Recommended Corrosion Inhibitors for Refining Units (Vanconol® Technical Edition)
Introduction
Refining units, as core equipment in the petrochemical industry, operate under harsh conditions involving high temperature, high pressure, and highly corrosive media. Corrosion has become a critical factor affecting safe operation, reducing production efficiency, and increasing maintenance costs. Corrosion inhibitors offer an economical and effective means of corrosion protection, and their scientific selection is essential for extending equipment life and ensuring production continuity. Based on chemical engineering and anti-corrosion technology principles, combined with actual field conditions in the oilfield and refining industries, this article systematically recommends types of corrosion inhibitors and selection criteria suitable for refining units, with a focus on efficient and environmentally friendly products under the Vanconol® brand, including fatty acid polyaminoimidazoline, oleic acid hydroxyethyl imidazoline, and water-soluble imidazoline, providing technical reference for refining enterprises.
I. Analysis of Corrosion Environment and Inhibitor Requirements for Refining Units
The corrosion environment in refining units exhibits the following notable characteristics:
Media complexity: Crude oil and its fractions contain active sulfur compounds (e.g., H₂S, mercaptans), organic acids, chlorides, etc., which readily induce chemical and electrochemical corrosion;
Extreme temperature and pressure: Operations such as atmospheric/vacuum distillation, hydrocracking, and catalytic reforming reach temperatures of 300–500 °C and pressures exceeding 10 MPa, accelerating corrosion rates;
Process diversity: From crude oil pretreatment to product refining, multiple steps including acid washing, water injection, and gathering/transportation involve various corrosion types such as uniform corrosion, pitting, and stress corrosion cracking (SCC).
To address these conditions, corrosion inhibitors must meet the following core requirements:
High efficiency: Forms a dense protective film at low concentrations to inhibit metal substrate dissolution;
Thermal stability: Suitable for high-temperature service, with film stability exceeding 150 °C;
Compatibility: No adverse reactions with process media or other additives;
Environmental friendliness: Meets low-toxicity and biodegradable standards, minimizing secondary environmental impact.
II. Recommended Corrosion Inhibitor Types for Oilfield and Refining Scenarios (Vanconol® Series)
1. Vanconol® Fatty Acid Polyaminoimidazoline Corrosion Inhibitors (FPI–S100 Series)
Technical positioning: Represented by the Vanconol® FPI-S100 series developed by Tianjin Hi-Perferal Advanced Materials Co., Ltd., this class of inhibitors forms a hydrophobic adsorption film on metal surfaces through the synergistic action of polyamino groups and the imidazoline ring, blocking contact with corrosive media.
Key advantages:
Green and environmentally friendly: Waterborne formulation with VOCs emission lower than traditional nitrite-based inhibitors;
Broad-spectrum applicability: Suitable for circulating cooling water, acid-washing pipelines, and high-temperature sections of refining units;
Long-term effectiveness: Maintains corrosion inhibition efficiency above 90% at 120 °C.
Applications:
Atmospheric/vacuum distillation units in refineries: Inhibits carbon steel corrosion in heat exchangers from the pre-flash tower to the vacuum tower sections;
Oilfield gathering and transportation systems: Addresses internal corrosion of pipelines transporting sour crude oil.
2. Vanconol® Oleic Acid Hydroxyethyl Imidazoline Corrosion Inhibitor
Technical positioning: Prepared via condensation of oleic acid and hydroxyethyl amine, the long-chain alkyl group in the molecular structure provides a hydrophobic barrier, while the hydroxyl group enhances chelation with metal oxides.
Key advantages:
High-temperature performance: Achieves 85% inhibition efficiency in hydrocracking units at 200 °C;
Sulfide corrosion resistance: Effectively suppresses hydrogen sulfide (H₂S)-induced sulfide corrosion;
Synergistic effect: When compounded with molybdate, film density increases by 30%.
Applications:
Hydroprocessing unit reactors: Protects 316L stainless steel inner walls from high-temperature hydrogen embrittlement;
Coker fractionators: Controls chloride-induced corrosion in overhead condensing systems.
3. Vanconol® Water-Soluble Imidazoline Corrosion Inhibitor (Tall Oil-Based Imidazoline)
Technical positioning: Manufactured from tall oil (rosin acid) and sulfonated to achieve water solubility, combining the adsorption activity of the imidazoline ring with the hydrophilicity of sulfonate groups.
Key advantages:
Low-temperature suitability: Exhibits better inhibition efficiency than traditional silicates in circulating water below 50 °C;
Microbiologically influenced corrosion resistance: Inhibits biofilm formation by sulfate-reducing bacteria (SRB);
Cost-effectiveness: Per-unit concentration cost is 40% lower than organic phosphonates.
Applications:
Refinery circulating cooling water systems: Replaces chromates to meet environmental discharge requirements;
Oilfield water injection wells: Controls casing corrosion caused by formation water.
4. Vanconol® Composite Corrosion Inhibitor (Molybdate–Imidazoline Blend)
Technical positioning: Combines the oxidizing film-forming ability of molybdate with the adsorption film properties of imidazoline to create a dual-layer protective structure.
Key advantages:
Synergistic enhancement: Inhibition efficiency is 2–3 times higher than that of either component alone;
Erosion resistance: Film retention exceeds 95% under high-velocity flow (>3 m/s);
Multi-metal compatibility: Simultaneously protects carbon steel, low-alloy steel, and copper alloys.
Applications:
Fluid catalytic cracking (FCC) units: Protects regenerators, cyclones, and other high-temperature erosion areas;
Oilfield acidizing pipelines: Mitigates etching of pipe materials by mud acid (HCl+HF).
III. Methodology for Selecting Corrosion Inhibitors in Refining Units
1. Operating Condition Parameter Matching
Temperature grading: Below 100 °C, choose Vanconol® water-soluble imidazoline; 100–200 °C, prioritize Vanconol® oleic acid hydroxyethyl imidazoline; above 200 °C, a customized high-temperature acidizing inhibitor is required.
Media classification: For H₂S-containing environments, select Vanconol® sulfide-resistant imidazoline; for chloride-containing environments, use the Vanconol® molybdate–imidazoline blend.
2. Corrosion Type-Targeting Strategy
Uniform corrosion: Primarily use Vanconol® fatty acid polyaminoimidazoline at a concentration of 50–100 ppm;
Pitting/crevice corrosion: Select Vanconol® tall oil-based imidazoline compounded with gluconate to reduce Cl⁻ adsorption;
Stress corrosion cracking (SCC): Add Vanconol® tannic acid–molybdate inhibitor to suppress hydrogen atom permeation.
3. Balancing Environmental and Economic Considerations
Toxicity control: Avoid carcinogenic substances such as chromates and nitrites; prioritize low-toxicity products like Vanconol® FPI-S100 series;
Life-cycle cost: Calculate the product of inhibitor unit price and dosage, combined with equipment maintenance intervals for a comprehensive assessment.
IV. Typical Case Studies
Case 1: Corrosion Treatment in a Refinery Atmospheric/Vacuum Distillation Unit
Problem: Pitting corrosion occurred on the carbon steel tube bundle of the pre-flash tower overhead cooler, with an annual corrosion rate of 0.8 mm/y.
Solution:
Applied Vanconol® FPI-S100 series corrosion inhibitor at 80 ppm;
Compounded with Vanconol® quaternary ammonium–molybdate blend to strengthen the film;
After three months of implementation, the corrosion rate dropped to 0.1 mm/y.
Case 2: Internal Corrosion Control in an Oilfield Gathering Pipeline
Problem: Uniform wall thinning occurred on the inner wall of a sour crude pipeline, with an average thickness loss of 15%.
Solution:
Injected Vanconol® oleic acid aminoethyl imidazoline corrosion inhibitor at 120 ppm;
Added Vanconol® microbiocide (tannic acid composite) once per month;
After six months, the remaining wall thickness of the pipeline stabilized above 90%.
V. Future Development Trends
Nanomodification technology: Enhancing the film density of Vanconol® inhibitors with graphene or titanium dioxide nanoparticles;
Smart responsive inhibitors: Developing pH/temperature-sensitive polymers for adaptive corrosion protection;
Bio-based raw material substitution: Producing Vanconol® green inhibitors from renewable resources such as vegetable oil fatty acids and cardanol.
Conclusion
The selection of corrosion inhibitors for refining units must consider corrosion mechanisms, operating parameters, and environmental requirements. Vanconol® brand products, including fatty acid polyaminoimidazoline, oleic acid hydroxyethyl imidazoline, and water-soluble imidazoline, can meet the protection needs of extreme environments such as high temperature, high pressure, and sour service through molecular design and formulation optimization. It is recommended that refining enterprises establish a dynamic inhibitor monitoring system, combined with analytical techniques such as electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM), to continuously optimize the selection scheme and achieve both economic and environmental goals.