Calculation of Strength of Facing Sheet of Flat Covers of Heat Exchangers Operating Under Vacuum
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RESEARCH, DESIGN, NUMERICAL ANALYSES, AND OPERATING EXPERIENCE PROCESSES AND EQUIPMENT OF CHEMICAL AND OIL-AND-GAS TECHNOLOGIES CALCULATION OF STRENGTH OF FACING SHEET OF FLAT COVERS OF HEAT EXCHANGERS OPERATING UNDER VACUUM M. V. Klykov and T. V. Alushkina
UDC 621.565.954.6+624.046
A procedure has been developed to calculate flat cover facing sheet fixed by electric rivets and welds along its outer and inner contours and loaded with external pressure. The calculation is based on the procedure for calculating key parameters of annular plates clamped along the inner and outer contours. The contours of two adjacent plates lying around the rivets join at a point that is equidistant from the adjacent rivets. Radial and annular stresses in the plates are calculated taking account of the load (design pressure) distributed uniformly over the surface of the plates and of the bending moments obtained from the condition that the angle between the normal and the curved middle surface of the annular plates is zero at the boundary of their joint. The inefficiency of using electric rivets, around which significant radial stresses develop due to their small diameter, is shown. It is recommended that the facing sheet be made in the form of annular plates fixed to the cover by annular welds, which will significantly reduce labor input. Keywords: durability, facing sheet, flat cover, electric rivet, vacuum.
Flat covers are used in heat exchanger designs (round covers are used for shell-and-tube multistream and spiral types of exchangers and rectangular covers are used for plate type of exchangers). To reduce the cost of exchangers, the flat covers can be made from carbon or low-alloy steels and to protect them from corrosive media they can be covered with a facing sheet made from corrosion-resistant materials (Fig. 1). During operation under vacuum (when the weld attaching the facing sheet to the base material along the outer perimeter of the flat cover leaks), atmospheric pressure will act on the cladding layer and the absolute pressure in the system will act under the cladding sheet. Microleakage of the weld is difficult to detect, and with passage of time the pressure between the base metal and the facing sheet will rise to the atmospheric. One of the ways of fixing the facing sheet with rivets is illustrated in Fig. 2a. There are no data in standards [1–3] for calculating the strength of facing sheets of flat covers. So, development of a method for calculating facing sheet strength for operation under vacuum is an urgent task. Ufa State Petroleum Technological University (Branch) [Ufimskii Gosudarstvennyi Neftyanoi Tekhnicheskii Universitet (Filial)], Salavat, Russia; e-mail: [email protected]. Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, Vol. 56, No. 8, pp. 3−7, August, 2020. 0009-2355/20/0708-0599
© 2020
Springer Science+Business Media, LLC
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M. V. KLYKOV
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T. V. ALUSHKINA
Fig. 1. Schematic diagram of a flat cover with a facing sheet: 1 – housing; 2 – flat cover; 3 – facing sheet; 4 – unit for fi
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