Introduction
One of the primary problems facing Iran today is our country’s aging infrastructure. Across the nation, bridges, highways, rail lines, water lines, and sewer systems are deteriorating at a rapid pace. Likewise, one of the principal factors related to the deterioration of infrastructure is corrosion.
The underground infrastructure of Iran is particularly exposed to corrosion because its core components are often installed in contact with soil and 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.
The principal materials used to build the millions of manhole covers, frames and other access covers in these underground systems are steel, cast iron and concrete. This makes them inexpensive, strong, and heavy, usually weighing more than 50 kilograms (110 lb.). All of these materials, including to a lesser extent concrete, are subject to corrosion. When manhole covers or grates are used in areas with vehicular access, they must be capable of bearing heavy loads. Load-bearing manhole covers or grates installed in streets, parking lots or sidewalks are typically constructed from cast iron.
However, as the underground systems currently installed are retrofitted or upgraded, engineers are strongly considering using corrosion-resistant materials in place of steel, cast iron or concrete. This is particularly true of underground infrastructure located in areas that are more prone to corrosion (e.g., coastal regions or colder areas where salt is commonly used as a deicing agent) or in infrastructure applications that store or convey water, wastewater or corrosive liquids. Such piping systems are common in the sewer and wastewater treatment industry as well as the petrochemical, pharmaceutical and pulp and paper industry.
Composite manhole covers and frames 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 addition, as chemical reactions are accelerated at higher temperatures, the hot steam accelerates the electrochemical corrosion of metals. For this reason, it is critical to utilize corrosion-resistant composite manhole covers and frames for accessing steam vaults. Composite covers are also extremely resistant to corrosion caused by road salts.
Description of manhole cover
A manhole cover is a removable plate forming the lid over the opening of a manhole to prevent anyone or anything from falling in, and to keep out unauthorized persons and material.
Manhole covers are often made out of cast iron, concrete or a combination of the two. They may also be constructed from glass reinforced plastic or other composite material (especially where cover theft is of concern). Because of legislation restricting acceptable manual handling weights, we have seen a move towards lighter weight composite manhole cover materials, which also have the benefits of greater slip resistance and electrical insulating properties. Surface anti-slip thread guarantees safe road condition even in extreme weather.
The covers usually feature “pick holes,” into which a hook handle tool is inserted to lift them. Pick holes can be concealed for a more watertight lid, or can allow light to shine through. A manhole pick or hook is typically used to lift them, though other tools can be used as well, including electromagnets.
Despite their weight and cumbersome nature, manhole covers are sometimes stolen, usually for resale as scrap, particularly when metal prices rise.
Advantages of using composite manhole cover
The composite material resists to chemical and is not subject to rust and corrosion caused by constant exposure to atmospheric agents. It maintains its load bearing capacity unchanged when tested at -80 C° and at +100 C°. For this reason the composite cover has never to be painted. The use of the cover is particularly suitable in areas with flammable liquids because it resists to corroding substances and reduces the risk of dangerous sparks. For this reason, the cover made of composite material can be installed in refueling stations or fuel storage plants.
The cover made of composite material is particularly suitable for installation in pedestrian areas as it protects pedestrians, especially in moist and wet environments. Composite material is not an electro-conductive material and it works as a barrier against magnetic fields from underground cable infrastructure. Composite material is also a low thermal conductor which offers protection against hot steam leakages in district heating piping systems.
The weight of composite material covers is 70% lower than the weight of cast iron covers. Thanks to its low weight the cover is easy to handle and to install, which means manpower and tool costs saving and a substantial reduction of injuries during Installation and maintenance. Low weight also reflects into a considerable reduction of transport expenses. The cover designed to meet and exceed A15/B125/C250/D400 loading rating, according to En124: 1994.
Another advantage of using the composite manhole cover, compared to cast iron manhole covers, is noise reduction in pedestrian and traffic areas. The material and sealing used for installation make it suitable for the reduction and of smell release in the environment.
Sewer and collection systems can have significant problems with Hydrogen Sulfide (H2S) and other odors. Fiberglass manhole covers and frames are engineered and fabricated to seal better resulting in better odor control. Fiberglass manhole covers are ideal for areas sensitive to sewer odors: high density neighborhoods, parks, recreation areas, trailer parks, campgrounds, islands, beaches and resorts.
The manufacturing of covers in composite material ensures a remarkable reduction of CO2 emission compared to cast iron. This becomes clear when comparing the energy required to reach the temperature to mould cast iron (higher than 1200°C) and the energy required to reach the temperature to mould composite materials (near 60°C). The lower amount of C02 released in the atmosphere is strictly connected with the lower weight of each single cover allowing to load on a truck a number of covers three times higher than cast iron covers with subsequent reduction of pollution due to the lower number of transports. The composite material can also be recycled for successive use which allows further reduction of the environmental impact of the product.
The value of scrap iron is rising increasingly and the number of thefts to the detriment of local authorities and service companies are rising as well. Every day we read that covers have been stolen to be sold and melt. Beside an economic damage caused by the need to replace the stolen products, there is also the risk of serious accidents and injuries caused by dangerous openings on the road. Once the strong point of cast iron covers, their high weight is becoming now their weak point because it makes them even more attractive to thieves.
The cover can be made with the logo of the agency, the service or the sponsor printed on the front side. Frame can also be forged in different colors.
Application of manhole covers
Manhole Covers find wide application in: