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In this work, we aim to validate the efficiency of the previously created and patented laboratory test installation for simulating the high-pressure operation of a thermal barrier of high-pressure reservoirs and for determining the thermal conductivity of thermal barrier materials. Simulation of thermal barrier operation in the test installation was carried out under elevated pressures (up to 50–70 MPa). The pressure on the thermal barrier layer was created and regulated by an Instron 5989 test machine as part of the installation. Control of temperature changes and evaluation of the thermal insulation performance were performed by a calculation method based on temperature readings in the control points of the upper and lower rods of the installation. These values were obtained by contact (using thermocouples of surface temperature control) or non-contact (using thermal imaging equipment) methods. A pilot study into the performance of a thermal barrier material “tennesite” was carried out at different pressures. At pressures of 30, 40 and 50 MPa, the thickness of the tested samples comprised 4.64 mm, 4.35 mm and 4.00 mm, respectively. Variations in pressure were established to have a negligible effect on the thermal conductivity of the studied material. Thus, at pressures of 30, 40 and 50 MPa, the temperature drop in the samples comprised 198°С, 188°С and 190°С, respectively. The installation showed high efficiency in simulating the thermal protection of the studied material. Thus, at a layer thickness of 4 mm under the internal pressure of 50 MPa and the working temperature inside the equipment housing up to 300°С, the material is capable of reducing the thermal impact on the protected part of the structure by about three times (from 298.6°С to 108.4°С). The presented design can be used when investigating the behavior of various thermal barrier materials operated under elevated pressures. The results obtained confirm the efficiency of the proposed laboratory installation.

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Formulas are presented for calculation of residual post-bending stresses that develop in pipe fittings. The formulas are derived as a result of solution of the elasto-plastic problem of the bending of a straight pipe.Residual stresses σ res (axial stresses) that develop in fittings after bending are defined as the sum of the stresses that are manifested in the fittings during bending σ bend and unloading σ unl (see Fig. 1):(1)The stresses that develop in a fitting during bending σ bend are determined from the following formulas: in the region of elastic deformations:(2) in the convex (tension) region when 0 ≤ y < y y ,in the concave (compression) region when -y y < y ≤ 0; and in the region of plastic deformations:in the convex (tension) region when y y ≤ y ≤ r out ,in the concave (compression) region when -r out ≤ y ≤ -y y , where y is the distance from the neutral axis to the layer under consideration in the cross section of the fitting, y y is the distance from the neutral axis to the region of plastic deformations in the cross section of the fitting (the coordinate of the boundary between elastic and plastic deformations)ξ y is the deformation for which the stresses are equal to the yield point at 20°(R e/20 ) (7) ξ y / = R E e 20 20 ; y y max out y r = ξ ξ ; bend / σ = −R e 20 bend / σ = R e 20 σ bend = − y R E 20 σ bend = y R E 20