Evaluation of Sandvik APMT After 4 Years in Service As Radiant Coils in a Steam Cracking Furnace

This paper presents material and performance analyses of Sandvik APMT cracker tubes, after four years in service in commercial steam cracker furnaces. The emphasis in this study has been on process performance and material degradation. The results indicate that the APMT tubes did not suffer from carburization or extensive material loss. Carbide formation was limited in the hottest section of the coil and nowhere else. Chemical analysis from this section confirms a very low carbon uptake. A dense and protective aluminum oxide was found on all studied surfaces. It is believed that this pure alumina scale arrests carburization and prevent the formation of catalytic coke. It was estimated that the coke formation could be decreased by 30-50% depending on feedstock. Both mechanical and chemical testing revealed no significant signs of degradation of the Sandvik APMT tubes. Creep testing of samples from the outlet weld showed increased creep strength compared to as-delivered condition. Process data indicate lower tube metal temperature (TMT) and increased coil outlet temperature (COT) which points to an increased heat transfer through tube wall, i. e. low coking rate, compared to that of the reference tube. The reference coils used in this study was a common centrifugally cast 25Cr35Ni alloy. This paper is a follow-up on a paper presented at the AIChE Conference 2007.