The main manufacturing processes for pressure vessels

Manufacturing process
The manufacturing process of pressure vessels includes preparation of raw materials, scribing, undercutting, bending, forming, edge processing, assembly, welding, inspection, etc.
Preparation of raw materials
Before scribing the steel, the steel should first be pre-treated. The pre-treatment of steel refers to the purification, straightening and application of protective primer to materials such as steel plates, pipes and sections.
Decontamination is the removal of rust, oxidation, oil and welding slag from the surface of steel plates, pipes and sections before scribing, cutting and welding and after cutting, beveling, forming and welding.
Straightening is the process of correcting the deformation of steel produced during transport, lifting or storage.
Protective coating is mainly applied to the surface to improve the corrosion resistance of steel, prevent oxidation and extend the life of parts and equipment.
Scribing
Scribing is the first process of the pressure vessel manufacturing process, it directly determines the dimensional accuracy and geometric shape accuracy of the parts after forming, and has a great impact on the subsequent grouping and welding process.
Scribing is in the raw material or by the initial processing of the billet scribed out of the material line, processing line, a variety of location lines and inspection lines, and hit (or write on) the necessary signs, symbols. The scribing process usually includes the unfolding, placing and marking of the part. The billet size should be determined before scribing. The dimensions of the blank consist of the unfolded dimensions of the part and various machining allowances. Determine the size of the part unfolded mainly the following methods:
1) drawing method: refers to the use of geometric drawing method to expand the part into a plane figure.
2) calculation method: refers to the unfolding principle or pressure (pull) deformation before and after the area of the same principle deduced from the calculation formula.
3) test method: refers to the test formula to determine the shape of the more complex parts of the blank unfolded size, this method is simple and convenient.
4) integrated method: refers to overly complex parts, can be used for different parts of the diagramming method, calculation method to determine the size of the blank unfolded, sometimes also available with the test method to verify.
The parts of manufacturing containers can be divided into two categories: unfoldable parts and non-unfoldable parts, such as round cylinder and oval head belong to unfoldable and non-unfoldable parts respectively.
Cutting
Cutting, also known as undercutting, is the process of separating the required blanks from the raw material on which the lines have been drawn. There are two methods of cutting: mechanical cutting and thermal cutting
1. Mechanical cutting
Mechanical cutting mainly includes shearing, sawing, milling and punching, etc., which is characterized by mechanical force playing a major role in the cutting process.
  (1) shear
Shear is to press the scissors into the workpiece, so that the shear stress exceeds the shear strength of the material and achieve the purpose of cutting. This method is highly efficient, high accuracy of the cut, as long as the material hardness and size can be used, but 2 ~ 3mm from the cut near the metal has obvious hardening phenomenon. According to the shear plane shape, can be divided into linear shear and curve shear.
1) Linear shear
The use of linear long shear edge for shear bed there are two, respectively, for the flat shear bed and oblique shear bed.
Flat shear, two straight cutting edge parallel, shear process along the length of the cutting edge at the same time, so the shear force and impact is strong, suitable for cutting thick and narrow strips of material.
Oblique shear, two straight cutting edges oblique intersection into a certain angle, shear process along the cutting edge length gradually, so the shear force than flat shear in cutting the same thickness of the workpiece to be small, impact reduced, suitable for cutting thin and wide plate material.
In the manufacture of equipment, shear linear-shaped workpiece more gantry shear bed. The shear bed is easy to use, feeding simple, fast shear speed, high precision.
(2) sawing
Sawing belongs to the cutting process, the equipment used are grinding wheel saws, circular saws, etc.. Sawing is generally used for the cutting of pipe fittings and profiles.
2. Oxygen cutting
Oxygen cutting is referred to as gas cutting, also known as flame cutting. Oxygen cutting belongs to the thermal cutting, cutting requires a preheated flame, but only the flame does not achieve cutting, the key is to have a high-speed pure oxygen airflow.
3. Plasma cutting
Plasma is a state of matter, matter is all ionised into positive and negative ions. Plasma cutting is the use of high temperature, high speed plasma flame flow to fuse the material to form a kerf, it belongs to the thermal cutting of high temperature melting cut off. It is not limited by physical properties and can cut metals as well as non-metals, but is mainly used for cutting stainless steel, aluminium, copper, nickel and their alloys.
Forming
Forming of the barrel
The barrel is made up of a number of barrel sections welded by circular welds, the barrel sections are formed by rolling the plate round and welding the longitudinal welds. The roll-round principle of this barrel section barrel section roll-round, also known as roll-round or roll-plate, is the basic manufacturing method for barrel sections. The roll-round principle is the use of a plate rolling machine to apply continuous and uniform plastic bending to the steel plate in order to obtain a cylindrical surface.
Forming of head

There are three main methods of head forming, namely stamping, spinning and explosion forming. At present, the commonly used methods are stamping method and spinning method.
Welding
Welding is the process by which a welded part is heated or pressurised, or both, to achieve inter-atomic union 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
The workpiece to be welded is partially heated until it melts and condenses to form a weld that joins the components together. These include arc welding, gas welding, electroslag welding, electron beam welding, laser welding, etc. Fusion welding is a widely used welding method, most of the low carbon steel, alloy steel are welded using the fusion welding method. Special fusion welding can also be welded ceramics, glass and other non-metals.

(2) Pressure welding
The welding process must apply pressure, which may or may not be heated to complete the welding. The main purpose of the heating is to soften the metal, to plasticise it by applying pressure and to bring the atoms closer to a distance where they are firmly attracted to each other, which is fundamentally different from the heating in fusion welding. Pressure welding includes resistance welding, friction welding, ultrasonic welding, cold press welding, explosion welding, diffusion welding and magnetic welding. It is characterised by small welding deformation, less cracking, easy automation, etc.

(3) Brazing
The brazing material with a lower melting point than the base material is heated until it melts, but the heating temperature is lower than the melting point of the base material, and the melted brazing material is used to fill the weld, wet the base material and diffuse with the base material to form an integrated welding method. Brazing is divided into two main categories: hard brazing and soft brazing. Hard brazing has a heating temperature of more than 450°C and a tensile strength of more than 200 MPa. It is often used with silver- and copper-based brazing materials and is suitable for applications with high working stress and high ambient temperatures, such as the welding of carbide turning tools and geological drill bits. Soft brazing, with a heating temperature of less than 450°C and a tensile strength of less than 70 MPa, is suitable for environments with low stress and low working temperatures, such as tin-based brazing of electrical circuits.
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