Analysis of failed ethylene cracking tubes

Abstract

The failure of ethylene cracking tubes at an elevation of about 5 m in radiant chambers after one-year service has been analysed. Bulges and circumferential cracks, oriented towards the walls/burners, are the result. The investigation included tensile tests, optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analysis. Analysis revealed that ruptures found in the tubes were caused by overheating of the tubes because of inappropriate burning of bottom burners. Significant growth of precipitates of carbide was observed in the failed zones which results in the drastic reduction of material ductility. The bulged zones also showed a globular form of grains. Tube bowing, due to the restricted growth during the hot expansion, promotes cracks. To avoid such overheating, precautions should be taken while improving the burning condition of the bottom burners and decreasing the peak tube metal temperature. It is necessary to check the tube temperature periodically in critical positions and one should ensure that the temperature is less than the design temperature.