Selection of pressure vessel manufacturing methods

Ordinary containers typically use rolled sheet metal; high-pressure containers are classified into single-layer and composite types based on their cylinder structure. Due to different manufacturing methods, single-layer cylinders are further divided into integral forging type, single-layer rolled welding type, electroslag remelting type, and forge-welded type, among others. For the fully forged type, the advantages are: a dense microstructure after forging, resulting in high strength. Disadvantages: Manufacturing requires large-scale forging and heat treatment equipment, as well as a significant amount of metal consumables. During operation, the stress distribution along the wall thickness of the container is uneven; the inner wall of the cylinder experiences high stresses, to the point where yield or plastic flow may occur, while the stresses on the outer wall remain low ； When thick-walled cylinders operate in the inelastic range, it **affects the lifespan of the container** ； To ensure that the cylinder operates within its elastic range, it is necessary to use high-strength materials for its construction. However, as the strength of the material increases, its plasticity and toughness decrease, raising the risk of brittle fracture and thus compromising safety. Moreover, using high-strength steel for the entire cylinder is not economical ； Furthermore, for single-layer thick-walled cylinders, once a crack forms, it will continue to expand under high stress; such cracks cannot be contained within the wall layer and will eventually penetrate the cylinder, leading to failure. As a result, single-layer thick-walled containers rely solely on the material’s inherent fracture resistance as their only reliable means of protection. Application range: It is mainly used in ultra-high pressure vessels with a diameter of φ300~500mm, and is suitable for various temperature conditions. For single-layer roll welding, the advantages are: simpler manufacturing, fewer processing steps, and a high degree of automation. Disadvantages: The performance of thick plates is far inferior to that of thin plates; there are significant differences in properties along the thickness direction. There are considerable variations in ductility and toughness both in the rolling direction and perpendicular to it ； Due to the plate thickness, metal elements tend to segregate, and the content, distribution, and shape of inclusions are uneven. Additionally, during heat treatment, the quenching effects on the interior and surface differ because of the thick plate, resulting in non-uniformity in the material properties inside and outside. This makes cracks more likely to occur during welding ； Thick plates have higher transformation temperatures, increasing the likelihood of brittle failure. Application range: Diameter φ400~3200mm, design pressure 10~32MPa, suitable for various temperature conditions. Advantages of the electroslag remelting process: the manufacturing process is highly mechanized and automated; no large-scale tooling is required, labor time is low, and the cost is low ； The material composition is relatively uniform throughout the wall, with no defects such as inclusions or stratification. Composite cylinders are available in several forms, including multi-layer wrapping type, steel strip interleaving type, and multi-layer heat-shrink fitting type. This type of cylinder is composed of several layers or dozens of layers of thin metal sheets stacked closely together, and it has the following advantages: First, pre-stress can be generated between the layers through the manufacturing process, allowing the stress in the shell wall to be distributed more evenly across the wall thickness; this enables more efficient use of the shell material, so the wall thickness can be made slightly thinner ； Secondly, when the container medium is corrosive, corrosion-resistant alloy steel can be used for the inner cylinder, while carbon steel or other high-strength low-alloy steels can be used for the lining plates; this allows for the full utilization of the advantages of different materials and helps to save precious metals ； Third, when there are serious defects such as cracks in the shell wall material, these defects generally do not spread to other layers ； Fourth, since thin plates are used, which possess good crack resistance, the possibility of brittle failure is relatively low ； Fifth, large-scale forging equipment is not required during the manufacturing process. Disadvantage: The welds that connect the thick-walled cylinders made of multi-layer sheets to the forged end flanges or heads often suffer from welding defects due to the significant differences in heat conduction between the two components, and brittle fracture may also occur as a result. Advantages of multi-layer wrapping type: The material consists of thin or medium-thick plates, with uniform steel strength, microstructure, and properties across each layer ； Since multi-layer containers achieve the desired wall thickness by stacking thin sheets layer by layer, their manufacturing process only requires specialized tensioning and wrapping devices; the use of gantry-type wrapping devices increases the level of automation. The longitudinal seam welding of thick and medium plates, as well as laminated thin plates in the inner cylinder, is easy to ensure in terms of quality ； Welding of the thick circumferential joints between tube sections or between tube sections and end caps does not require post-weld heat treatment ； Excellent corrosion and hydrogen resistance ； At normal operating pressures, multi-layer containers exhibit the same elastic properties as single-layer containers ； Due to the material’s good toughness, it is not prone to failure ； When a multi-layered container explodes, the internal pressure causes the container to undergo significant plastic deformation; subsequently, when the internal pressure reaches its maximum value, cracks form sequentially from the outer layer toward the inner layers, resulting in slow plastic failure ； Generally, the outer walls of high-temperature vessels have good insulation, so the effect of thermal stress is minimal. Disadvantages: The manufacturing process is time-consuming and labor-intensive; furthermore, the material utilization rate for cutting the laminates is low, at around 60%, resulting in poor economic efficiency when producing large containers ； Welding multi-layer, thick circumferential welds is difficult; ultrasonic testing cannot be used, and only 100% radiographic testing is feasible ； The thermal resistance between the layers is high, so the device walls are not suitable for heat transfer. Application range: Diameter φ500~3200mm, design pressure ≤50MPa, design temperature ≤500℃. Advantages of multi-layer heat-shrink type: It combines the advantages of both integral and modular cylinders, features high material utilization, is easy to manufacture, and requires no special processing equipment. Disadvantage: Due to its fewer layers and the use of medium-thickness steel plates, its resistance to brittle fracture is lower compared to multi-layer wrapped types. Rating

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