Pressure pipelines slowly start to become a potential threat to our daily life as they age. Watermains may burst, potentially disrupting traffic; gas mains may explode, causing an even greater risk. Instead of waiting until it’s too late, many companies have started taking proactive measures. Over time pipeline rehabilitation, in particular trenchless pipeline renovation, can save a lot of hassle and money.
Close-fit lining
Techniques belonging to the close-fit lining family were developed from traditional sliplining, but with the intent of avoiding the substantial reduction in diameter that comes with this technique.
For pressure pipe applications, polyethylene (PE) is generally the choice of pipe material because of its excellent memory ability and relatively high flexibility.
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There are two options for reducing the cross-section: onsite or in the pipe manufacturing plant.
A common technique utilising reduction onsite is swagelining, and a common technique utilising reduction in the pipe factory is Compact Pipe.
Both techniques have widespread use, particularly in pressure pipe applications, where they generally produce a new independent close-fit pipe.
Quality assurance of plastic liners
The approach taken by International Standardisation Organisation (ISO) is to provide standards that demonstrate and assure the long-term quality of the liners in their manufactured state and installed state.
In order to tackle performance in the installed state, two distinct stages are recognised:
- M stage – stage as manufactured
- I stage – stage as installed.
The approval of installed products before they have even been installed is quite unique in pipeline construction, even with newly installed pipes. Type tests should demonstrate that all characteristics of the product conform to requirements given in the respective standard.
Batch release tests should be performed by the manufacturer at the start of production for each batch of pipes, which have to be satisfactorily completed before the batch can be released.
By using the ISO standards, which assure the quality of the liner product both at the M stage and the I stage, installers nowadays are capable of demonstrating the viability of the installed liners.
Once installed, the pipe is camera-inspected to check the geometric shape and then tightness-tested to make sure that a leak-free new pipeline has been achieved.
Conclusions
Today, Trenchless Technologies are being used widely to rehabilitate existing underground assets. Close-fit lining techniques are enjoying increasing popularity, particularly for pressure pipelines in urban areas.
The recently published ISO standards for pipeline renovation require product characteristics to be tested both at the as-manufactured M stage and the as-installed I stage.
These standards also ensure that the quality assurance after installation of close-fit liners is now possible.
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