Most metallic constructions and equipment which come in contact with petroleum products are made of steel and are exploited at ambient temperature which can range between −50°C and +50°C in different regions of our planet. When metals and alloys are in contact with pure hydrocarbons (CnHm), they do not react with them. However, rust or different types of depositions can be observed in tanks and pipelines containing gasoline, naphtha, and gas oil. The complex phenomenon of contamination is described in this paper in order to demonstrate its importance, as the number of failures of steel components is growing every year. It is important to understand that the corrosion process proceeds at the interface of different phases. Water, H2S, corrosion products, ions, phenols, organic acids, and other organic sulphur-, oxygen- and nitrogen-containing compounds dissolved in petroleum products are the contaminants that are responsible for the further destruction of the steel components.
In this study, stainless steel and
titanium (Ti) tubes obtained
from a turbofan engine after the end of its lifetime were analyzed
in order to compare the amount of pyrolytic coke present and its influence
on the parent, base material. Various analytical techniques including
microhardness and topographical evaluations, optical emission spectrometry
(OES), scanning electron microscopy (SEM), energy-dispersive X-ray
spectroscopy (EDX), Raman spectroscopy, and X-ray photoelectron spectroscopy
(XPS) were applied. On steel surfaces, a thick pyrolytic coke deposition
layer consisting of carbon and oxygen and also containing elements
from the tube material, fuel, and fuel additives was found. The concentration
of elements from the pyrolytic coke continuously decreased with distance
from the surface of the deposit, while the concentrations of elements
from the tube material continuously increased, with the concentrations
of elements from the fuel and the fuel additives being relatively
constant. With ultrasonic cleaning in distilled water, most of the
deposits could be removed. Only carbon-rich patches with a thickness
of more than 300 nm remained adhered to the surface and/or had diffused
into the original material. On Ti surfaces, the thickness of the C-rich
fuel deposit layer was significantly thinner as compared to that on
the stainless steel; however, the surface was covered with an ∼3
μm-thick oxide layer, which consisted of elements from the fuel
additives. It is believed that the beneficial properties of Ti covered
with a thin layer of TiO
2
, such as low adhesion and/or
surface energy, have promoted different deposition mechanisms compared
to those of stainless steel and thus prevented pyrolytic coke deposition
and the related material deterioration observed on stainless steel.
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