Effect of Environment on the Oxide Layer Formation in AFA vs CFA Materials Miguel Jaimes, Lizeth Ortiz, Dr. Benjamin Church Department of Material Science & Engineering 1

Use Case & Material Comparison Steam Cracking High temperatures Traditional Equipment Material: Chromia Forming Alloys New Emerging Equipment Material: Alumina Forming Alloys Maintenance Oxide layer formation and longevity Coke formation Pipe under high pressure to clear coke Reaction efficiency loss Less carbon deposition Slow oxide layer formation Higher creep resistance Cracking Furnace Reformer Tubes 820°C Carbon Fouled Pipe Chromia Forming Alloy Carbon Fouled Pipe Alumina Forming Alloy 730°C (“Reformer and Heater Tubes Temperature Accuracy”) 2

Chromia Forming Alloys vs Alumina Forming Alloys 50x50 µm CFA & AFA Primary Ingredients wt%: Iron Nickle Chromium Aluminum 50-60 32-37 23-27 N/A 25-30 14 3.5-5 Distinct, thicker Oxide Layer Looks rough, possibly discontinuous CFA Oxidized in Air ​ In many petrochemical processes AFAs seem to out-perform CFAs More chemically stable More electrically insulating Better ceep resistance Better protection against corrosive factors (Ortiz Reyes) 50x50 µm Oxide layer visually indistinguishable at mounting material - metal interface AFA Oxidized in Air ​ 3

Elemental Mapping of Metal Oxides Chromia Former Alumina Former 5000x 5000x Thin aluminum oxide layer is revealed by energy dispersive x-ray spectroscopy element mapping Electron Image Electron Image Chromium Map Aluminum Map Oxygen Map Oxygen Map 4

Methods & Statistical Analysis Mean Specific Mass Change Overview 2 factors investigated Material Oxidation Environment 12 samples were oxidized at 900°C for 10h 3 replicates for each group Specific mass change (mg/cm2) was recorded Error bars are standard deviation of measurements 5

Conclusions & Statistical Analysis Cont. Main Effect Plot for Specific Mass Change Source P-Value Material 0.000 Environment 0.026 Material *Environment 0.086 Material Environment Probability values of less than 0.05 indicate significance Mean Specific Mass Change Anova & Conclusions: GLM Two factor ANOVA w/ 95% confidence interval Confirmed: Material and environment have a significant and independent effect on mass change. AFA CFA Steam Air AFA Steam lower change in specific mass lower change in specific mass 6

References: Ortiz Reyes, Lizeth Nayibe, "Coking Resistance of Alumina Forming Cast Austenitic Stainless Steels" (2017). Theses and Dissertations. 1520. http://dc.uwm.edu/etd/1520 Otegui, Jose Luis, et al. “Effect of Coking in Massive Failure of Tubes in an Ethylene Cracking Furnace.” Engineering Failure Analysis, vol. 48, Feb. 2015, pp. 201–09. ScienceDirect, doi:10.1016/j.engfailanal.2014.11.004. “Reformer and Heater Tubes Temperature Accuracy.” IRINFO.Org, https://www.irinfo.org/02-01-2015-james/. Accessed 11 Apr. 2019. Acknowledgements: This work is sponsored by ARPA-E; DE-AR0000690. Electron microscopy conducted in the UW-Milwaukee Advanced Analysis Facility. Alumina-Forming Austenitic Alloys Resist High-Temperature Corrosion. http://www.materialsperformance.com/articles/material-selection-design/2015/12/alumina-forming-austenitic-alloys-resist-high-temperature-corrosion. Accessed 1 Apr. 2019. Li, Ping, et al. “Advanced Process Control of an Ethylene Cracking Furnace.” Measurement and Control, vol. 48, no. 2, Mar. 2015, pp. 50–53. SAGE Journals, doi:10.1177/0020294015571498. Cracking Furnaces - an Overview | ScienceDirect Topics. https://www.sciencedirect.com/topics/engineering/cracking-furnaces. Accessed 20 Mar. 2019 7