Recycled plastic pipes have proven reliable, economical and long-lasting over time

The construction of modern sewer lines must take into account some essential elements, both technical, as we will see, but also environmental, in order to minimize the impact of the products used for the hydraulic work.

In the past, ducts were made with metal or concrete pipes, but since the plastics industry has been able to create alternative products, the diffusion of double-walled HDPE corrugated pipes has become widespread.

The first step to take in the construction of a sewer line is its design, which must take into account various aspects that affect the construction area.

How to size a sewer line that uses plastic pipes

Like any good project that must be carried out, the collection of precise, detailed and reliable information is the basis of the subsequent work. We can list some points that will enter into the design evaluation:

The estimate is the maximum daily flow rate that the sewer will have to handle. To do this, it will be necessary to consider the wastewater collection area, population density, industrial uses and other factors that could influence the quantity of liquids to be collected.

It is also important to determine the available or desired slope for the sewer line and its diameter.

For this information, hydraulic formulas (e.g. Manning's formula) may be useful to calculate the flow speed based on the diameter of the recycled plastic pipe, the slope and the roughness of the material.

It will be important to choose a plastic pipe diameter that provides an adequate flow velocity (e.g., between 0.6 m/s and 3 m/s) under full or near-full flow conditions.

Additionally, you will need to ensure that the depth of the sewer is sufficient to prevent freezing (in cold climates) and to maintain adequate coverage over the recycled plastic pipe.

From a structural point of view it will be necessary to verify that the HDPE pipe chosen can withstand external loads, such as the weight of the soil above it and the traffic above it (if applicable).

You will have to think about the connecting elements of the recycled plastic pipes, checking the correct distance between the inspection wells and that the connections between the pipes and the wells are watertight.

The design of the sewer line also includes environmental aspects, therefore the possibility of infiltration or loss of waste water from the line must be considered and prevented.

However, the use of HDPE pipes, as they are watertight, provides good safety, considering the joints between the various pipes are made in a workmanlike manner, also taking into consideration whether an aquifer can be found nearby.

Finally, you will need to ensure that the design complies with all local sewer regulations and guidelines.

What technical characteristics must a HDPE corrugated pipe for sewerage have?

HDPE corrugated pipes for sewerage must meet specific technical characteristics to guarantee their suitability for use and their durability over time.

- The recycled polymer with which the corrugated pipe is constructed must be of good quality and resistant to UV rays

- The corrugated pipe must have good mechanical resistance to crushing and lateral deformations stressed by the ground without breaking

- The joints between the pipes or between the pipe and fittings must guarantee watertightness, avoiding dispersion of waste water into the ground

- The internal part must be smooth enough to allow liquids to flow so as to facilitate their outflow

- The HDPE pipe must resist corrosion from wastewater and other chemicals in the sewer system

- Under the effect of variations in ground temperatures the pipe must be able to withstand them without losing structural integrity

What are the advantages of using HDPE corrugated pipes for sewerage compared to PVC, concrete and metal

HDPE corrugated pipes offer several advantages, especially when used in sewer applications:

Durability and Corrosion Resistance

HDPE is inherently corrosion resistant, unlike metal pipes which can rust or corrode in the presence of wastewater or aggressive soils, ensuring a longer life.

Flexibility

HDPE pipes are flexible, which means they can adapt to ground movements, such as settlements or earthquakes, without breaking. A particularly important advantage compared to concrete pipes, which are rigid and can break with ground movements.

Lightness

Plastic pipes are significantly lighter than concrete or metal pipes. This simplifies transportation, handling and installation, reducing labor costs and heavy equipment needs.

Watertight welding

HDPE pipes can be welded to create watertight joints, reducing the risk of leaks or seepage. This can be an advantage over PVC or concrete pipes, where the joints may be less reliable in terms of sealing.

Chemical Resistance

The HDPE polymer that makes up the pipes is resistant to many chemicals, making it ideal for sewer applications where aggressive chemicals may be present.

Reduced costs

In many cases, the overall installation costs of HDPE pipe can be lower than other options.

Eco-compatibility

HDPE is a recycled and recyclable material, which may make HDPE pipes a more sustainable choice than some alternatives.

Extended Useful Life

With proper installation and maintenance, HDPE pipes can have a very long service life, often exceeding 50 years.

Low Internal Roughness

The smooth internal surface made using HDPE allows efficient flow, reducing the risk of blockages.

How to lay a HDPE corrugated pipe for sewerage

Entering the construction phase, the installation of a corrugated HDPE pipe for sewerage follows a series of key steps, in order to guarantee a safe and long-lasting installation.

First of all, it will be necessary to dig a trench of the right depth and width for the pipe you have decided to install, creating a flat and solid trench bottom.

At the bottom of it, a layer of compacted sand or fine gravel should be placed to create a stable base for the pipe, the thickness of which should be at least 10-15 cm thick.

Once the trench and the suitable bottom have been created, the HDPE corrugated pipe is laid, taking care not to damage it with the laying machines. Also make sure that the hose is straight and free of bends or tension.

Once the pipe line is laid, you will begin to fill the trench with material such as sand or fine gravel. You will need to carefully place the fill material around the pipe to ensure a solid base and to prevent the pipe from shifting.

After checking that there are no leaks in the sewer line, the trench can be completed with the soil dug previously, compacting everything from the outside.

How to weld two corrugated HDPE pipes for sewerage

Many plastic materials, including HDPE, are suitable for making long-lasting and effective welds between pipes, manholes and fittings.

But for welding two HDPE corrugated pipes, special equipment and some experience are required.

It will be necessary that the ends of the pipes to be welded are clean and free of dirt, grease or other impurities, to ensure a high quality weld.

The tubes will then be positioned so that their ends are perfectly aligned and in contact with each other.

At this point you will use an HDPE welding machine, ensuring that it is correctly set up according to the pipe manufacturer's specifications.

Most welds for HDPE are performed using a heating plate to bring the pipe ends to melting temperature. You will insert the heating plate between the ends of the tubes and wait for them to reach the appropriate temperature.

Once the ends of the tubes are adequately heated, you will remove the heating plate and bring the ends of the tubes together, allowing them to fuse together. At the same time, uniform pressure must be maintained during this process to ensure good welding.

Once welded, the pipes must be left to cool for a certain period of time, in fact, during this time, the welding solidifies and strengthens.

Once soldering is complete, you should visually check the joint to make sure there are no air bubbles, cracks or other defects. Depending on the specifics of the project, it may be necessary to perform pressure tests or other tests to verify the quality of the weld.

Automatic translation. We apologize for any inaccuracies. Original article in Italian