A resin saturated lining tube is installed in a pipeline by pull in place or inversion and once in place the resin is usually heated to induce a chemical catalyst or hardener set off the curing process. The curing process is usually by hot water, steam or UV light for hot cured methods while ambient cured technologies can be used for smaller diameter renovation projects e.g. house drain connections to sewers.
CIPP Lining techniques can be used to renovate most gravity pipelines and culverts and pressure pipelines used for utility services such as water, sewage and gas as well as other process effluents pipelines e.g. food and drink industries; oil and gas etc. In general, circular pipes from 2” to 100” diameter can be lined depending on the curing methods available. In addition, non-circular pipelines such as egg-shape, other ovoid and box culvert sections can be lined.
To install a CIPP liner, inflation or inversion techniques using air or water pressure may be used.
The installation length can vary from short sections over a joint or defect for a localized repair to full length linings typically 10 feet to 600 feet although lengths of up to 3000 feet have been installed in a single operation.
This technique was invented by Eric Woods in the early 1970’s, the liner being pulled in to the pipe or inverted and then cured under pressure. Over the years, techniques and installation methods have developed, however the end result is a new pipe, inside an old pipe.
A CIPP liner can be designed withstand the total load imposed on the host pipe by external groundwater pressure, internal service pressure (if any) and ground and traffic loading – thus achieving ‘a pipe within a pipe’ structural solution. In some cases where the host pipe is structurally sound, a thinner lining can be designed as a non-structural lining solution to address infiltration.
Prior to lining with a CIPP technique, the pipeline must be removed from service for the duration of the installation, curing and re-commissioning processes and over pumping, diversion or tankering may be required to achieve this. The pipeline must then be cleaned usually by high pressure water jetting or manually (size dependent) to remove any debris, corrosion or other materials from the pipeline as a close ‘fit’ to the host pipe is essential to ensure structural integrity and maintain water tightness where appropriate. Any intruding or defective lateral connections also must be removed and may need repairing prior to the lining process commences. If a pipeline is deformed by more than 10% of its diameter or height, the defective section(s) must be re-rounded before lining proceeds. Similarly large areas of damage may require attention and localized repair before renovation of the full length is progressed. Water infiltration through defective joints and/or other defects may need to be addressed to ensure that the lining does not fail during the curing process.
The CIPP liner is made of a non-woven polyester needle felt or glass fiber although for pressure pipes it is normal to provide a woven product to ensure extra strength to withstand the internal pressures within the pipeline. A coating made from PU, PE or PVC protects the liner during transportation and installation procedures. The factory prepared liner is impregnated with a polyester, vinyl ester, epoxy or silicate resin, which has been mixed either in a vat or through static mixers, often using a vacuum pressure method and roller to ensure the full thickness and full length of the liner is saturated. This process takes place either in the factory and then the liner is transported to site. If the impregnation takes place at the job site e.g. for a short, small diameter pipeline, it is undertaken either in a truck or using a small table adjacent to the pipeline access manhole or chamber.
The resin will include a chemical catalyst help start the curing process, depending on the curing type i.e. hot water, steam, UV or ambient cure. Apart from UV cured liners, transportation to a site should be by a refrigerated vehicle to ensure that curing is not triggered by premature heat. Such liners usually have a shelf life of 2 to 3 weeks while liners for UV curing can be stored in cool, light excluded containers for up to 6 months.
A liner is either pulled or inverted into place and inflated with compressed air or water. Afterward, the liner is inverted into the host pipeline using air pressure through a drum or liner gun/shooter or historically, from a water scaffold tower using static water pressure to push the liner through the pipeline. The height of the scaffold tower is determined by the water pressure required for the liner to reach the furthest point of lining. Care is required with any insertion method to avoid fast inflation which could lead to stretching of the liner, wrinkling of the liner around bends and in the case of large sized liners an H&S hazard.
Curing of Lining
An important part of the process is the curing of the liner with resin. Early forms of ambient curing required the liner to be left under pressure overnight, however there were risks with pressure loss and possible collapse as well as issues regarding the time factor and production rate. Hence improved curing techniques have been developed.
Hot Water: A boiler varying in size, circulates hot water through the liner. These boilers vary from small 90kw to large 3 million BTU, depending on the volume of water required to be heated. Curing temperatures vary depending on the resin but are in the order of 85°C for polyester and 65°C to 70°C for epoxy resin curing.
Steam: Instead of using a hot water boiler, a steam boiler or generator is used. The advantages of steam are that the curing time is much faster, however the liner used must have a coating resistant to steam. With some use of other resins, steam curing can also make the finished product stronger that those cured with hot water.
Ultra Violet Light (UV): UV technology has developed over recent years and is the favored method of installation and curing for CIPP lining in countries such as Germany. The liner tube material is a combination of non-woven felt and fiberglass, impregnated at the manufacturer’s plant before being shipped to the installation team in black plastic covers inside boxes to prevent exposure to sunlight. The liner is pulled into place inside the pipe, inflated with air to allow a UV light train to pass through the inflated liner. The light train is controlled by computer and allows UV light to penetrate the polyester resin impregnated liner – the resin having a light sensitive catalyst added. Once the UV light comes in contact with the lining, curing commences – the technique is fast and once the light train has passed a point, the lining at that point is cured consequently the operator does not have to wait until a number of hours for curing of the full pipeline. Generally, the UV liners use higher quality resins etc. and are of a thinner thickness design than standard non-woven liners which in turn can be a major benefit for larger diameter pipe renovation.
Post Curing Actions
After the lining has cured, the liner is allowed to cool before the ends are cut and removed flush with the pipe ends and sealed if required – it is essential that the liner is cool before it is cut, in the unlikely case that shrinkage occurs after cutting. The waste curing water or steam condensate and the trimmings cut from the liner are removed for safe disposal. A sample of the CIPP liner should be taken from the pipe ends or from a mold cured in the access chamber say, for testing purposes and to verify the liner has met its performance specifications.
Service connections and laterals are reinstated once curing has been completed and the pipeline is returned to service. Similarly, lined water mains must be disinfected to the appropriate standards before returning to service.
Lining of Lateral Connections
The CIPP lining of laterals is to pipes usually of 100mm or 150mm diameter and 5m to 20m in length, however many of these pipelines have bends varying from 45° to 90°.
The process of lining lateral pipes started as an extension of mainline CIPP lining in the 1990’s. Initially the non-woven liner was impregnated with a polyester resin and dragged or pushed into the pipe. The installation operator would then use a piece of pipe to ‘invert’ a calibration hose into the liner – this is a PVC plastic tube liner that expands under water or air pressure to the size of the CIPP liner inside the pipe. Once the liner is cured the calibration hose is removed leaving the cured liner behind.
Although technology advanced and dragging or pushing a liner in place has improved, inversion is now frequently used to put the liner into place. This give a much better finish and also allows pipes with bends in to be relined. Polyester resins have largely been replaced with epoxy resins and ambient curing (unpredictable, as no consistency with cure times) replaced with the use of small boiler or steam generators. The liners are now mainly inverted into the lateral using air drums or air guns.
Curing with epoxy can take from 30 minutes for steam cured to 3 hours for hot water cured systems.