Determination of dangerous weakening of the metal chimney cross-section

Introduction. A simple approach is proposed to determine the dangerous weakening of the cross-section of metal chimneys, which inevitably occurs due to the aggressive action of flue gases. Considering that, according to some estimates provided on the Internet, about 107,000 chimneys are in operation in Russia, this task seems to be quite relevant. Materials and methods. The object of the study was a real chimney, operated in Moscow for more than 20 years, consisting of six cylindrical shells. As a result of corrosion wear, the cross-sectional areas of the shells decreased to varying degrees, as a result of which there was a danger of loss of stability of at least one of the shells. The stability of a cylindrical shell subjected to the combined action of a bending moment and a compressive longitudinal force was investigated based on the approaches described in the scientific and technical literature. Since the actual thickness of the shell was included in the calculation, its corrosion wear is already taken into account. Results. As a result of the calculations, a simple formula was obtained that determines the conditional critical thickness of the cross-section of the most weakened shell. This weakening of the section requires engineering or management decisions to ensure further safe operation of the pipe. It is noted that the solution obtained is applicable at relatively early stages of chimney operation. As pipe deformations develop, due not only to the effect of the operating load, but also for other reasons, the pipe stretches go into a state of fluidity. The study of the stress-strain state of the “pipe trunk – extension” system under these conditions can be a continuation of the present work. Conclusions. The identification of a conditional critical thickness during a routine inspection of the pipe, established by the relevant regulatory documents, does not mean that the pipe must be decommissioned or reinforced. In this case, according to the wall thicknesses determined during the examination, the calculation should be carried out according to the methodology described in this article, the actual values of the bending moment of the longitudinal force in dangerous sections should be calculated, and the stability of the pipe should be checked again.