|Content Type||Conference Paper|
|Title||Sulfate Reducing Bacteria Influence on the Cathodic Protection of Pipelines That Transport Hydrocarbons|
|Authors||Geraldo Zavala-Olivares, Guillermo Munoz-Mejia, Graciela Garcia-Caloca, Rafael Garcia-Esquivel, and Isaac Guzman-Lopez, Instituto Mexicano del Petroleo; Carlos Manuel Ulloa-Ochoa and Francisco Rivera-Dabur, PEMEX, CTO|
|Source||CORROSION 2003, March, 2003 , San Diego Ca|
|Copyright||2003. NACE International|
|Keywords||Sulfate Reducing Bacteria, Cathodic Protection.|
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.
Generally, the hydrocarbon transporting pipelines, for control and security reasons, are buried and/or submerged, and are further protected against corrosion by means of an anticorrosive coating and cathodic protection. However, even with this protection, there have been some failure cases due to external corrosion, where several environmental factors, generated by different types of soils or natural waters, are involved. These factors can be physical, chemical as well as microbiological. This situation is favorable for the growth of anaerobic microorganisms, such as the sulfate reducing bacteria (SRB), which is very important in the corrosion processes, because they change the environmental conditions in the metal/soil interface and increase the corrosion rate.
In Mexico and other parts of the world, external corrosion problems in hydrocarbons and water transport pipelines have occurred, where iron sulfates were observed as corrosion products. This attracted the attention of many researchers. Harris1 did a complete study about the soil profile, from the surface to underneath the pipe, and found interesting physical, chemical and microbiological data. He concluded that the environmental conditions around the pipelines are favorable for the SRB development, among other anaerobic bacteria. Booth2 used the model proposed by Von Wolzogen Kühr and Van Der Vlugt3 to further detail the interactions between the sulfate reducing bacteria and the corrosion process in transport pipelines.
Recently, some people have been working on the interaction of the microorganisms and the cathodic protection; for example, Little and Wagner4 explained this interaction in transport marine pipelines. The Mexican Petroleum Institute (IMP) participated in a study of some anticorrosive coating and soil samples coming from the 48 . gas transport pipeline Cactus-Los Ramones in the southeast of Mexico, where some failures occurred. A scanning electron microscope (SEM) was used to examine the metal surface and fungi remained on the coating surface were found
|File Size||1685 KB||19|