Publications

The research goal presented here is to model the electrical response of gold plated copper electrical contacts exposed to a mixed flowing gas stream consisting of air containing 10ppb H 2S at 30°C and a relative humidity of 70% This environment accelerates the attack normally observed in a light industrial environment (similar to, but less severe than, the Battelle class 2 environment). Corrosion rates were quantified by measuring the corrosion site density, size distribution, and the electrical resistance of a probe contact with the aged surface, as a function of exposure time. A pore corrosion numerical model was used to predict both the growth of copper sulfide corrosion product which blooms through defects in the gold layer and the resulting electrical contact resistance of the aged surface. Assumptions about the distribution of defects in the noble metal plating and the mechanism for how corrosion blooms affect electrical contact resistance were needed to close the numerical model. Comparisons are made to the experimentally observed corrosion-bloom number density, bloom size distribution, and the cumulative probability distribution of the electrical contact resistance. Experimentally, the bloom site density increases as a function of time, whereas the bloom size distribution remains relatively independent of time. These two effects are included in the numerical model by adding a corrosion initiation probability proportional to the surface area and a probability for bloom-growth extinction proportional to the bloom volume, due to Kirkendall voiding. The cumulative probability distribution of electrical resistance becomes skewed as exposure time increases. While the resistance increases as a function of time for a fraction of the bloom population, the median value remains relatively unchanged. In order to model this behavior, the resistance calculated for large blooms is heavily weighted by contributions from the halo region.

Two mitigation strategies including the use of corrosion resistant alloys (CRA) for the tubing and the application of a corrosion inhibitor and anti-fouling package in the water were used in the laboratory simulation of corrosion in large oil coolers at US Strategic Petroleum Reserve. A closed-loop, recirculating system was designed and constructed. The corrosion sensors were monitored over time using a commercially available linear polarization resistance (LPR) meter. The ERW steel exhibited significant localized attack along the entire weld root, in addition to pitting along the rest of the surface, as observed on the seamless tubing.

The goal of this study was to first establish the fitness for service of the carbon steel based oil coolers presently located at the Bryan Mound and West Hackberry sites, and second, to compare quantitatively the performance of two proposed corrosion mitigation strategies. To address these goals, a series of flow loops were constructed to simulate the conditions present within the oil coolers allowing the performance of each corrosion mitigation strategy, as well as the baseline performance of the existing systems, to be assessed. As prior experimentation had indicated that the corrosion and fouling was relatively uniform within the oil coolers, the hot and cold side of the system were simulated, representing the extremes of temperature observed within a typical oil cooler. Upon completion of the experiment, the depth of localized attack observed on carbon steel was such that perforation of the tube walls would likely result within a 180 day drawdown procedure at West Hackberry. Furthermore, considering the average rate of wall recession (from LPR measurements), combined with the extensive localized attack (pitting) which occurred in both environments, the tubing wall thickness remaining after 180 days would be less than that required to contain the operating pressures of the oil coolers for both sites. Finally, the inhibitor package, while it did reduce the measured corrosion rate in the case of the West Hackberry solutions, did not provide a sufficient reduction in the observed attack to justify its use.