Novel Volatile Corrosion Inhibitors with High-Cost Efficiency for Top of the line Corrosion Mitigation
Authors: Jinarakpong Suthasinee , Punpruk Suchada , Ruengsangtongkul Sureeporn , Puratane Chonnipa , Yotapan Nattawut , Limthongkul Pimpa , Sombatmankhong Korakot 
Published: November 2024

Top of the line corrosion (TLC) is a major concern in the oil and gas industry, causing accelerated corrosion rates and expensive pipeline failures. Volatile Corrosion Inhibitors (VCI) are crucial for combating TLC, but improvements in their formulations are necessary to enhance effectiveness and reduce costs. The goal of this work is to develop VCI formulations that offer higher cost efficiency by prioritizing inhibition efficacy and reducing dosage requirements as the TLC corrosion prevention strategies.

A range of VCI formulations, labelled as VCI-A to VCI-D, are developed utilizing a newly synthesized active VCI agent known as fatty-imidazolines. These formulations are compared to various existing alternatives, available in different forms and TLC protection mechanisms. The VCI formulations are thoroughly characterized to assess their inhibitor mechanisms, TAN, and volatility. These evaluations aim to gauge their performance in simulated gas-pipeline conditions, particularly targeting TLC efficiency. Volatility screening is conducted via weight loss measurement, while pH and TAN levels are determined following ASTM-D664 standards. Additionally, Bottom of the Line Corrosion (BLC) rates are measured using a linear polarization resistance (LPR) test.

Four VCIs are formulated based on their primary compositions, which categorize them into two distinct groups according to their dominant inhibition mechanisms for mitigating TLC. Group I VCIs (A and B) create a protective inhibitor film on metal surfaces through vaporization, transportation, and film formation. This film mitigates corrosion via absorption, dissolution, and hydrophobic effects. Group II VCIs (C and D) reduce corrosion rates by combining CO2 scavengers with a colligative property that lowers vapor pressure. The experimental results reveal significant differences in volatility and TAN values between the two VCI groups. Group I VCIs exhibit nearly double %weight loss in the 3-day experiment compared to Group II VCIs. Additionally, Group II VCIs have almost negligible TAN values, while Group I VCIs range from approximately 40-70 mg KOH/g. Despite these differences, both groups show similar TLC protection efficiency, ranging from 95-99% even when using with a dosage of 100 ppm. However, Group II VCIs provide slightly higher BLC corrosion protection, with rates of 80-90% compared to over 90% for Group I. Overall, the inhibition efficacy of the formulated VCIs for BLC and TLC mitigation is notably superior to existing alternatives with additional benefits of lowering VCI dosage and overall cost.

This study shows promising results in using eco-friendly imidazoline-based compounds as effective VCIs for carbon steel pipelines in the petroleum industry. Various TLC mechanisms are discussed, providing guidance for selecting or developing suitable VCIs for different conditions. Group I VCIs, though volatile, may face thermal stability and efficiency concerns at high temperatures, making Group II VCIs preferable for scenarios where TAN control is crucial.