The manufacturing of pressure vessels usually refers to the entire process carried out by production enterprises with qualifications for pressure vessel manufacturing, starting from accepting customer requirements, followed by design, review, production commencement, and finally completing the processing of the finished vessel, which is then inspected and certified by the special equipment inspection institute. This specifically includes various components attached to the vessel, such as cold and hot processing and assembly, inspection and testing, experiments (such as pressure tests, leakage tests, etc.), surface polishing or acid treatment, coating, as well as packaging and transportation.

1. Theory of Pressure Vessel Manufacturing

       Pressure Vessel Manufacturing, usually refers to production enterprises with pressure vessel manufacturing qualifications, from undertaking customer demands to designing, reviewing drawings, starting production until the container's finished product processing is completed and passes inspection by the special equipment inspection institute. This specifically includes various processes such as cold and hot processing and assembly of various components attached to the container, inspection and testing, experiments (such as pressure tests, leakage tests, etc.), surface polishing or acid treatment, coating, and packaging and transportation.

       The main materials of pressure vessels involved in industrial or civil building HVAC systems usually include steel, cast steel, cast iron, non-ferrous metals, and non-metallic materials. Among them, steel includes three types: carbon steel, low-alloy steel, and high-alloy steel. In addition to using a single type of steel as the container wall, there are also composite process pressure vessels with carbon steel as the base layer and high-alloy copper or aluminum as the coating, or lined pressure vessels, as well as thermally sprayed cladding vessels.

       Steel pressure vessels mainly have single-layer welded pressure vessels, forged welded pressure vessels, and multi-layer pressure vessels in terms of structural form, in addition to integrally forged pressure vessels. Among them, multi-layer pressure vessels include multi-layer wrapped pressure vessels, sleeve pressure vessels, and steel band helical pressure vessels. Multi-layer wrapped pressure vessels are further divided into multi-layer cylindrical segment wrapped pressure vessels and multi-layer integral wrapped pressure vessels.

2. Main Characteristics of Pressure Vessel Manufacturing

1. Assembly of Formed Auxiliary Components

       Essentially, the manufacturing process of pressure vessels mainly consists of the forming of components and welding assembly.

       Component forming: Components such as the cylinder body, end caps, flanges, opening connecting pipes, sealing structures, and supports. Among them, the first five components constitute the shell of the pressure vessel and are classified as pressure-bearing components, which mainly bear the pressure load of the medium during operation; while the supports are classified as load-bearing components, generally welded onto the outer shell of the vessel.

       Welding assembly: According to the specifications, dimensions, shapes, and structures of different components, different processing techniques are used for welding and forming, and then these components are assembled into a whole using fastening connections and other methods, thus forming a complete pressure vessel. For a representative pressure vessel, in addition to installing various safety accessories, instruments, and pre-welded parts on the shell, various internal components such as heat exchange tubes on heat exchange equipment also need to be assembled inside the shell.

2. The Level of Welding Determines the Safe and Reliable Operation of Pressure Vessels

       The manufacturing of pressure vessels usually requires several cold and hot processing techniques to complete, and the quality control of each processing method will affect the safe operation of the product. Due to the complexity of the technology, the diversity of influencing factors, and the difficulty of quality inspection, hot processing has a greater impact on the safe operation of container products. Among various hot processing methods, welding, as an efficient and high-quality manufacturing method, is widely used in the manufacturing process of pressure vessels. However, due to the diversity of performance requirements, the complexity of influencing factors, and the particularity of quality inspection of welded joints, the quality of welding becomes a key factor affecting the quality of pressure vessel products.

Welding quality involves three aspects:

1. Mechanical properties and bending properties of the welded joint;

2. Various surface and embedded defects of the welded joint;

3. Shape and size requirements of the welded joint.

In addition, in most cases, it is also required to consider the performance of the welded joint under various corrosion conditions.

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2.2 Factors affecting welding quality also include the chemical composition of the base material and welding material, as well as the welding method and process, welding structure or welding environment, or the skill level of the welder. Any error or deviation in any link can lead to non-compliance of welding quality.

2.3 In addition to the visual inspection of the shape and size of the welded joint, the quality inspection of pressure vessel welding must also use special inspection methods such as non-destructive testing, metallographic inspection, and performance testing to determine the quality.