1.
Close fit
The technique is intended to make the inserted liner fit tightly inside the existing pipe.
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Close-fit Lining
A lining technique using a temporarily deformed or reduced pipe that is subsequently restored to fit closely against the existing pipeline.
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Close-fit lining uses a liner pipe deliberately deformed before insertion and then restored toward its original shape after installation.
1.
2.
Temporary reduction
Pipe diameter can be reduced by rollers, tooling or compression and then allowed to recover after insertion.
3.
Fold and re-form
Some systems use pipe folded into a “U” or “C” shape and subsequently restore its circular form using heat or pressure.
Concept of close-fit lining
Using a liner pipe deliberately deformed before insertion and subsequently restored toward its original form allows the liner to fit closely against the existing pipe.
This process is known as close-fit lining and is also described as modified sliplining.
These methods are a logical development of basic sliplining and can be used in both gravity and pressure pipelines.
Diameter reduction and recovery
The pipe diameter is reduced by passing it through rollers or tooling. After insertion, the pipe recovers toward its original dimensions.
Close-fit systems often make use of the shape-memory characteristics of polymers used in pipe manufacture.
The principal objective is to produce a tight-fitting liner that maximizes the final internal diameter and avoids the need for annular grouting.
Compression-reduced pipe
One approach temporarily reduces the liner diameter by roller compression, sometimes described as a reduced-diameter process.
The reduction allows the liner to be inserted into the existing pipe and subsequently recover toward its normal dimensions.
Because of the limits on achievable dimensional reduction, this approach is generally better suited to pressure pipelines than to sewers with significant dimensional irregularities.
Fold and re-form
A second approach folds the liner into a “U” or “C” shape before insertion.
After installation, heat or pressure is used to restore the pipe to a circular form.
This technique is commonly referred to as fold-and-form.
Materials and process variations
Liner diameter and wall thickness are the main limitations of this process.
Variants are available for polyethylene and PVC and can be applied to pressure pipelines and gravity sewers.
In addition to these two principal types, other systems use different folded configurations or thermoplastic materials capable of expanding to a close fit after insertion.
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