Prediction of Relaxation Property for Long Term in Bolted Flange Joints Based on Viscoelasticity Model of Gasket

Creep/relaxation occurs when gaskets for bolted flange joints are used over extended periods. Creep/relaxation of gaskets may cause leakage of an internal fluid from the joints. In order to prevent leakage of a contained fluid from flange joints, it is important to establish a method for the prediction of gasket creep or stress relaxation. In the present study, the relaxation behavior of the axial bolt force was measured in order to estimate creep/relaxation of gaskets by referencing the ASTM F-38 test method [1]. The tests were accomplished at room temperature over a period of 240 hours (10 days). The strain behavior of gaskets was obtained using the viscoelasticity model and the finite element (FE) model of the test equipment based on the ASTM F-38 test method. In addition, the creep strain behavior of gaskets obtained through finite element analysis (FEA) and applied to gaskets in the FE model of the bolted flange joints, and the stress relaxation in the bolted flange joints were estimated over the long term. In the FEA of the bolted flange joints, the relaxation behavior of the axial bolt force that includes internal pressure load was predicted using the creep strain behavior of the gasket. Then, the radial gasket stress is investigated for tightening, for internal pressure load and for stress relaxation. It was found that the radial stress of the gaskets approaches uniformity, and the effect of flange rotation in the bolted flange joint decreases due to the creep strain behavior of the gaskets.