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The design, pressing, and assembly welding of spherical shell plates are several key stages in the construction of spherical storage tanks. These processes are highly complex, involve long time frames and vary across different regions; it is necessary to take into account factors such as the supply capacity of steel plates, the geometric precision of pressing, the maintenance of material properties, and the assurance of welding quality. The key points are analyzed below from three aspects: design, pressing, and welding. 1. Key points in the design phase: Selection of structural format and strip angle. The structural format of the spherical shell plates needs to be determined based on factors such as the volume of the spherical tank, the type of material used, and its thickness. Common formats include the orange-segment type, the football-segment type, and the hybrid type; the hybrid type combines elements of both the orange-segment and football-segment types. As it reflects the principle of moderation favored by most people in China, it is widely used. The number of supports and the design of the zoning angles for spherical tanks must be determined by taking into account factors such as the internal diameter of the tank, the width of the steel plates supplied by the steel plant, limitations on width during transportation, the lifting weight during pressing and assembly, the total length of welds, and the material cost efficiency. When lacking experience, it is possible to design directly in accordance with the national standard GB/T 17261 \"Types and Basic Parameters of Steel Spherical Storage Tanks\". II. Key points of the pressing process 1. Determination of the material thickness In construction drawings, in addition to the nominal thickness, the minimum formability thickness of the spherical shell plates should also be specified. When purchasing steel plates, in addition to meeting the nominal thickness requirement, manufacturers also need to determine the starting thickness and thickness tolerance of the steel plates based on the minimum formability thickness and the amount of thinning that occurs during pressing. General engineering experience: curvature, steel plate strength, steel plate thickness, and pressing processes are all factors that affect the amount of thinning. 2. Cold pressing process parameters: Based on the strength and specifications of the steel plate, select the appropriate hydraulic press along with upper and lower dies, and carry out die pressing according to a reasonable sequence of operations. Generally, it is necessary to compress in multiple passes following the sequence of \"first the ends then the middle\" and \"first horizontally then vertically\"; overloading in a single attempt to cause damage to the steel plate is strictly prohibited. After pressing, the curvature must be checked using a template with a string length of ≥2m; the gap should be ≤3mm. If these specifications are not met, correction is carried out by adding shims or flat steel strips using molding fixtures. 3. After the curvature of the groove preparation is satisfactory, the groove cutting line is marked, and the peripheral grooves of the spherical shell plates are cut using tracks and semi-automatic cutting carts, as well as flame (or plasma) cutters. 4. Geometric accuracy control: After pressing, it is necessary to check whether the geometric properties of the spherical shell plate, such as curvature, chord length, arc length, and thickness, meet the requirements of relevant standards and design drawings. For example, the curvature must satisfy the following: when the chord length of the spherical shell panel is 2000 mm or more, the chord length of the sample must also be 2000 mm or more; when the chord length of the spherical shell panel is less than 2000 mm, the chord length of the sample must not be less than that of the spherical shell panel. The gap between the template and the spherical shell plate shall not be greater than 3 mm. Allowable deviation for geometric dimensions: For spherical shell plates with poor rigidity, their geometric dimensions should be measured on a support frame; the allowable deviation for the lengthwise chord length is not more than ±2.5 mm, the allowable deviation for the widthwise chord length is not more than ±2.0 mm, and the allowable deviation for the diagonal chord length is not more than ±3.0 mm. The two diagonals should be in the same plane. When measuring diagonally with two lines, the deviation in the perpendicular distance between the two lines shall not exceed 5.0 mm. III. Key points of assembly and welding 1. Assembly sequence and process 1) When assembling spherical tanks on site, the bulk assembly method is commonly used. The bulk method is an assembly method that uses a single spherical shell plate as the smallest assembly unit. First, fix the equatorial plate with supports to the foundation, then install the adjacent equatorial plates with supports. Next, insert an equatorial plate without supports between the two equatorial plates with supports and secure it; repeat this process until the entire equatorial band is assembled. After the equatorial strip is installed, the lower polar strip plate is installed next, followed by the upper polar strip plate. Taking the five-zone mixed spherical tank as an example, the construction procedure for assembly by the bulk method is as follows: alignment of the struts and equatorial plates → assembly of the equatorial zone plates → installation of the central column → assembly of the lower temperature zone plates → assembly of the upper temperature zone plates → removal of the central column → assembly of the lower pole plate → assembly of the upper pole plate → erection of internal and external scaffolding → adjustment and overall inspection of the assembly quality. Controlling the assembly accuracy is a prerequisite for ensuring welding quality; during adjustments and overall inspections of the assembly quality, it is essential to keep the fitting gap and edge misalignment of the spherical shell plates within acceptable limits. 2) On-site welding of spherical tanks is a critical aspect for ensuring product quality. The principle welding sequence is: weld the longitudinal seams first, then the circumferential seams ； Weld the short seams first, then the long seams ； Weld the side with the greater groove depth first, and then the side with the smaller groove depth. Welders should be distributed symmetrically and weld simultaneously ； The length of lead or lag within the same time period should not exceed 500 mm; for shielded metal arc welding, the first pass should be carried out using a segmented back-pulling method ； Welding should be carried out using multiple passes and layers; the arc initiation points for each layer should be spaced 25–50 mm apart in sequence. The interpass temperature should also be controlled to minimize deformation and reduce welding residual stresses. 2. Welding quality control: Before welding, slag, oxide scale, rust, oil stains, and dust within a range of 50 mm on both sides of the groove must be thoroughly removed ； During welding, try to avoid starting the arc in areas that are not to be welded, in order to prevent arc-induced scratches that could lead to microcracks. Any arc scars or pits that may form accidentally must be removed by grinding. The thickness of all areas that have been ground must meet the relevant technical requirements, and they must also pass surface inspection. During on-site welding of spherical tanks, the weld heat input is quite sensitive; therefore, the welding current and welding speed must be strictly controlled, and the weld heat input must not exceed the maximum value specified in the welding procedure qualification report. After welding the side welds of the large groove on the spherical tank, gas tungsten arc cutting is used to clean the back side of the groove; all of the weld metal resulting from the tack welding must be completely removed. After cleaning, grinding with a grinder is carried out to expose a metallic shine. The groove should have a U-shaped shape, and then surface penetrant testing is performed – the results must meet the requirements of Grade I as specified in standard NB/T 47013. 3. Non-destructive testing of welds and post-weld overall heat treatment 1) The butt joints formed during the on-site assembly of spherical tanks should be inspected using radiographic testing or ultrasonic testing. Among them, radiographic inspection includes radiographic film detection (RT), digital radiography (DR), and computerized radiography (CR); ultrasonic inspection includes phased array ultrasonic testing (PAUT), time-of-flight diffraction ultrasonic testing (TOFD), ultrasonic imaging testing by pulse reflection (UIT), and unrecorded pulse reflection ultrasonic testing (UT). 2) Overall heat treatment (usually using the internal combustion method). When the medium is highly toxic, there is a risk of stress corrosion in the medium, the wall thickness of the spherical shell reaches a certain level, or the designers deem it necessary to carry out post-weld heat treatment, then overall post-weld heat treatment of the spherical tank must be performed in accordance with standard specifications and drawing requirements, after non-destructive testing shows satisfactory results. During heat treatment, it is necessary to control the heating rate, the holding time at a constant temperature, and the temperature difference between any two points, in order to ensure that welding residual stresses are eliminated and to minimize the adverse effects of heat treatment. IV. Conclusion The design of shell plates requires careful consideration of various factors, including the supply dimensions of the steel plates, the efficiency and precision of pressing processes, the control of the total length of welds, and the assurance of welding quality. An experienced professional designer of spherical tanks can make the most appropriate choices throughout the entire process – from the selection of the main material and the optimization of the segment angles to the design of welding grooves and the choice of non-destructive testing methods after welding. This ensures the safe and stable operation of the spherical tank, while also achieving economic efficiency and aesthetic appeal in its design. (The above content is partially sourced from the internet, and partially consists of standard citations and personal opinions; please evaluate it before using it.)