This is particularly true in the case of spot repairing gravity sewers and stormwater pipes. That is, when does it make sense to spot repair a pipeline rather than renew the entire pipeline? The answer to this question depends on many factors such as the age of the pipeline, its overall condition, its criticality and the number of defects/length and the relative costs of a local repair versus total renewal.

Because of the wide variety of individual circumstances there is no universal rule that can be applied to specify when to reline (renew) the whole pipe and when to spot repair. However from experience Interflow has found that the following guidelines are a good starting point.

• If the pipe has less than 20 years service life left, then reline the pipe (renew).
• If the pipe has more than 20 years service life left, then the following table provides a guide for the maximum number of patches per 50 metre length that should be installed. If more are required, typically it would be more economical to reline (renew) the pipe.

Beyond these basic guidelines, it may be beneficial to seek the opinion of a specialist pipeline renewal contractor who can inspect and assess the condition of the pipeline and recommend the appropriate asset management solution.

Having determined that spot repairs are necessary, it is important to select the right product. Interpatch is a product specifically developed for trenchless spot repairs. Interpatch is constructed of high strength fibre-glass matting which is saturated with high performance, fast curing silicate resin. The patch is applied directly at the location of the defect, bonding to the host pipe and providing an effective, long lasting repair.

Interpatch can be installed in a wide range of pipe sizes from 100 mm to 750 mm and bonds to most common pipe materials such as concrete, PVC, vitrified clay, brick asbestos cement, and cast iron. A standard repair length is 1.2 metres.

One of the key features of Interpatch is its fast cure time. In common pipe diameter’s between 100 mm to 300 mm the resin cures in as little as 45 minutes, even underwater. The faster cure time means installation is quicker, safer, lower risk, and less disruptive to nearby residents and traffic.

The Interpatch resin is safe, non-toxic, and environmentally friendly. It is supplied to site in pre-packaged in sealed cartridges. There is no mixing required and the resin is dispensed using a cartridge gun ensuring a clean work site.

Interpatch has been designed to be a structural component as well as a seal. The glass fibres give Interpatch high strength and stiffness. Interpatch is typically installed with a strength equivalent to that of a stand-alone pipe. The high flexural modulus of fibreglass patch means that the strength can be attained from a relatively thin wall. For example in a 450 mm diameter pipe, the standard Interpatch wall thickness is only 7 mm and the resulting loss in cross-sectional area is just over 6 per cent.

The thickness and strength of Interpatch is achieved by layering sheets of fibreglass. Therefore Interpatch can be readily tailored to meet a wide variety of situations by selecting the number of layers needed.

Installation of Interpatch is achieved using an inflatable packer to move the patch to the repair location from the nearest manhole. The packers are available in a range of sizes and are fitted with flow through tubes to enable installation during live flows. In most cases this eliminates the need for bypassing and/or the risk of sewerage backing up during installation.

The value of a spot repair solution relates to how long it will last, not only in normal operation but also when the pipeline is cleaned or has maintenance tools passed through it.

Interpatch has been extensively exposed to high pressure jetting and other common mechanical root cutting tools. During these trials the product was shown to exhibit no damage. As such it can be concluded that Interpatch will not only effectively repair the localised defect, but it will also survive the rigours of subsequent pipeline maintenance.

In summary, Interpatch is an excellent trenchless product for spot repairing defective sections of pipe. Effective spot repair solutions are an important product to reside within the product offering of pipeline renewal companies. Knowing when and where to use spot repairs is also very important. Specialist renewal contractors can provide advice and assistance in recommending the optimum solution in many circumstances. Combining the best products with the right expertise allows the asset owner to get the best value for money in the maintenance of its assets.