HDPE Lining: A Protective Liner Fitted Inside the Concrete Pipe

HDPE, that is, high-density polyethylene, is a thermoplastic resistant to many chemicals. The sheet used as the lining has anchor projections on its back face. The sheet is fitted over the inner core of the mould, the concrete is placed, and as it sets these projections remain embedded in the concrete. The result is that the liner is not bonded to the concrete but interlocked with it.

Mechanical anchorage is a method that holds the liner to the concrete. Performance is assessed taking into account factors such as anchor geometry, weld seams and external water pressure.

One of the main reasons for its use is that the fluid conveyed, or the environment within the line, is chemically aggressive. HDPE is resistant to many chemicals; its suitability is assessed according to the type of chemical, its concentration, temperature and contact time. Appropriate liner and joint details limit contact between the aggressive environment and the concrete surface.

Biogenic sulphuric acid corrosion can also occur in domestic wastewater lines. Hydrogen sulphide formed under oxygen-free conditions can pass into the gas phase; by dissolving in the water film on moist surfaces, it can, under suitable conditions, lead to the formation of sulphuric acid through the action of microorganisms. An appropriate liner system is considered for protection against this effect.

• Applied in the factory: In these products, the liner is part of pipe production. Factory application makes quality control easier; the integrity of the line also depends on the quality of jointing and welding on site.
• Liner thickness and mechanical strength: Liner thickness and material properties are assessed against the mechanical effects expected during installation and operation.
• Continuity can be achieved at joints: Once the pipes have been joined, the liner ends can be welded together. In this way, protection does not stop at individual pipes but becomes continuous along the line. Joint zones are critical points at which continuity of protection must be ensured separately.
• Can contribute to hydraulic performance: In addition to surface roughness, the net cross-section after lining, the gradient and the joints are also taken into account.
• Broad chemical resistance: Beyond domestic wastewater, it is resistant to many of the chemicals encountered in industrial discharges.
• Contribution to service life: Appropriate material selection, joint details, application and maintenance contribute to the protection of the concrete body and to the intended service life.

In these BİR BE SAN products, the HDPE liner is applied during pipe production. The liner sheet is prepared on the mould core; the concrete is placed in the space behind the liner and compacted. The anchor projections of the sheet remain embedded in the concrete and provide mechanical retention.

The sequence in which the mould and liner are prepared is arranged to suit the production line. The liner surface, the encasement of the anchors in concrete and the joint zones are assessed together during production checks.

In these products, the internal surface protection is formed at the production stage. The extent of the lining and the joint details are defined in the product documentation; during installation, continuity of protection is ensured in accordance with these details.

The choice is made by assessing together chemical attack, temperature, geometry, joints and maintenance options:

• HDPE: Provides protection by means of an anchored liner and welding details. In these products, it is planned at the production stage.
• Epoxy: A surface coating that can also be considered for complex geometries. Chemical suitability, surface preparation and application thickness are determined for each product.

Within the same project, a liner may be used in the pipes and a different protective coating in manholes or special structures. Where different systems meet, continuity of protection is resolved separately.

• Wastewater lines in industrial zones and organised industrial zones
• Discharge structures and collector sewers exposed to chemical attack
• Main sewer lines where high H₂S levels are expected
• Rising main outlets and transition points with high turbulence
• Sea outfalls and coastal lines

An HDPE internal lining option is available in our product groups. For a level of protection suited to the wastewater characteristics of your line, you can consult our technical team.