Manhole covers are an important aspect of both urban and rural infrastructure, just as manholes are. Manholes provide access to underground utilities such as sewer systems, water mains, gas pipelines, or electricity cables. Manhole covers not only cover the access point, which is large enough for a person to pass through, but it also protects pedestrians from falling into the manhole and keeping unauthorised persons from having access.
Manhole covers come in different shapes and sizes and are made from different materials such as cast iron, concrete, steel, and composite material,
A cast iron manhole cover is a high strength removable plate mainly made from ductile iron, that acts as a cover for a manhole. They can also be made from grey cast iron.
In this article, we will look at the strengths and weaknesses of cast iron manhole covers.
Strengths of cast iron manhole covers
- Durability and longevity: Ductile iron has high tensile strength, making it extremely reliable in the urban infrastructure. Its superior strength makes cast iron manhole covers durable and they can be used for over 30 years.
- Resistance to heavy loads: Cast iron manhole covers can withstand heavy loads from pedestrian to vehicular traffic without any impact or distortion. The lightest class of cast iron manhole covers (A15) can withstand a load of 1.5 tonnes which is used for light pedestrian areas such as gardens. The heaviest class is the F900, which can take a load of 90 tonnes and is used in docks, airports, and other heavy-duty applications.
- Low maintenance: The covers do not require regular cleaning or painting to maintain its appearance.
- Cost-effectiveness: Iron costs less than other metals like steel, making it cost-effective.
Weaknesses of cast iron manhole covers
- Weight and difficulty in handling: A typical cast-iron manhole cover can weigh from 175 to 300 lbs (79 to 136 kgs). This makes it extremely heavy for handling and lifting and can cause lower back injuries.
- Vulnerability to corrosion: Cast iron corrodes when exposed to conditions from sewer systems, especially when exposed to H2S gases. It deteriorates easily because of corrosion which can cause the ring and cover to seize, making it difficult to open the cover,
- Lack of sustainability: The manufacture of cast iron manhole covers involves high use of energy and resources, from mining earth to heating, handling, and transporting, which is not environmentally sustainable.
- Safety concerns: because cast iron manhole covers are heavy, manual lifting of cast iron manual covers can cause injuries and is hazardous to spinal health.
- High maintenance costs: Cast iron manhole covers are prone to damage from prolonged use. As they are vulnerable to corrosion, rust can make them brittle, requiring high maintenance costs. Ductile iron covers are less brittle than grey cast iron and will have a lower maintenance cost.
Comparison with other manhole cover materials
Manhole covers are also made from other materials such as concrete, steel and composite materials, including fiberglass and plastic.
- Concrete: Cast iron and concrete are two common materials for manhole covers. Similar to cast iron covers, concrete manhole covers are heavy, long-lasting and have a low-cost. However, concrete manhole covers have low bearing weight, unlike cast iron covers.
- Composite: These manhole covers are more widely used as they are cheaper to produce. They are also more manageable compared to cast iron covers as they are lightweight but have high tensile strength and impact resistance. They also seal better, are anti-corrosive and can be moulded into various designs.
- Steel: Stainless steel manholes are a strong alternative to cast iron covers. They are lightweight but extremely strong to withstand weight from domestic traffic. However, they are not suitable for heavier traffic and other applications like cast iron covers.
In Summary
Despite being heavy and having high maintenance costs, cast iron manhole covers are used for a variety of applications because they are durable, can take heavy loads, and can last for a long time with little maintenance. Besides using cast iron manhole covers for sewage systems, they are also used for gas, electricity, and communications systems. They can be used for residential and commercial projects, from homes and offices to roads and airports.
Check out our range of cast iron access covers, including grates and frames.
