Should I patch or line to repair my sewer pipe?
The decision around whether to patch or line a sewer pipe in poor condition can be challenging for city and utility engineers. Sewer pipe repairs are a critical task that requires careful consideration to ensure long-term results. Two common techniques frequently employed in the industry are patching and lining. Each method addresses specific issues and offers distinct advantages. In this blog post, we will delve into the world of sewer pipe repair, exploring the differences between patching and lining, and helping you make an informed decision for your specific needs.
Figure 1– Vitrified clay pipe with large cracking and breaking
When do sewer or stormwater pipes need repair?
Deteriorating sewer and stormwater pipes often have cracks, holes and other defects that affect the structural integrity of the pipe. Inflow and infiltration into older pipe networks is also a common problem. When a pipe is inspected and observed to have significant structural defects, engineers will need to decide on whether action is required to manage this risk. This will involve selecting a suitable repair or rehabilitation option, and deciding how soon this needs to occur.
Digging up and replacing with a new pipe is often cost prohibitive, a common way to extend the life of these underground pipes is to use trenchless renewal methods. This includes patching or lining a pipe to mitigate the existing structural defects.
What is a pipe patch?
Pipe patches are used for spot repairs along a pipe to fix a specific issue where full-length repair is not necessary. Pipe patches are often constructed from a cured-in-place-pipe (CIPP) material such as glass fibre patch that is hardened with fast curing resin during installation. There are also stainless-steel patches with rubber seal which mechanically lock into place on expansion in pipe.
Pipe patches can be installed across a large range of pipe diameters with the different patch lengths available depending on the situation (400mm-1200mm, 16in-4ft).
What is trenchless pipe relining, and how does it repair pipes?
The trenchless lining of pipes eliminates the need to dig down and repair long lengths of pipe which can be expensive and intrusive. Pipe lining options include:
Figure 2 – Cured-in-place pipe lining installed within an older host pipe (Courtesy M Tucker & Sons)
CIPP (Cured-In-Place Pipe) lining
CIPP (Cured-In-Place Pipe) lining is a method of rehabilitating existing pipes without the need for traditional excavation methods. It involves inserting a flexible liner that has been pre-coated with a resin into the damaged pipe. The new pipe uses an inversion technique to insert and inflate this new inner pipe and achieve bonding with the original host pipe wall. The result is a new, durable pipe within the existing one.
Fold-and-Form lining is like CIPP, but rather than using an inversion method to insert the new plastic pipe (e.g., thermoformed PVC), it involves heating and then folding and forming the material into a flattened shape and pulling it into the existing pipe with a winch. It is then inflated, matching to the shape of the host pipe. The liner then cools to harden the thermoplastic material, creating a new pipe within the old pipe.
Figure 3 – Spiral Wound Lining inserted into an existing pipe
Spiral Wound Lining
Spiral Wound Lining is another common structural lining solution that can be used to rehabilitate defective pipes. It uses a continuous strip of profiled plastic (typically PVC or HDPE) that is mechanically wound into the host pipe and locked in place. There is no requirement for resin and can often be inserted under live flow conditions.
What to consider when choosing to patch or line an existing pipe that needs repair
Pipe patches are an excellent option to repair pipes with a specific defect at a few locations along an otherwise healthy pipe. Conversely, a pipe that has many defects from start to finish will most likely benefit more with full lining between maintenance holes. The grey area that engineers must consider is when the pipe falls somewhere between these two scenarios. It is good to have a discussion within an organisation around how many patches would be recommended before switching to a full trenchless lining solution. This will involve looking at the various patch and lining options available from the available contractors in your area. What will be the structural grade of your pipe after completing repairs, and has the observed risk been managed? Will the option chosen affect your asset valuations and recorded useful life?
Once you have answers to some of these questions it will be easier to settle on a more agreed organisational approach to whether patching or lining is the preferred option in each scenario.
Recording Repair Decisions and Completing Work
It is important that organisations have an efficient system in place that is able to record pipe repair decisions and package the required repair work into programs that ensures that budgets are allocated to the right areas of the network at the right time.
About the Author
Mark Lee is the Business Development Manager (AUS/NZ) at VAPAR and a former Senior Asset Engineer who has spent more than a decade managing the asset lifecycle of infrastructure. He has extensive experience managing pipeline networks, including design, construction, condition assessment and decommissioning.