Installation Methods of The High-density Polyethylene Liner

Installation method of the high-density polyethylene liner can be passed through into the existing pipe by using two techniques. However, sometimes both techniques are required in together to speed up the project steps. The pushed and pulled techniques are the most common in this matter that is used to keep the liner in place. In pushing technique, for water-tight sealing a gasket jointed profile pipe need to be introduced.

This method consists of some arrangements like cable and winch. The winch arrangement with the cable pulled into the existing pipe for slip-lining. The cable is attached with the segment on the other side and the cable with the polyethene liner need to pull through the existing or host pipe with the help of winch arrangement. The cable is fastened with this arrangement to make the pulling method into the right position.

To facilitate this pulling technique a pulling head is required to attach the cable. There are different types of pulling heads that are available in the market. Types can be varied in project to project based on the nature of the work condition and site environment. It also depends on the project budget especially in installation process. Among them leading edge footage liner that attached with a leading central bolt in one side and liner in other end is the classiest pulling head. A steel pulling head relates to the liner with the help of some bolts. The main purpose of this head is to ensure the uniform load on the liner wall. The conical shape of pulling head facilitates the new pipe to go through the host pipe. It also adjusts the minor deflections in liners. Diameter of this head must be same as the liner diameter or lower than the outside diameter (OD). This helps to pull the pipe smoothly when it inserted into the host.

Due to the pulling process, an elongation may occur in polyethene liner. For that reason, it is recommended that left the liner minimum twenty-four hours rest after elongation. Polyethene liner should be extend 3-5% more than the existing pull to keep the safe due to the reduction instinct when it gets back to its normal position (PPI, 2008). In the large diameter and heavy welded joint connection lining, this process may not perform well so on the longer pipe system.

A bend strap is installed around the liner wall that helps to push into the host. Construction vehicle such as back hoe or track hoe is used to pull the pipe and push into right direction through the pipe. Sometimes other equipment is used to push the liner.

Vehicle stroke the pipe after it has been connected to the belt. Strap need to be placed in position after each stroke. Placement of the strap is done by manually. The whole process can be completed with the help of the combination of a front head loader and a bulldozer.

In this process gasket pipe is used to make the proper place and ensure water-tight condition. This system does not require any cable and hoist to push the liner through the existing system. However due to the project nature or other circumstances both push and pull techniques sometimes need to be applied simultaneously. This technique is more efficient when polyethene liner is pulled through a large diameter host where need heavy pulling instruments. Pushing or pulling flow speed is not same in the entire system. The flow speed while positioning the line into the system is different than the flow in the pipe while it moves through the host. It is recommended that flow speed should be kept in a level in the entire system that it does not exceed the 50% of pipe capacity. When liner is placed into the host annular space provide sufficient flow to carry the liner. At the end of the lining system, upstream blockage flows need to be controlled to avoid flooding. Pump station, flow control equipment, bypass system can mitigate and control the flow system during this technique.

There are different types of method to connect the laterals and home service with liner. Types of connection depend on liner and lateral line properties. When liner passes through the host line, restoration work starts after a certain time. As polyethene has the instinct to expand in pushing or pulling and return to its original position while in rest, for that reason restoration work need to be start after 24 hours of liner placing. In pressure pipe line connection made with pressure rated pipe line. This type of connection requires the capability to take full pressure. A polyethene branch saddle is placed on the top of the liner hole that connect to the lateral line. The connection is made by using either a tees or side wall bonding branch saddles with connectors.

Sometimes spool pieces are inserted by using electrofusion process. Existing pipe is removed from the connection place to connect laterals. When connected to laterals with HDPE, joint of line should fixed by using wrap around saddle. In gravity pipe line, a stainless-steel band is used that placed on the connecting point on the liner with a gasket. The saddle base and the liner then welded to confirm the joint integrity. After that flexible coupling is used to connect the service lateral with the new polyethylene pipe. The service saddle method is common in gravity pipe line where gasket and steel band clamps are used.

Reconnection of new valves and the existing pipe at the end of project: Reconnection with the existing pipe is the final stage of slip lining process where connection is conducted by using fittings and flanges. Reconnection of the pipe system may follow either in heat fusion method or in mechanical fittings. Connection must be made in such a way that reduces the point load at joint. There are different types of techniques that reconnect the system confirms the continuation of existing pressure flow. Connection methods may have varied based on pipe diameter of the system. In pressurized pipe network connection is made by using some specific accessories. Fusion technology is used to reconnect the pressurized pipe.

There are three methods in fusion technology that commonly used to connect the liner to the existing system. Besides butt, saddle and socket fusion, electrofusion method is also used with the help of couplings and saddle fittings. Fusion system bond the liner and existing pipe surface by using heat at specific temperature and force. This method keeps the joint area structurally sound and ensures leak protection. System is ready to run as soon as the joint return to its normal temperature. In Butt fusion method heat and force is applied after cleaning the end of the pipes. Liner and existing pipe need to hold until the joint temperature is cool.

After cooling the joint area, a bead between two pipes are formed. The type of this bead is called fusion bead. It is important to check the bead thickness that ensures the proper.

At the end of the process, sometime external and internal bead are removed from the joint by using run-around planning tools. In saddle fusion connection method heat needs to be applied in the external pipe and the saddle surface. Heat is continued until the proper bonding temperature. A special machine called saddle fusion is required to accomplish this job.

On the other, Heat needs to apply on both external pipe surface and internal fittings area in socket fusion method. At certain temperature when fittings are melted, pipe end then insert to this area and hold it until it gets sufficient bond strength. As like the other methods the pipe end and the fittings inner part need to be clean. In electrofusion method, the heating system is different than the conventional method. Heat is being conducted internally rather than outside heating system. This can be done by using a heating conductor or polymer at the internal joint area. Electric current is applied to generate the heat inside the apparatus and pipe. Connection made between the pipe and pipe connections due to the electrofusion couplings.

There are different types of methods that commonly used to connect the existing pipe. In addition, the selection of fittings is also important that create impact on the bonding system. For small size diameter pipe, mechanical compression coupling is an option to connect the system. In this method due to the compression of seal ring around the pipe causes pressure tight seal in the joint. The wall around the joint should be fixed tightly by stiffener and ring that protect the deformation.

Bolt mechanical coupling joint method can bond different types of pipe such as PVC, steel, cast iron etc. This system seals the joint by using a combination of compression and elastomeric gasket that is applied around the pipe joint. A stiffener is also needed that support the sealing ring area and other gripping devices. When line is connected to the existing ductile iron or PVC pipe, the stiffener should add inside the pipe that insures sound bonding. In flange joint method an adapter called Flange Adapter is used to connect the PE liner with metal or other types of pipe. The diameter of the flange is same as PE pipe diameter at one side and the other side it has flange type diameter. Flange provision gives the structural support to the joint. Stiffener is not needed in this method where it has its own back-up ring. A flange gasket and flange bolt are required to install the flange adapter. It is recommended that when PE liner is connected to the cast iron the tightening torque should not be exceed 10 ft-lbs. Excess torque may cause a bending stress in the connection place.

To connect the ductile iron pipe solid sleeves fittings can be used at the joint area. This fitting has a flange or a mechanical hub that connect the pipe. The flange called mega lug and gasket are installed at the ductile iron pipe end. Whereas One Bolt solid sleeves design has a special ring that prevent liner to pullout. A stiffener is placed in the liner pipe for better stability. This installation method is very quick rather than other system. When liner is joined to the existing valves or pipes, a mechanical joint adaptor is used to the system. Before bonding the joint a ring is placed at the back of the adaptor. Other joining method is called transition fitting which is applied to connect between the liner and the metal pipe. This fitting consists of the combination of an adapter with an O-ring and a retainer. Fittings are available in various sizes and the joint is welded after the connection.

There are some methods also need to be implemented that prevent the pipe disjoining. The restraint joint technique is used in all connection system such as fusion, electrofusion, socket fusion etc. Wall anchor, mechanical restraint anchor, buried poly anchor, above ground pipeline anchor are the most common restraint method that is applied in line joining. In gravity pipe lines, there is no need to install the above-mentioned connection features. Only annular space that exists around the pipe is required to seal to prevent the infiltration. Sealing materials also prevent the buckling of the liner.