熱負荷を受ける管フランジの締め付け特性の評価

Abstract

The leakage of fluids from pipe flange connection is the most critical problem for the safe operation of power and chemical plants. It is well known that such leakage is likely to occur in the case of fluids under high or low temperature. The tightening operation of pipe flange connection is usually conducted under room temperature. The temperature of pipe flange connections starts to increase when the plant is in operation. Then, the difference in thermal expansion between bolt-nut connection and fastened plates causes significant changes in bolt force, which might lead to the leakage of the contained fluid. This phenomenon is largely influenced by the complex non-linear behaviors of gaskets.This study has experimentally examined how the bolt clamping forces of pipe flange connections vary under high temperature. Two types of commonly used gaskets made of asbestos and aramid have been used in the experiments. It has been found that the bolt forces significantly decrease with the progress of the heating operation, and the reduction of bolt forces is remarkably observed with increase of gasket thickness. Bolt clamping forces of pipe flange connections under high temperature are reduced to less than 70% and as much as 70 % of the initial values, in the cases of thick asbestos and aramid gaskets, respectively.