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The manufacturing process for pressure vessels includes the preparation of raw materials, marking, cutting, bending, shaping, edge processing, assembly, welding, inspection, and more. Preparation of raw materials: Before marking the steel, it is necessary to pre-treat the steel first. The pre-treatment of steel refers to the purification, straightening, and application of a protective primer to materials such as steel plates, pipes, and shaped steel. Purification treatment mainly involves removing rust, scale, oil, slag, and other contaminants from the surface of steel plates, pipes, and shaped steel before processes such as marking, cutting, and welding, as well as after the steel has been cut, beveled, formed, and welded. Straightening is the process of correcting the deformations that occur in steel during transportation, lifting, or storage. Applying a protective coating is primarily done to enhance the corrosion resistance of steel, prevent oxidation, and extend the lifespan of parts and equipment, by applying a layer of protective paint on the surface. Marking is the first step in the manufacturing process of pressure vessels; it directly determines the dimensional accuracy and geometric shape accuracy of the parts after they are formed, and has a significant impact on the subsequent assembly and welding processes. Marking involves drawing cutting lines, machining lines, various position lines, and inspection lines on raw materials or preliminarily processed blanks, and applying (or writing) the necessary marks and symbols. The marking process usually includes steps such as unrolling the part, lofting it, and making markings. The blank size should be determined before marking. The blank size consists of the expanded dimensions of the part and various machining tolerances. The main methods for determining the unfolded dimensions of a part are as follows: 1) Drawing method: This involves using geometric drawing techniques to transform the part into a planar diagram. 2) Calculation method: Refers to deriving the calculation formula based on the principle of expansion or the principle that the area remains unchanged before and after compression (tension) deformation. 3) Experimental method: This refers to determining the unrolled dimensions of blanks for parts with complex shapes using experimental formulas; it is a simple and convenient approach. 4) Comprehensive method: For overly complex parts, the drawing method and calculation method can be used separately for different sections to determine the unfolded dimensions of the blank; sometimes, experimental methods can also be employed for verification. The parts used to manufacture containers can be divided into two categories: expandable parts and non-expandable parts; for example, circular cylinders and elliptical heads belong to the expandable and non-expandable parts respectively. Cutting, also known as blanking, refers to the process of separating the desired blank from the raw material by making cuts along predefined lines. There are two cutting methods: mechanical cutting and thermal cutting. 1. Mechanical cutting: Mechanical cutting mainly includes shearing, sawing, milling, and punching, etc. Its characteristic is that mechanical force plays a primary role during the cutting process. (1) Shearing involves pressing scissors into the workpiece so that the shear stress exceeds the material’s shear strength, thereby achieving severing. This method is efficient and provides high precision in cutting; it can be used as long as the material hardness and dimensions are appropriate. However, the metal within 2–3 mm of the cut site experiences significant hardening. Based on the shape of the plane being sheared, it can be divided into straight-line shearing and curved-line shearing. 1) There are two types of shear machines that use straight, elongated cutting blades for shearing: straight-blade shear machines and bevel-blade shear machines. In straight-blade shears, the two linear cutting edges are parallel, and the cutting process occurs simultaneously along the entire length of the edges. Consequently, the cutting force is high and the impact is intense; these shears are suitable for cutting thick and narrow strips. In oblique-cutting shears, the two straight cutting edges intersect at a certain angle, and the shearing process takes place gradually along the length of the cutting edges; as a result, the shearing force is lower than that of straight-cutting shears when cutting workpieces of the same thickness, the impact is reduced, and such shears are suitable for cutting thin and wide sheets of material. In equipment manufacturing, gantry shear machines are commonly used for cutting straight-shaped workpieces. This shearing machine is easy to use, simple to feed materials, fast in cutting speed, and highly accurate. (2) Sawing is a type of cutting process, and the equipment used includes grinding saws, circular saws, etc. Sawing is generally used for cutting pipes and profiles. 2. Oxygen cutting: Oxygen cutting, also known as gas cutting or flame cutting. Oxygen cutting is a type of thermal cutting; a preheating flame is required for cutting, but the flame alone is not sufficient for cutting – what’s essential is also a high-velocity stream of pure oxygen. 3. Plasma cutting: Plasma is a state of matter in which the matter is completely ionized into positive and negative ions. Plasma cutting uses a high-temperature, high-speed plasma jet to melt the material and create a cut; it falls under the category of high-temperature melting cutting in thermal cutting methods. It is not restricted by material properties; it can cut both metals and non-metals, but it is mainly used for cutting stainless steel, aluminum, copper, nickel, and their alloys. The forming cylinder is composed of several cylinder sections welded together by circumferential welds; these cylinder sections are formed by rolling sheet metal and welding it with longitudinal welds. The principle of tube section rolling: Tube section rolling, also known as rolling or sheet rolling, is the basic manufacturing method for tube sections. The principle of roll bending involves using a rolling machine to apply continuous and uniform plastic bending to the steel plate in order to create a cylindrical surface. The methods for forming end caps include stamping, spinning, and explosive forming. The commonly used methods at present are stamping and spinning. Welding is a process in which, through heating or pressure, or both, the materials to be joined are brought together at the atomic level to form a permanent joint. 50% of the world’s annual steel consumption involves welding processes. Welding can be divided into three main categories: fusion welding, pressure welding, and brazing. (1) A processing method in which the part to be welded is locally heated to melting point, and after cooling, a weld is formed to join the components together. These include arc welding, gas welding, electroslag welding, electron beam welding, laser welding, etc. Welding by fusion is a widely used welding method, and most low-carbon steels and alloy steels are welded using this method. Special fusion welding can also be used to weld non-metals such as ceramics and glass. (2) Pressure must be applied during the pressure welding process; the welding can be completed with or without heating. The main purpose of heating in this case is to soften the metal, enabling it to be deformed under pressure so that the atoms come close enough to exert a strong mutual attraction – this is fundamentally different from the heating used in fusion welding. Pressure welding includes resistance welding, friction welding, ultrasonic welding, cold pressure welding, explosive welding, diffusion welding, and magnetic welding. Its features include low welding deformation, few cracks, and ease of automation. (3) Brazing is a welding method in which a filler metal with a lower melting point than the base material is heated to melt, but at a temperature lower than the melting point of the base material; the melted filler metal is used to fill the weld seam, wet the base material, and diffuse with it to form a single integrated structure. Soldering is divided into two main categories: hard soldering and soft soldering. The heating temperature for hard brazing is above 450°C, and the tensile strength is greater than 200 MPa. Silver-based and copper-based brazing alloys are commonly used; this method is suitable for applications with high working stresses and high ambient temperatures, such as the welding of cemented carbide cutting tools and geological drill bits. Soldering has a heating temperature of less than 450°C and a tensile strength of less than 70 MPa; it is suitable for environments with low stress and low operating temperatures, such as tin-based soldering in circuits.