Reduced Chemical Use and Toxicity in Produced Water Systems
(Microbial Corrosion Control Methods)

Problem/Opportunity

Many unexpected failures in pipelines and storage vessels can be traced to sustained, localized pitting corrosion. Bacteria can catalyze this pitting by setting up a localized corrosion cell and producing organic acids that pit the metal and remove reactants from the surface. Detecting such pitting is often difficult because standard corrosion probes can only measure generalized corrosion, not the localized corrosion that can drill holes into metal. The development of an inexpensive probe to identify conditions under which sustained localized pitting can occur would allow companies to target their mitigation efforts rather than treating an entire system with chemical corrosion inhibitors and biocides. This detector research is coupled with the use of simulated pipeline test loops to evaluate new treatment methods that involve non-toxic chemicals and less-frequent applications.

Microbes can act as environmental "catalysts" to accelerate sustained localized pitting, even when general corrosion rates are low (this can cause rapid through-wall pitting in steel, as shown in this gas pipeline sample).

Approach

Argonne has used both laboratory and preliminary field experiments to design a corrosion probe that employs electrochemical noise measurements to detect sustained rapid localized pitting corrosion. Metal corrosion is an electrochemical process. The electrical potential and current signal that are generated during corrosion are very complex and chaotic. With the proper signal acquisition and processing algorithms, the slope of the power spectral density versus frequency measurement can be directly correlated to the mechanism of corrosion. This method allows the electrochemical probe to differentiate between generalized and localized pitting corrosion.

Argonne researchers have developed an online, real-time method to detect sustained localized pitting. This approach includes new software and improved probes to interpret real-time electrochemical noise signals. It allows early detection and evaluation of treatment methods.

The electrochemical noise monitoring technique can be used for the early detection of sustained localized pitting corrosion associated with microbial corrosion. The technique can also provide a useful tool for in situ evaluation of chemical treatment procedures. This research program was funded by the U.S. Department of Energy's Natural Gas and Oil Technology Partnership (DOE/NGOTP) and the Gas Technology Institute (GTI) in collaboration with SoCal Gas, BP-Amoco, and Rhorback Cosasco.

Results

Argonne has developed and patented a sustained localized pitting corrosion probe. The improved system can be adapted to work with existing commercial corrosion probe designs and data analysis and gathering equipment, does not appear to be sensitive to a variety of chemical environments, and yields data that are easy to interpret. Using the tool may lead to development of a method for the early diagnosis of environments in which sustained, localized pitting are likely; evaluation of treatment options through on-line measurements; and integration into existing probes and equipment use to assess environmental conditions.

The parallel development of an effective electrochemical noise probe that can distinguish between general corrosion and the more destructive rapid localized pitting corrosion has provided a new tool to evaluate microbiologically influenced corrosion. By adding the localized corrosion test probes to our experimental test loops, we now have a dynamic on-line test system that can be used to evaluate the effect of different metals, microbes, and chemical treatments on localized pitting corrosion. The dynamic test loops, used with corrosion probes, will permit the accurate pre-qualification of new corrosion detection and mitigation technologies prior to their expensive and time-consuming evaluation in the field.

Future Plans

The corrosion probe has been evaluated during both laboratory and field testing. A new, more sensitive electrode design has been developed and is currently being evaluated. The software that is used to collect and analyze the corrosion data is being improved and updated to make it more "user-friendly" for field operations. Both the software and probe technology are currently available for licensing.