Installation Methods of The High-density Polyethylene Liner

High-density polyethylene (HDPE) liners are widely used in various applications, particularly in the rehabilitation of existing pipelines. The installation methods for these liners are crucial for ensuring their effectiveness and longevity. This essay discusses the primary techniques for installing HDPE liners, emphasizing the pushing and pulling methods, their components, and considerations during installation.

Installation Techniques for HDPE Liners

The installation of HDPE liners can typically be accomplished through two primary methods: pushing and pulling. In some cases, both techniques may be employed simultaneously to enhance efficiency and expedite the project timeline. The choice of method often depends on the specific conditions of the existing pipeline, the type of liner being used, and the project budget.

Pushing Technique

The pushing technique involves the use of a gasket-jointed profile pipe to create a water-tight seal. This method is effective for shorter distances and is often utilized when the existing pipeline is in relatively good condition. Key components of the pushing method include:

• Gasket-jointed profile pipe
• Pushing equipment, such as hydraulic jacks or construction vehicles
• Support structures, like bend straps, to guide the liner

During the pushing process, the liner is inserted into the existing pipe while ensuring a secure connection is maintained. A construction vehicle, like a backhoe or a track hoe, is often used to facilitate the movement of the liner into position.

Pulling Technique

The pulling technique, on the other hand, employs a winch system and cable to draw the HDPE liner through the existing pipeline. This method is advantageous for longer distances and when the conditions of the existing pipe are less favorable. The pulling process involves several components:

• Cable and winch system
• Pulling head, which connects the cable to the liner
• Supporting structures to maintain the liner's alignment

The pulling head is a critical component that ensures the uniform distribution of load along the liner wall. Various types of pulling heads are available, each suited for different project requirements. For example, a leading edge footage liner is commonly used, which features a central bolt on one end and the liner on the other. The conical shape of the pulling head allows for smooth passage through the host pipe, accommodating minor deflections in the liner.

Considerations During Installation

When installing HDPE liners, several factors must be taken into account to ensure a successful operation:

Additionally, the installation should adhere to safety standards and project specifications to prevent complications during and after the installation process.

Connecting Laterals and Home Services

Once the HDPE liner is in place, connecting laterals and home services becomes the next step. The type of connection depends on the properties of both the liner and the lateral lines. Common methods include:

• Using polyethylene branch saddles for pressure-rated pipeline connections
• Inserting spool pieces using electrofusion processes
• Employing stainless-steel bands for gravity pipelines

When connecting to laterals, it is crucial to start restoration work after the liner has settled for a minimum of 24 hours to account for any natural contraction or expansion of the material. Proper installation techniques, such as using tees or side wall bonding saddles, are essential for maintaining the integrity of the connections.

Reconnection of New Valves and Existing Pipes

The final stage of the installation process involves reconnecting the newly installed HDPE liner to the existing pipe system. This reconnection can be achieved using various methods:

• Heat fusion methods
• Mechanical fittings

Each method must be executed with precision to reduce the point load at the joint, ensuring a seamless flow in the pipeline. The choice of method may vary depending on the pipe diameter and material.

Fusion Technology for Connection

Fusion technology is a widely used method for connecting HDPE liners to existing systems. Three common fusion techniques include:

• Butt fusion
• Saddle fusion
• Socket fusion

These methods utilize heat and pressure to bond the liner to the existing pipe surface, creating a structurally sound joint that is resistant to leaks. The application of heat is crucial, and once the joint returns to its normal temperature, the system is ready for operation.

Conclusion

In conclusion, the installation of high-density polyethylene liners is a complex process that requires careful planning and execution. The choice between pushing and pulling techniques, along with the appropriate connection methods, plays a significant role in the success of the project. By adhering to industry standards and best practices, contractors can ensure that the installed liners perform effectively, providing a durable solution for pipeline rehabilitation.

References:

• PPI (2008). "Guidelines for the Installation of High-Density Polyethylene (HDPE) Liners."
• ASTM International. "Standard Guide for the Installation of HDPE Pipe."
• American Water Works Association. "HDPE Pipe and Fittings: Guidelines for Design and Installation."