Large Diameter HDPE and PP Corrugated Sewer Pipes through the use of recycled granules

The sewer lines are designed according to the workload that the inhabited centers impose on the drainage system and, on the basis of other technical-design parameters, the characteristics of the waste liquid transport pipes are established.

Non-pressure pipes made of plastic material , especially those made of high-density polyethylene and polypropylene, have been widely used for decades following the advantages that are inherent in the raw materials constituting the pipes themselves.

Granules can be used in Recycled or virgin HDPE that has an MFI 0.4-0.7 at 190°/5 Kg., or in PP with MFI 1.5-2 at 230°/2.16 Kg. with correct thermal stability and the right quantity of carbon black.

The characteristics normally required in the design phase are:

• Resistance to external loads

• Resistance to chemical and electrochemical aggression

• Bidirectional sealing of the joints

• Hydraulic characteristics constant over time

• Reduced adhesion to encrustations

• Easy assembly and installation

• Reduced installation and maintenance costs

HDPE and PP pipes can be corrugated , i.e. have a reinforcing corrugation on the external part of the structure and a smooth finish on the internal part.

In the presence of large pipes it is possible to place a metal structure in the intrados of the corrugation with the aim of increasing the resistance of the product to the phenomenon called "creep" , which takes the form of a visco-elastic behavior of the material, with the consequent deformability temporary tube.

We mentioned the presence of the two layers of the tube, the corrugated external one and the smooth internal one, elements which therefore have two very distinct functions.

The smooth internal layer, in direct contact with the transported fluids, must have correct chemical and mechanical resistance towards the transported liquids and low sliding resistance.

The external layer, corrugated , has the function of counteracting the compression forces acting on the laid pipe, guaranteeing its durability and the absence of breakages.

In the case of reinforced pipes, a product developed in Japan in the 90s of the last century and subsequently widely used also in the United States, the characteristics of plastic materials such as resistance to abrasion, lightness, the minimum roughness coefficient, the inertness to chemical substances and ease of installation, to the characteristics of steel which has, for example, a much higher elastic modulus than polyethylene.

The use of PP instead of HDPE occurs due to small differences in the materials:

• Slightly higher elastic modulus

• Better behavior at high temperatures (but less so at low temperatures)

• Lower density and specific weight

Among the three characteristics listed, the difference in the elastic modulus is certainly the most important one, as the modulus influences the rigidity of the tube and therefore the resistance to compressive loads.

Therefore, for the same thicknesses, a higher elastic modulus corresponds to greater resistance to loads and, in the case of HDPE the instantaneous elastic modulus is normally > 800 MPa, while in PP it is > 1250 MPa.

As we have said, the pipes made of HDPE and PP have excellent hydraulic characteristics both in terms of the roughness of the walls in contact with the fluids, but also in terms of resistance to abrasion, guaranteeing a constant hydraulic flow rate and great durability of the sewer line.

Among the competitors of PP and HDPE pipes, such as cement, coated concrete, fiberglass, stoneware and PVC pipes , it has been verified, through laboratory tests, that the internal abrasion resistance is lower among the competitors therefore, these are subject to greater mechanical wear. Among these products, those composed of PVC have given results close to PP and HDPE pipes.

To give us an idea of what is meant by large diameter sewer pipes, we can say that on the market there are pipes with an external diameter of up to 2500 mm. and internal of 2400 mm. about.

When laying HDPE, PP and PVC pipes in trenches, the role of the substrate on which the line will be laid is fundamental , as these products are subject to visco-elastic mechanical behaviour, therefore subject to constant deformation over a defined time " creep”.

In the case of substrates that are not extremely compact or subject to small movements, the use of corrugated pipes with metal armor in the intrados of the corrugation can help to contain this phenomenon.

As regards the chemical characteristics of HDPE and PP pipes, we can say that the constituent materials have characteristics of resistance to electrochemical corrosion phenomena or to galvanic coupling, as they are not electrically conductive per se.

Category: news - technical - plastic - recycling - pipes - sewerage - HDPE - PP