Advanced 3D Fatigue Life Prediction of Expansion Bellows in Fixed Tube-Sheet Heat Exchangers Using Continuum Damage Mechanics

This paper presents a three-dimensional finite element framework coupled with continuum damage mechanics for predicting the fatigue life of expansion bellows in fixed tube sheet heat exchangers. The approach captures circumferential stress non-uniformity, local ovalization, and out-of-plane deformations induced by combined internal pressure and axial thermal displacement—effects inherently neglected in conventional axisymmetric analyses. A systematic comparison between 2D and 3D models is conducted, validated against ASME BPVC Appendix 26 fatigue equations. Results demonstrate that simplified 2D approaches overestimate fatigue life by up to 63%, yielding non-conservative designs. The proposed 3D damage model predicts 16% mean absolute error relative to ASME allowable cycles, with consistently conservative estimates and reduced scatter. Ultimately, this model offers a robust, physics-based approach for evaluating the structural integrity of critical petrochemical assets. It supports better design optimization and helps create smarter, data-driven inspection schedules.