Root cause analysis and damage mechanisms of radiant tube failure in the atmospheric distillation unit of an oil refinery

This study investigates the root causes of the failure of a radiant tube in the atmospheric furnace of a distillation unit of a refinery. The tube’s failure resulted in crude oil leakage and significant damage. The research involved collecting data, reviewing records, measuring the remaining wall thickness at various points, and conducting detailed visual and microscopic examinations of the damaged tube. The crack path and its edges were analyzed using microscopy. For comparison, chemical composition analyses were performed on both the failed tube and an unused tube of the same material. Metallographic microstructure examinations were conducted using a Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectroscopy (EDS). Surface corrosion was visually inspected and analyzed with SEM and EDS, while corrosion products were identified using X-ray diffraction (XRD). Hardness measurements were taken at different points, and tensile tests were conducted to compare the mechanical properties of the failed and unused tubes. The results indicated that localized temperature increases occurred due to the impingement of flames or combustion products on the tube’s surface. Additionally, heat transfer was reduced because of coke deposition inside the tube. External corrosion mechanisms, such as scaling and fuel ash corrosion, significantly decreased the tube’s thickness. Observations included carburization, the formation of continuous networks of carbide, carbide growth, carbide spheroidization, and softening of the steel. The final failure happened under increased stress resulting from the reduced thickness, which was further aggravated by localized temperature rises. This ultimately led to creep-induced cracking at the grain boundaries, accompanied by minor plastic deformation.