Development and evaluation of miniature electrodes for electrochemical measurements in a CO₂ top of line corrosion environment

Abstract

This paper presents an experimental and theoretical investigation into water condensation and corrosion under non-film forming conditions at the top of line in a static, CO2 environment. An experimental test cell is developed to measure droplet lifetimes, condensation rates and corrosion rates, as a function of the surface and gas temperatures, when the gas flow is dominated by natural convection. Experimental results for non-film-forming conditions show clearly that the water condensation rate becomes increasingly influential on corrosion rate as the surface temperature increases between 10 o C to 40 o C. These findings are summarised in a new empirical correlation for TLC rate as a function of the condensation rate and surface temperature that agrees well with previous, relevant studies. A model for condensation at the top of the line for static, buoyancy-driven conditions is also presented and shown to predict dropwise condensation rates accurately for a range of experimental conditions.

CO2 Top-of-Line-Corrosion; Assessing the Role of Acetic Acid on General and Pitting Corrosion

“…Each electrode is individually isolated by a lacquer coating and shrink wrap tubing. The miniature solid electrode set up has been used in a previous study by de Carvalho et al 10 and in both studies produced comparable results to the conventional three-electrode setup in solution chemistries indicative of the condensate produced in these TLC experiments.…”

“…A thermocouple probe was placed laterally across the 10mm diameter specimens in specific experiments, touching its exposed surface for surface temperature (T s ) measurements; these specimens were not used for mass loss measurement due to the potential occurrence of galvanic effects. A bespoke laboratory scale TLC rig was used in this study, 10 with the schematic drawing provided in Figure 2. The setup consists of a 2L glass cell with a specific custom lid integrated with an internal channeled matrix and test specimen slots, allowing flow of refrigerant to cool the surface of the TLC specimens to specific temperatures.…”

“…The same test methodology, used to reach the aforementioned desired conditions, and accuracy of temperature control for this specific rig can be found in previous work. 10 The bulk test solution consisted of CO 2 -saturated 3.5 wt.% NaCl solution with the presence and absence of 1000 ppm HAc, which was purged with CO 2 for a minimum of 12h prior to each experiment, to minimize the dissolved oxygen content. CO 2 was continuously bubbled into the cell throughout the test to avoid oxygen ingress.…”

“…where WCR is the water condensation rate in mL/m 2 s, V w is the volume of condensed water in mL, t c is the duration over which the condensed liquid is collected in s, and L s is the internal area of the lid surface exposed to the vapor condensation (m 2 ). 10 The condensate collector itself was also deaerated by bubbling continuously with CO 2 during the experiment to maintain the same environmental conditions. The pH of bulk solution was measured at the beginning and at the end of each test using an automatic temperature correction pH probe.…”

“…Based on previous studies on the role of HAc in CO 2 TLC conditions, a set of laboratory-scale experiments and conditions are devised here, consisting of four different water condensation rates and temperature combinations commonly reported or evaluated in TLC cases. For this purpose, a real-time corrosion monitoring setup 10 was implemented in order to evaluate the transient corrosion response throughout experiments, and evaluate the role of HAc across a range of environments.…”