Dr. Kod Pojtanabuntoeng’s NACE trip and Berkeley
NACE TLC presentation
There has no efficient approach to study TLC but Mr. Mayeedul Islam (PhD candidate), who has been actively working in this area under Kod and Rolf supervision, has successfully developed an electrochemical method to monitor TLC in-situ. The results obtained from this electrochemical probe were in good agreement with results from non-electrochemical based technique. This has opened up more possibilities in TLC monitoring as real time corrosion rates and instantaneous changes of reactions at metal/electrolyte interface can now be detected.
“Development of an electrochemical method to study top-of-the-line corrosion” Top-of-the-line corrosion (TLC) is a concern for subsea wet-gas transportation pipelines operating in a stratified flow regime. The insufficient volume of electrolyte at the top-of-the-line combined with the low electrical conductivity of the condensed liquid has confined the majority of TLC studies to the weight loss method which only provides integrated corrosion rate over long period of exposure. The instantaneous monitoring of TLC rates using electrochemical methods is still a challenge for researchers and in the field.
To overcome this limitation, this study presents a novel TLC monitoring cell capable of measuring in-situ corrosion rates of carbon steel under condensing condition by electrochemical methods such as linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM). The data presented in this paper have been conducted over 5 days at varying condensation rates to evaluate the feasibility and accuracy of the methods applied. In addition, TLC rates have also been measured by weight loss and monitored in situ by measuring the iron concentration in the condensed liquids in order to compare these results with electrochemical methods. A comparable result is obtained between electrochemical and non-electrochemical method which validates the design and provides a promising tool for further investigation into TLC process and its inhibition.
NACE CUI presentation
Kod also shared the recent industry sponsored-project on CUI at the NACE CUI symposium. CUI has undermined industry because of its insidious nature. Thermal insulations designed to conserve energy acts as a trap for water to accumulate and allow corrosion to initiate and propagate. Further, its presence challenges inspection and monitoring. The presentation compared 2 commercial thermal insulations and their influences on CUI. The presentation also emphasised the direct correlation of insulation dry out time and corrosion rate using an impedance method developed at CCEIC. Facilitating the insulation dry-out by using non-absorbent insulation in conjunction with drain holes was found to be the most effective at controlling CUI.
“Comparison of insulation materials and their roles on corrosion under insulation” Thermal insulation is used in petrochemical and refinery plants where pressure vessels and piping system are insulated to conserve energy. Over time, water enters into the insulation through various pathways and is entrapped at the steel surface leading to corrosion under insulation (CUI). Mineral wool is one of the most used thermal insulation even though it is prone to absorbs water and causes CUI. A water repellent insulation can be an alternative thermal insulation to prevent CUI. However, limited research has been done in the public domain.
Therefore, the present study investigates and compares the roles and influences of mineral wool and a water repellent insulations on CUI. In addition, the presence of drain holes and its ability to reduce CUI was evaluated. The susceptibility to CUI of carbon steel was investigated at 80 °C using a newly developed test rig in a controlled environment (25 °C and 50 %RH). An electrochemical impedance spectroscopy technique was used to monitor the rate of insulation dry-out. Due to localized nature of CUI, a 3D light microscope was used to analyse the surface profile of the samples after exposure to CUI. The results has emphasized the correlation between the wet time and severity of CUI.
Experience at UC Berkeley
Kod also had the opportunity to spend 2 weeks working with eminent scientist Prof. Digby MacDonald and Dr. Elmira Ghanbari at Dept. of Materials Science and Eng. University of California, Berkeley. She has explored an advance EIS interpretation technique or the so-called EIS optimization and applied it to existing experimental data on FeCO3 precipitation kinetics in the presence of monoethylene glycol. EIS optimisation is a powerful technique than the current approach (equivalent circuit) in interpreting EIS data. The technique is also used in point-defect-model which explains corrosion of metal exhibiting passivity.
The knowledge and experience can and will be further applied to other corrosion research at CCEIC.