Laboratory Evaluation of Materials for Resistance to Anaerobic Corrosion by Sulfate-Reducing Bacteria: Philosophy and Practical Design Available to Purchase

Reliable laboratory test methods for the evaluation of the performance of materials against anaerobic corrosion by sulfate-reducing bacteria are not readily apparent in the literature. Traditionally, such testing has been carried out in small scale “batch cultures” using filled and stoppered vessels or small cells contained in anaerobic jars. The problem with such tests is that they give much lower rates of corrosion than those frequently experienced in the field. This is almost inevitable, as the total quantity of hydrogen sulfide produced is small compared with the surface area of the test coupons, and quickly becomes denuded. From our knowledge of the microbiology and electrochemistry of anaerobic corrosion by sulfate-reducing bacteria, any realistic test must meet certain conditions. The duration must be long enough to allow the stable crystallographic forms of metal sulfide to form. These tend to be nonprotective and cathodic to the metal. The vessel should be sufficiently large to present a realistic volume of test medium to exposed specimens. It should contain a medium that supports the growth of sulfate-reducing bacteria, but excludes organic constituents, which act as inhibitors. It should operate in a semicontinuous culture mode to maintain the organisms in an active state of growth and sulfide production. It should be maintained at a temperature which is compatible with the active growth of the sulfate-reducing bacteria. Air should be effectively excluded. Large anaerobic culture vessels (20-L capacity) have been constructed containing both aqueous and soil environments. These have been used in a number of tests involving various environments. Electrochemical monitoring by linear polarization, electrical resistance, and advanced electrochemical techniques has been incorporated. Results of a 250-day test involving cast iron pipe sections are outlined. The test regime described provides a reliable method for the evaluation of the likely long term anaerobic corrosion behavior of any selected materials and associated corrosion protection methods.