This phenomenon mainly affects metal structures. To prevent and eliminate the microorganisms that inhabit and weaken the materials, interesting preventive and corrective analyses are carried out that we will know below.
by Duván Chaverra Agudelo
Metal infrastructures that have constant contact with water suffer in greater quantity from the activities that microorganisms perform there. This generates biocorrosion, which results in a lower performance of the infrastructure and generates failures that mean high increases in the costs of maintenance or replacement of parts.
To reduce this phenomenon, there are different analyses that can be executed in order to prevent or correct metal structures. For that reason we invited Dr. Pamela Chávez Crooker, CEO of the Chilean company Aguamarina, who shared everything related to the subject of biocorrosion and told us about the way in which her company performs in terms of making diagnoses.
INPRA LATINA: What is biocorrosion?
Pamela Chavez: Biocorrosion, or microbiological corrosion, is the corrosion induced/influenced by microorganisms (MIC, Microbiologically Influenced Corrosion). It is a phenomenon that is gaining more and more interest due to the strong economic impact on submerged metal infrastructures or aqueducts. Microorganisms, through a synergistic process with the environment, the electrolyte, and together with the metal surface, have the ability to modify by different biochemical actions the physicochemical structure of the surface-metal interface, changing the pH and helping the generation of corrosive products, causing the deterioration of the metal surface in the very short term.
IL: In what types of structures does this phenomenon occur most frequently?
PC: This phenomenon occurs in metal structures of different carbon alloys, stainless steel or galvanized that are submerged in seawater, well or river water. It also occurs in aqueducts or pipelines of the oil industries and pipelines. It is also possible to find serious problems in desalination plants and process water transport pipes.
IL: What are the tests that are done to detect biocorrosion?
PC: In the field there is a colorimetric method that detects the bacteria present in the water, called TEST BART®. This TEST identifies SRB bacteria (Sulfate Reducing Bacteria), IRB (Iron-Related Bacteria), SLYM (Slime Bacteria), APB (Acid Producing Bacteria), the main bacterial groups involved in MIC. In addition, there are the analyses of SEM microscopy (Scanning Electron Microscopy), which help characterize the damage caused microstructurally on the surface of the metal by the presence of pitting, which are the microperforations suffered by the metal product of biocorrosion.
At the same time, we apply controls to calculate the corrosion and risk rates associated with material wear. We also use cores to choose the best material to build the ducts.
IL: What kind of protection processes should be carried out to prevent biocorrosion from occurring in structures?
PC: The best protection is to keep the systems clean and a plan of maintenance of the ducts, at first it is difficult to comply, since you do not always have the proper cleaning mechanism due to lack of knowledge. However, any engineering project should take into account in its baseline the microbiological quality of water, in particular the microbiological diversity associated with the MIC. The biggest error that we have detected in the piping operation tasks is that this important biological parameter has not been included in the studies prior to the implementation of the engineering project, due in large part to ignorance of the threat.
Additionally, once the piping systems are already operational, bacterial monitoring of the MIC should also be implemented in the water collection systems and pumping stations. There are products that can be used to control the amount of bacteria that enter the ducts.
IL: In a biocorrosion project, are coatings used to protect structures? Which are the most used?
PC: Yes. The most commonly used coatings are FBE, FBE – MAX, HDPE, mortar cement, epoxy paints and antifouling paints. When a material is selected, its exposure to the environment must be taken into account to avoid deterioration.
IL: Are there mechanisms other than the use of coatings to protect structures from biocorrosion?
PC: Yes, there are alternative mechanisms, which apply directly to the electrolyte. Among the most used, there are anticorrosives with bacterial growth inhibitors, biocides, there are also biocorrosion inhibitors that act on the medium that surrounds the metal, based on organic or inorganic compounds. Whatever type of inhibitor is chosen, it is very important that it is chosen based on the bacterin diversity found in the place.
IL: What are the benefits of running a biocorrosion project?
PC: The biggest benefit is to make the MIC phenomenon known to engineers, as it is a sometimes unknown term. Then it is the application of maintenance standards, which will help visualize problems and lower costs in repair or plant shutdowns within a production process. But perhaps the most relevant thing is to be able to understand during the project what percentage of the total corrosion problem would eventually correspond to a problem of biological origin, since the measures to be used are different.
IL: What are the difficulties that can arise in the execution of a biocorrosion analysis?
PC: One of the biggest difficulties of detecting biocorrosion is that the MIC is found in a biofilm that protects them. Accessing them in the field is sometimes very difficult, especially for taking samples in situ, as they can be concealed under the application of coating paints and are only detected when the damage has perforated the pipe. That is why it is important to know the microbiological quality of the water before implementing and executing operations.
IL: Tell us about some of the most important projects you have done in this regard and about the differences that exist between them.
PC: We have intensively studied the detection of MIC bacteria in groundwater, seawater and river waters located between 4,800 and 5,200 snm; this makes the solution to this problem as specific as MIC niches are found. The experience so far, tells us that the measurement is fundamental, waters that were thought to be more corrosive than others due to their thermal origin, were less corrosive than those of the river. Fully desalinated water presented extremely serious corrosion problems with intolerably corrosive levels. In this problem it cannot be generalized and it is necessary to see it case by case.
IL: Do you think that companies invest what is necessary in the protection of their systems against biocorrosion? Are these kinds of projects high in cost?
PC: There is always the cost factor compared to the decision of the protection to be used, although, today there is no single solution that guarantees 100% protection, the decision goes hand in hand with the characteristic of the quality of water to be used. Until now, the common case never considered using biocorrosion analysis during project engineering and this resulted in a large deviation from the expected lifespan of coating and steels used. Pipes designed for 20-30 years barely lasted 5 years.
IL: How long can a biocorrosion study take from analysis to the protection process?
PC: A diagnosis of biocorrosion can take from fifteen days to a month, it all depends on how specific the study is. An R&D applied until obtaining a candidate control or prevention product takes approximately six months. We also perform simulation of conditions in reactors, this can take three to six months.
IL: Are the biocorrosion processes that occur the most preventive or corrective?
PC: The processes are preventive.
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