INTRODUCTION
Over the last several years a growing effort has developed in industry to move electrochemical noise equipment out of the laboratory and into plant and field monitoring applications. The movement of any piece of equipment from the development phase in the laboratory to the plant or field installation almost always involves unforeseen problems and unexpected difficulties. Two industries that have taken on these challenges and aggressively pursued the development of field-hardy electrochemical noise based corrosion monitoring systems are the nuclear waste storage and the oil and gas industries. Challenges encountered and solutions developed when moving systems developed in the laboratory to the field are described for several applications in the nuclear waste storage and oil and gas industries.
For many years, electrochemical noise (EN) has been observed during corrosion and other electrochemical reactions, and the phenomenon is well established [1-19]. Typically, EN consists of low frequency (<1 Hz) and small amplitude signals that are spontaneously generated by electrochemical reactions occurring at corroding or other surfaces. Over the last several years a growing effort has developed in industry to move EN equipment out of the laboratory and into plant and field monitoring applications. It has been reported that the measurement and analysis of EN data is an effective method for monitoring and identifying the onset of localized corrosion,and for measuring uniform corrosion rates [ 11-31 ].
The movement of any piece of equipment from the development phase in the laboratory to the plant or field installation almost always involves unforeseen problems and unexpected challenges no matter how much engineering, planning and forethought are put into the process. The transition for EN based corrosion monitoring equipment has been no exception. Two industries that have taken on these challenges and aggressively pursued the development of field-hardy EN based corrosion monitoring systems are the nuclear waste storage and the oil and gas industries [20-35, 38-46].
The majority of EN based corrosion monitoring work in the U.S. nuclear waste storage industry is at the Hanford Site in Richland, Washington. The Hanford Site has 177 underground waste tanks of a single-shell or double-shell design that store approximately 253 million liters of radioactive waste from 50 years of plutonium production [36]. Leaks are now confirmed or suspected to be present in a significant number of single-sheU tanks [37]. No double-shell tanks are leaking. Waste is currently being transferred out of all single-shell tanks and into double-shell tanks. To help ensure the continued integrity of the site's double-shell tanks, a laboratory development effort was started in 1995 to create a double-shell tank EN- based corrosion monitoring system [20-24]. This initial effort has grown into the current field system development and deployment effort. Four double-shell tanks have been instrumented with EN-based corrosion monitoring systems to date.
Over the past five years, the use of EN monitoring in the oil and gas industry has progressed from experimental to a viable option for field corrosion monitoring. Equipment used in upstream oil and gas production is typically carbon steel and is exposed to some extremely corrosive environments as well as being subject to localized corrosion mechanisms. EN is a tool that allows engineers to monitor corrosion in real time and to detect localized corrosion activity. This technique has been used successfully to predict general corrosion rates to determine pressure vessel inspection intervals [28], to define the effect of process variables on corrosi
