The goal of this project is to help maintain the integrity of the United States natural gas infrastructure.
Gas Technology Institute (GTI) – project management and research product
Des Plaines, Illinois 60018
Corrosion is a leading cause for pipe failure, and is a main component of the operating and maintenance costs of gas industry pipelines. Quantifying the cost of corrosion generally in the gas industry, and more specifically the cost associated with microbial corrosion, is not easily done and is controversial. Corrosion was estimated in 2001 to cost the gas industry about $13.4 billion a year and of this as much as $2 billion a year may be due to microbiologically influenced corrosion (MIC). Basic research to increase our understanding of the microbial species involved in microbial corrosion, and their interaction with metal surfaces and with other microorganisms, will be the basis for the development of new approaches for the detection, monitoring, and control of microbial corrosion. A thorough knowledge of the causes of microbiologically influenced corrosion and an efficient and effective means of detecting and preventing corrosion is lacking. It is well recognized that microorganisms are a major cause of corrosion of metal pipes; but, despite decades of study, it is still not known with certainty how many species of microorganisms contribute to corrosion, how to reliably detect their presence prior to corrosion events, or how to rapidly assess the efficacy of biocides/mitigation procedures.
The objective of this project is to develop, test, and apply an environmentally benign agent(s) to control microbial-caused corrosion on the internal surfaces of iron or steel pipes used for natural gas transmission. The approach is to evaluate natural products isolated from plants and possibly animals or microorganisms, for their abilities to block the attachment, physiology, or reproduction of the microbes responsible for microbial influenced corrosion. A commercially viable agent that aids in MIC control and is environmentally friendly is the ultimate target, with preliminary data to determine commercialization potential and cost benefits.
Basic research to increase our understanding of the microbial species involved in microbial corrosion, and their interaction with metal surfaces and with other microorganisms, will be the basis for the development of new approaches for the detection, monitoring, and control of microbial corrosion.
The results obtained in this project are consistent with the hypothesis that any compound that disrupts the metabolism of any of the major microbial groups present in corrosion-associated biofilms shows promise in limiting the amount/rate of corrosion. This approach of controlling MIC by controlling the metabolism of biofilms is more environmentally benign than the current approach involving the use of potent biocides, and warrants further investigation.
In cooperation with industry partners, GTI first located several pipeline sites that had sustained corrosion of an apparently biological nature (as judged by the presence of extensive microbial bio-fouling and film formation) to serve as sources of material from which microorganisms and microbial biofilms could be isolated. Samples were taken and studied with advanced methods (i.e. environmental scanning electron microscopy and epi-fluorescence microscopy). The microbial cultures, once isolated, were re-inoculated onto clean metal slides or coupons to ensure that their MIC capacity was maintained.
High-pressure devices in use at GTI were modified to create a natural gas pipeline test cell in which metal coupons could be loaded. The cell was used to simulate the conditions found in natural gas pipelines, allowing testing of biocidal and anti-biofilm constituents under near-field conditions. Various environmental parameters were evaluated in order to determine which parameters are critical to MIC under laboratory conditions. Using a variety of methods, GTI allowed the growth of the MIC-associated microorganisms in a manner that best approximated conditions encountered in actual operating pipelines. All sample bacteria assemblages from a particular site were maintained as mixed cultures, representative of their occurrence in the field. In addition, a chemostat system with a direct link to a pipeline test loop and/or Robbins device was designed and constructed. Two test loop units were constructed and operated with one used to maintain the biofilm-forming and MIC-causing activities, and one loop to test treatments, biocides and monitoring tools.
Planktonic cultures are easier to inhibit than mature biofilms but several compounds were shown to be effective in decreasing the amount of metal corrosion. Of the compounds tested, hexane extracts of Capsicum pepper plants and molybdate were the most effective inhibitors of sulfate reducing bacteria, bismuth nitrate was the most effective inhibitor of nitrate reducing bacteria, and 4-((pyridine-2- yl)methylamino)benzoic acid (PMBA) was the most effective inhibitor of methanogenic bacteria. All of these compounds were demonstrated to minimize corrosion due to MIC, at least in some circumstances.
and Remaining Tasks:
GTI is presently evaluating the ability of pepper oil components to inhibit and mitigate biofilm formation and MIC. Biocidal effects of pepper oil are possible (indeed likely) and the result of synergistic activities of various constituents within the highly complex mixture. An understanding of these interactions is one goal of these investigations. Glass slides and/or metal coupons pre-colonized with biofilms are being suspended in the pipeline simulation systems and exposed to the pepper oil components in order to determine what effects, if any, they may have on the established biofilms. The tests under optimum MIC or biofilm-generating conditions are being repeated at various concentrations of the pepper oil components, to determine the lowest possible concentration at which biocidal effects can be observed.
A list of coatings, biocides, corrosion inhibitors, and dehydration compounds commonly used by the pipeline industry has been generated. A number of the manufacturers and distributors of these chemicals have been contacted and samples of the chemicals requested. GTI's pepper extracts and their components will be tested, using the biofilm and biocidal testing procedures described above, with mixtures of these compounds.
Upon completion of these tasks, several delivery systems (e.g., foam pigging, pipeline flooding) will be tested as a means of delivering the biocide. It has been determined that the first delivery system to be evaluated will be foam. Initial testing will evaluate the effectiveness of pepper extracts and their components with various surfactants.
Following the determination of an adequate delivery system, a commercial/engineering model and a laboratory evaluation of the most likely available source of pepper oil (i.e., pepper sauce production waste) will be developed. In addition, the direct cultivation of the pepper species that furnish the highest concentrations of the MIC controlling constituents will be evaluated. At this point, commercial production avenues and potential pilot testing will be proposed if the data supports further activity.
All tasks are now complete. Final report has been received.
Final Report [PDF-1307KB]