1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. References:
Ortiz Reyes, Lizeth Nayibe, "Coking Resistance of Alumina Forming Cast Austenitic Stainless Steels" (2017). Theses and Dissertations
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: /j.engfailanal
“Reformer and Heater Tubes Temperature Accuracy.” IRINFO.Org, Accessed 11 Apr
Acknowledgements:
This work is sponsored by ARPA-E; DE-AR
Electron microscopy conducted in the UW-Milwaukee Advanced Analysis Facility.
Alumina-Forming Austenitic Alloys Resist High-Temperature Corrosion. Accessed 1 Apr
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: /
Cracking Furnaces - an Overview | ScienceDirect Topics. Accessed 20 Mar. 2019 7