In general, the hydrocarbon transporting pipelines are protected against external corrosion using coatings and with cathodic protection systems. However, even with this protection, there have been some failures due to external corrosion. The soil and environmental factors can be very important, because they may increase the conditions for some microorganisms to grow, including sulfate reducing bacteria (SRB), which play a very important role during the microbiologically influenced corrosion processes. The SRB can grow under the pipeline coating, causing a depolarization effect and increasing the corrosion rate, even if the pipeline is cathodically protected. This is due mainly to the bacteria action, that forms a dielectric film and the cathodic protection can not reach the metal surface. The pipelines located in the southeast of Mexico are buried and/or immersed, and microbial analysis of the surrounding environment (soil, mud and water) have shown that microorganisms, including the SRB, can grow easily next to the pipelines, and the metal surface may be exposed to microbiologically influenced corrosion processes, which can occur easily. According to these observations, it is very important to identify the possible effect of these microorganisms on the pipelines integrity. In this work, typical d.c. laboratory techniques were carried out, along with field and laboratory weight loss experiments, in order to study the influence of the Sulfate Reducing Bacteria (SRB) on the cathodic protection system of the pipelines that transport hydrocarbon from Atasta to Cd. PEMEX, in México. The results were complemented with some surface examination.
Keywords: Sulfate Reducing Bacteria, Cathodic Protection.