What is the life expectancy of your sewer pipes?

The old saying, "out of sight, out of mind", couldn't be truer than when it comes to your sewer system. As the sewer system is buried underground, most people never think about it until their sewerage starts backing up. So what is the life expectancy and when should you consider getting your sewer system checked?

Types of sewer pipes

To answer this we must first look at the different types of Sewer Pipes that may have been used on your property. These are generally one of the following:

Cast Iron - not as common in Brisbane, but can be found in multi-storey buildings
Terracotta or Vitrified Clay - very common, particularly in the older parts of Brisbane
PVC - is used in newer houses or sewers that have been replaced.

If you're not sure what your sewer system is made from, a sewer inspection with a drain camera can easily identify them for you.

The life expectancy of different sewer pipes

Each of the different pipes has its own strengths and weaknesses; which can have an impact on the different life expectancies. Let's consider these:

Cast iron sewer pipes

Cast Iron pipes can last between 30 and 100 years.

Like all metals, Cast Iron can rust. This rusting process can be accelerated if corrosive materials are poured down drains or if the pipe sits in damp ground. Internal rust can actually cause blockages and sometimes it can rust a channel into the bottom of the pipe.

Vitrified clay sewer pipes

Clay Pipes can last up to 100 years.

One of the biggest weaknesses of Clay Pipes is that they are very rigid and can easily crack if the ground around them moves. This has been quite a common occurrence around Brisbane with the recent drought causing the ground to dry out, crack and shift. The other issue is that the vitrified lining of Clay Pipes can be easily scratched if a mechanical drain cleaner is used (eg. Plumbers Eel). This then catches toilet paper and other solids, leading to a blocked drain.

PVC sewer pipes

PVC Pipe can last between 50 to 80 years.

PVC Pipe is great when there is small ground movement as it is flexible and can move with it. However, as it ages it can become brittle and then crack with any ground movement.

But what about root intrusion?

Root intrusion can happen with any of the common sewer pipes. As both Cast Iron and Clay Sewer Pipes are put together in shorter lengths, any ground movement can result in offsets between the lengths; thus allowing root access. Similarly, older PVC can become brittle and crack allowing access.

What does it all mean?

Pretty much any sewer pipe over 30 years old can start to have issues (assuming no major ground movement etc). This means that we shouldn't just forget about them until we have a problem, but should consider regular plumbing inspections to ensure they are all okay. After all, we don't expect the paint, roof, gutters etc on our house to last indefinitely without regular maintenance, so why should our sewer system be any different?

And remember; if you do identify a problem in your sewer system, a pipe relining can have it as good as new for another 30-50 years.