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Production of quality tank metal structures demands high-quality materials. Svell Shipping Line has achieved that by implementing the system of incoming test (initial check) of materials used in production. It ensures using only materials meeting the requirements of technical norms and conditions, state regulations and project documentation for each exact item.
Initial material check includes the test of surface quality, geometric parameters, chemical composition and mechanical features.
The system of incoming test allows reducing the level of manufacturing defects to a degree, much lower than the one, stipulated by the branch standards. This is because our initial check system is far more strict than the requirements of the state norms and
The basic parameters of the income material test: regulations.
* Quality of the rolled products’ surface;
* Geometric parameters (shape, dimensions and extreme deviations) of the units;
* Chemical composition of metal-roll;
* Stretch test;
* Bending test;
* Impact bending test.
Storage and relocation of materials
In the course of storage and relocation of materials within the territory of production site it is essential to ensure their safety, in particular – to protect them against moisture and mechanical damage.
We keep materials and other units in dry warehouse facilities. Metal-roll, taken for storage, is sorted and marked after the initial check. It is kept in steady stock piles, selected by types and profiles. At the same time its contact with the floor is avoided.
Welding materials are stored separately by types and lots. Prior to production, welding rods and flux should be dried or decrepitated; welding wire needs to be cleaned from rust, oil and other dirt.
Metal preparation
Flattening of the sheet metal-roll
Sheet metal-roll, used for manufacturing bottoms and walls, is subject to flattening. It is carried out in ways that avoid appearance of compression marks, dents, buckles and other damage. Multi-corporate enterprise “RussianTankWorks” uses multi-roll flatteners with special bending tool. As a result of bending certain changes in the sheet material structure occur and the paste forming properties improve as well.
After flattening the whole 100 % of metal-roll is checked for external defects.
Edging of the sheet metal-roll
Edging is performed before producing coil-able strip panel and before rolling of the wall sheets of the tank, assembled by per-sheet method. Fore and cross cut edges are processed.
Edging provides clearing of irregularities, barbs (flashes), it ensures firm adherence of the spare parts to each other (edge matching), which determines quality of the planned welding joints, meeting the line dimension and shapes requirements, stipulated in the design project.
Edging is carried out with plane milling-machines and end-milling machines.
Manufacturing of walls, bottom and tank roof
Coiling method
This method is one of the two industrial approaches for producing the metal structures of a tank. It implies that tank wall, bottom and roof are brought to the construction site in the form of coiled strip panels, meant for welding. The advantages of this method are to be seen in making the tank installation period 3-4 times shorter as a result of cutting down the volume of welding procedures in the building area by about 80 % at the average and providing high quality of welding joints due to the use of two-side automatic welding.
Strip panels are produced from steel sheets of modular size 1500x6000 mm.
Panels are automatically welded on a special coiling machine. It consists of welding and assembly sites – top and bottom level, edging tumbler and rolling (coiling) device.
Coiling machine’s operation is performed in two basic schemes (upper and lower coiling). Lower coiling is meant for producing tank walls up to 18 mm thickness, upper coiling is used for thicknesses not exceeding 16 mm.
The length of the coils amounts to 18 m, the weight is adjusted to the load-lifting capacity of motive power.
Stages of strip panel manufacturing by coiling method:
1. production of technological structure;
2. arranging the sheets according to the detailed metal framework graphical drafts;
3. welding and coiling;
4. preparation of coils for transportation.
Preparation of technological frame
Before welding the strip panels a special frame is prepared, on which the sheets will be coiled. The diameter of the frame should not be less than 2.6 m, and its length should be equal to the height of the tank wall.
Shaft staircase is often used as a technological frame for coiling the walls. This is usually applied for tanks not exceeding 2000 m³ of loading capacity. In this case metal economy is provided.
Arranging the strip panel sheets
Arranging of wall sheets, bottom and roof is carried out on the upper welding and assembly level of the coiling machine. In the course of arranging process the prepared sheets are laid out on the site in accordance with the graphic drafts and are fixed with the installation instruments.
Coil-able wall strip panels must have a certain technologic allowance in length, which enables to assemble the installation joints.
Welding and coiling of the strip panels
Welding is the basic stage of tank production, as regards coiling method. We use automatic two-side welding of fore and crosscut joints. At first the original seam is welded on the top welding and assembly level of the coiling machine, then the strip panel is rewound through the edging tumbler and the second seam is done at the bottom level.
The order of coiling the strip panels of different tank frames is planned in reverse sequence of unrolling them in the course of installation. The wall sheets are coiled in a way, that implies that they are meant to be unrolled in clockwise direction.
To ensure quality of the welding joints our factory applies a complex of measures.
The welding procedures were originally worked out and tested by our Welding Laboratory. They were taken as the basis for the Welding Operating Conditions, which determine the requirements for welding joints and the order of technological operations as regards the types and the thicknesses of metal roll, type of the weld, steel edge preparation and other parameters. Following the Welding Operating Conditions provides conformance to the requirements of the State Standards (GOST).
Our Welding Operating Conditions represent the basic operation document, determining the work of welders and the quality control of the joints.
Execution of the Welding Operating Conditions is controlled by the General Welding Operator Service and Quality Control Department.
As a result of thorough work through and strict execution of the Welding Operating Conditions we were able to provide the highest quality of the welding joints. It is considered to be one of the main advantages of the metal frameworks, produced by the company. It often happens that imperfections of welding technology or/and its violations cause a range of serious problems, as:
* Non-conformance of the welds’ crown to the requirements of the State Standard GOST-31385-2008. This means that the smooth connection of the weld and the main metal is not provided.
* Main metal undercuts and cold laps appear.
* Defects in welding joints appear: cracks, ripples, gas pockets and their chains, burn-through and blowholes.
As a result of these, full strength of the welding joint does not meet the standards and may cause welding deformations, bringing about bulges, dents and canning.
Per-sheet method
The second method of production of tank frameworks is the per-sheet assembly of the walls and bottoms. It implies that the wall sheets of maximum size 2500x10000 mm and the bottom sheets are prepared at the factory site; they are rolled to the radius, stipulated by the design project. Then the sheet elements are packed in a special way to be prepared for transportation. Wall and bottom assembly (welding) is carried out on the construction site.
Non-coil-able frameworks are produced in accordance with the design project and the requirements of the State Standards GOST-31385, Safety Regulations 03-605-03 of Federal Mining and Industrial Inspectorate of Russia.
The main factor determining the quality of the tank framework, produced by per-sheet method, is strict provision of their shape (referred to the design project), and the set of technological decisions, preventing residual distortion of the metal frameworks in the course of edging and transportation.
The basic stages of per-sheet production of vertical tanks’ walls and bottoms are as follows:
1. Preparation procedures
The first stage includes preparation of wall and bottom sheets. This stage ensures meeting the planned sheet dimensions and their geometric parameters. Pre-welding edging is also done.
Extreme shape deviations of the sheets are controlled in the course of preparation. The company’s Technical regulations set the maximum width deviation within the limits of ±0,5 mm.
2. Rolling
Rolling is done afterwards, meeting the radius, planned by the engineering design project. Rolling gives the cylindrical shape to the tank wall while installation is carried out.
Sheet-bending machines IB2426 (Russia) and XZC 3000/25 (Czech Rep.) are used by “RussianTankWorks” for rolling sheets up to 40 mm and 25 mm correspondingly. This equipment gives the opportunity to make the radius equal within the whole length of the sheet.
The radius is checked by the pattern. The clear gap between the pattern (2 m) in an arc and the bent sheet surface should not exceed 3 mm.
Another rolling quality parameter is the waviness of the front edge. It may not exceed 4 mm on the whole length of the sheet. The waviness parameter per 1 m of sheet length should fall into the limits of 2 mm.
3. Packing.
The sheet frameworks of the walls are packed and carried in special lodgments (containers).
Lodgments are constructed in a way, providing:
* Keeping the radius of rolled sheet as a result of exact conformance of the lodgment to its geometric parameters;
* Tough fixing of the sheet frameworks, aimed at avoiding edges’ damage;
* The units’ safety in the course of transportation, preventing residual deformation.
The bottom parts are packed and transported in containers, constructed in accordance with their types and dimensions.
Tank roof metal frameworks production
Production technologies for the roof metalwork of a storage tank vary depending on its type, determined by the design project. In relation to the type and dimensions of the tank, and other specific features as well, either permanent-type roofs or floating roofs are used. Permanent roofs include either frameless or framed roofs conical or spherical in shape.
Quality control
The system of welding joints’ quality control
Our multilevel quality control system includes:
* 100% visual and measuring welding joints’ control;
* Physical methods of control;
* Radiographic control (it is performed after visual control acceptance. Wall welding joints and butt-joined seams are subjected to the radiographic control);
* Ultra-audible defect detection, used for revealing internal and surface defects in welding joints and weld-affected zone;
* Magnetic particle method;
* Color (chromatic).
The results of the quality tests are included in the set of associated documents for the tank.
Welding joints’ quality control by test sample.
This method is not obligatory. Anyway, “RussianTankWorks” applies it to 100% of fore welding joints of the coil-able sheets.
The method’s main idea is that 2 metal plates (test sample) are fixed to the edge of the welded sheet. The sample is identical to the welded sheets as regards the material and the type of edge processing. Welding operator thus makes two welding joints – including the seam of the test sample. The joint of the test sample is subject to expert appraisal and checked for breakage, bend and impact resistance.
Implementing of this method has resulted in absolute absence of welding joints defects in coiled sheets. Accordingly, we reduce the problems of welding deformations to minimum, avoiding bulges and dents.