Influence of Experimental Injection Method on the Inhibition Efficiency of Volatile Corrosion Inhibitors for Top-of-the Line Corrosion Mitigation

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In oil and gas industry, during the transportation of wet gas with a stratified flow regime, the temperature difference between the fluid inside the pipelines and the surrounding environment leads to condensation of water on the upper internal surface and causes metal degradation. This phenomenon is known as Top-of-the-Line Corrosion or TLC.

The condensing phases can consist of not only water but also condensable hydrocarbons.

Product Number: 51323-19452-SG

Author: Maryam Eslami, Marc Singer

Publication Date: 2023

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The extent of Top-of-the-Line Corrosion (TLC) can be reduced using volatile corrosion inhibitors (VCIs). The selection of the correct VCIs depends of course on the operating conditions (pCO2, pH2S, temperature, hydrocarbon co-condensation, organic acid concentration) and on the intrinsic properties of the inhibitor itself (water solubility, volatility, active components). Yet, the method used to inject the VCIs inside the producing pipeline could also be of practical importance, especially considering the complex environment of a multi-component condensing system. A concern among the related industries is the lack of a methodology that would allow for conducting experiments mimicking the field conditions and provide a guideline for extrapolating the experimental results to a larger scale. In this study, a methodology was developed to investigate the effect of injection methods on the inhibition efficiency of VCIs (model compounds decanethiol and hexanethiol). For this purpose, a system of two connected glass cells was designed enabling the injection of the VCIs into the system either through the liquid or directly into the gas phase. The experiments were conducted in the presence of a condensable hydrocarbon (n-Heptane) to investigate the partitioning effect. The results show that injection of the inhibitor through the gas or liquid phase has no influence on its inhibition efficiency, as long as the VCI is sufficiently volatile. Moreover, regardless of the injection method, the hydrocarbon phase interferes with the inhibition by decanethiol while it has no influence on hexanethiol. For a larger scale, it can be concluded that any length of pipe can be protected by an inhibitor injected through the liquid or gas phase if the inhibitor is an effective VCI.