Sewerage renovation speeded up by UV curing

Dr John De Rosa of Subterra reports on European trials of an environmentally sustainable FastPatch repair system.

The UK’s Subterra and Inpipe Sweden AB have completed field trials of a prototype FastPatch system for the local repair of sewers using long-length patches that are cured by means of UV light. The work has been carried out with funds from the European Commission’s LIFE programme for the development of environmentally sustainable technologies.

Drawbacks of CIIP
Over the past 30 years, cured-in-place pipe (CIPP) lining systems have been developed for the in-situ repair of leaking (and structurally unsound) buried sewer networks. These CIPP systems typically comprise a felt tube impregnated with a suitable resin that is inflated in an existing, defective sewer pipe and cured in place to form a pipe within a pipe, either at ambient temperature, or by using hot air, hot water, steam or ultra-violet (UV) light.

Whilst this manhole-to-manhole lining has become a popular alternative to sewer pipeline replacement, it can be wasteful of resources where the sewer defect is localised. Local patch repair systems have been developed, typically based on cut-down versions of the full-length lining systems. Although more economical in terms of materials usage than their full-length counterparts, there are drawbacks. Specifically:

  • Many of the existing sewer patch repair systems require the patch material to be ‘wetted-out’ with raw resins on site. There is therefore an inherent risk of accidental spillage of unmixed resins and other components on the work site, with the associated potential for environmental damage;
  • Site-prepared sewer patch repair systems also pose a hazard for operatives who have to handle the uncured resins and associated materials under sometimes adverse environmental conditions, and also for the general public in the vicinity;
  • For site-prepared systems, it is difficult to ensure consistent product quality on site under all potential operating environmental conditions;
  • Most of the existing sewer patch repair systems rely on either on ambient curing or heat curing of the resin, once the prepared patch is positioned over the defect. Both of these processes tend to be relatively slow, typically taking upwards of one hour, during which period the patch installation equipment necessarily remains tied to the patch being installed, and cannot be moved to the next repair site until the patch has sufficiently cured, which can be socially and commercial disruptive.
In particular, those systems that can repair relatively long localised sewer defects (say, 1-3 metres long) are generally associated with relatively long curing times (1-3 hours depending on the method of cure), whilst those patch systems that rely on UV for a more rapid cure are limited in the length of patch that can be installed by the configuration of the curing equipment.

Key features
The prototype system comprises two key innovations, namely:

  • a fully-flexible, 2.0 metre long inflatable packer containing UV-lamps that is capable of inducing a satisfactory cure of a UV sewer repair patch in under 15 minutes.
  • a UV-cured patch based on a simple adaptation of a commercially available, high performance full-length sewer liner produced by Inpipe giving an effective seal against sewer exfiltration and infiltration.
The prototype UV-cured repair patch installation system met all of the project partners’ original design objectives. In particular, it was shown that a repair patch whose length is greater than the internal diameter of the access manhole chamber, can be installed and cured by means of ultra-violet light using a fully flexible, inflatable packer of an innovative design. The curing time was found to be well within the original installation production target of 15 minutes.

Leak-tightness tests of the annulus between the host pipe and the installed UV-cured repair patch have shown that the patch is capable of effectively sealing sewer pipe defects against an external head of groundwater of at least 5 metres (0.5 bar) (the European Standard for new sewer pipeline joints). The prototype system therefore met the project partners’ objective of providing a cost-effective, rapid curing, local patch repair alternative to the lining of complete manhole-to-manhole sewer lengths as means of eliminating infiltration into and/or exfiltration from leaking sewers.

A focused Life Cycle Assessment comparison of the prototype UV-cured sewer patch repair system with two other alternative patch repair techniques (based on steam or ambient cure) has shown that, for similar applications, the prototype UV-cured system is more environmentally friendly than the other two alternatives, owing to the greater rate of patch installation that can potentially be achieved using UV light.

Factory production of the UV-cured patch product minimises the risk of accidental spillage of chemicals into the environment that is associated with other, site-prepared patch systems. The encapsulated design of the prototype UV-cured patch also effectively eliminates any risk of the repair system operatives (or the general public in the vicinity) coming into contact with uncured resin (and/or glass fibre) materials.

Analysis has shown that the prototype UV-cured patch repair system is cost-competitive with other sewer patch repair systems, due to the greater rate of installation that can be achieved by UV-curing.

Environmental benefits include reduced groundwater pollution; negligible emissions on site - resin impregnation of patch carried out in the factory under strictly controlled conditions and delivered to site in sealed packages (compare with systems involving wetting-out with resin on site immediately prior to patch installation).

There is also negligible risk of environmental damage due to spillage of uncured resin on site Factory-prepared and individually packed patch technology is consistent with EC regulations on emissions into the environment; UV-curing requires little energy and can be rapidly installed thus keeping disruption of local communities to a minimum. In terms of costs, localised patch repair can return the sewer condition to a higher grade at less cost per unit length than full-length liners.


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