Corrugated metal pipe, also known as corrugated pipe culvert or corrugated steel pipe, is the "go to" material for the majority of drainage and pipe system applications, including culverts, storm sewers, and infiltration systems. Corrugated metal pipe (CMP) is easy to work with because of its wide range of sizes, its long and predictable service life, its customizability and its availability. However, it can be easy to make mistakes while installing a CMP system; environmental damages, internal damages, wrongly-chosen material, or faulty installation can lead to costly replacements. Here are a few factors that you must consider before and during CMP installation:
Design
The CMP's gage determination is based on the intended use, the intended life of the culvert, and the weight of its buried condition. Two principal types of loads must be taken into consideration when designing the size of the CMP: the dead load, which is the weight of the embankment or trench, and the live loads, such as moving cars and vehicles. The design of the CMP should also consider other factors, such as:
- Buckling
- Installation and Handling
- Riveted seam strength
- Wall compression
- Strain limits
- Deflection
Coatings
CMP can be purchased with or without coating. The coating is applied to the pipe after the base metal has been clad with aluminum or galvanized with zinc. The coating can be painted, adhered, sprayed, or dipped, and asphalt coatings are the most common for CMPs. Coatings have been found to add anywhere between zero and ten years of life to a CMP; the length of its life depends entirely on the coating's interaction with its environment, though it is reasonable to assume the coating can add an average of five years of extra life.
Possible Damages
Some CMPs can last for several decades, while others can stay in the ground a minimum of twenty years before they have to be replaced. This is due to damages that may happen, and knowing the common types of damages can help you take preventative measures. Some damages stem from faulty manufacturing while other damages are brought on by the environment. These include:
- Lack of rigidity
- Ragged or diagonal edges
- Dents or bends in the metal
- Elliptical shape instead of round
- Loosely formed lockseams
- Variation from the straight centerline
By inspecting your CMP before and after installation of these various possible problems, you can raise the likeliness that your CMP will last for several decades before requiring replacement.
Proper Installation
Some common mistakes when installing CMPs can be avoided by remembering the following tips:
- The engineer must consider the possibility of flotation when selecting the pipe material; sometimes CMP can rise out of its buried position due to flooding, thus damaging the system.
- The initial trench width should be at least sixty centimeters wider than the pipe; for poor soils, consider wider trenches, to allow the CMP more space.
- Well-graded granular material should be stacked thirty centimeters over the pipe and compacted to 95% relative density. By ensuring compact and uniform material around the pipe, you lessen the possibility of external elements slowly damaging the pipe over time.
Installing CMP should be treated seriously and meticulously, because a few mistakes can lead to costly replacements, in both time and money. A perfectly installed CMP system will serve you for decades to come.
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