Understanding Corrosion in a Water and Wastewater Environment

This water treatment plant, and others, are susceptible to various types of corrosion, as well as chemical attack. Photo courtesy of Carboline.

The importance of water and wastewater systems, whether it’s to a town or city on the micro level or to a state or country on the macro level, cannot be overstated. 

When working properly, these systems quietly and efficiently support communities by providing clean drinking water and removing or eliminating contaminants from water in order to be reused or returned to the water cycle. It’s only when water and wastewater systems malfunction or break down that we begin to appreciate how important they are to our daily lives. 

One of the main causes of system failure is corrosion, which is defined by the Association for Materials Protection and Performance (AMPP) as “the deterioration of a material, usually a metal, that results from a chemical or electrochemical reaction with its environment.”1 

While the material in question is often a metal, the definition can also include other ubiquitous substrates such as concrete. For a variety of reasons, water and wastewater assets are particularly prone to various forms of corrosion, affecting assets such as dams; aqueducts; transmission, collection, and distribution pipelines; treatment and pumping plants; and storage reservoirs. 

As a result, responsible asset owners, engineers, and other key stakeholders are obligated to understand what causes corrosion and how to mitigate, if not eliminate, its effects.  

What Is Corrosion? 

Materials Performance (MP) magazine recently presented a free webcast entitled “Understanding Corrosion in a Water and Wastewater Environment.” Sponsored by Carboline, the webcast was hosted by Rebecca Bickham, editor in chief for MP, and featured two Carboline subject matter experts: Jeremy Sukola, market manager for water and wastewater, and Jack Walker, product line manager for linings. 

A protective coatings industry veteran with 25 years of experience, Sukola is a Senior Certified Coatings Inspector and Protective Coatings Specialist with AMPP, as well as an instructor for the AMPP Coatings Inspector Program. Walker has worked in the world of paints and coatings for more than 20 years, 15 of which have been spent in various roles at Carboline, and is currently one of the hosts for The Red Bucket, a protective coatings podcast from Carboline. 

In the webcast, Sukola and Walker provide a definition of corrosion as it relates to water and wastewater assets, identify vapor and liquid phase corrosion mechanisms within a waste stream, and discuss the galvanic series of dissimilar metals. Their presentation also examines how concrete is affected by environmental chlorides and other factors, as well as explores other physical forces that contribute to corrosion in a water and wastewater system. 

Corrosion Costs and Effects 

One of the more salient parts of the webcast presentation is “The Cost of Corrosion.” According to Walker, about 30 years ago AMPP (then known as NACE) issued a report to Congress in which the annual direct cost of corrosion in U.S. water and wastewater systems was $36 billion per year. As Walker muses, “One can only imagine the amount of inflation and more corrosion that has happened in the last 30 years” that would make that billion-dollar estimate even higher. 

Sukola cites statistics from the 2021 Report Card for America’s Infrastructure2 from the American Society of Civil Engineers (ASCE), which found that the direct cost of corrosion in the U.S. to wastewater infrastructure totaled $276 billion, along with $36 billion for drinking water and wastewater systems. 

Another pertinent statistic that Sukola cites: as of 2019, the wastewater spending gap was $81 billion, with $48 billion spent on such infrastructure versus the actual estimated need of $129 billion. In reviewing these figures, he points out that the estimated need factors in direct costs and doesn’t include other costs, such as lost time or litigation, that would make the total estimate even higher. 

After analyzing the economics of corrosion, Sukola and Walker spend the bulk of their presentation reviewing how corrosion effects steel and concrete substrates. Sukola explains the basics of a corrosion cell, also known as a Daniell cell, and the four basic conditions or elements that enable corrosion: an anode, which is the most corrosive part of a metal; a cathode, the most noble part of a metal; a metallic pathway, defined as any ferrous or non-ferrous substrate; and an electrolyte that can simply be water or any aqueous solution. 

As Sukola explains, adjusting or eliminating any of these four conditions or elements can increase or decrease the occurrence of corrosion. 

Walker explores how concrete is designed and what makes it prone to corrosion. In short, concrete consists of coarse aggregates, fine aggregates, and water, along with capillaries that carry contaminants and other foreign materials. A concrete surface with a high pH will not allow bacterial growth, whereas most cementitious materials below pH 7 are prone to attack by both natural and manmade agents. 

When turning to the topic of factors that contribute to corrosion of structures in a water and wastewater environment, Sukola points to the following factors: elimination of heavy metals, longer detention times, odor control rules/regulations, increased turbidity, and overdesign for increased capacity. He points out that while some of these factors, such as eliminating heavy metals and odor controls, have positive benefits to human and aquatic life, they have detrimental effects in terms of mitigating corrosion. 

To counteract these factors, Sukola recommends corrosion control methods such as designing systems that are built for a specific use and take metallurgical considerations into account, and using protective coatings and linings to keep water and other intrusive elements from permeating steel and concrete surfaces. 

Sukola and Walker concluded the presentation by detailing forms of corrosion commonly found in water and wastewater environments: vapor phase corrosion, including microbiologically induced corrosion; liquid phase corrosion, including chemical and acid attack; chloride-induced reinforcing steel corrosion; galvanic corrosion; general corrosion; concrete carbonation; and physical forces such as abrasion and impact. 

Along with describing each form of corrosion in depth, they also provided examples from the field and the conditions that allowed the relevant form of corrosion to occur. 

To access an on-demand version of the webcast, visit the Materials Performance Webcasts page at www.materialsperformance.com/webinars.  

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