Effect of creep on the failure probability of bolted flange joints

The case of a bolted flange joint that is part of a model steam generator (SG) for sodium-cooled fast reactor (SFR) is studied to establish the statistical nature of the time to failure due to relaxation of gasket stress. Continued relaxation over a period of time lowers the gasket stresses to a critical sealing limit, causing failure due to leakage, one of the key modes of failure of bolted joints. An analytical model based on deformation compatibility is used to predict gasket load relaxation with time, which includes flexibility and creep behavior of joint members. A corresponding structural analysis was carried out to validate the analytical model. A probabilistic approach is taken to quantify the effect of uncertainties associated with the design variables on the failure of joint using the analytical model. In order to obtain probability of joint failure, Monte-Carlo sampling method was used for statistical trials. Further, sensitivity analysis was carried out to identify the critical design parameters.