Production of Steel Structures

Steel structures are the structures made of metal used in the construction of industrial buildings, large-span buildings, bridges and overpasses, steel-plate structures, towers and masts, frames of multi-storey buildings, crane and other movable structures and other structures.
Manufacturing of steel structures is composed of a series of operations, the execution of which is carried out in organized basic production shops. They are:
• metal preparation shop with a warehouse;
• metal processing shop;
• semiproduct warehouse;
• assembly and welding shops;
• paint and loading shop with a warehouse of finished products.

The metal preparation shop produces unloading, sorting, labeling, leveling, warehousing, storage and delivery of metal-roll. In addition, the preparation workshop conducts acceptance and storage of crops and manufacturing waste, delivery of manufacturing waste, cutting of crops and shipment of scrap metal.

In the processing shop the operations on production of parts made of metal-roll, which comes from the preparation workshop, are carried out. Owing to the available high-precision gas-plasma drilling equipment, manufacturing of parts is now mainly carried out without sketching and basting. In case of necessity of sketching or basting, contours of the parts, centers of the holes, knuckle lines, as well as signs and labels are initially applied to the metal surface. Cutting of metal on parts is produced by lines, marked on the metal. Cutting is performed by shears, saws or oxygen on automatic or semi-automatic machines. Formation of holes in the parts is produced on presses or drills. Bending in the cold or rarely warm state is applied for some parts of blast furnaces, gas holders, tanks, pipes, pipelines, silos and bunkers. In certain parts, edges are planed and butts are milled.
Many processing shops have production lines and automated systems for multiple operations. These lines and facilities include flow lines for production of large sheet metal parts, a flow line by "Boulton And Paul Ltd." (England) for cutting and drilling of section steel, mechanized machinery for cutting of edge piercing by "Ficep" (Italy) and "Vernier" (France), a mechanized system for cutting and drilling of section steel by "Gustav Werner" (Germany), a mechanized facility for flattening, cutting and piercing of pipes for junctions.
Finished parts are labeled and passed to a semiproduct warehouse in sets, separately by each production drawing. Long parts are usually stored in compartments, and small ones are held in containers.

In the assembly and welding shops, the assembly of structures from individual parts, delivered from the semiproduct warehouses, is performed. The assembly process consists of placing of parts in accordance with the drawings and their junction between themselves by short welds (tacks). Assembled structures are subject to automatic arc welding and MIG in carbon dioxide.
Some kinds of large-size and complex structures require some additional works to ensure high quality of erection joints (milling ends, drilling holes for erection joints by jigs or sketching, general and reference assembling). The general assembling is performed to ensure the design dimensions of structures, fitting edges for welding and reaming mounting holes. The reference assembling is performed to verify the precision of the elements manufacturing and their interchangeability. Finished structures are labeled by paint with a number of order, a working drawing and a structure mark.

Manufactured structures are transported to the pain and loading shop, where structures are primed, put in stacks and loaded on railway platforms or vehicles for shipment to an installation site.

In order to ensure the required quality of steel structures, the plant has a system of quality control and testing of the materials, equipment, appliances and tools conditions, qualification of the personnel, functional inspection and acceptance of the quality of performed work. The quality of finished steel, electrodes, welding wire, flux, carbon dioxide, coatings, used in fabrication of structures, shall meet the requirements of the relevant standards and specifications.

Steel Structures Welds
The junction of steel structure elements by means of welding is based on the principle of formation of a monolithic connection as a result of interatomic cohesion of metals in a welding seam.
The main advantages of welded connection are:
• high durability and reliability;
• possibility of joining elements directly without additional parts and openings (unlike riveted and bolted joints);
• simple structural shape;
• metal economy;
• possibility of mechanization and automation of the welding process.
The disadvantages of welded connection are:
• deformation of products due to the shrinkage of welds;
• residual stresses in a structure, which in some cases lead to increase of steel shortness.
Junction of steel structures is predominantly performed by consumable electrode arc welding.

Types of Welding:
• manual arc welding is the most slow and labor-intensive type of welding. By its application the junction is of lower quality than by mechanized methods. However, it is widely spread due to its universality: welding can be performed in any position and nooks. In most cases, the manual arc welding is used for installation of steel structures;
• automatic and semi-automatic submerged welding. The peculiarity of this type of welding is that the welding arc burns between an electrode wire and a welded workpiece under a layer of special flux. Flux is preliminarily supplied to the place of welding. The arc melts the wire, the base material and a part of flux. The weld pool gets deeper and of a longer form. As the welding moves on a weld is formed, closed by slag coverage, which can be easily separated after cooling-down and exposes the surface of a seam. Currently, the semi-automatic flux-cored arc welding is widespread. Flux-cored wire is a rolled steel band with pressed flux inside it.
• gas-shielded welding is performed by s semi-automatic method by a consumable electrode wire. An electrode wire and carbon dioxide are automatically fed to a welding head by flexible hoses. Carbon dioxide displaces the air from the zone of arc burning and protects molten metal from oxygen and nitrogen.
• electro-slag welding. In this case, welded plates are positioned vertically with a gap of 20-40 mm; the bottom of a gap is limited by a steel backing bar, sides – by copper sliders, cooled by running water. As the welding advances an electrode wire is automatically fed and copper forming sliders move in the direction of welding. Electro-slag welding is used for welding thick (over 20 mm) elements.

Welded connections can be:
• butt - welded parts are put together in a butt joint, and the place of their connection is fused with a weld;
• overlapping - one part is laid over another and welded by individual borders or around the contour of connection;
• combined - parts are welded in a butt joint with overlapping covers to strengthen the connection.

Bolting of Steel Structures
In addition to welding, bolted and riveted joints are also used in production of metal structures. Bolted connections are primarily used for installation of steel structures, as the accuracy of the installation of elements and their positional relationship is automatically controlled by the coincidence of holes of the connecting elements; bolts enable firm constriction of the connecting elements. It is extremely easy to install a bolt and it does not require special equipment and energy supply.

Corrosion Protection of Steel Structures
All steel structures, fabricated and accepted by QCD, shall be primed or painted prior to shipment to protect the metal against corrosion. Metal corrosion is the destruction of metal materials due to their chemical or electrochemical interaction with the environment. The environment, where metal corrosion usually appears, is various liquids and gases.
The corrosion rate of steel structures substantially depends on the air moisture and its composition.
The main method of protecting steel structures against corrosion is paint covering.
Protection quality of paints largely depends on the quality of surface preparation prior to painting. By any method of painting, the defects, left after cleaning the surface, are in the sequel the main cause of premature corrosion. The type of surface preparation depends on the environmental aggressiveness, which the structures are intended for. The degree of aggressive impact on structures by the environment is determined by the average rate of corrosion.
Surface preparation of the structures, designed for use in non-aggressive and slightly-aggressive environments, is performed manually or with the help of mechanized tools. If required, the wiping of the surface with rags, wetted with mineral spirits, as well as compressed air blasting are performed to remove grease and other contaminants. In this case, the metal surface shall be free from loose scale, rust, welding spatter, flux residues, grease and other contaminants.
Surface preparation of the structures, designed for use in medium- and highly-aggressive environments, is produced by a shot-blasting method with cleaning of welds manually or with the help of mechanized tools. The surface shall be free from scale, rust, welding spatter, flux residues, grease and other contaminants.
After preparation, the surfaces of steel structures are primed and painted. Steel structures are covered with special connections to strengthen their anti-corrosion properties.

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2000-2012 results

Rolled Tanks – 87,000 tons
Layer Installed Tanks – 82,000 tons
Steel Structures – 77,700 tons

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