Causes of Corrosion

The need for polymer sewer lining coating

When OBIC was founded, it was with the mission of providing a long-lasting, cost-effective barrier of protection for water and wastewater structures. Polymer coatings and lining systems have proven time and time again that they offer the best combination of price and performance for addressing sewer system inflow and infiltration issues. Our website and blog posts are filled with data and information to support this.

If you are wondering why polymer sewer lining coatings are necessary in the first place, you have come to the right blog post. The following paragraphs give an overview of what causes sewer inflow and infiltration issues and why polymer coatings are needed in the first place.

Most common issues that make sewer lining repairs necessary

The two most common problems affecting sanitary sewer structures are groundwater infiltration and deterioration caused by corrosion. Infiltration is relatively easy to understand.  Corrosion, on the other hand, is slightly more complicated.

Ultimately, there are two main culprits to corrosion. The first one is hydrogen-sulfide; the second one is microbially induced corrosion (MIC).

Hydrogen-sulfide corrosion (H2S) will always be a problem

Hydrogen-sulfide corrosion, or H2S corrosion, occurs as an acid attack caused by the biological conversion of hydrogen-sulfide gas (H2S) to sulfuric acid (H2SO4), in the presence of moisture. Of course, there is always moisture present in a sewer system.

Unfortunately, sulfuric acid is highly corrosive to the concrete surfaces commonly used to construct sewer collection systems. Now imagine that highly corrosive sulfuric acid running down the wall of a concrete manhole. Over time, it will begin to erode the concrete surface. Left unaddressed, as is too often the case, it will eventually erode several inches of thickness and begin to impact the structural integrity of the manhole. In this situation, a manhole replacement may be required rather than a more affordable, less disruptive manhole repair with a polymer lining system.

Wondering where hydrogen-sulfide gas comes from? It comes from sulfate in the wastewater. Sulfate is biologically reduced to sulfide in the wastewater residing in the sewer pipe. Those sulfates come from discharged human and industrial waste, but mostly from sulfate added into potable water as part of the drinking water treatment process. The presence of sulfate in wastewater and its conversion to sulfide in anaerobic sewer collection systems is generally considered unavoidable. In other words, hydrogen-sulfide corrosion is always going to be a problem.

Polymer sewer lining coatings protect from H2S corrosion

Polymers are not attacked by hydrogen-sulfide, making OBIC sewer lining repair systems ideal for protecting wastewater structures. Rather than letting minor corrosion issues continue to worsen until a replacement is unavoidable, a polymer sewer lining coating can be installed. Not only will this address corrosion and infiltration issues, but it will also add approximately 50-years of life to the structure.

Microbially induced corrosion (MIC)

Now for the second culprit – microbially induced corrosion (MIC). MIC causes corrosion of concrete by producing acids that degrade the concrete.

Imagine newly installed concrete, such as a recently installed precast manhole. At this point, the structure is usually immune to biological attack because of its high alkalinity. Over time, the general environment of a wastewater system, coupled with the deterioration caused by hydrogen-sulfide gas, lowers the pH of the concrete. When the pH is lowered toward neutral (7.0), conditions are created for microbial colonization.

Scientists have identified six different bacteria and twelve different fungi present which contribute to the biological corrosion of concrete. As the pH continues to drop, increasingly aggressive microorganisms produce acids such as acetic, butyric, and lactic as well as carbon dioxide, all of which are extremely corrosive to concrete. Additionally, those microorganisms can penetrate inside the concrete matrix through microcracks or the capillaries in the concrete.

The result of the microorganisms within the concrete is increased concrete porosity. Higher porosity leads to higher surface wear and a reduced life cycle. Fortunately, OBIC polymer lining systems are impervious to MIC and protect concrete substrates from MIC attack, typically adding 50 years of additional life.

Schedule a virtual demonstration

Still have questions about how the OBIC polymer lining system can address your specific sewer system inflow and infiltration issues? Schedule a virtual demonstration and get all of your questions answered. Simply email info@obicproducts.com, and a member of our team will reach out to schedule your virtual demonstration.