Evaluation of Electrical Resistivity of Oxide Scale Formed under Different Conditions

Abstract

The nature of direct current potential drop (DCPD) on carbon steel (SS400) having different surface conditions is investigated in this study. The spring-loaded macroscopic DC four-point-probe sensor was used for the measurements of potential drop. Three samples from the same type of carbon steel are prepared under three different conditions, namely, exposures for short and long periods in atmosphere and heat treatment at low temperature of the sample experienced short exposure. In an attempt to verify the repeatability nature of DCPD, the measurements are performed on different locations of the test surface under the same experimental conditions and used for analysis. The natures of potential drop on oxide scale free surface and oxidized surfaces were compared. The effect of oxidized surfaces on DCPD in all the three cases is observed markedly. From these observations, it is worth understanding that the DCPD technique through spring-loaded macroscopic four-point-probe is able to distinguish the oxidized surface from oxide scale free surface. Finally, electrical resistivities of oxide scale in all the three cases were successfully evaluated by using electrical image method with oxidized sample considering as a two-layer structure. The almost unique value of evaluated electrical resistivity of oxide scale in all the cases indicates that the oxide materials are similar in type in respect to electrical resistivity.