ABSTRACT

The light rail transit system in Minneapolis, Minnesota began revenue operation on June 28, 2004. The LRT system is state-of the art, with stray current being well controlled at the source. This paper is a follow on to Paper 03711 (Corrosion 2003) ~ which described the precautions taken by the LRT and the testing facilities and other preparations made by the gas company prior to and during LRT construction. Initial data on pipe to soil potentials and pipeline current flow to evaluate stray current effects are presented. To date, no adverse reactions due to the operation of the LRT system are evident at points tested on the gas piping.

INTRODUCTION

The Hiawatha Light Rail Transit (LRT) system in Minneapolis, Minnesota is a modem, state of the art operation. Figure 1 shows a two-car train at the intersection of Portland Ave. S. and 5 th St. S. in downtown Minneapolis. The LRT began revenue operation on June 28, 2004. Its purpose is to ease ~eeway congestion and move more people as some 500,000 new residents are expected in the metropolitan area by 2020.

Minneapolis has had no direct current (DC) operated transit since the days of the trolley cars. Those old ear lines were not designed with any stray current control in mind. Utility operators simply had to live with whatever stray current occurred, and they designed their facilities to control it. With the demise of the trolley ear, however, in~astrueture design changed and today it is not set up to handle stray current. Therefore, modem rail transit systems are designed to control stray current at the source and thus have minimal impact on the infrastructure. The LRT in Minneapolis is no different. State of the art engineering, including stray corrosion control has been used in its design and construction. As with all transit projects, however, some small stray current will occur.

To prepare its underground plant for detection, monitoring and control of stray current, Center Point Energy installed permanent reference electrodes/cells (PRC), current measuring hoops and various test stations on its gas distribution piping. Many pipe replacements or relocations were done with plastic pipe. Electrical isolation was placed at various locations such as at tie ins between relocated/replaced piping and existing lines. Example are the 20" (508mm) crossing the north end of LRT maintenance the yard and the 2" (51mm) yard service line that is tapped offthe 20." Test stations were installed at each isolating joint with wires on the pipe on either side along with a permanent copper-copper sulfate reference electrode/cell (PRC).

Base line surveys were performed before the start of revenue operation. Present data compare favorably with those l~om the base line surveys. Some transit systems run extensive test trains before beginning revenue operation. Various test cars were run on the LRT system, but a formal test program was not utilized. Stray current tests were therefore conducted shortly after revenue operation began.

This content is only available via PDF.
You can access this article if you purchase or spend a download.