Controlling Corrosion Costs

Composite manhole covers offer a variety of advantages to their traditional counterparts in corrosive environments.
Controlling Corrosion Costs
Composite manhole covers are more resistant to all forms of corrosion than their traditional counterparts (left), and most are equipped with watertight silicone gaskets.

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Aging infrastructure is one of the primary problems facing the United States today. Across the water lines, sewer systems and other infrastructure are deteriorating at a rapid pace, and corrosion is one of the principal factors.

According to a study by the National Association of Corrosion Engineers (NACE), the direct cost of infrastructure corrosion was over $22 billion in 2002 in the United States alone. Adjusted for inflation, the direct cost of corrosion in 2013 is estimated to be over $42 billion on an annual basis. It has been estimated that at least 25 to 30 percent of annual corrosion costs could be saved if optimal corrosion management practices were employed.

Underground infrastructure

The underground infrastructure of the United States is particularly exposed to corrosion because its core components are often installed in contact with soil, often convey water or more corrosive liquids, and many components such as manhole covers, frames and grates are installed at grade and are completely exposed to the elements. The scale of the affected systems that are subject to corrosion and decay is immense. According to the American Waterworks Association, there are approximately 876,000 miles of municipal water piping in the U.S. The country’s sewer system network is estimated to exceed 800,000 miles of underground piping.

Sewer, water and stormwater utilities all utilize extensive networks of underground piping. Typically, manhole covers are installed every 100 feet or so to allow for accessing the underground pipeline or conduit. It is estimated that there are at least 100 million manhole covers and grates installed in the United States alone. The principal materials used in these underground systems are steel, cast iron and concrete. All of these materials, including, to a lesser extent, concrete, are subject to corrosion.

FRP products now widely used

Fiberglass-reinforced plastic (FRP) products are now being widely used for applications where corrosion can destroy underground infrastructure. Perhaps the prime reason for using FRP products is because of their inherent corrosion resistance. In many cases, they are the only materials that will handle a given service environment; and in other cases their corrosion resistance is combined with their lower unit cost to make them the most economical acceptable solution (e.g. when compared to high grade stainless steel). Corrosion resistance of FRP is a function of both the resin content and the specific resin used in the laminate. There are various resin systems available today, all of which provide long-term resistance to almost every chemical and temperature environment. 

Composite manhole covers are highly resistant to all forms of corrosion. For this reason, they have been specified for use in highly corrosive environments such as steam manhole vaults. In many major cities, district energy networks operate large underground piping systems used to transmit steam from a central plant to nearby office buildings, hotels, hospitals and apartments. The steam or superheated steam that is transmitted in such systems can often reach temperatures as high as 400 degrees F. Due to the high heat of the steam, many utilities require the use of a thermally nonconductive composite manhole cover to prevent the accidental burning of pedestrians that may come in contact with the cover. 

Most composite covers are equipped with watertight silicone gaskets that seal against the manhole frame. These gaskets can significantly reduce the amount of surface water infiltration into the steam vault. Surface water is often contaminated with road salts that can cause corrosion in the piping and valves located in the vault. In addition, by keeping surface water from entering the manhole, spilling directly onto the hot steam valves and piping and thereby turning into steam, the internal temperature of the vault is kept at lower temperatures.

Composite covers are also extremely resistant to corrosion caused by road salts. This is extremely important for municipalities and utilities in colder climates where road salt is routinely applied during the winter months. 

Corrosion resistance is also critical for industries that are transmitting or storing corrosive liquids. In applications involving highly corrosive or environmentally damaging liquids, engineers often design concrete trenches to contain the piping. Fibrelite’s extensive line of composite trench covers are now being used across an array of industries as a strong, lightweight and corrosion resistant alternative to metal or concrete panels.

Making an impact

Today, composite materials are used in a wide variety of industries and applications. Composites offer several advantages over traditional materials: higher tensile strength, lighter weight, greater corrosion resistance, no resale value (deterring theft), better surface finish and easier processing.
By helping to reduce the costs of corrosion, composite covers can allow municipalities, utilities and other operators of underground infrastructure to improve the financial strength of their enterprises.


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