ON LINE REPLACEMENT
On line replacement is replacing existing pipes with the same size pipe, or upsizing, without trenching. In some cases, this operation can be carried out whilst the pipeline being replaced remains in operation.
Pipe bursting or pipe splitting has been developed to exploit the existing hole-in-the-ground. Pipes are split using a pneumatic rammer or hydraulic reamer, displacing the existing pipe material to enable a new pipeline (usually polyethylene) to be drawn in.
Upsizing from 100mm to 200mm, and 200mm to 300mm is now well established, and pipes up to 600mm in diameter have been replaced.
Pipe eating is an on-line microtunnelling replacement technique. The existing, defective pipeline is crushed and removed through the new pipeline, which is installed at the same time. Concrete pipes of diameter 300mm to 500mm have been replaced by 600mm and 750mm pipes in lines up to 100 meters.
RENOVATION OF EXISTING PIPELINES
Where the hydraulic capacity of a pipeline is satisfactory, and the existing pipeline, although defective, has some structural value, repairs may be appropriate.
A new pipeline of smaller diameter is inserted into the defective pipe and the annulus grouted. This is simple and inexpensive, but reduces hydraulic capacity. Roll-down and swage lining, two modified slip lining processes, use the property of polyethylene pipes to be temporarily reduced in diameter prior to insertion into the defective pipe.
The pipes subsequently expand to form a tight fit. These systems are typically used for renovating 100m and 150m diameter water mains and gas mains.
Cured In Place Lining
This is a widely used structural renovation system using a resin impregnated sock inserted in the pipe and subsequently forced against the wall using water or air. Curing of the resin occurs by heat or ultra-violet light.
This method is used for renovating pipe from 50mm to 750mm diameter, and pipes do not need to be round. When a pipe is structurally sound, and a liner is only necessary to prevent leakage, a loose fit, reinforced hose can be used.
This is pulled through the existing line in a collapsed state and pressured when in position. This system has application in the range 100mm to 355mm diameter. Other insitu formed liners include:
- spirally wound PVC strips
- PVC “U” shaped liners
Spirally Wound Liners
Spirally wound liners are formed by taking a strip of plastic and winding it, locking the edges together to form a “pipe within a pipe.”
The most advanced forms of this technology can be expanded to maximize the liners internal diameter, or are wound by a machine that traverses the pipeline winding the liner against the pipe wall.