(26b) Ethylene Cracker Radiant Tube Life Optimization

Ethylene cracker radiant tubes are exposed to the most severe operation conditions found anywhere in the chemical process industries such as elevated temperatures, oxidizing atmospheres, and high carbon potentials. In addition to that, decoking; burning off the accumulated carbon on tube internal walls after each run accelerates the active damage mechanism and results in premature tube failure. Early identification of such active damage mechanism and replacement of affected tubes is most important for reliable and safe furnace operation.

Saudi Polymer Company (SPCo) ethylene plant started operation during 2011 with conventional alloy radiant tube. Since startup, run length for ethane feed was around 20 days and propane was 25-30 days which is significantly lower than the design. To address the low run length, extensive analytical study had been performed on collected coke samples and tube sample during preventive maintenance (PM) outage in 2013. The tube indicated depleted chrome oxide surface and spalled oxide layer on tube inner surface. Coke samples showed a characteristic “green” color – conclusively identified as chromium. All these finding was the result of low performance of the conventional radiant tube against oxidizing reducing atmosphere and promoted high coke formation and eventually low run length. Based on these findings a strategical decision was taken and radiant tube upgraded with alumina forming metallurgy that with higher structural stability, good high temperature stress rupture strength and excellent carburization /oxidation resistance. With alumina forming metallurgy, the run length found to be significantly improved even beyond the initial design run length of 60 days.

This paper presents the Ethylene Cracker Radiant Tube Life Optimization and inspection method to identify the pitting corrosion on radiant tube ID.