There will be site-specific characteristics that influence the choice and suitability of using CIPP.
These will include: the number and location of access points and connections, the existence and characteristic of bends, the working space available above the line and along its alignment for equipment, site processing and product storage, and various environmental considerations which may include local restrictions on traffic flows, noise, dust and public safety issues.
There will also be important considerations about bypass of flows and temporary service provisions for residents and utility customers.
The availability and experience of the contractor will also be a factor.
We must also consider application specific requirements.
For drinking water lines these should include adequate provisions to safeguard the consumer from contaminants that may be injurious to health.
Chemicals used in the lining material must be adequately mixed and substantially cured in situ to ensure that any release of component materials into the water at the time of installation or subsequently during the service life of the water main is sufficiently below safe limits to minimise risk to the installer, consumers and the general public who may be accidentally exposed to them.
This author considers that the standards set in North America by NSF and under the EU Drinking Water Directorate should be met and maintained worldwide.
For sewer force mains the liner must be designed to withstand the cyclic stresses imposed over the working life of the main, the positive and negative surges associated with the pumping operations and the abrasion from particulate matter often conveyed of domestic and industrial sewerage.
Performance requirements are considered in a series of established classifications in US and European codes, Elzink and Gumbel amongst others have described in some detail the ISO 11295:2010 Independent and Interactive Classes A – D and
contrasted them with the AWWA M28 Manual Classes Non Structural (1), Semi Structural (2&3) and Structural (4). Elzink included a helpful chart (Fig 1) in his paper presented at Trenchless Asia in 2012.
Elzink further described the categories as follows: “Class A are independent liners, which do not rely on the existing pipeline for radial support.
They may be loose-fitting or close-fitting according to installation technique.
Class A liners are capable of surviving future structural failure of the host pipe and will then continue to carry the internal pressure loads over the remaining design life.
“Classes B and C are interactive liners, which are not capable on their own of resisting all applicable internal loads, and therefore rely on the existing pipeline for some measure of radial support.
A liner is considered interactive if, when tested independently from the host pipe, the long-term pressure strength is less than the maximum operating pressure of the rehabilitated pipeline.
An interactive pressure pipe liner is always a close-fitting installation.
Class B liners stand on their own, while Class C liners depend on adhesion to the old pipe’s interior.
The existing pipeline may contain holes or joint gaps, which can be bridged by the liner to a certain extent.
“Class D are liners which may improve the condition of the existing pipeline, but from a structural point of view they do not contribute at all.”
A brief history
CIPP has been used for rehabilitation of pressure lines from very early days, records kept by the UK pioneer Insituform Permaline list a lining installed in 1976 for a 600 mm cast-iron sewer force main for Thames Water.
The 2nd International No Dig Conference held in London in 1987 included a paper by Morinaga describing the development of PALTEM by Tokyo Gas in 1980 and listed over 1,000 km of hose-lining of gas and watermains.
That technology was taken into Europe by Osaka Bosui and into the US by Ashimori in the 1980s and 1990s, and gave rise to the Tubetex and Nordipipe technology used by Sekisui worldwide today.
Insituform utilised its felt liners with epoxy resins in many of its licensed territories and worked through a range of lining options including Kevlar fabric tubes and flexible resins to the glass and carbon fibre Insitumain products it offers today.
CIPP pressure liners appear to have developed along two principal strands, the Class B interactive hose liner and the Class C/D semi-structural and structural reinforced liners.
As it stands today, hose lining appears to work for hole and gap spanning applications where the external conditions are not expected to cause significant on-going deterioration of the original pipe, and where internal pressures are at the lower end of the application range.
Semi-structural and structural liners that are predominantly reinforced are suitable for hole and gap spanning at higher pressures and for stand-alone service, where the pressures are moderate and the pipes are small and medium diameter, up to about 1,200 mm.
High pressures and larger diameters are beyond the capability of all but the strongest materials available.
Semi-structural liners may be traditional felt and resin for the lowest pressure applications but are more usually glass reinforced felt or polyester fibre woven hoses.
Structural liners usually involve a woven glass or polymer fibre.
Resins are usually epoxy for potable water applications but may be vinyl ester resins for force mains, raw water or industrial pipelines.
These resins have enhanced tensile properties and better strain at first break than the polyester resins customarily used for gravity sewer applications.
Epoxy resins can be quite expensive, up to more than three times the price of polyester resin.
The materials have a shorter pot life, typically 12-24 hours, and they are sensitive to the working temperature and the liner thickness.
Careful mixing, using static mixers is recommended and refrigerated storage is essential for the security of the impregnated tube.
Vinyl ester resins are intermediate in cost when compared to polyester and epoxy resins.
The impact of engineered lining tubes, epoxy resins and skilful process controls is reflected in the market price of epoxy pressure pipe liners.
With CIPP there are associated safety issues and human health considerations in the use of engineering polymers; polyesters contain 30-50 per cent styrene, which has a low odour threshold and can be detected in just a few parts per million.
Styrene has been classified in the US as “÷reasonably anticipated to be a human carcinogen’.
There is much debate in the glass reinforced composites industry about the long term implications for human health.
NASSCO has published working practice guidelines to limit workers exposure and deal with short term spills into the environment.
There are similar concerns about Bisphenol A, Epichlorohydrin and other organic components in epoxy resins.
For potable water use, CIPP liners need extra care in batching, mixing and cure and have to undergo stringent water quality testing under protocols established by NSF, KIWA, UKDWI and other agencies.
Conclusions
Insertion of a reinforced CIPP liner can provide a durable semi-structural or structural pipe for small and mid-sized mains with a modest site footprint.
However, working periods may be extended due to curing, testing and disinfection.
The process of resin mixing, impregnation, installation and curing requires attention to detail and a high level of supervision to minimise any risks from the potentially hazardous chemicals of construction.
At the present time the backlog of ageing infrastructure is daunting.
Much of the low hanging fruit has been picked, good progress has been made in many countries tackling sewer flooding and water quality issues.
The upcoming challenge is how to deal with water, gas and sewer force mains and how best value can be obtained by launching programmes on a scale that can drive down costs of replacement.
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