By Mark Lewis and Kathy Riggs Larsen
The world of corrosion engineering, finding its roots in electric street railways (also called trolleys or streetcars), came into existence and blossomed between the 1880s and mid-1930s. Most streetcars relied on direct current (DC) for their traction, and the rails not only supported the cars but also served as one leg of the electric circuit—the return path for the large amounts of DC (many hundreds of amperes) required to operate the system. Rail sections were connected with mechanical bonds (metal straps or cables) to establish long lengths of electrically continuous track. If a rail lost its electrical continuity, from faulty or missing rail bonds, the current would enter the ground and force its way back to the source (the substation) by taking whatever path it could. This often included water mains, gas lines, and other linear metallic utilities that were buried just beneath the city streets.
Where the current left the pipe, it took metal with it, which led to rapid failure of buried water and gas pipelines. This phenomenon was referred to as electrolysis and was considered to be caused by “vagrant” or “vagabond” current, which is known presently as electrical interference or stray current. At the time, all corrosion of buried utilities was blamed on electrolysis, and many electrolysis departments, committees, and engineers came into existence as a result.
The East Bay Municipal Utility District (EBMUD) (Oakland, California), organized in 1923 to provide reliable, high-quality water for the people of San Francisco’s East Bay area, employed a corrosion engineering staff early on to help mitigate corrosion of its buried water pipe infrastructure. Known originally as the Electrolysis Department of the East Bay Water Co., this group helped pioneer the implementation of corrosion-control techniques for EBMUD, including the use of cathodic protection (CP) on large water transmission mains, which was groundbreaking at the time. Their corrosion laboratory was housed on the second floor of the District’s Claremont Center building, a critical pump station in Berkeley, California.
The Electrolysis Department used a variety of equipment to conduct comprehensive surveys to track the flow of the electrical current. Results of the surveys were recorded by hand, compiled, and mapped. Before the pump station building was demolished and reconfigured in 1996, a collection of historic instruments used by the District was discovered—antique tools that date from about 1893 through 1950.
The tools span the period from the beginnings of commercialization of electricity in the 1880s to the development of CP in the 1930s, and beyond. Aside from the fact that these antique instruments are beautifully and artfully crafted of fine materials such as black walnut, cherry, mahogany, oak, and polished nickel and brass, they represent what might be called the golden age of electrical instrumentation. Also retrieved from the building were historical records of the Joint Committee for the Protection of Underground Structures in the East Bay Cities, a group formed in 1922 that was dedicated to the preservation of underground utilities.
The instruments in this collection were used not only in the early studies of electrolysis, but were also witness to the emergence of electrical bonds as a method of corrosion mitigation. The electrolysis engineers recognized that bonding the rail to buried pipelines was one method of mitigating stray current. Where current flow was determined to be detrimental, they installed drainage bonds between the pipe and the rail itself, or at railway substations, to drain excessive current from the affected structure. In its simplest form, a bond was a wire that connected a rail to a buried pipe.
To monitor and manage this current exchange, amperage and voltage measurements were taken at bond stations using ammeters, voltmeters, and shunts. Ammeters measured the amount of electric current in amperes in a circuit. Voltmeters measured the electrical potential difference between two points in an electrical circuit. Shunts were used to measure current. When a shunt was placed in the wire or bond that connected the rail and the pipe, current passing through the drainage bond could be measured. By knowing the resistance of the shunt and measuring the voltage with a millivoltmeter, the amount of current passing through the shunt could be calculated using Ohm’s Law (I=V/R, where I is current, V is voltage, and R is resistance).
Over the years, testing and remote monitoring techniques have advanced significantly; and these antique meters have been replaced with smaller, lighter, more accurate digital versions, with some digital meters combining many functions in one tool. For the early electrolysis engineers who were mitigating corrosion 80 to 100 years ago, today’s range of corrosion-control equipment available for the modern corrosion professional surely would have been unimaginable.
This article was originally published on MaterialsPerformance.com. It is a condensed version of the article published in the November 2017 issue of Materials Performance Magazine. A complete version of this article can be viewed here.