCP)—tempering treatment. The controlled rolling and controlled cooling process is an effective method to improve the final structure and performance of the product. With reasonable component design and welding process, a HAZ mixed fine-grained structure with mainly acicular ferrite and excellent comprehensive mechanical properties can be obtained. This process has been widely used to produce high-strength steel plates with low susceptibility to welding cold cracking because its grain refinement reduces the carbon content of the steel while still achieving the same high strength and toughness. The tempering treatment is combined with the quenching treatment corresponding to the TMCP process rapid cooling process (Su-per-OLAC) to complete the quenching and tempering treatment of the steel plate and optimize its organizational structure to ensure excellent overall performance. The quenching and tempering treatment of steel plates for large petroleum storage tanks includes two heat treatment methods: online and offline. The main processes involved are:: Direct quenching-tempering process (DQ+FT), direct quenching-on-line heat treatment process (DQ+HOP), offline quenching-tempering process, etc. 3 Performance and organizational structure characteristics 1) The organizational structure characteristics can be seen from the production process of steel plates for large petroleum storage tanks. This type of steel plate is usually delivered in a quenched and tempered state. The corresponding normal temperature organizational structure is the quenching-high temperature tempering structure, including all the structural and morphological characteristics presented in the phase transformation, recovery, recrystallization, and precipitation of alloy compounds of the quenching structure during tempering. The corresponding phase structure is mainly:: The structure of lath-like tempered martensite + tempered sorbite or tempered troostite + a small amount of bainite or a small amount of bainite + ferrite. The volume proportion of each phase changes in different parts along the plate thickness direction. The type of alloying compounds and their presence characteristics depend on the added alloying elements and the corresponding rolling process conditions. Obviously, it is this structural characteristic that determines the performance characteristics of this type of steel plate. 2) High strength performance characteristics: The yield strength is above 490MPa and the tensile strength is 610~730MPa. ； good plasticity: Elongation is not less than 17% ； High toughness: -The transverse impact energy at 15℃ is not less than 80J ； Excellent weldability: After welding with an input energy of 50~100kJ/mm, the -15℃ impact energy in the heat affected zone shall not be less than 47J. 3) Factors affecting the microstructure and properties-alloying elements and their addition amounts. Through the influence of the melting behavior, hot rolling deformation behavior and heat treatment behavior during the production process, the final microstructure and performance of the steel plate are determined. For example, the combination of special alloy design with accelerated cooling and online heat treatment processes can significantly reduce the carbon equivalent and Pcm value of the steel plate and improve the weldability. -Smelting process. The reasonable selection of smelting technology and process parameters will ensure perfect alloying treatment, pure steel quality, and continuous casting billet structure that meets the requirements. For example, the use of TiO fine dispersion technology can significantly improve the toughness of the steel plate base material and HAZ. -Hot rolling deformation conditions. Different deformation conditions lead to different thermal deformation behaviors, thereby producing different organizational structures, especially differences in ferrite morphology, size and crystallization direction in bainitic structures. -Post-rolling heat treatment process. The post-rolling heat treatment system has a great influence on the structure and performance of the steel plate. For example, the quenching temperature or tempering temperature, cooling rate, tempering time, etc. in different areas have different effects on the structure and performance of the steel plate. Reasonable selection of heat treatment process parameters has an important impact on ensuring the structure and performance of the steel plate.