Multi-layer wrapped pressure vessel

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I. Multi-layer wrapped pressure vessels: Pressure vessels formed by wrapping layer plates around the inner cylinder in successive layers. The longitudinal joints of the layer plates in multi-layer wrapped pressure vessels are of Class C welding joints. The Q245R and Q345R materials used for the inner cylinders of such vessels should be in a normalized state. Multi-layer wrapped pressure vessels come in two structural forms: 1) Layer plates are wrapped around a single inner cylinder to form multiple cylindrical sections, which are then joined together through circumferential welding joints to create the vessel. 2. A container formed by wrapping layer plates layer by layer around the inner cylinder as a whole. III. Advantages of multi-layer wrapped pressure vessels: 1. No deep longitudinal welds, and the layers are thin with good toughness ； 2. Prestress is generated during wrapping, resulting in good stress resistance ； 3. The inner cylinder can be made of a material different from that of the layered dielectric, in order to meet the requirements of different dielectrics. IV. Laminated plate wrapping 1. Before wrapping, the rust, oil stains, and other substances that affect adhesion on the surfaces of the already wrapped and those to be wrapped laminated plates must be removed from the inner cylinder ； 2. The longitudinal weld joints of the inner cylinder and the Class C weld joints of each layer’s laminates should be staggered evenly, with multiple layers being wrapped together as a whole. 3. The circumferential weld joints of the inner cylinder of the container and the circumferential weld joints of each layer’s laminates should also be staggered from one another, and the minimum distance between adjacent layers’ circumferential weld joints should be greater than the value specified in the drawings ； 4. Before wrapping the next layer of plates, the weld of the previous layer should be ground smooth ； 5. After grinding the weld joints of the laminates, a visual inspection for appearance should be carried out; cracks, undercuts, and dense pores are not allowed. 6. After the laminates are wrapped, an inspection of the areas where loosening may occur should be carried out: a. For containers with an inner cylinder diameter Di ≤ 1000 mm, for each area where loosening might happen, the circumferential length shall not exceed 30% of Di, and the axial length shall not exceed 600 mm; b. For containers with an inner cylinder diameter Di > 1000 mm, for each area where loosening might happen, the circumferential length shall not exceed 300 mm, and the axial length shall not exceed 600 mm. 7. Leak detection holes shall be fabricated on the laminates of each multi-layer cylinder section in accordance with the requirements specified in the drawings ； 8. For the connection between the layers of a multi-layer integral wrapped container and the end flanges or spherical heads, the misalignment amount at the joints shall not exceed 0.8 mm. V. Heat Treatment 1. For various weld joints on multi-layer wrapped containers that are welded to the wrapping sleeves, no post-weld heat treatment is permitted after welding. 2. Class A welded joints of the carbon steel and low-alloy steel inner cylinders in multi-layer wrapped containers shall undergo post-weld heat treatment. 3. Regardless of the material and thickness of the inner tube, post-weld heat treatment must be carried out on Class A joints to eliminate welding stresses and ensure the quality of the inner tube. VI. Test pieces and specimens 1. The product welding test pieces for multi-layer tubular section wrapped containers shall include inner tube welding test pieces and layer plate welding test pieces. The welded specimen of the laminate is fabricated at the extension of a longitudinal joint (type C) in one layer, and a gasket made of the same material as the laminate and with the same thickness must be placed at the root of the weld in the specimen. 2. Welding test specimens of the product shall be prepared for the inner cylinder of the multi-layer integral wrapping container. VII. Non-destructive testing: 100% RT/100% UT testing shall be conducted on the splice joints of the laminated plates, the Class A weld joints of the inner cylinder of multi-layer wrapped containers, the Class A and B weld joints of the inner cylinder of fully wrapped multi-layer containers, the weld joints between each layer of laminated plates and the end flanges or spherical heads, as well as the longitudinal and circumferential weld joints of the outermost layer of laminated plates. VIII. Relief Holes 1. Relief holes shall be drilled in each multi-layer tube section in accordance with the requirements of the drawings ； 2. The discharge holes are usually located at both ends of the cylinder section, at a depth reaching the outer surface of the inner cylinder ； 3. The diameter and number of vent holes vary depending on the diameter of the container. IX. Function of the relief hole: 1. Since the inner cylinder is subject to relatively high stress levels and comes into direct contact with the medium, making it susceptible to corrosion, defects typically originate on the inner wall of the cylinder and spread outward gradually. Once a defect in the inner cylinder penetrates through, the pressurized medium will flow out through the relief hole, serving as a safety alarm mechanism; this adheres to the safety design principle of \"leakage before failure\" ； 2. There is gas between the layers of the plate; when welding the circumferential weld, if the gas that expands due to heating cannot escape, it will mix into the weld, resulting in defects such as pores. Vent holes can help reduce the occurrence of such defects ； 3. During the manufacturing process, a small amount of liquid may remain between the layers; when the container is heated, this liquid vaporizes and its volume expands. The excess gas can be released through the vent holes, thereby preventing an increase in pressure due to volume expansion that could lead to local yielding of the material.