Installation of double-wall tanks

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Installation of double-wall tanks: Double-wall tanks consist of an inner wall and an outer wall, and are used for storing liquefied petroleum gas at low temperatures. Their volume is over 10,000 cubic meters, and the installation process is much more complex than that of ordinary oil tanks. These types of storage tanks are all constructed using the vertical installation method. I. Construction process flow: The standard method involves first installing the outer tank, then the top cover, and finally the inner tank. The construction process is shown in the figure below. http://www.mrgyq.com/web/art/SGFF.files/image038.gif II. Installation of double-wall tanks (I) Installation of the outer tank 1. Installation of the tank bottom plate Just like in the construction of ordinary oil tanks, the first step is to install the tank bottom plate. 2 Laying and welding of edge plates: Start laying the edge plates from the starting position specified in the drawings. The diameter of the bottom plate should be increased appropriately to account for welding contraction; after adjustment, perform spot welding – first on the short seams and then on the long seams – followed by welding. The welding sequence is the same as that for spot welding ； 2 Laying and welding of medium-sized plates: Start from the center line and lay the plates sequentially toward both ends and sides, paying attention to the direction of overlap; cut an angled edge at the junction of the two plates. After verifying that the dimensions are correct, secure them in place using clamps. During welding, click on the seam that needs to be welded, and remove the clamps as you weld ； 2 Marking on the bottom plate: Mark and indicate clearly the circumference of the outer tank, the location of the cement layer at the bottom of the inner tank, the foundation for the insulation blocks of the inner tank, and the position of the inner tank walls. After marking, conduct a thorough inspection and verification. 2. Installation of the outer tank wall panels: Mark positioning points around the outer tank, and start lifting the first panel from the starting position specified in the drawings (spot welding is required at this starting point to prevent movement). Use a plumb line to check for verticality; support both ends of the panel with angle irons and fix them with spot welds. Install the panels one by one in sequence, making sure to leave space in the direction of the main entrance ； 2 After the first layer of wall panels is in place, adjust the angle of the longitudinal seams first, then carry out spot welding, welding 3 arc-shaped panels at each longitudinal seam simultaneously. After all longitudinal seams have been adjusted, proceed to adjust the verticality and ellipticity of the tank wall, making adjustments one by one using support methods ； 2 The second layer of wall panels can be aligned, adjusted, and fixed by means of back bar fixtures and support methods; for the installation of subsequent layers, adjustment can only be carried out using expansion rings and guy ropes ； 2 It should be noted that after the third layer of wall panels is installed, it is necessary to assemble the top cover inside the tank first; as the wall panels become higher, it becomes more difficult to align them and lift the materials. 3. Installation of the roofs: Since the outer tank is generally designed with an arched roof structure, while the inner tank has a flat roof structure, the two are connected by steel members. Moreover, with the tank diameter reaching several dozen meters, there are no vertical supports in the middle; therefore, it is advisable to lift both the inner and outer roofs simultaneously during installation, along with any attachments such as manholes, connections, and walkways on these roofs. This approach avoids the need to set up scaffolding later, which would make high-altitude installation more difficult. 2 Internal roof installation: First, mark lines and make templates on the outer tank bottom plate to determine the positions and directions of the internal and external roofs as well as the pipes, along with the main dimensions of various components. A temporary platform frame should be set up; this frame is made from angle steel with dimensions of ∠80 × 80 × 60 mm. A level should be used to ensure that the frame is level. It is essential that all joints on the inner top plate lie on the beams of the frame, in order to avoid deformation due to welding. The frame must be sturdy enough to prevent it from collapsing under the pressure from the inner and outer roofs ； 2 After the inner tank top cover is in place, welding is carried out. The welding requirements are the same as those for the bottom plate; pay attention to the key points and sequence of welding to prevent deformation. 2 External roof installation: Draft on the inner roof panel to outline the framework pattern of the external roof cover as well as the dimensions and positions of various components; install temporary supports and the steel sections used for the roof framework. All the determined steel sections should be at the specified elevation, and on these temporary supports, install the outer ring beams, roof support beams (beams), and intermediate ring beams. When installing the outer top panel, the outer layer should be laid first, followed by the inner layer, and then the middle layer; these layers should be secured with clamps before welding. 2. Hoisting of the top cover: Holes are made in the top cover, 4 lifting lugs are installed and the structure is reinforced; then it is lifted into place using two 150t cranes and aligned with the tank wall. Only after welding is complete can the crane release its hook. 4. Outer tank doors: On the first, second, and third layers of panels of the outer tank, there are 3 panels that serve as temporary doors; these are not welded yet. During installation and adjustment of the panels, only spot welding is used. (There are also 3 panels in corresponding positions on the inner tank.) These reserved doors are provided to facilitate construction work on the inner tank. The door frame should be made of angle steel with dimensions of ∠ 100 × 100 × 10 mm; it is welded to the wall panels. Once the wall panels used for the door are removed, work on the inner tank can proceed. (II) Installation of the inner tank 1. Installation of the inner tank foundation: 2. Markings are made on the bottom plate of the outer tank to determine the location and dimensions of the perlite concrete support blocks under the edge plates of the inner tank. Each block is aligned and leveled using 4 sets of shims, and then installed according to the dimensions specified in the drawings. After verifying that the dimensions are correct, each block is secured in place by spot-welding it to 4 positioning angle irons. Once the inner wall has been installed, secondary grouting is carried out using cement-based grout ； 2 Build an inclined path outside the tank to facilitate crane operations inside it; lay a thick layer of steel plates in the area where the crane moves inside the tank to prevent deformation of the outer tank’s bottom plate ； 2 First, lay the edge plates; once they are in place, the welder shall carry out welding at the gaps in a symmetrical manner