It is critical to maintain uniformity of gasket stress in control against leakage in piping and heat exchangers. Many innovative bolting tools have been developed, but their benefit could be downgraded if there were sources disrupting initially achieved uniformity of gasket stress.
The characteristics behaviors of gasket stress in flanges with NATD (Non-Axisymmetric Temperature Distribution) were studied using finite element analysis on ANSI standard flanges.
It was found that change of gasket stress was independent of the magnitude of initial bolt stress and size of flange, but strongly dependent upon type of flange class. Empirical curves (curve fitting equation) were proposed to determine change of gasket stress which was function of degree of NATD and flange class (rigidity index). The change of bolt stress with NATD was relatively small compared to the change of gasket stress, which may make it difficult to assess flange integrity by monitoring bolt stress in service.