ANALYSIS OF NAPHTHENIC CORROSION BY ATOMIC FORCE MICROSCOPY
Heloisa Pinto Dias1, Natwrie Seny Malta Almeida1,2, Ricardo Boldrini3, Pedro Vitor Dixini1,4, Luiz C.
P. Almeida 1, Gabriela Vanini1, Eustáquio V. R. Castro1, Alexandre O. Gomes 5, Robson R. Moura5,
Valdemar Lacerda Jr. 1, Boniek G. Vaz6, Wanderson Romão1,2 and Glória M de F Viégas Aquije1,2
1
Petroleomic and Forensic Laboratory, Department of Chemistry, Federal University of Espírito Santo,
29075-910, Vitória, ES, Brazil.
2
Federal Institute of Education, Science and Technology of Espírito Santo, 29106-010, Vila Velha, ES,
Brazil.
3
Federal Institute of Education, Science and Technology of Espírito Santo, 29106-010, Vitória, ES,
Brazil.
4
Federal Institute of Education, Science and Technology of Espírito Santo, 29106-010, Aracruz, ES,
Brazil.
5
Petróleo Brasileiro S/A – PETROBRAS, CENPES, Rio de Janeiro, RJ, Brazil.
6
Chemistry Institute, Federal University of Goiás, 74001-970, Goiânia, GO, Brazil.
Presenting author: Natwrie Seny Malta Almeida; [email protected]
Naphthenic acids are considered primarily responsible for corrosion in the oil refining process [1],
and if not properly monitored, the naphthenic corrosion can cause severe damage to the petrochemical
industry [2]. The Atomic Force Microscopy (AFM) has also demonstrated be useful to in situ
morphologic analysis on metals surface in a nanometric scale [3]. With objective to monitor the
naphthenic corrosion on steel AISI 1020 and AISI 316, using the AFM as an analysis tool, this work
was realized. The images were measured dry, using the AFM (WITec/ Wissenschaftliche Instrumente
und Technologie GmbH®) in non-contact mode, with Si3N4 cantilever tips, nominal constant of
42N.m-1 and resonance frequency of ≈ 285 kHz, scan rates of 0.3-1.0 Hz and scan size of 5.000 to
10.000 nm. Oil samples treated at 350°C/6h, were brought in contact with carbon steel AISI 1020 for
15 days. The acidity of the original and products from oil heat treatment was monitored by TAN ESI
(-) - FT-ICR-MS and corrosion on steel was monitored by AFM. The ESI (-) - FT-ICR MS showed
that the O2 class, the major species detected were majority carbon number of C 25-C32 and DBE = 3.
For treatment at 350°C/6h, there was a reduction of ~ 80% in the TAN. The results showed that AFM
topography (Figure 1: A, B, C and D) of the steel surface exposed to the oil treated at 300°C/6h has
higher effects of corrosion, since the pattern of measured by "peak-peak height" of the surface,
indicated that the surface exposed to the oil 300°C/ 2h presents a number of irregularities (Figure
1C and D). The AISI 316 showed that the major classes were identified in the samples classes O 2 and
N2. Regarding O2 class, the major species detected were majority of carbon number C 24 and C35 = 3
DBE and DBE and C29-C35 = 4. The AFM images, in different periods of time (0, 7, 14, 21, 28 and 36
days), showed that the interval for 14 days, the steel exposed to oil J, showed strong topographic
changes from white, characterizing the onset of the corrosion process (Figure 2: G and H). This
information is consistent with the Raman spectra that for this period of time the formation of goethite,
hematite and magnetite were evidenced (data not shown). Topographical changes to the exposed steel
to oil G could only be observed after 21 days of analysis by AFM (Figure 2: E and F). The AFM has
detected a topographic profile much altered for the stell AISI 1020 when compared to steel AISI 316.
The potential of the combination of two powerful analytical tools, ESI (-) FT-ICR MS, and AFM in
the study both the chemical composition of acids naphthenic as its corrosive power, allowing involve
the molecular composition of oil samples with its corrosive power of carbon steel. This fact evidences
the importance of developing physical and chemical parameters based on data from AFM and FT-ICR
to evaluate and monitor the extent and type of corrosion due to exposure time to the particular type of
oil.
Keywords: naphthenic acids, corrosion, ESI (-) - FT-ICR MS and AFM.
Acknowledgements: FAPES, FAPEG, PETROBAS, CNPq and CAPES for their financial support.
Figure 1: AFM measurements on the AISI
1020 stainless steel samples surface before
(blank) and after exposure to crude oil for a
period of 15 days. A and C: topographic
image. B and D: cross section graph of the
topography, showing the surface profile of
the steel and peak-peak height. A- steel
surface without exposure to petroleum,
showing the irregularities resulting from
pre-treatment sanding; B- cross section
graph of the topography, showing the
surface profile of the steel and high values
for peak to peak height; C- corrosion is
evidenced by pit formation on the steel
surface (arrow); D: topographic profile,
indicating corrosion presented in previous
image (arrow) and reduced values for peak
to peak height.
Figure
2:
AFM
measurements on the AISI
316 stainless steel samples
surface before (blank) and
after exposure to crude oil
for a period of 36 days. A,
C, E and G: 3D
topographic images; B, D,
F and H: cross section
graphics along of the line
of the topography.
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