Application of non-destructive and fracture mechanics techniques for the condition assessment of naphtha hydrotreater furnace tubes in oil refinery

• Condition assessment of furnace tubes of naphtha hydrotreater plant.
• Evaluation based on non destructive methods and fracture mechanics analysis.
• Loss of hardness and other mechanical properties such as strength and impact energy.
• Microstructural degradation with grain coarsening and carbide precipitation.
• Predominantly cleavage fracture with intergranular and transgranular cracking.

Furnace tubes of oil refineries undergo thermal, mechanical and environmental loadings during the lifetime of the plant. Apart from highly corrosive conditions, components are also under severe temperatures and pressures which lead to the material degradation and ultimately causing failure. Due to these loadings, the tubes have a finite life and it is important to monitor the condition of the tubes during inspection to avoid any rupture during the service.The aim of the present work is to evaluate the condition of the naphtha hydrotreater furnace tubes of an oil refinery. These tubes were manufactured of SA 312 P321 material and remained in service for about twenty-five years. Two different techniques were applied for the condition assessment of used and fresh tubes – non-destructive (ND) examination and fracture mechanics based fractographic evaluation. Based on the ND testing, significant deterioration of material was noted in the used specimens. Similarly, besides micro-structural defects, the used material also exhibited sufficient loss of hardness. On the other hand, mechanical properties obtained from standard tension, impact and bend tests also exhibited the poor condition of the tubes. A comparison of the used specimens with the un-used one shows that the condition of the furnace tubes has been considerably deteriorated and its further use for the long term service cannot be considered as satisfactory.