100 Years of Corrosion Testing—Is It Time to Move beyond the ASTM D130? The Wire Corrosion and Conductive Deposit Tests

Abstract

<div>The ASTM D130 was first issued in 1922 as a tentative standard for the detection of corrosive sulfur in gasoline. A clean copper strip was immersed in a sample of gasoline for three hours at 50°C with any corrosion or discoloration taken to indicate the presence of corrosive sulfur. Since that time, the method has undergone many revisions and has been applied to many petroleum products. Today, the ASTM D130 standard is the leading method used to determine the corrosiveness of various fuels, lubricants, and other hydrocarbon-based solutions to copper. The end-of-test strips are ranked using the ASTM Copper Strip Corrosion Standard Adjunct, a colored reproduction of copper strips characteristic of various degrees of sulfur-induced tarnish and corrosion, first introduced in 1954. This pragmatic approach to assessing potential corrosion concerns with copper hardware has served various industries well for a century.</div> <div>Driveline lubricants have always been required to protect hardware, and transmission fluid specifications have always included a version of the copper corrosion strip test to assure this. In conventional transmissions, copper and its alloys are present in the form of mechanical parts such as bushings, bearings, and washers. Corrosion of these parts, while detrimental, does not typically result in immediate failure. However, the incorporation of electronics and electric motors has resulted in new failure modes which can have immediate and devastating consequences. Designing a lubricant to protect new electrified hardware requires an understanding of corrosion that occurs under actual operating temperatures, as well as potential damage from corrosion products. While the ASTM D130 provides general insight regarding the susceptibility of the hardware to corrode, the information is typically gleaned at elevated temperatures, and no information is gathered about the impact of corrosion products. The ASTM D130 is simply not sufficiently specific to adequately assess the risk of these new failure modes that may occur within electric drive units (EDUs). Newer methods, in particular, the wire corrosion test (WCT) and conductive deposit test (CDT), have been created to fill these gaps.</div> <div>In this article, we provide the history of the creation and evolution of the ASTM D130 standard, which is important in understanding both its significance and limitations. We then assess the corrosion characteristics of five lubricants using both the ASTM D130 strip method and the WCT method. We contrast these results, which demonstrate the greater understanding gleaned from the WCT. We then assess the five lubricants with the CDT, which provides insight into whether the corrosion products might endanger the system. We conclude that both the WCT and CDT are needed to provide a holistic understanding of corrosion in electrified hardware necessary to minimize the risk of corrosion-related failure modes. We anticipate that the WCT and CDT will establish themselves in original equipment manufacturer (OEM) specifications over the next decade and will provide a useful assurance of lubricant performance in corrosion, especially for hybrid (HEVs) and electric vehicles (EVs).</div>