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Welding at the bottom of the tank: 1. Welding of the edge plates – When assembling the edge plates, unequal gaps are used; the gap on the outer side is smaller, at 6–7 mm, while it is larger on the inner side, at 8–12 mm. This arrangement allows the gaps to become equal due to the thermal contraction of the welds as welding progresses over an area of 300 mm on the outer side, thereby ensuring the flatness of the edge plates after welding and preventing local bulging； In addition, shims are used at the joints of the edge plates; when aligning them, it is necessary to ensure not only that there is an appropriate gap but also that the two edge plates being joined as well as the shims are in close contact during spot welding, in order to prevent internal defects such as bulges and lack of fusion during welding ； It is also advisable to install a deformation-resistant plate on the outside, near the end of the plate; this plate should be secured with pins during welding, and removed after welding is complete and the material has cooled down ； Welders should be distributed evenly. The welding of the remaining part of the edge plate to the seam shall be completed after the corner weld connecting the tank bottom and the tank wall has been finished, and before the shrinkage joint between the edge plate and the web is welded. 2. Welding of medium-width plates: The welding sequence for medium-width plates depends on their arrangement pattern, but the general principle is to weld short seams first and long seams later, to leave space for contraction, and to weld in a radial pattern from the center outward. The principle for determining the welding sequence is to first weld the tank bottom plates into groups of two from a single plate, then weld those groups of two into groups of four, and so on. The spot-welded joints reserved for contraction before welding should be separated, so that each group of tank bottoms can contract independently, thereby reducing or preventing misalignment at the center of the tank bottom due to temperature changes and uneven welding contraction. Welds of the same type that are adjacent to each other should not be welded simultaneously; instead, one weld should be performed after another. For longer joints, welding should be carried out in segments, with each segment being approximately 1.5 to 2 meters long. In the case of long joints in corridor slabs, welding should be done in segments starting from the center and moving towards the ends. The joints between successive weld layers should be offset by 50 to 100 mm. After all other welds have been completed, spot welding should be used to seal any contraction gaps. In actual construction, it is common to leave a 500–800 mm gap unwelded at each joint connecting with the edge plates; this gap is welded together during the welding of the contraction joints between the middle plates and the edge plates. This approach is very effective in preventing deformation and reducing difficulties in alignment. 3. The edge plate is welded to the first ring of wall panels. The corner joints where the tank bottom meets the tank walls should be welded after the longitudinal seams of the bottom ring wall panels have been completed; several welders carry out welding in segments from both the inside and outside of the tank in the same direction, with the initial weld passes being created by welding in segments and then retracting the weld pool. Based on the stress conditions of the storage tank, the corner joints between the edge plates and the wall plates adopt a welding joint that is larger on the inside and smaller on the outside. Since the connection between the wall panels and the bottom of the tank is a T-shaped fillet weld, and it is asymmetric on both sides, the temperature distribution is also uneven; as a result, the amount of melting metal that contracts on each side of the panel differs, which can lead to angular deformation. Therefore, after the tank wall panels are lifted into place, several diagonal braces are installed on the inside of the tank (with an interval of 1 meter between each brace), in order to counteract the effect of angular deformation caused by welding at the internal and external corners on the tank’s verticality. During welding, an equal number of welders should be arranged evenly on the inner and outer sides, and they should weld in the same direction at a constant speed. The welders on the inner and outer sides should work alternately to prevent concentrated heat input. Each welder should perform multiple passes within their respective area, using a step-back welding method for the first pass. 4. Welding of the shrinkage joint between the edge plate and the mid-span plate: The interface between the mid-span plate and the edge plate is treated as a circumferential reserved shrinkage joint; it is not fixed by spot welding during assembly, but rather secured using gantry clamps and shims. During welding, first weld the radial reserve seams of the edge plates, then the reserve seams of the middle plates, and finally the circumferential contraction seams. Throughout this process, welders should be distributed evenly, with each welder working in segments in the same direction within their own welding area. 5. Control of welding deformation of the floating deck: There are two types of floating decks: double-disc and single-disc. The double-disc type consists of upper and lower cover plates, and edge ring plates as well as radial and circumferential partitions separate the floating deck into several leak-proof compartments. Being double-layered, the welding deformation caused by mutual restraint between them is small and easy to control. The steel plates used in individual discs are generally thin, usually ranging from 4.5 to 5 mm, which makes it very easy for significant welding deformation to occur, resulting in excessive unevenness on the surface of those discs. During construction, the laying of individual discs is carried out on a temporary platform erected using angle steel. When welding the ship’s compartments, start by welding the vertical seams and the joints where the trusses meet the bottom plates, followed by welding the other joint areas, and finally weld the fully continuous sections. This approach is intended to reduce welding deformation. Once the entire floating deck compartment has been assembled, all the connection points of the individual plates should be welded together. The single-disc layout patterns are generally strip-shaped and herringbone-shaped. Its welding sequence is similar to that of welding the tank bottom; before welding on the surface, intermittent welding is carried out on the back side first, and this method is very effective in preventing welding deformation. During welding, the first layer of welds is laid in segments by moving backward; for long seams, welding is carried out from the middle toward the ends. For the joints between individual coils and the floating vessel, welders are also arranged evenly to carry out welding in the same direction. Welding of the tank wall: The main factors causing deformation of the tank wall are the straight edges formed during the rolling process of the tank plates, as well as the longitudinal and circumferential welding angle deformations that occur during welding. Such deformations affect the ellipticity and verticality of the storage tank, and they also impact the lifting and lowering of the floating deck. Since the thickness of the wall plates in the first ring is the greatest, it is very difficult to reverse the welding-induced deformations; therefore, controlling the welding deformation of the first ring of tank walls is essential for ensuring the geometric dimensions of the entire tank. The tank wall plates, after being pre-formed into arcs, should be placed around the tank foundation according to the layout specified in the tank wall plan, and supports should be used to lift both ends of these plates, so as to prevent any changes in the already formed arc shape due to prolonged placement. When enclosing the first layer of wall panels, triangular baffles are spot-welded on the inner and outer sides of the tank wall; these triangular baffles are arranged alternately at equal intervals on both sides. During assembly, large pins are used to adjust the ellipticity of the tank wall. The higher the density of the triangular baffles, the more precise the control of ellipticity is – generally, one baffle is placed every 500 mm. The adjustment of verticality can be achieved by adjusting the diagonal braces inside the tank wall. Since the longitudinal groove grooves are of X-type and V-type. In the case of a large groove, one side is located on the outside of the tank wall; after welding on that outer side, it is necessary to use carbon arc gas gouging to remove any residual material from the root. Therefore, when aligning the components, it is necessary to decide whether to allow for any reverse deformation based on the specific shape of the groove. The welding direction for the vertical seams is upward welding; the higher up the vertical seams on the wall panels are, the greater the amount of contraction, which in turn affects the verticality of the tank wall. During welding, it is advisable to use segmented welding and strictly follow the welding procedures. For root welding, small-diameter electrodes are used to ensure full penetration, thereby reducing the amount of material that needs to be removed from the back side; this helps avoid welding distortions caused by overly deep grooves. The welding of circumferential seams is similar to that of longitudinal seams; the difference is that circumferential seams are welded in rows, requiring that the welding process parameters not be too high, and that the joints of each weld pass be offset by 50–100 mm. The floating upright method is employed; the circumferential force generated by hydraulics during floating helps to correct the deformation that occurs during the welding of the tank walls. When installing wall panels using the inverted construction method, they should be tightened at the sealing plates using a hand chain hoist, so that the wall panels fit tightly against the surrounding panels; this can **reduce the out-of-roundness of the tank wall as well as the deformation that occurs during welding. In tank construction, apart from the welding of the tank bottom, floating deck, and tank walls, welding in other areas can also lead to welding deformation. This applies to the welding of wind resistance rings, reinforcement rings, and edge steel members. As circumferential welds, it is necessary to follow the principle of welding in segments in the same direction, starting with intermittent welding before moving on to continuous welding, in order to prevent warping. It should be noted that the joints of the wind-resistant ring itself must ensure full penetration during welding; if necessary, shims can be used, and continuous welding must be ensured in the area between the wind-resistant ring and the tank wall, in order to prevent rainwater from entering the insulation layer through the gaps between the tank wall and the wind-resistant ring.