How do you locate nylon and polyethylene gas mains? 


Being a non-metallic pipe, nylon, and similarly, polyethylene gas pipes definitely have their challenges to being found using electromagnetic locating methods.

In this article, we are going to break down the top four ways to locate the nonmetallic gas pipe, the reasons why locating these gas pipes is challenging, and the dangers of working near non-metallic gas pipes.

Geoscope Utility Detection Gas Pipe Locating Services
Image of Geoscope Utility Detection Gas Pipe Locating Services

Let’s start with the reasons why gas pipes are challenging to locate:

  • Electric current doesn’t travel through plastic or nylon pipes.
  • The pipes do not reflect well to Radar energy as they typically have similar dielectric properties as the surrounding soils.
  • Access to trace wires can be difficult or nonexistent.
  • Trace wires can be found on the pipe, although pipes can be in close proximity or parallel to other metallic pipes and conductors.

The dangers of Gas Pipes

Gas Pipe location danger signage taken by Geoscope
Image of gas pipe location with signage of danger
  • Gas pipes will explode when ruptured and introduced into the atmosphere as an ignition source. Sparks from excavating hard ground or rock, internal combustion engines, and faulty electrical circuits.
  • Low-pressure gas does not dissipate in the surrounding atmosphere as it slowly moves upwards compared to high-pressure gas. It hangs around so to speak.
  • It is very easy to damage gas pipes that are made of soft nylon. There is no forgiveness when it comes to plastic versus metal. A poly gas main has little chance when coming into contact with a metal excavator bucket. Using a shovel or a digging bar can have similar effects being made of metal and coming into contact with the plastic pipe.
  • There are usually little signs on the surface that gas mains may be present below. 
  • Gas plans typically show an offset measurement from the boundary or building line though these measurements can be few and far between on a long street.

Why should you find out where the gas pipes are before any excavation is planned on-site?

Geoscope's utility locating service located gas pipe on-site
Image of gas pipe

As a person, contractor, or company planning to dig, you should know that you have a duty of care to protect and keep safe from harm not only yourself and your workers, but also the underground infrastructures that already exist.

Underground gas networks and gas pipes are included in the assets you need to protect.

As we mentioned, gas pipes are not to play around with. They can be the difference between going home to your family in the evening for a nice roast dinner, or being in the hospital emergency ward with severe burns and injuries.

They are very easily damaged if they aren’t found and identified early in the construction stage.

How do we locate nylon and polyethylene gas pipes?

Thankfully, it is not impossible to find where these non-metallic gas pipes are underground, as there are a couple of options out in the field to locate them with electronic and GPR location methods.

In order of most effective pipe locating methods, here is the list you should follow:

  1. Have a professional and Certified Locator take care of this for you.
  2. Directly connect to an accessible trace wire (buried with gas pipe).
  3. Induction scan (if the pipe has trace wire and is away from nearby parallel conductors, such as Telstra and electrical).
  4. GPR – Ground Penetrating Radar
  5. Non-destructive excavation i.e., AKA – NDD Non-Destructive Digging sucker truck, vacuum excavation, potholing, etc.

1. The first approach and ideal method to locate these mains are to directly connect to an accessible trace wire and transmit a traceable current down the gas pipes’ trace wire.

Located gas pipe utility taken by Geoscope
Image of gas pipe utility locating

A major problem we have as utility locators is the difficulty or no access to the trace wire. 

The problem with this trace wire locating method is often, there is very little access to these trace wires as they aren’t often found unless you excavate on top of the gas main to have access to uncover this trace wire. 

There are very few Jemena gas valves in the street which have trace wire access which limits the chances of attempting this method of directly connecting to the gas mains trace wire.

This is the best method to quickly locate a pipe, although not every gas main has a trace wire buried with it. 

Often, when we go to pothole the pipe, it is just a yellow plastic pipe in the ground with no metallic wire to be found.

So what if you don’t have access to the gas mains trace wire?

2. We can always try inducing a signal/current into the trace wire by using the electromagnetic induction method.

Located underground utility by Geoscope
Image of locating the gas pipe using induction method

The induction method works by placing the transmitter on the ground at the approximate location we believe the gas main is to be found. We can then pass by with our receiver (wand) and check for any readings of a signal being detected.

The induction method doesn’t go without its challenges.

  • It is spilling current into the ground below and hoping to transmit the signal into the metallic pipe or cable underneath it. The signal does not discriminate, nor select a particular pipe or cable. It is going to target the service with the least resistance. Often, this would be an electrical service or a large copper communication cable.

What if there are no trace wires laid with the plastic gas pipe?

If there are no trace wires buried with the gas main, you can’t exactly induce a current through a non-metallic pipe. 

We learned in high school that plastic will not transfer electricity or electromagnetic energy. 

So what do we do in this case?

There’s a method out there that uses a piece of equipment that pulses electromagnetic energy into the ground and what we want to be looking for is reflections and targets that the energy bounces off.

When we see these readings of possible underground infrastructure buried below. I.e non-metallic nylon gas pipes or utilities, it’s often thanks to GPR.

3. Ground Penetrating Radar 

Geoscope's ground penetrating radar being used on-site
Image of Ground Penetrating Radar on-site

By using offset measurements found in the before-you-dig – BYDA plans, often provided by Jemena Gas, we can make educated guesses of where we should perform our ground penetrating radar scans to check for positive signs of reflections of this electromagnetic energy being bounced off gas pipes.

Ground penetrating radar is another topic all by itself. 

What you need to know is that some soils are more effective at allowing electromagnetic energy to pass through them, and user interpretation is often the difference between knowing what’s below and just having a wild guess.

That’s why having professional and expert GPR technicians on your work site is the ideal way to locate the gas pipes below your site.

So we have located the gas pipe, and now we are looking to confirm the location

Danger signage on gas pipe utility locating site
Image of gas pipe location with danger signage

What do we do when we have to prove where the gas pipe is actually located?

Do you remember when we discussed the duty of care?

If you are reading this far down into the article, I’m taking it that you are a person who is interested in keeping people safe and wants to dig down and get an understanding of how to do this.

Everyone has a duty of care to keep people safe on the worksite. When you are excavating around gas pipes, you also have a duty of care to protect the gas pipes from damage.

If you know where the gas pipes are, great! This will make the proving and verification of where these gas pipes are a lot easier.

If you do not know where these gas pipes are, it is going to be a little bit trickier, but it is not impossible to find with a little perseverance and some tactical test holes in the ground to locate these gas pipes.

We do this through non-destructive digging or non-destructive excavation techniques.

  1. Non-destructive excavation
Non-destructive excavation done by Geoscope on-site
Image of gas pipe locating using potholing

Using a truck that has a large spoil tank and vacuum unit mounted onto it, a large vacuum hose is able to suck dirt from the ground to leave a hole, which hopefully, is where we have marked the gas pipe.

We call this potholing and it is done with a vacuum truck.

By using air and water, the name non-destructive process becomes clear. We are doing no damage at all by just using water pressure, even to fragile plastic gas pipes.

We can keep the pothole very tight and accurate when we know where the gas main is by using electromagnetic and ground penetrating radar locating methods. 

This saves not only backfill material but labour and time by using precise techniques and the vacuum excavation truck.

What if you still don’t know where the gas main is when you have already used electromagnetic and ground penetrating radar locating techniques?

We can perform a technique called slit trenching.

Geoscope Utility Detection Slit Trenching Service
Image of Geoscope performing Slit Trenching method for gas pipe locating

Slit trenching is a calculated guesstimate. 

If we have an idea of the expected offset the gas pipe is from the property boundary, we can dig down with that non-destructive digging technique and continue the pothole and dig a slit trench in the ground.

The slit trench will uncover any pipes or cables inside that have been buried to the depth of the open slit.

This technique can be time-consuming, although it is the safest way to find a gas pipe that is untraceable. 

Slit trenching is definitely a safer option than using Mechanical excavation equipment before finding out where this gas pipe is in the first place.

So in this article, we have looked at the ways how we perform our locating of underground plastic gas pipes at Geoscope Utility Detection Services, the dangers of working around plastic gas pipes, the dangers of damaging gas pipes, and the challenges of locating plastic gas pipes.

If you found this article helpful, give us a shout-out on our social pages and feel free to share it wherever you feel your network could use this information.

If you need help locating underground plastic gas pipes, I hope this has helped you choose a locating company that has your best interest in mind, not only in keeping your team safe but keeping your costs as long as possible to keep your margins on target.

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