The failure of G4852-Micro radiant tubes in an ethylene cracking unit in a petrochemical plant (Arya Sasol Polymer) was investigated. Tubes in this plant were replaced after approximately 38,000 hours of service, which is much shorter than the anticipated service lifetime (100,000 hours). She did the failure analysis by gathering process and operational history and conducting visual and microscopic examinations. Both optical and scanning electron microscopes (SEM) were used to analyze the microstructure of damaged tubes. For the sake of comparison, the microstructure and mechanical properties of a tube after 10,000 hours were also investigated. Different phases were identified using energy dispersive spectroscopy (EDS). Micro-hardness profilometry was also done on the thickness of the tubes, showing a significant decrease of hardness on both inner and outer surfaces. This was in accordance with the observed chromium depletion, at both ends. There was no indication of presence of creep voids, inferring that the failure was not due to the coalescence of voids and advanced creep. The recorded data from operational history showed that number of shut-downs in this unit was almost twice of the normal operational conditions. The failure is concluded to be due to higher-than-normal repeated shut-downs, associated with thermal shocks. This was confirmed by microscopic images.
This research was done by Mrs. Pourmohammad and Mr. Taghipour.
