Use of the environmentally controlled scanning vibrating electrode technique for the investigation of localised corrosion in pipeline steel.

The aim of this project was to explore the design criterion for a scanning vibrating electrode technique (SVET) assembly with partial environmental control. To facilitate this goal an SVET has been designed which incorporates an enclosed sample chamber equipped with a means of gas purging. The design allows for prepurging of electrolyte prior to sample immersion since corrosion initiated prior to stabilising the atmosphere is likely to dominate the corrosion profile. In addition, dosing of the electrolyte with prepurged solution such as corrosion inhibitor is possible through injection ports. The apparatus has been built and rigorously calibrated using a point current source as described in Chapter 3. The apparatus has a spatial resolution of ~220mum at 100mum scan height, this is slightly larger than the theoretical value due to the finite size of the SVET tip. The use of the point current source enabled a calibration factor 1 of 5445 Am-2V-1 to be obtained in 0.1% NaC1. This acts as a means of converting SVET voltages to current densities and is also a routine calibration check. The first use of the equipment described in chapter 4 has been to analyse the efficiency of a commercial filming amine inhibitor on the kinetics and mechanisms of corrosion. The addition of inhibitor to the electrolyte served to reduce the levels of corrosion of the pipeline material. However low concentrations (