51314-4213-Evaluating the Behavior of Sulfur Compounds in Controlling Preferential Weld Corrosion in CO2-saturated Brine

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Product Number: 51314-4213-SG

ISBN: 4213 2014 CP

Author: Richard Barker

Publication Date: 2014

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An Assessment of the Capabilities of White Light Interferometry in Comparison to the Zero-Resistance Ammetery Technique in Determining Preferential Weld CorrosionThe application of zero-resistant ammeters (ZRAs) has become the generally favored laboratory technique to assess the propensity of preferential weld corrosion to occur in oil and gas systems. This paper presents the application of white light interferometry as a new technique to determine regions of selective attack on 1% Ni welds in a simulated service environment. Unsegmented electrodes consisting of a parent material heat-affected zone (HAZ) and weld were subjected to long duration immersion tests and subsequently profiled using white light interferometry to assess which regions (if any) preferentially corroded and the extent of the difference in preferential corrosion rates. In parallel tests a multi-array electrode was developed consisting of segmented carbon steel parent metal HAZs and welds. Each electrode facilitated electrical connections allowing each segmented material to be electrically connected externally via a potentiostat simulating a fully un-segmented sample. A multi-channel ZRA arrangement was adopted to simultaneously quantify the current transfer between the areas of interest as well as the mixed potential established between the metallic couples. All possible combinations of metal coupling were considered in an effort to identify the role the parent HAZ and weld material play in the overall degradation of the welded steel material. The two techniques are compared with each other to help understand the validity of the ZRA technique.