During plastic deformation of metals, the deforming stress increases with the degree of plastic deformation due to the development of strain hardening. If the plastic deformation is interrupted by removing the load and then loading the specimen in the same direction, then to continue it, it is necessary to apply a stress, in general, equal to the acting stress at which the plastic deformation was interrupted. This stress is always higher than the initial yield strength of the unstressed metal. When the specimen is loaded in the opposite direction, the stress that causes the onset of deformation is significantly lower not only than the stress that must be applied to continue deformation in the initial direction, but also lower than the yield strength (elasticity) of the original specimen. This phenomenon is called the Bauschinger effect.

In the process of manufacturing pipes from rolled plates, the mechanical properties of steel change: yield strength (type of stress-strain curve, length and the very presence of a yield point, etc.), ductility, impact strength, brittle fracture transition temperature and even temporary resistance. Properties change both in the transverse and longitudinal directions (in the latter case, the Bauschinger effect does not appear and the yield strength can only increase). But the most important is the yield strength in the transverse direction, as it can both increase and decrease when the sheet is converted into a pipe. This is important because you need to determine what requirements to order metal with, knowing the requirements for the pipe.

When pipes are formed, different stress and strain gradients are created across the cross-section. As a result, different layers of material acquire different properties. This in itself determines the presence of high residual stresses. Thus, the magnitude of the effect depends on a number of parameters, including the chemical composition of the steel, rolling and cooling parameters, and strain aging. With the same pipe forming technology, the magnitude of residual macro-stresses can be determined mainly by the degree of unevenness in structure and properties across the thickness of the plate. The structure heterogeneity also contributes to the increase in residual stresses and the effects of incomplete elasticity. All of this determines the need for careful normalization of process parameters (in particular, the degree of expansion) in order to optimize and distribute residual stresses. Expansion is the only process (other than heat treatment) that can effectively eliminate residual stresses and incomplete elasticity of the base metal of large-diameter pipes.

The technical requirements for repair structures are quite stringent in terms of the geometric parameters of the bent parts they consist of. This is due to the need to ensure a precise fit of the elements and high-quality welding conditions. Non-destructive testing of bent parts is also mandatory. The elements are protected against atmospheric corrosion (priming). Each type is additionally equipped with mounting kits and lining tapes.
The customers paid special attention to the requirements for product packaging, labeling, identification and traceability.

The development of new types of products is a priority for UKRTRUBOIZOL LLC. Today, our company is already a supplier of integrated solutions for main product pipelines (large-diameter steel pipes, internal and external coatings, joint protection materials, repair structures, etc.)

UKRTRUBOIZOL LLC is the largest Ukrainian manufacturer of longitudinal SAW steel pipes with external anticorrosion and internal anticorrosion or smooth coatings for main gas and oil pipelines.

The products of the plant are certified for compliance with the requirements of national, interstate and international standards ISO 3183:2019, DSTU ISO 3183:2017 (ISO 3183:2012, IDT), API Spec 5L, DIN EN 10219-1,2, DIN EN 10217-1,3,5,6, DSTU 8943:2019, DSTU 9219:2023, DSTU 9218:2023, TU U 24.2-05757883-095:2022 GOST 20295-85, GOST 10706-76, GOST 10705-80, Technical Regulations for Pressure Equipment, CMU No. 27 of January 16, 2019, European Directive 2014/68/EU and the requirements of the Construction Regulation EC 305/2011/EU with the right to apply the CE mark, as confirmed by the international certification body TÜV Thüringen.

The company has an integrated management system that meets the requirements of international standards: ISO 9001:2015, ISO 14001:2015 and ISO 45001:2018, the welding process complies with EN ISO 3834-2, which is confirmed by an independent certification body TÜV AUSTRIA SERVICES GMBH.