Analysis of ethylene cracking furnace tubes

The working life time of the radiant coils tubes (RCTs) utilized in ethylene production unit of Jam petrochemical complex (Asalouyeh-Iran), is lower than the nominal life time (100,000 h) which is the main problem of this unit. The aim of present study was to evaluate the important characteristics of the RCTs for identification the failure mechanisms. Tensile test, hardness and microhardness analyses were employed to examine the mechanical properties. Also, scanning electron microscopy (SEM) together with energy dispersive spectroscopy (EDS) were used to characterize the morphological features and chemical compositions of the samples. These experimental results revealed that the creep resistance of RCTs decreases due to the formation of coarse grains and coarse primary carbide layers which resulted from carburization and overheating at high temperatures. Furthermore, a decrease in ductility of RCTs leads to the propagation of micro-cracks and the embrittlement of tubes. Decoking and passivation are the crucial processes during operation cycle and the use of materials with higher creep and carburization resistances is essential for attaining longer working life time.