Carburization tests and analysis were performed on some samples of radiant tube alloys of ethyleneudfurnaces at three petrochemical plants. These tubes had undergone carburization in service with someudlosing their structural integrity. This study evaluates and compares the carburization resistanceudperformances of some of these tubes in service and identifies the cause of their degradation. Theudpolished surfaces of the test samples were visually observed. The depth of carburization zones for eachudtest sample was measured. Scanning electron microscopy and energy dispersive x-ray spectroscopyudwere used to examine the carburization zones and the rest part of the specimens and to characterizeudthe microstructure and elemental composition of the tubes’ material. Optical microscope (Imageudanalyzer) was used to examine the etched surface of each of the test samples. Microhardness testingudwas performed to determine their mechanical strength. Visual inspection revealed the sagging in someudof the tubes. Metallurgical assessment indicated that the selected furnace tubes showed relative greateruddepths of carburized zones when compared with other tube materials tested. Microstructure of theudtubes showed coarse Cr-carbide precipitation and continuous carbide networks at austenite grainudboundaries
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