Failure analysis of bolt connections in fired heater of a petrochemical unit

The main function of a fired heater in a petrochemical site is to produce supersaturated steam. Due to extremely difficult working conditions and high temperatures, there is a very high probability of failures in different parts of a fired heater. In the fired heater under study, tube guides are frequently damaged due to malfunctions and fractures in bolt connections. To investigate the nature of such fractures, Computational Fluid Dynamics (CFD), Finite Element (FE) method, Charpy impact test and fractography were used. To obtain the temperature of various components of the fired heater, a CFD analysis was carried out by considering the combustion process and modeling the central and side burners. Next, stress and displacement values in different components of the fire heater, particularly tube guides, were calculated using the uncoupled thermal-structural finite element analysis. It is found that when the dummy drain at the bottom of the tubes is stuck at the bottom of the fired heater, the expansion of tubes is impeded in addition to creating distortions in tube bundles and increasing the stress on the bolts of tube guides. Moreover, according to the performed tests, it is revealed that the increase in the stress of bolts leads to the activation of creep and Hydrogen embrittlement, causing the bolts to experience fractures in a considerably shorter amount of time.