Study of Carbon Formed on Stainless Steel 304H in a Simulated Environment of the Convection Section of the Ethane Cracking Furnace System

The stainless steel 304H (SS304H) is one of the important alloys used in petrochemical industry, such as in the convection section of the ethylene production furnaces. The exposure to carburizing gases makes this alloy susceptible to carbon formation and potential carburization. The present study focuses on understanding the coking behavior of SS304H in ethane/steam environment and the effect of H₂S at 700^oC. Long-term (90 hours) experiments in such environment show that the addition of ppm amounts of H₂S has a pronounced effect on the morphology of the carbon formed on the SS304H surface, as shown by scanning electron microscopy. In the absence of H₂S, the deposited carbon forms distinct fibers, which are distributed homogeneously on the surface. The addition of 15 ppm H₂S results in the formation of carbon clusters, consisting of very thin fibers that are tightly entangled. Also, experiments in the presence of H₂S showed a systematic decrease in the amount of carbon as H₂S increased from 1 to 2, 5, 7, and 10 ppm. At 10 ppm H₂S, no carbon was observed on the SS304H surface after 4 h of exposure to ethane/steam at 700^oC. Mass spectrometry studies showed that the addition of H₂S does not affect the temperature or products of ethane cracking. The effect of the SS304H coupons on the ethane cracking products was also studied by mass spectrometry, and showed that the ethane cracking process is not significantly affected by the presence of the metal coupon.