Design and Life Prediction of Fired Heater Tubes in the Creep Range

Abstract

Realistic fired heater tube-life predictions are essential to safe and economical design, proactive inspection strategy and meaningful tube retirement evaluations. The traditional method of heater tube design (API RP 530), that is based on the “mean-diameter equation,” sometimes implies tube-life in excess of actual operating experience. The main reason for this discrepancy is the interaction of cyclic radial thermal gradient, that exists across the tube wall, with the pressure-induced stresses resulting in enhanced creep damage. Upper-bound estimates for creep deformations and creep damage are obtained in this paper using a simple analytical procedure. Some broad guidelines relating to the assessment of remaining tube-life, tube retirement and inspection frequencies are presented.