How are sewer pipes inspected?

What is involved in a pipe inspection?

Most of the time required to undertake the inspection is dedicated to finding the access point and securing access. This means finding the right maintenance hole on either the upstream side of the pipe and the downstream side of the pipe. The surrounding areas near the access point must also be made safe and secure, as sometimes they are in roadway, foot paths or private property. Establishing the site is an important part of the inspection process so that there is no risk to the public and the workers involved in the inspection. Once the access point is located and the secured,then an inspection can begin.

An operator will lower the camera crawler into the pipe and remotely drive the camera along the length of the pipe, stopping to make notes of any faults or defects that they might find inside the pipe. They will continue this until they get to the end of the pipe. Once they get to the end, they will pull the camera back (the inspection cameras are usually tethered by a power and data cable) and return to the access point for retrieval.

Another aspect of a pipe inspection that takes time is the actual coding of the defects in the pipe. When the camera is inside the pipe, the trained operator must watch the video feed and identify and classify the type and location of the defect along the pipe.

What information does an inspection record?

Operators are trained to undertake this classification and quantification in alignment with their regional coding guidelines. These guidelines are used widely, and help to ensure consistency in understanding across organisations, stakeholders, and professionals.

How can we increase the speed of inspections?

Some ways to increase the speed of an inspection is by implementing new hardware, new software, more effective training methods and materials, or by applying an improved process to inspections. Given that most of the inspection is concerned with locating the right asset and establishing the site, methods that make those processes more efficient would also have an impact on the turnaround of sewer pipe inspections.

About the Author

Amanda Siqueira is an Australian civil and environmental engineer who has worked in design, construction and remediation of drainage and sewer pipes in Australia, New Zealand and the UK. She has passion for all things pipes and is also one of the Co-founders of VAPAR.

Why am I being charged for sewer?

If your water authority is charging you for the capture, treatment and delivery of potable drinking water, then there is a high chance they are also charging you for the capture, treatment and discharge of wastewater. There are a number of processes that take place for water authorities to deliver these essential services to rate payers. If this service is not delivered well, there is an increase in risk to public health and the environment.

What does the money go towards?

The primary functions of wastewater services is to collect, treat and discharge wastewater. The objective of any wastewater system is to do this in the most efficient manner that meets the public health and environmental goals of the community. This can be really challenging, as there are several technical and non-technical outcomes that need to be achieved. But at the heart of it, the system can be broken down into:

Collection systems- these are generally the pipes, manholes, trunk sewers, pumping stations etc.
Storage systems- these are generally septic tanks, temporary storage tanks, etc.
Treatment/discharge systems- these are generally wastewater treatment/recycling facilities and discharge structures.

Each of the above sub-systems needs to perform well in order to meet the public health and environmental goals of the community. There is an expense to keep these systems performing 24/7, and that is what the sewer charges go towards.

How do the charges get applied?

Each water authority charges differently depending on the regulation and legislation in the region. For most water authorities, the charges are split up into fixed charges and variable charges, and the way they charge their customers often differs by customer type. Fixed charges are charges that customer pay on a regular basis (e.g. quarterly) for the fact that there is a connection into the public sewer system. Variable charges are charges based on a usage metric (e.g. per kilolitre or per hundred cubic feet). From what I have seen, most variable usage charges are applied to commercial and industrial customers, and less likely to apply to residential customers. The usage of residential customers is usually covered in the fixed charge. Because commercial and industrial wastewater discharge has a higher load of contaminants, there is a greater level of treatment complexity required that the water authorities have to account for, therefore levying an additional usage charge to cover the associated costs.

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How frequently are sewer pipes inspected?

There are over 11 billion meters (36 billion feet) of wastewater pipes that have been installed underground around the world, and this number continues to grow as the number of dwellings increases to support a growing population. A lot of these wastewater pipes have been installed in the last 40-70 years, and the pipes themselves come in a variety of materials and diameters.

The design life of a wastewater pipe?

Engineers design pipes for a certain design life, meaning the duration of time that the asset is expected to be in use before it deteriorates to the point of failure. In the case of underground wastewater pipes the design life is generally between 100 years and 150 years. During the pipes design life, it is prudent to check the pipes regularly to make sure that they are not blocked or broken.

How frequently are these wastewater pipe inspections carried out?

This process is called an inspection and is usually carried out by trained professional using a small CCTV camera that is remotely driven through the pipe, capturing video footage of the internal condition of the pipe as it goes. The best practice is to undertake these inspections at a frequency of around once every 10 years, equivalent to inspecting 10% of the network every year. This frequency means that it would take the relevant water authority 10 years to get around to the same pipe if it were to continuously inspect their pipe network. Water authorities are inspecting their network continuously, but not at the ‘best practice’ frequency of once every 10 years. The frequency at which pipes are inspected differs based on the water authorities’ budgets and the risk of that asset’s failure to the community and environment. In some areas and countries, it is common for pipes to be assessed at a much lower frequency i.e. Inspected at less than 10% of the network every year. In the United States, almost 7% (source: https://www3.epa.gov/npdes/pubs/sewcl.pdf) of the network is inspected each year, but other countries like the United Kingdom and Australia (based on anecdotal industry experience) is less than 5%.

How frequently are these wastewater pipe inspections carried out?

One way to increase the frequency of wastewater pipe inspections is to decrease the cost of the inspection itself. To decrease the cost of an inspection there must be an associated increase in productivity. This can come from new hardware, software, more effective training methods and materials, or by applying an improved process to inspections. Another way to increase the frequency of inspections is to increase the budget associated with carrying out inspections, however, this is a very challenging method since most water authorities are budget constrained and therefore have a limited ability to apply this method.

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What material types are used for sewer pipes?

What are sewer pipes and where do they go?

Wastewater pipes are pipes that carry wastewater from a property to the source of disposal. The source of disposal may be different depending on where the property is located relative to major urban centres, but for most people the source of disposal is a bigger ‘trunk main’ pipe that eventually leads to a sewage treatment plant or ocean outfall. Because these pipes manage wastewater from every property, they are under the ground almost everywhere people live. There is an estimated 11 billion metres (36 billion feet) of wastewater pipes in the world. That’s a lot of pipe!

What are sewer pipes made of?

With so much pipe being put in the ground, what are they actually made of? Well, it depends. Depending on the use of the pipe, and the design of the installation, different materials can be considered. For example, pipes that are used for collecting wastewater from residential dwellings can be small diameter and the pipe can be made from a variety of flexible plastics. However, pipes that are large diameter trunk mains are more likely made of stronger materials such as concrete or HDPE.

What are the other different sewer pipe materials?

If you’re looking for some great information and data to answer this question, the US EPA has a useful fact sheet on the common pipe construction and materials here. There is also a data breakdown of pipe materials in sewer pipes in a previous post that we did here. From the dataset that we analysed, the most common pipe material for sewer pipes was vitrified clay, followed by concrete, then by flexible plastics. Vitrified clay was popular because it was a cost-effective solution. More recently, flexible plastics are more common in new installations, so over time we will likely see the percentage of sewers in the ground that are plastic increase.

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Trunk sewers – changes in inspection methods

What is a trunk sewer?

A trunk sewer is usually a large diameter pipe that wastewater from smaller diameter sewer pipes connect to downstream. These carry the wastewater from upstream catchments and carry the flow downstream to a discharge point. Depending on the size of the catchment and population upstream, the trunk sewers can be quite large in diameter, most of them are large enough for people to walk through.

Why are sewer trunk mains needed?

A trunk sewer is the most cost-effective way to transport large amounts of wastewater from upstream populations to a downstream discharge point. If we didn’t have trunk sewers we would need to take wastewater from every property all the way from the most upstream point in the network through to the discharge point, which is cost prohibitive. Due to the importance of these large pipes to urban centres, it is imperative that they are in good condition and maintained and inspected regularly.

Due to their sizer and flow capacity, trunk sewers often have a higher consequence of failure compared to the smaller upstream collection network. If a trunk sewer was to fail due to a blockage or a collapse the results can be extremely expensive to repair, damaging to the local environment, and disrupt the use and access to surrounding public and private infrastructure.

How are trunk sewers inspected?

Traditionally, because of large diameter nature of trunk sewers, trained and certified professionals should be used to carry out inspections, and they do these inspections by walking through the trunk sewer. These highly skilled and trained professionals not only carry out the condition inspection of the pipe, but also complete this in a safe manner. It is normal for these inspections to be carried out while the sewage is still flowing in the pipe which means the inspection should only be carried out in low flow times of the day (i.e., not during peak usage or after recent rainfall) and when the section of pipe to be inspected is well ventilated and monitored.

The airspace in the truck mains is considered to be a hazardous environment due to the H2S gas generated from raw sewage. Additionally, the pipes are ‘confined’ in nature (i.e., There is no free flow movement of air). For that reason, forced ventilation equipment is sometimes used and people inspecting the pipes wear gas masks and gas monitors for the duration of the inspection.

What are the changes in the trunk sewer inspection technology?

There is new technology available on the market that means that people don’t need to enter these hazardous and confined environments. This new technology improves the safety outcomes for the inspection process dramatically as they can reduce or eliminate the physical entry of personnel. The devices used can be tethered or untethered, meaning that the inspection device may or may not be connected to a particular location. An example of this technology is floatable cameras that undertake 3D imaging of the pipe as they flow through. There are also vendors that provide wheeled robotic inspections, whilst others provide drone hardware that fly through the pipe.

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BOM National Performance Report 2021-22: A wastewater snapshot

Targeting the Correct Pipe Grade

Why is pipe grade pipe important?

Most wastewater networks rely on gravity to function. The term ‘💩 runs downhill’, wasn’t coined by accident. Interconnected gravity sewer pipes collect flow from customers and transport the wastewater downstream to a treatment plant through a series of gravity pipes, pump stations and pumped mains.

When designing new gravity sewer mains, the ground topography and required grade of the sewer is the driving factor in determining where it will be constructed and how deep it will need to be. A sewer that is too steep will result in fast flow and increased turbulence. A sewer that is flat or has a sag (belly) is problematic and likely to result in ponding water and a build-up of sediments and solids. This gradual build-up of deposits can create blockages and overflows.

Figure 1 – Problematic flat spots in a pipe

Different ways to measure pipe grade and straightness?

Following the construction of a new sewer, a range of tests and checks are carried out to ensure it has been constructed as per design and is fit for purpose. These checks can include an air pressure test, hydrostatic test, ovality test, and pipe grade check.

Utility organisations, who are the owners of the pipes, may use a variety of methods to be satisfied the new pipe has been constructed to design by housing developers or contractors. These tests check to see if the pipes are straight, free from obstruction and will achieve self-cleansing velocity. Tests can include:

Ball Test
A smooth ball is placed at the upstream end of the sewer pipe and should run unobstructed to the downstream end.
Light & Mirror Test
A light and mirror are sometimes used to ensure a new sewer main is straight with no unintended horizontal or vertical bends. The projection of a strong light through a straight sewer can be confirmed with a full circle of light visible at the end.
Dynamic Inclination
Many CCTV camera crawler systems come with inclinometers that will display the grade of the pipe directly onto the inspection video. Sections of the pipe that are too flat or have a sag/belly can be identified from this displayed value.

Figure 2 – Digital inclination recorded by a CCTV crawler

An out of the box solution!

On a recent trip to the USA, the VAPAR team discovered an out of the box solution from a pilot project in Oregon. The City of Salem have been using an alternate inclination testing approach for decades. It has worked so well for them; they continue to use this unique method to check new pipe meets their requirements. Just prior to the CCTV pipe acceptance inspection, tracing dye is released into the pipe to be tested. If the pipe has a consistent negative slope the dye will not collect and pool in a sag. If there is a pool of dye, then there is a sag present, but the dye will not be able to quantify the magnitude of sagging.

The method employed by City of Salem is novel in its ability to identify and quantify a sag in a pipe. A target is installed in front of the CCTV camera that clearly identifies if a sag is present. The magnitude of the sag can be observed using a target where the rings correspond to their internal acceptance levels. Any significant sag in the pipe is immediately obvious as the dye level will reach the 4th target ring.

Figure 3 – Crawler camera with dye target mounted out front

When the pipe doesn’t meet the grade

If there are a number of these instances of this occurring, it may trigger a complete pipe relay. A single instance where the dye reaches the 5th target ring will generally require a dig-up to address the sag and remove the risk of settling deposits and blockages. In-service pipes with sags/ponding often require regular jetting to minimise this risk.

Figure 4 – The City of Salem target

Evolution of ideas

The team at the City of Salem are an excellent example of not limiting the approach to a problem or task with a narrow and set method, but rather to think about the job at hand and include innovative ideas to achieve a desired outcome. Testing alternate equipment, technology, and methodologies is an important part in process evolution throughout the world.

We would love to hear from others who have a unique solution to complete a part of their job!

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.

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Targeting the Correct Pipe Slope

Why is pipe slope important?

Figure 1 – Problematic flat spots in a pipe