CHAMPAIGN, Ill. - The U.S. Army Engineer Research and Development Center (ERDC) is developing a new technology to quickly and reliably monitor large-structure impressed current cathodic protection (CP) systems. Funded by the Department of Defense Corrosion Prevention and Control Program, the prototype is currently being demonstrated at Fort Leonard Wood, Mo.
“Corrosion is the number one cause of damage to industrial waste lines, potable water distribution lines, heat distribution pipes, and underground storage tanks,” said Dr. Charles Marsh, project leader at ERDC’s Construction Engineering Research Laboratory (CERL). “Besides costing millions of dollars annually to repair, corrosion at military installations can potentially shut down mission-critical infrastructure through catastrophic failures.”
Large metallic underground structures can be protected from corrosion through a combination of impressed current CP systems and specially formulated coatings. However, to ensure a system is working properly, inspectors must regularly monitor the buried structures’ level of polarization.
According to Marsh, “CP involves shooting a positive current at a structure to change its relative potential in the surrounding environment. If you polarize it enough, you not only can mitigate, but often stop corrosion.”
NACE International Standard RP0169-2002 establishes the metrics for effective corrosion mitigation and the process for measuring polarization. To check for adherence to the standard (and sometimes the law), a polarization decay curve must be created. To do this, the impressed current must be shut off and the structure’s polarization monitored for sometimes up to 24 hours. Besides the cost in manhours, this process is also prone to errors in the measured data.
“Because of the long timeframes needed to collect the data, polarization readings can vary greatly from passing rainstorms or changes in temperature between mid-day and midnight,” said CERL’s Andrew Friedl, who co-leads the technology demonstration. “The new process will be able to take a reliable, predictive snapshot of the structure’s polarization, which will eliminate the possibility of changes in the environment skewing the data and giving a false indication of CP.”
The new technology has two components. A field-portable instrument is used quickly collect the required electrical potential and current data. It is coupled with software that can analyze and then extrapolate the data to give a fast, accurate representative estimate of the structure’s ultimate equilibrium polarization. Features of the prototype include:
- A unit to measure and store direct current voltage with resolution of 0.1 millivolt at accuracy of ± 1 milllivolt using 12 bits of precision.
- Variable data logging rate of one reading/sec through eight readings/sec
- Multiple scans with choice of 300, 600 or 900 data readings for each test and up to 215 individual structure tests before downloading to computer for analysis.
- Capable of using all of its onboard memory (2 megabytes) to store a data run for a week at the rate of one reading/eight seconds for a total of 131,000 data readings.
- Device is USB 2.0 compatible.
“In the near future, the device will be able to indicate whether a structure passes or fails the cathodic protection test just by measuring the structure for 15-30 minutes instead of a few days. We will be testing this in the next few months,” said Friedl.
If proven successful, the new technology will greatly reduce the cost of labor for performing the lengthier monitoring process. In addition, by providing more reliable information about the CP system, it will prevent corrosion-related failures that can result in costly environmental cleanup and disruptions to an installation’s military mission.
Fort Leonard Wood serves as the demonstration site for the prototype. The fort has many decades-old ferrous pipelines and storage tanks along with heavy seasonal rainfall that produces high levels of corrosive soil moisture. The new device is being used to monitor six water towers currently protected by an impressed current system that requires a 24-hour window to track the polarization decay.
The demonstration will be ongoing for the next several months. Results from the new technology will be compared to those using the conventional NACE method. Following its validation, the technology may be proposed to NACE International as part of a revised standard.