Wrapping welding

Multi-layer wrapped high-pressure vessels have the following advantages: 1. The manufacturing requirements are low, and no complex large-scale equipment is needed. 2. Unlike single-layer vessels, since the layers are typically made of plates about 12 mm thick, there are no metallurgical changes in the thickness direction regardless of the wall thickness; as a result, they possess good toughness and a lower likelihood of brittle failure. Multi-layer pressure vessels are very reliable in terms of materials and offer a high level of safety. 3. Adopt the correct laminated wrapping process, and utilize the prestress generated by the contraction of the longitudinal welds between the layers, so as to ensure a more uniform distribution of stress across the wall thickness of the cylinder during operation, thereby improving the stress conditions of the cylinder. 4. Since the welds of each layer are offset when the laminates are wrapped, there are no two or more consecutive weld layers on the radial surface of the cylinder, so the impact caused by weld weakening is minimal. 5. The multi-layer plate cylinder is equipped with alarm holes that penetrate the layers. When the inner cylinder leaks due to corrosion, it can be detected during dry periods and addressed promptly. The manufacturing characteristic of multi-layer wrapped containers is that the process of wrapping the cylindrical body with layers is rather complicated, time-consuming, and results in a long production cycle. In recent years, layer wrapping machines developed in China have been used to improve this manufacturing process; these machines enable continuous performance of tasks such as positioning, pre-tightening, and tightening, thereby significantly increasing the efficiency of wrapping.

II. Key control points for laminate manufacturing 1. Surface quality of steel plates: There shall be no defects such as cracks, scratches, large-area pitting, or depressions. Fixed-length boards should be used; a board width of 2 meters is relatively appropriate. 2. Before sheet metal is formed, it must be leveled. A steel plate thick enough can be placed between the upper and lower rolls of the rolling machine, and then the layered plates can be placed under the upper plate to be leveled by rolling. 3. After leveling, drill 3 holes of φ50 each at both ends of the steel plate; these holes serve as leakage signal holes for the laminates, as well as for allowing the clamping jaws of the wrapping machine to apply the force necessary to firmly hold the laminates in place. The distance from the hole edge for holes ranging from 3 to φ50 should include the cutting head allowance. Generally, without including any allowance for pre-bending and cutting, the distance from the edge to the center of the φ50 hole is 90 mm; the holes are arranged symmetrically, with the center φ50 hole being 700 mm away from each of the other φ50 holes. 4. The edges of each plate must be pre-bent. After pre-bending, the straight edges are cut off, the groove is cut and ground at the same time, and then it is rolled into a circle. 5. For curling the laminated plates, arc templates (δ = 1.5 mm) must be made according to the theoretical dimensions corresponding to the different positions of the laminated plates, and these templates should be constructed from galvanized iron sheet. 6. The inner and outer surfaces of the laminate must be sandblasted to remove rust. To facilitate handling during rust removal, sheet metal is generally formed into coils and then sandblasted for rust removal. 7. The actual manufacturing dimensions of each layer of laminate should be matched to the actual dimensions of the previous layer, after it has been wrapped, welded, and passed inspection. 8. To stagger the welds between layers, the weld distribution lines for the wrapping layer must be marked based on the welds of the previous layer. The requirements for staggered arrangement of longitudinal circumferential welds shall comply with the provisions of HG3129‑1998 and the requirements of the drawings.

III. Laminated plate wrapping process and quality inspection 1. Install the \"inner cylinder tensioning and inflation devices\" in the inner cylinder at the positions and in the quantities specified by the manufacturing requirements. Generally, there are no fewer than 2 within the width dimension of each layer board. 2. After using the device to stretch apart (elastically) the individually formed and rust-removal-tested layer boards, slip them onto the inner cylinder (or onto the already wrapped layer boards). Each layer of the laminate is inserted all at once. 3. Then, fit the steel wire rope, and while using the tensioning device on the laminating machine to tighten it, roll the cylinder back and forth. The weld gap is adjusted; the groove gap for longitudinal seams is generally set at 6–14 mm, while that for circumferential seams is 6–8 mm. When determining the actual expansion dimensions, 10 mm is taken as a reference value (as determined by the welding process). After pre-tensioning, no fewer than 4 stirrup plates can be spot-welded at the openings of each layer plate. Then release the tensioning clamp to tension the next layer of plates. 4. The length of the wire rope used for pre-tensioning should be determined based on the following parameters: (1) the theoretical outer diameter of each layer of plates in the wrapping device; (2) the appropriate height of the mold arms of the wrapping machine; (3) the stroke range of the pre-tensioning device; (4) the supporting conditions of the welding turntable, etc. When wrapping and tightening the laminates of various types of equipment on each layer, the length of the steel ropes required is calculated one by one. Then, based on the range of movement of the tightening mechanism in the wrapping machine, the steel ropes are classified into 1#, 2#, 3#, 4#, etc., and the applicable ranges for each type of rope are determined and specified in the processing procedures for each wrapping device.

5. When the laminate wrapping machine starts to tighten, first insert the clamping pliers of the machine into the process holes φ50 that are pre-distributed along the edge of the board. Turn on the oil pump to increase the pressure gradually; the oil pressure gauge on the control panel will display the actual pressure during operation. At this point,

7. Welding and inspection of welds 7.1 Welding shall be carried out in strict accordance with the specified welding procedures; generally, after all the longitudinal seams have been welded and the laminate has further contracted, the circumferential seams are welded one by one. 7.2 Manual welding or submerged arc automatic welding can be used. 7.3 A reasonable welding sequence should be adopted to prevent the spot welds at other grooves from breaking apart due to welding only one weld seam. IV. Grinding of weld reinforcement on the layer plates
1. After all welds have been completed and fully cooled, remove the weld reinforcement, then use a grinding wheel to grind it down so that it becomes flush with the curvature of the cylinder. Generally, an air-driven grinding wheel is used for manual grinding. 2. This process must be carried out carefully; while grinding, use tools to check the curvature and straightness of the weld area. It is absolutely not allowed for any welds to be higher than the base material. It is strictly prohibited to use an angle grinder for grinding. The quality of grinding directly affects the welding of the layers below.

I’ve seen a mixing tank whose cylinder body was covered with an additional layer of steel plate, mainly to address severe wear and corrosion.

That type of equipment generally uses a process called lining, with an inner layer of stainless steel or wear-resistant material