Failure analysis of oil refinery heater treater's fractured fire tube.

• The embrittlement X factor for weld metal is 45, which is three times more than the recommended value (≤15). • It is apprehended that the fractured metal part could be susceptible to temper embrittlement. • The Charpy impact energy absorbed by the fractured metal is 13 J, which is lower than impact energy absorbed by the base metal 300 J. • The scanning electron microscopy demonstrated intergranular crack propagation, discontinuous cracking along grain boundaries, and blunted cracks at grain interiors. • The fractography is performed on the fracture surface of the impact test specimens and it indicated heavily cavitated intergranular facets along the grain boundaries and deep secondary cracks on the fracture surface. • These findings suggested that the severe cracking observed in the fire tube at the U-bend is likely due to temper embrittlement (TE) induced by exposure of the fire tube material to elevated temperatures. Overheating, corrosive degradation, hydrogen embrittlement, creep, erosion, and corrosion are the cause of most failure problems in fire tubes. Herein, we have evaluated the macrostructural, microstructural, and mechanical properties at welded U-bend of the fractured fire tube to analyze the failure of the SA 387 grade 22 steel heater treater fire tube that has been under continuous use for 18 years at an oil refinery. We have found that the embrittlement factor at U-bend proved to be the most significant factor in its failure. The embrittlement X factor for weld metal is 45, which is three times more than the recommended value (≤15). It is apprehended that the fractured metal part could be susceptible to temper embrittlement. There is a significant higher hardness value of weld metal as compared to base metal, which is due to metallic phase transition at high temperature. The Charpy impact energy absorbed by the fractured metal is 13 J, which is lower than impact energy absorbed by the base metal 300 J. The macroscopic examination reveals that the crack initiated on the emulsion side and propagated radially in welded U-bend before extending further into the base metal in the axial direction. The scanning electron microscopy demonstrated intergranular crack propagation, discontinuous cracking along grain boundaries, and blunted cracks at grain interiors. The fractography is performed on the fracture surface of the impact test specimens, and it indicated heavily cavitated intergranular facets along the grain boundaries and deep secondary cracks on the fracture surface. Energy disperse spectroscopy identified the carbides formation at the U-bend cracking parts, which counter confirm the microstructural phase transition. These findings suggested that the severe cracking observed in the fire tube at the U-bend is likely due to temper embrittlement (TE) induced by exposure of the fire tube material to elevated temperatures. [ABSTRACT FROM AUTHOR]