A pressure vessel is a closed device that holds gas or liquid and bears a certain pressure. The most commonly used materials for pressure vessels are generally steel, such as carbon steel, low-alloy steel, and stainless steel. In addition to steel, some pressure vessels are made from non-metallic materials such as aluminum, titanium, fiberglass, prestressed concrete, and ceramics. For example, aluminum alloy compressed gas cylinders and fiberglass pressure vessels used for water treatment.

1. What materials are used for pressure vessels?

       Pressure Vesselis a sealed device that holds gases or liquids and withstands a certain pressure. The most commonly used materials for pressure vessels are generally steel, such as carbon steel, low alloy steel, and stainless steel. In addition to steel, some pressure vessels are made from non-ferrous metals like aluminum and titanium, as well as non-metallic materials like fiberglass, prestressed concrete, and ceramics. For example, aluminum alloy compressed gas cylinders and fiberglass pressure vessels for water treatment.

2.Manufacturing Process of Pressure Vessel ManufacturersThe manufacturing process of pressure vessels includes preparation of raw materials, marking, cutting, bending, forming, edge processing, assembly, welding, and inspection.

       1. Preparation of Raw Materials

Before marking, the steel must first undergo pretreatment. The pretreatment of steel refers to the purification, shaping, and application of protective primer on materials such as steel plates, pipes, and profiles. Purification mainly involves removing rust, oxide scale, oil, and welding slag from the surface of steel plates, pipes, and profiles before marking, cutting, and welding, as well as after cutting, beveling, forming, and welding. Shaping is the process of correcting deformations that occur during transportation, hoisting, or storage. The application of protective paint is mainly to enhance the corrosion resistance of steel, prevent oxidation, and extend the lifespan of components and equipment by coating a layer of protective coating on the surface.

       2. Marking

Marking is the first process in the manufacturing of pressure vessels, which directly determines the dimensional accuracy and geometric shape accuracy of the formed parts, significantly affecting subsequent assembly and welding processes. Marking involves drawing cutting lines, processing lines, various position lines, and inspection lines on the raw materials or semi-finished products, and marking (or writing) necessary signs and symbols. The marking process typically includes unfolding, laying out, and marking parts. The dimensions of the blank should be determined before marking. The dimensions of the blank consist of the unfolded dimensions of the part and various processing allowances. The methods for determining the unfolded dimensions of parts mainly include the following:

       (1) Drawing Method: Refers to using geometric drawing methods to unfold parts into flat shapes.

(2) Calculation Method: Refers to deriving calculation formulas based on the principle of unfolding or the principle of constant area before and after deformation (compression or tension).

(3) Experimental Method: Refers to determining the unfolded dimensions of blanks for parts with complex shapes through experimental formulas; this method is simple and convenient.

(4) Comprehensive Method: Refers to using different methods such as drawing and calculation for different parts of overly complex components to determine the unfolded dimensions of the blanks, and sometimes using the experimental method for verification.

The parts for manufacturing containers can be divided into two categories: unfoldable parts and non-unfoldable parts, such as circular cylinders and elliptical heads, which belong to unfoldable and non-unfoldable parts, respectively.

       3. Cutting

Cutting, also known as blanking, refers to the process of separating the required blanks from the marked raw materials. There are two cutting methods: mechanical cutting and thermal cutting.

       (1) Mechanical Cutting

Mechanical cutting mainly includes shearing, sawing, milling, and punching, characterized by the primary role of mechanical force during the cutting process.

       a. Shearing

Shearing involves pressing scissors into the workpiece to exceed the material's shear strength and achieve cutting. This method is efficient and provides high cutting accuracy, and can be used as long as the material's hardness and dimensions are suitable, but there is a significant hardening phenomenon in the metal 2-3mm near the cut. Depending on the shape of the cut surface, it can be divided into straight shearing and curved shearing.

       Straight Shearing: There are two types of shearing machines that use straight long cutting edges, namely flat shears and inclined shears. In flat shears, the two straight cutting edges are parallel, and the shearing process occurs simultaneously along the length of the cutting edge, resulting in a large shearing force and strong impact, suitable for cutting thick and narrow strips. In inclined shears, the two straight cutting edges intersect at a certain angle, and the shearing process occurs gradually along the length of the cutting edge, resulting in a smaller shearing force compared to flat shears when cutting the same thickness of workpieces, with reduced impact, suitable for cutting thin and wide plates. In equipment manufacturing, straight shearing of workpieces is often done using a gantry shear, which is easy to use, simple to feed, fast in cutting speed, and high in precision.

       b. Sawing

Sawing is a type of cutting process, with equipment such as abrasive saws and circular saws. Sawing is generally used for cutting pipes and profiles.

       (2) Oxygen Cutting

Oxygen cutting, abbreviated as gas cutting, is also known as flame cutting. Oxygen cutting is a type of thermal cutting that requires a preheating flame, but the flame alone cannot achieve cutting; the key is also to have a high-speed stream of pure oxygen.

       (3) Plasma Cutting

Plasma is a state of matter where the material is fully ionized into positive and negative ions. Plasma cutting uses high-temperature, high-speed plasma flame flow to melt materials to form cuts; it belongs to high-temperature melting cutting in thermal cutting. It is not limited by material properties and can cut both metals and non-metals, but is mainly used for cutting stainless steel, aluminum, copper, nickel, and their alloys.

       4. Forming

(1) Forming of the Cylinder Body

The cylinder body is composed of several cylinder sections welded together by circumferential seams, and the cylinder sections are formed by rolling plates into circles and welding longitudinal seams. The principle of rolling the cylinder section, also known as rolling or plate rolling, is the basic manufacturing method for cylinder sections. The rolling principle uses a plate rolling machine to apply continuous and uniform plastic bending to the steel plate to obtain a cylindrical surface.

       (2) Forming of the Head

The methods for forming heads mainly include stamping, spinning, and explosive forming. Currently, the commonly used methods are stamping and spinning.

       5. Welding

5、焊接

       Welding is a process that involves heating or applying pressure, or both, to achieve atomic bonding of the workpieces and form a permanent joint. Welding processes are involved in 50% of the world's annual steel consumption.

Welding can be divided into three main categories: fusion welding, pressure welding, and brazing.

(1) Fusion Welding

       A processing method that locally heats the workpiece to melting, and after cooling, forms a weld seam to connect the components together. This includes arc welding, gas welding, electroslag welding, electron beam welding, laser welding, etc. Fusion welding is a widely used welding method, and most low-carbon steels and alloy steels are welded using fusion welding methods. Special fusion welding can also weld non-metals such as ceramics and glass.

(2) Pressure Welding

       Welding that must apply pressure during the process, which may or may not involve heating to complete the welding. The main purpose of heating is to soften the metal, and by applying pressure, the metal is plastically deformed, bringing the atoms close enough for mutual stable attraction, which is fundamentally different from the heating in fusion welding. Pressure welding includes resistance welding, friction welding, ultrasonic welding, cold pressure welding, explosion welding, diffusion welding, and magnetic welding. Its characteristics include small welding deformation, fewer cracks, and ease of automation.

(3) Brazing

       A welding method that heats a filler metal with a melting point lower than that of the base material to melting, but at a temperature lower than the melting point of the base material, filling the weld seam, wetting the base material, and forming a unified joint through mutual diffusion. Brazing is divided into two main categories: hard brazing and soft brazing. Hard brazing has a heating temperature greater than 450°C and a tensile strength greater than 200MPa, often using silver-based or copper-based fillers, suitable for applications with high working stress and high environmental temperatures, such as welding of hard alloy cutting tools and geological drill bits. Soft brazing has a heating temperature less than 450°C and a tensile strength less than 70MPa, suitable for environments with low stress and low working temperatures, such as soldering of circuits with tin-based fillers.