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Introduction. The paper deals with relaxation and creep coefficients, long-term ultimate bending deformation under long-term exposure to moisture and chemically active environment (10,000 hours) of sewer pipes.Materials and methods. 400, 1,200 and 1,400 mm diameter sewer pipes made of glass-reinforced polyester. A compressive load was applied to the specimen at a constant rate until a specific annular strain of (3.0 ± 0.5) % was achieved in (60 ± 10) s. The obtained specific annular strain was kept constant for 2 minutes, after this time the compressive load and annular strain were determined and recorded. The essence of the method is to load a test specimen, placed horizontally and immersed in water, at a given temperature, with a diametrically compressive load for a time during which the annular strain remains constant. The load is measured at specified intervals until 10,000 h is reached. According to the test results, the long-term specific annular stiffness and relaxation coefficient under the influence of moisture are determined in accordance with the methodology of GOST R 57008–2016. Two specimens shall be used for testing, unless otherwise specified in the normative document. Long-term specific ring stiffness and relaxation coefficient are the arithmetic mean obtained for two specimens.Results. It was found that the performance characteristics (long-term ultimate bending deformation, relaxation and creep coefficients when exposed to moisture) of the investigated sewer pipes are determined by the specific ring stiffness and their diameter. For polyester pipes with initial ring stiffness of 5,000 N/m2 increasing their diameter from 400 to 1,400 mm leads to linear increase of relaxation coefficient (from 0.79 to 0.96) and decrease of long-term ultimate bending strain (from 0.84 to 0.75 %) when exposed to moisture during 10,000 hours.Conclusions. The durability of the investigated sewer pipes made of glass-reinforced polyester exceeds 50 years.

The results of investigations of multi-component nanostructured coatings of (TiAlSiY)N/CrN type are presented. The influence of different variants of substrate surface pretreatment on adhesive strength and hardness of coatings was studied. Pre-treatment of samples was carried out in plasma of two-stage gas discharge according to various technological schemes. Except for ion-plasma purification, some samples were pretreated with a sublayer of chromium within 5 minutes. The coatings were formed by a vacuum-arc deposition method at simultaneous spraying of two cathode targets. The first cathode is made of chromium, and the second cathode is made of multicomponent Ti - Al - Si - Y alloy obtained by vacuum-arc remelting of powder mixture of the mentioned elements. The coatings were deposited on polished stainless-steel substrates at negative 280 V bias potential. The geometry of the unit and its elements, as well as technological characteristics of the processes of evaporation-condensation were selected so that at a speed of rotation of samples 8 revolutions per minute the formation of the coating with a total thickness of about 9.0 microns occurred in approximately 60 minutes. The analysis of the composition of the coatings shows that the content of elements in the coating differs greatly from the content of elements in the sprayed cathodes. The X-ray diffractometry has shown that all deposition modes are characterized by the formation of phases with cubic (fcc) crystal lattice in both phase layers of multilayer coatings. In the layers formed at spraying of TiAlSiY alloy, a multi-element disordered solid solution (TiAlSiY)N with a crystal lattice of NaCl type and a lattice parameter of 0.4241 nm, as well as chromium mononitride CrN with a lattice parameter of 0.4161 nm, is determined. It has been established that preliminary formation of a chromium sublayer on the substrate leads to significant changes in adhesive strength of multi-component coatings compared to coatings without a sublayer.