Coke drums are pressure vessels used in the delayed coking process in oil refineries, which transform heavy residual oil into light-weight hydrocarbon molecules and solid coke through thermal cracking. Due to the severe thermal and mechanical loading during operation, these experience low-cycle fatigue failure, which leads to shell and skirt damage such as bulging and cracking. External weld repairs using the temper bead technique have been widely applied to recover the mechanical properties of damaged regions to prevent catastrophic failure. However, a substantial proportion of the external repairs have been reported to experience post-repair cracking issues. In this study, external weld repair mockups using Alloy 182 filler metals were evaluated as alternatives for repair procedures using metallurgical characterization and isothermal low-cycle fatigue tests. Mockup with backing plate design was evaluated to estimate the lifetime reduction at root pass compared with the one without the backing plate. Fractography analysis was performed to characterize the crack initiation and propagation of heat affected zone samples under isothermal low-cycle fatigue testing. The results showed that weld metal cracking along fusion boundary occur predominantly in Alloy 182 transition zone samples, which reduced the fatigue life of joint despite its matching mechanical properties with the base material.


Isothermal Low-Cycle Fatigue Evaluation of External Weld Repairs Using Alloy 182 Filler Metal With Backing Plate Design

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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