Sheet by sheet
Production of VST oil tanks by sheet assembly method
Besides the manufacturing of reservoir steel structures with the industrial roll method at the enterprise, the production of VST tanks is carried out by the method of sheet-by-sheet assembly of the walls and bottoms of reservoirs for petroleum products with sheets of maximum dimensions 2500x12000 mm.
There are two methods for machining sheet edges and chamfering with set welding parameters:
- on the stationary machines (face milling machine, longitudinally milling machine);
- manual edge milling machines BM20.
High quality processing of sheet structures fully prepared for installation can be guaranteed if tank metal structures are produced by any of these manufacturing methods.
Rolling of sheets is carried out on a sheet bending machine of the type IB2426 (Russia) up to 40 mm and AKYAPAK AK 300 AHS 30/25 (Turkey) up to 25 mm with bending of the sheet bends which makes it possible to obtain a stable radius along the entire length of the sheet.
Sheet wall constructions are packed and transported in specially made lodgements (containers), providing:
- the geometric dimensions of the sheet rolled to a radius;
- the prevention of the mutual movement of the sheet structures and damage on the edges of the sheets;
- safety of products during transportation.
The parts of the bottom are packed and transported in containers corresponding to the design dimensions.
MOUNTING of the VST sheet assembly
Services for the delivery and installation of th tank include:
- development of PPR;
- hydro testing
- other works on the installation of VST.
During sheet assembly, the walls of the tank are mountedby the following methods:
- build-ups: the wall is assembled from the 1st belt and the sheets are set up along the belts;
- growths: the wall is assembled from the upper belt and then the lower ones are assembled lifting the already welded structure.
While assembling a fixed roof, a central pillar is used, or it is assembled from above or from inside the tank. When assembling a floating roof, the tank is first checked out for any leaks and then mounted on the bottom.
While installing the bottom, special attention is paid to the motionlessness of the foundation and the preservation of the waterproofing layer from loads
Storage tanks for petroleum products depending on the purpose and climatic conditions of operation can be manufactured with mild, low alloy and stainless steel usage. Regardless of the construction type of the fuel storage tank, the materials used and the methods, the diesel fuel tanks must be of a high quality and an exact adherence to the timing and production standards.
This method differs from the roll-up in that the design of the body and the bottom of the VST are transferred to the installation in separate sheets. They are specially prepared at the plant: reduction to design dimensions, cutting edges for the each type of a welding, rolling (bending to the desired radius) and packaging. Welding work is carried out mainly on the installation.
With the usage of the sheet assembly method it is preferable to produce VST of large volumes. Also, this method is often chosen for the construction of tanks in cramped conditions and their repairing.
The manufacturing quality of the tank with the sheet method is ensured by 4 key factors:
- metal rolling quality;
- achieving accurate sheet geometry as a result of processing;
- precision cutting edges for welding;
- packaging of processed and rolled blanks, excluding deformation during transportation.
In our factory for processing workpieces edgewise, a longitudinally - planed - milling machine is used. It allows you to immediately process a pack of metal, moreover, with planing and milling sequentially for one installation. According to the technology with the help of a special conductor an even bundle of sheets is formed first of all , then it is fixed on the machine. After that, on the one hand, there is a planing of the longitudinal surface , which ensures its evenness, then, on the other hand, the milling, which achieves the design width.
Longitudinally - planing - the milling machine that our plant is equipped allows to bring sheet metal in size with a deviation from the design not more than ± 0.02 mm (despite the standard tolerance of ± 0.5 mm).The technology of sequential planing - milling provides the maximum possible speed of work on this site since it does not require reinstalling a pack of metal.
After planing / milling, the workpieces are sent for trimming. For this purpose we use hydraulic guillotine shears for metal rolling up to 16 mm thick. This machine is most convenient for this operation, because it allows you to quickly chop off the ends of the sheet in a high degree of accuracy. We cut thicker steel by means of plasma gas cutting.
Each processed sheet undergoes visual and measuring control which is confirmed by applying the QC stamp on it without that it will not be transferred to the next Technological section of the plant.
ROLLING AND PACKAGING
The main structural elements of the tank that need to be rolled ( that is, bent in the radius specified by the project ) are wall sheets. This operation provides a cylindrical shape of the tank body after the sheet assembly.
Four-roll bending machines with the possibility of bending the ends of the sheets are used at this technological site.
The quality of the rolling is checked, first of all, for ensuring the stability of the bending radius along the entire length of the sheet. Measurements are made by a template with the measurement of the clearance between its arc and the curved surface of the sheet. Then the waviness of the edge is checked.It should not exceed 2mm per 1 meter of sheet length.
WHEN A SHEET TANK IS PREFERRED
When a tank has a volume more than 20,000 cubic meters The method of sheet assembly of tanks provides a more correct geometry. The shell and bottom are fully consistent with the design shape and size. When installing rolled metal structures of large tanks, it is quite difficult to ensure their exact deployment, especially at the significant thicknesses. As a result, the actual internal diameter of the tank may differ from the design which affects the reliability of the design and its operational characteristics. Therefore, with the significant storage volumes, it is recommended that the tank should be produced by the sheet method.
When the tank is “non-standard” in height.The sheet assembly method allows you to provide any volume and height. With the rolling method, the height does not exceed 18 m, and it is limited to 12 m in most cases (the “classic” width of the roll stand). Therefore, if the task is to save built-up land, leaf tanks often prove to be the right solution.
Cramped construction conditions on the site.Vertical cylindrical sheet assembly tanks are easily erected in cramped conditions which is not uncommon for all industrial facilities, especially re-equipped and reconstructed ones. To deploy a tank with a volume of, for example, 10'000m³, a free space of at least 20m from the wall are erected, and the possibility of maneuvering awith bulldozer and so on are required. The site should be dumped and equipped so that heavy equipment does not fail.This is often an additional cost to the customer.Also, the method of tank sheet assembly is the only solution if they need to be installed indoors.
When there is a problem with heavy equipment at the construction site.The sheet tank is mounted without the heavy-duty cranes usage.This simplifies greatly the work at remote sites where a crane with a lifting capacity of, for instance, 100t. is very problematic to find , and relocation from the nearest major city is very expensive financially and organizationally.Also, if the conditions of the site are cramped, a crane with a large outreach is often required to “throw” the roll through the facilities available on it, and this costs additional money and consumes organizational efforts.