Spinel Oxide Layer Analysis for Naphthenic Acid Corrosion Prediction
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Solution Overview
Problem
Current corrosion models for petroleum refineries, particularly those involving heavy and acidic crude oils, fail to accurately predict corrosivity due to limitations in accounting for the interaction between naphthenic acid and sulfur compounds, and the protective nature of corrosion layers formed on metal surfaces.
Innovation Solution
A method involving the exposure of metal coupons to crude oils under specified temperature conditions to form and analyze spinel-type oxide corrosion protective layers using transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD), which assesses the morphology, chemical composition, and phase composition of the corrosion protective layer to determine its protective nature against naphthenic acid corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current corrosion models (McConomy curves, iso-corrosion curves, iron powder test) are used to predict corrosivity, then corrosion rate prediction is attempted, but accuracy is insufficient due to failure to account for protective layer formation and interaction between naphthenic acid and sulfur compounds
Solution Approach 1:
The patent performs preliminary exposure of metal coupons to crude oil fractions under controlled conditions before analysis, allowing protective layers to form naturally. This preliminary action enables the subsequent characterization of the actual protective layers that form during service, rather than relying on empirical models that fail to account for these layers.
Solution Approach 2:
The patent replaces empirical corrosion prediction models with direct physical and chemical characterization methods. Instead of using empirical correlations (McConomy curves, iso-corrosion curves), the invention uses transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD) to directly observe and analyze the protective layers, substituting mechanical/empirical prediction with direct scientific measurement.
2Adaptability or versatility
If empirical corrosion models are used, then corrosion prediction is achieved, but the interaction between naphthenic acid and sulfur compounds is not properly accounted for
Solution Approach 1:
The patent uses protective corrosion layers as intermediaries between the crude oil environment and the metal substrate. By characterizing these intermediate layers using TEM, EDS, and XRD, the invention captures the complex interactions between naphthenic acid, sulfur compounds, and metal surfaces without needing to directly model all interaction mechanisms.
Solution Approach 2:
The patent changes the approach from using chemical composition parameters (TAN, sulfur content) to physical and structural parameters of protective layers (morphology, elemental composition, phase composition). This parameter transformation enables direct observation of corrosion mechanisms rather than relying on indirect empirical correlations.
3Reliability
If traditional corrosion assessment methods are used, then corrosion risk is evaluated, but the protective nature of formed corrosion layers is not assessed
Solution Approach 1:
The patent segments the corrosion assessment into distinct analytical components: morphology analysis via TEM, elemental composition via EDS, and phase composition via XRD. This segmentation allows each aspect of the protective layer to be characterized independently using specialized techniques, making the complex overall assessment manageable and systematic.
Solution Approach 2:
The patent creates physical copies of the protective layers for analysis by preparing thin sections for TEM and collecting diffractograms for XRD. These copies enable detailed characterization of the protective layers without destroying the actual corrosion protection mechanism, allowing comprehensive assessment while preserving the integrity of the corrosion system.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively evaluates the corrosion protection provided by the corrosion protective layer, demonstrating that spinel-type oxides like magnetite and chromite offer significant protection against naphthenic acid corrosion, even in the absence of oxygen, and can be applied to carbon steels and chromium-enriched steels, improving the reliability of corrosion prediction and mitigation in refinery settings.
Implementation Method 1
exposing metal coupons to the subject fluid under specified temperature conditions to form a spinel-type (e.g. Fe3O4 or FeCr2O4 and may include sulfur) oxide corrosion protective layer
Implementation Method 2
The coupon and associated deposition are examined using transmission electron microscopy (TEM). TEM analysis provides corrosion protective layer morphology information and elemental composition of the corrosion protective layer near the metal surface with nanometer resolution
Implementation Method 3
elemental composition of the corrosion protective layer near the metal surface with nanometer resolution using energy dispersive x-ray spectroscopy (EDS)
Implementation Method 4
the methodology includes the use of x-ray diffraction (XRD) to examine the corrosion protective layer phase composition as a means to detect and distinguish between spinel-type oxides
Data Source
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AI summary
A method for determining and identifying corrosion protective layers that provide corrosion protection against crude oils and crude oil fractions is disclosed. The method identifies naturally occurring constituents in crude oils that indirectly provide corrosion protection. A method assessing the potential of these constituents is also disclosed. The method includes exposing metal coupons with the crude oil or crude fraction of interest at the expected operating temperature of concern. The corrosion potential assessment further analyzes the exposed coupons with transmission electron microscopy and an additional high temperature exposure that challenges the tenacity of the protection offered by the corrosion protective layer.