Semi-structural spray lining
In recent trials, DVS Pipelines has shown the advantages of a spray-applied, semi-structural lining developed for the rehabilitation of water and wastewater pipes
The rehabilitation techniques available to water undertakers have always been limited to non-structural spray lining (to resolve water-quality issues) or replacement or inserted polyethylene technologies. The decision to spray line or replace has historically been made by determination of the residual asset life on the basis of a simple corrosion model predicting the time for full-wall penetration to occur.
Non-structural spray lining – the scrape-and-line process – provides a minimum cost solution but assumes the host pipe maintains adequate structural integrity. Replacement or polyethylene technologies effectively provide a new asset but can be disadvantaged by cost, disruption and low productivity, particularly in urban areas where extensive service connection reinstatement is inevitable.
A next-generation rapid-setting polymeric spray lining has been developed, which provides a semi-structural alternative to existing technologies. Reinstatement of service connections is obviated, and the ductility of the material ensures longitudinal continuity is maintained in the event of local damage to the host pipe. The new polymeric spray lining was developed by E Wood in conjunction with DVS Pipelines, which was responsible for the implementation of the trials discussed in this article.
Insitu spray lining is a method of lining pipes with a thin layer of resin (typically 1mm thick), which is sprayed on to the inner surface of a cleaned main. This isolates the host pipe from the conveyed medium, water, and prevents leakage and infiltration, protecting water quality.
However, the 1mm lining confers little structural support to the rehabilitated pipe. And, while there is a requirement for structural support, historically, it has not been possible to apply thicker coatings in a single pass.
However, E Wood has developed a lining, known as Copon Hycote 169 HB, which can be applied to a depth of 3mm. It is approved under Regulation 31(4) (a) of the Water Supply (Water Quality) Regulations 2000 for contact with potable water. The new 3mm lining provides all of the benefits of a sprayed lining with the additional advantage of structural support.
To test the claims for substantial structural support, Copon Hycote 169 HB was applied at 3mm to a 150mm cast-iron pipe that has then subjected to a transverse shear displacement of 25% of the pipe diameter. (Figure 1).
Despite this significant invasion, the pipe maintained it longitudinal continuity (Figure 2). Semi-structural pipe spraying (SSPS) is a no-dig technique that enables pipeline reinstatement within a single working day. The application procedure can be summarised as:
n Pipe cleaning
n Pipe checked by CCTV survey
n Spray lining plus curing (1h/150m)
n Post lining survey
n Return to service
DVS Pipelines was commissioned to rehabilitate around 1.8km of mainly 152mm iron and FRC water main in Ireland over a short period either side of Christmas 2005.
Early results indicate that SSPS looks set to command a significant share of the pipeline rehabilitation market.
SSPS was not originally specified within the project, however the water undertaker became aware of the technique during 2004 and decided that the potential benefits offered by the process were sufficient to justify a full trial.
Initially, a few teething problems were experienced because the polymer lining had run slightly resulting in an irregular surface. However, DVS and E Wood made a slight alteration to the technique and the problem was eradicated.
Speed is a key feature of the SSPS process, not least because unlike most other rehabilitation techniques such as pipe bursting, directional drilling and open cut, service pipe connections do not have to be reconnected. The spraying process does not block the ferrules and as a consequence, it is possible to rehabilitate pipes and return them to service within a single day.
Once a successful application technique had been established, WRc assessed the SSPS of the pipes and as a result DVS Pipelines is now the first approved contractor for the application of 3mm semi-structural polymeric pipe lining systems in a single pass.
DVS has successfully conducted manhole to manhole rehabilitation of both cast iron and bonded asbestos cement (BAC) sewers using insitu polymeric spray lining copon 169 SL (a similar formulation to the 169 HB used in clean-water applications). Copon 169 SL was developed as a solution to the increasing problem of infiltration into the sewerage system.
While conventional no-dig lining techniques consolidate the strength of the
host pipe, conventional cured-in-place liners offer little protection from infiltration due to liner shrinkage. DVS Pipelines claims that the advantage of the polymeric spray lining system is that there is no liner shrinkage, thereby mitigating groundwater flows from entering the sewer annulus between the liner and host pipe.
The rehabilitation work was conducted in an area in which sewers are constructed primarily from BAC pipes. There had previously been instances of flooding and pollution within the catchment and this was partly attributed to high levels of infiltration into the sewerage system.
Research has shown that one of the main disadvantages with BAC pipes is the inability of the joints to resist leaks. The pipe joints typically use a natural rubber ring to form a seal, which can prematurely deteriorate over time from attack by alkalis in the groundwater and sewage itself. This can give rise to significant quantities of groundwater infiltration.
BAC pipes are often found to be in reasonable structural condition however because the joints tend to be the weak point, localised joint sealing has generally been the favoured solution in the past. However, the long-term benefits of joint sealing are not clear and consequently a more permanent solution was required to deal with such a significant problem.
Previously, the only way to remove such a joint problem would be to remove all BAC pipes and relay in a modern material. However, this would have major cost implications and would cause widespread disruption to the local community. In addition, the safe disposal of large quantities of asbestos-containing pipes would represent a significant health and safety issue.
Thames Water has conducted trials on the application of the 3mm polymeric lining in test rigs to replicate a sewer situation. Technical consultant for sewerage, Don Ridgers, says: “Our work has indicated that spray lining sewers may offer good protection from corrosion and encrustation in cast-iron pipes. Our current plans are to roll out this application to a full field trial.”
Looking forward, DVS operations director Peter Neen says: “Initial work with the new formulation polyurethane looks set to have a major impact on the pipeline rehabilitation market.
“The new thicker linings provide structural enhancements and thereby offer major advantages to both the clean and wastewater sectors. It is highly likely that this technique will become the rehabilitation method of choice in a large number of circumstances.”