NU FLOW TECHNOLOGY STOPS LEAKS, INCREASES FLOW, AND RENEWS ORIGINAL PIPE WITHOUT EXPENSIVE DIGGING OR DISRUPTION
Nu Flow Technology has the experience and technical knowledge to specify the right thickness and right resins to meet your specific needs regardless how deep the pipe or how corrosive the environment.
Resin formulas are custom specified to meet your specialized requirements…structural strength enhances structural strength of host pipe and acts as a stand-alone pipe meeting or exceeding test results using ASTM D790 as our benchmark.
The main alternative to
traditional sewer replacement involving trenching is cured-in-place lining,
sometimes referred to as ‘soft lining’ or ‘cured-in-place-pipe’ (CIPP),
which has dominated the non-man-entry sewer renovation market in many countries
for over twenty years. For brevity, these Guidelines refer to all cured-in-place
lining techniques as CIPP systems, although it should be noted that not all
providers of such systems use this term.
Although several competitive
systems are now available, the common feature is the use of a fabric tube
impregnated with polyester or epoxy resin. The tube is inserted into the
existing pipeline and inflated against the pipe wall, then cured either at
ambient temperature or by re-circulating hot water or steam. Some variations use
ultra-violet light to cure the resin.
CIPP systems create a close-fit
‘pipe-within-a-pipe’ which has quantifiable structural strength and can be
designed to suit various loading conditions. The ring-stiffness of the liner is
enhanced by the restraint provided by the host pipe and the surrounding ground,
but systems designed for gravity pipelines do not rely on a bond between the
liner and the substrate. Systems which rely on the host pipe for some measure of
structural support are sometimes known as `interactive lining’ techniques.
As well as minimizing bore
reduction, an inherent advantage of cured-in-place liners is their ability to
conform to almost any shape of pipe, making them suitable for relining
non-circular cross-sections. Provided that the liner perimeter has been
correctly measured and that the material does not shrink significantly during
cure, a close-fit liner should result. Their main limitation is the wall
thickness, and hence the quantity, weight and cost of material, which may be
required for larger sizes or for severe loading conditions, particularly in
Laterals can be re-opened remotely after lining, but care
must be taken during installation to ensure that surplus resin does not enter
branches. CIPP systems are also available for lining laterals from within the
The major disadvantage of CIPP
lining systems is the need to take the host pipe out of service during
installation and cure. In gravity pipes, where flows are very low, it may be
possible to plug any incoming pipes and to rely on the storage within the
system. In other cases flow diversion or over-pumping will generally be
One way to overcome service
intervention is with flow through plugs.
DESIGN & SPECIFICATION
Because liner specifications and
design procedures vary from country to country and are subject to periodic
amendment, it is outside the scope of these Guidelines to include reference to
all national standards.
In countries where established
local criteria do not exist, a widely-used standard is the Specification for
Renovation of Gravity Sewers by Lining with Cured-in-Place Pipes contained in
WIS 4-34-04, March 1995: Issue 2, published by WRc in the UK. Design procedures
for determining the required wall
thickness of circular and non-circular sections under different loading
conditions are given in the WRc Sewerage Rehabilitation Manual.
Specifications for pressure (gas
and water) applications are laid down by the relevant utility companies and
approvals bodies. Most countries have strict requirements and accreditation
procedures for all materials likely to come into contact with potable water.
INSTALLATION – GENERAL
As with all renovation systems,
thorough cleaning and preparation are essential prerequisites. In non-man-entry
sewers and other pipelines, inspection should be carried out by CCTV immediately
prior to relining – old surveys can be misleading. Man-entry sewers may be
surveyed by CCTV or manually.
All silt and debris must be
removed completely, and a further inspection is recommended after cleaning to
verify this. Care should be taken to avoid excessive pressures when using
jetting equipment in damaged sewers, since this can exacerbate the defects.
Intruding connections, encrustation and other hard deposits should be removed by
mechanical or high-pressure water cutting equipment, followed by cleaning to
remove the debris that this generates.
It is important to remove any
loose fragments of pipe which may fall in as the liner is being inserted. This
is particularly critical with ‘pulled in place’ liners where a broken piece
of pipe may fall onto the liner as it is being winched in, and then be trapped
between the liner and the pipe wall when the liner is inflated. Inverted liners
tend to cause less disturbance to the pipe fabric, but problems may still occur.
Most CIPP systems require flow
diversion during installation and cure. This period may be from a few hours to
over a day, depending on the system and the characteristics of the pipeline.
Lateral connections will be blocked by the liner until reopened, and provision
should be made for removing surcharged effluent if there is insufficient
capacity in the branch system. The build-up of effluent in a blocked lateral
creates an external pressure on the liner, which may be significant if the sewer
is deep. Measures may be required to limit the surcharge head.
Although CIPP systems are
trenchless and designed to minimize disruption, vehicles and plant are needed on
the surface throughout the installation procedure, especially at the entry
manhole. Traffic regulation may therefore be required.
There may be short-term
environmental implications with CIPP systems based on polyester resins, since
the styrene solvent present in the uncured resin gives off a heavy vapour with a
strong odour. However, although the vapour can be a health risk in high
concentrations, such levels are not typically found around CIPP installations.
Indeed, styrene vapour is detectable to humans at concentrations of less than
one part per million, and the odour becomes unbearably strong at levels below
those at which it represents a hazard. However, to avoid any nuisance, adequate
ventilation around the work site is essential. This problem applies only until
the resin has cured.
Polyester resins may be
adversely affected by water until they have cured, which may be of relevance in
a pipeline with infiltration or backed-up connections. In some cases, the use of
a ‘pre-liner’ (see below) can overcome problems of contamination.
Epoxy resins do not have any
environmental implication and are designed to stick to damp surfaces.
INSTALLATION IN SEWERS –
The following describes a
typical process for installing thermal-cured CIPP liners in sewers. Each
proprietary system has its own methodology, and the description below is
intended as a guide rather than as a statement of best practice.
The majority of thermal-cure
liners for gravity pipelines comprise a non-woven fabric – usually polyester
needle-felt – impregnated with resin. Some systems use a composite material
such as felt and glass-fibre. The formulation of the resin can be adapted to
suit different cure regimes and effluent characteristics.
The liner fabric is usually
coated on the outer face of the tube – which becomes part of the surface of a
liner – with a membrane of polyester, polyethylene, surlyn or polyurethane,
depending on the application. The membrane serves several functions – it
retains the resin during impregnation and transportation, it retains the air
during inflation, and it provides a low-friction, hydraulically efficient inner
surface to the finished liner. Some systems use a separate membrane rather than
an applied coating, and this may be removed after installation.
Impregnation is carried out in
the factory or onsite using rollers to ensure the uniform distribution of resin.
This is known as the wetting-out process. Depending on the characteristics of
the resin, the liner may be delivered to site in a refrigerated vehicle, to
prevent the curing reaction from starting prematurely.
Insertion into the existing
sewer is usually carried out either by winching into place or by an inversion
process. The following procedure is typical:
Some systems use a pre-liner
which is installed within the host pipe before inverting the impregnated liner
tube. The pre-liner is intended to stop surplus resin from entering lateral
connections, and it also prevents contamination of the uncured resin by water
infiltrating into the sewer or from surcharged connections.
Some systems involve winching in
the liner rather than using an inversion technique. Inversion may be difficult
in certain locations because of the need to create an adequate head of water,
and towing in the liner avoids the need for scaffold towers and overhead
working. However, there are limitations to the size and weight of liner which
can be winched in.
INSTALLATION IN SEWERS –
Ambient-cure lining systems are
used mainly for the renovation of small diameter sewers, drains and other
pipework, including vertical rainwater and soil pipes. They use similar fabrics
to thermal-cure systems – normally a coated felt – and most use resins which
are formulated to cure without the application of heat.
Ambient-cure systems avoid the
need for boilers or other heat sources, and therefore tend to be less expensive
than their thermal-cure counterparts.
The installation procedure is
generally as follows:
There are numerous variations on
the above theme, including portable pressure-vessels for inverting the inner
sleeve under air pressure.
Because of the low capital cost
of equipment, ambient-cure relining systems have become popular with many small
contractors as an alternative to carrying out drainage repairs by excavation.
CURED-IN-PLACE LINERS FOR WATER
AND GAS MAIN RENOVATION
The structural characteristics
required of a pressure pipe liner are quite different from those required of
sewer liners. The primary loading on sewer pipes is external, and the most
important structural parameters are elastic modulus and wall thickness which
together provide the ring stiffness to resist buckling.
Pressure pipes, except in small
diameters, fail less frequently through external loading. The most significant
forces on the pipe are generally caused by the internal pressure which creates
tensile stresses in the pipe or liner, and the most common pipe defects are
corrosion and leakage from joints. Pressure pipe liners do not generally require
as much ring stiffness as sewer liners, but they do need to withstand the
bursting forces generated by internal pressure.
For this reason, the fabric used
for CIPP pressure pipe liners tends to have a higher tensile strength than that
for sewer liners, and, because flexural stresses are not so critical, the wall
thickness of the liner is usually much less. Glass-fibre or a glass-fibre
composite is commonly used, except in woven hoselinings which generally use
The fabric of woven hoselinings
is normally impregnated with epoxy resin, rather than polyester, which may
produce an adhesive bond with the substrate and eliminates water-paths which
could allow internal corrosion to continue. Epoxies may also be more acceptable
in contact with potable water.
Most of the techniques aimed at
pressure-pipe renovation were initially developed for the gas market, mainly in
Japan, but several CIPP systems are now available to renovate potable water
The installation process is
similar in concept to the inversion method used for gravity pipe liners.
However, because pressure pipe liners are less bulky, it is possible to contain
the impregnated liner within a pressure vessel and to invert the liner through
the host pipe with compressed air. Curing is achieved by introducing steam into
In addition to the thin-walled
liners described above, there are also CIPP techniques using epoxy resins which
do not rely on a bond to the existing pipe wall. These systems develop their
strength from the composite action of the resin and fibres rather than a woven
jacket, and are designed to resist both internal pressure and external loading.
As an alternative to epoxy resin, vinyl ester resins are used for some