In this paper, a test protocol for the laboratory analysis of the coupon test stations (CTSs) exposed to alternating current (AC) interference from the adjacent power lines was discussed in detail. Corrosion of coupons from the CTSs are mainly due to AC interference, corrosive soil, or microbiological induced corrosion (MIC). This paper provides an overview of corrosion issues commonly experienced by coupons and presents specific case histories involving AC interference, corrosive soil, and MIC. During the laboratory analysis, coupons were examined visually and photographed, studied under stereo microscope, and the coupons were also examined in detail using scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) in the as received condition and correspondingly after ultrasonic cleaning. The findings of the laboratory analysis are correlated with CTS historical data and relevant field inspection data to identify the actual cause of the corrosion of the CTSs.
In this paper, we will introduce our AC corrosion detector and a description of the concept in a simplified form. Our proprietary sensor can identify the extent of magnetite on the CTSs. The sensor correlates electric current measurement with the quantity of a predetermined iron oxide in the test coupon to determine a proxy for the degree of alternating current interference corrosion in the metallic structure.
Several alternating current (AC) coupon test stations (CTS) located near AC power lines were investigated to assess the AC interference corrosion risk of the test coupons. As-received each AC test station consisted of two ½ inch (1.27 cm) diameter and 1-inch (2.54 cm) long carbon steel (CS) coupons. Coupons are much larger than 1 cm2 and current density measurements are not 100% relatable to the SP21424 or ISO 18086 criteria, since these refer to measurements on (typically) 1 cm2. The current densities measured on the coupons in this study will underestimate the AC corrosion threat.
