Development of Thin Film Electrical Resistance Sensors For In Situ Monitoring of Top of the Line Corrosion

Abstract

Top of the Line Corrosion (TLC) is a phenomenon exclusively encountered in wet gas transportation pipelines due to the thermal gradient between the hot inner fluids and the cold surroundings. Despite considerable efforts which have been made to understand the corrosion mechanism of TLC, the monitoring and the mitigation aspects still present major challenges. The dominant stratified flow pattern renders non volatile corrosion inhibitors ineffective in tackling TLC. The poor conductivity and the discontinuous nature of the condensed water at top of the line hinders the application of conventional electrochemical corrosion monitoring techniques. In this thesis, an innovative electrical resistance monitoring system has been developed for monitoring the internal corrosion of carbon steel pipelines. The monitoring system comprises Thin Film Electrical Resistance (TFER) sensors made of 50 micrometre carbon steel foils which were fabricated using the photochemical machining approach. High precision constant current circuits driven by batteries were also built which provided high current stability and the switching capability to correct for the induced thermoelectric voltages between the copper wires and the steel sensor element. Two TFER patterns were designed taking into consideration the proximity of the reference tracks to the corroding tracks and how this might affect the thermal compensation. The electrical resistance monitoring system is used to elucidate key factors influencing top of the line corrosion mechanism such as the effect of gas temperature, organic acids (acetic acid), and volatile corrosion inhibitors (monoethylene glycol, diethylamine, and decanethiol). The compact design of the TFER sensors (Pattern 2) with the integrated constant current relay switch circuit is shown to give the most sensitive results required to discern TLC measurable trends at short time scales, by improving the thermal agreement between the sensor tracks, and ultimately suppressing the effect of the induced thermoelectric junction voltages. The electrical resistance measurement is sensitive enough to record a reproducible average corrosion rate of 0.03 mm yr-1 in less than 24 hours. The monitoring results demonstrated the role of the gas temperature and the acetic acid in accelerating the rates of TLC process under film free forming conditions. Among the volatile corrosion inhibitors tested, decanethiol showed an excellent corrosion inhibition efficiency (> 97%) while diethylamine did not have any significant corrosion inhibition efficiency (< 15%).

Date of Award	26 Mar 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Stuart Lyon (Co Supervisor) & Nicholas Stevens (Main Supervisor)