Lightweight composite access covers

Paul Boughton

With recent statistics attributing over half of injuries (resulting in absence from work) to manual handling it’s already known that reducing hazards in this area is a priority on a global scale. 

Because of legislation restricting acceptable manual handling weights, we are seeing a global trend towards lighter weight FRP composite (fibreglass reinforced plastic) manhole and access cover materials, which also have the benefits of ease of handling and corrosion resistance.

Lightweight composite covers that provide safe and easy access eliminating unsafe manual handling issues are replacing aging concrete and heavy cast iron access covers all over the world. By using lighter materials, operational injuries are prevented, work sites are made safer and ease of installation and maintenance is made available to utility workers and contractors.

Composites are also becoming highly attractive as a result of the metal theft epidemic as they provide the perfect solution – they won’t be stolen for their resale value.

One of the primary problems facing the United States today is the country’s aging infrastructure. Across the nation, bridges, highways, rail lines, water lines and sewer systems are deteriorating at a rapid pace. One of the principal factors related to the deterioration of infrastructure is corrosion.

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 alone¹. 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 per cent to 30 per cent of annual corrosion costs could be saved if optimal corrosion management practices were employed².

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 (AWWA), there are approximately 876,000 miles of municipal water piping in the US. The country’s sewer system network is estimated to exceed 800,000 miles of underground piping³.   

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 (eg, 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 which provide long-term resistance to almost every chemical and temperature environment.

Composite manhole covers, such as those produced by Fibrelite, 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 300°F. Due to the high heat of the steam, many utilities require the use of a thermally non-conductive composite manhole cover to prevent the accidental burning of pedestrians that may come in contact with the cover.  

¹ “Corrosion Costs and Preventative Strategies in the U.S.”, NACE, July 2002, p. 1; ² Ibid., p.2; ³ “2013 Report Card for America’s Infrastructure”, American Society of Consulting Engineers.

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