An Overview of the Pipe Assessment Arsenal

From smoke testing to CCTV inspection, here’s a guide to the basics of pipe assessment and leak detection methods

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There was a time when the pipe cleaning game was trial and error. Stick a drain cleaner down the pipe, and if it doesn’t work, simply resort to digging it up.

Fortunately, today there are a variety of pipe assessment tools that make it a more nuanced endeavor. Here’s a quick-reference guide to all the basic pipe assessment tools available, including smoke testing, CCTV, acoustic inspection, and sonar and laser profiling.

Smoke testing

One of the earliest assessment tools, smoke testing remains one of the simplest, fastest and most cost-effective methods to find major cracks in nearly any pipe. 

The concept is simple: Flood a section of pipe with smoke and see where it breaches the surface. Anywhere that smoke is visible above ground is a good sign you’ve found a pathway created by water infiltration.

“Smoke testing is one of the oldest and I think most effective ways of finding defects that allow water in or out,” says David Guillory, vice president of business development for Compliance EnviroSystems. “If done correctly, it gives you the biggest bang for your buck. When I say done correctly, conditions have to be right for a smoke test to give you useful data.”

In order for smoke testing to be effective, the waterways that inflow and infiltration create from the surface to the pipe have to be open. If the ground is saturated, those channels will already be filled and smoke can’t escape through them. This means it only works in dry conditions — no rain, no snow.

“Generally, the contractor is going to smoke-test an entire neighborhood or industrial park. You can make it directional by using pipe plugs, but usually you’re testing a large area,” says Mike Hurley, president of Hurco Technologies. “You can’t smoke-test new construction, unfortunately — it needs awhile for the ground to settle. If there’s a leak in that pipe or a bad connection, water hasn’t found its way down to that opening yet. Eventually, water sinks down and makes it into that pipe, and that’s the route smoke takes out.”

You should always inform the public when smoke-testing in populated areas. Smoke can find its way into houses; and beyond simply eliminating the panic of owners of homes suddenly filling with smoke, there is a risk of smoke pushing sewer gases out of the system with it, even if the smoke itself isn’t hazardous. 

“Speed is the reason for smoke systems — it’s much faster to smoke-test than it is to run a camera through,” Hurley says. “It’s great to have that visual inside the pipe, but the bottom line is: If you want to cover a lot of ground very fast, cheap and effectively, then smoke testing is absolutely the fastest way to do it.”

Liquid-based smokers that have become more common in recent years are devices that fit over the manhole, with a small engine that heats a coil, which in turn burns a liquid additive, producing smoke. A gallon of Hurco Technologies’ liquid smoke is about $60 and will provide three to four hours of smoking time.

Hurley recommends that two workers be on site for smoke testing, walking in opposite directions to the next-closest manhole, then back in the other direction to do the same. That way, the area is covered twice.

“You can easily smoke test up to 1,000 feet in each direction from the manhole that you have the smoke machine on,” Hurley says. “What a lot of our customers do is they’ll smoke-test with our equipment, and then when they find places where they’re getting a lot of infiltration, they’ll mark it and send a camera crew.”


Video inspection has become the bread and butter of many utilities and, one could argue, the industry at large. Not only is it an effective tool in and of itself, it also feeds into just about every other pipe assessment method.

Smoke testing is a front-end technology used to cover large areas quickly and efficiently that would otherwise be too resource-intensive to video inspect. Once workers have narrowed infiltration issues to certain locations, they still need to run a camera through before crews can do anything to fix the leaks.

“CCTV is kind of the workhorse for wastewater inspection,” says Lisa Douglas, vice president of the water services division for Ace Pipe Cleaning (Carylon). “When you get through the pipe, you should have the inspection you need, the data you need, to make the assessment for the work.”

There are systems for every pipe size and application imaginable. Sewer cameras come in basically two types: pushrod and crawler.

Pushrod cameras are generally for smaller-diameter pipe in residential applications, and crawlers are more common in mainline inspections or municipal jobs. One important consideration is cost. On the low end, a decent pushrod system will cost around $10,000 to $15,000. Crawler systems, on the other hand, will start at closer to $50,000.

“Video inspection has completely revolutionized plumbing in the last 20, 25 years,” says Dave Dunbar, national sales manager for General Pipe Cleaners. “Before cameras, you really didn’t know what was going on in a pipe. You could guess, but the only way to really know was to dig it up. With a camera, you can go down and you can actually take a look and see what’s going on.”

Acoustic assessment

There are a few pipe assessment methods that fall under the umbrella of acoustic assessment.


A common tool that many contractors use is the SL-RAT from InfoSense. This device has a transmitter and a receiver that are attached to opposite ends of a pipe, and they send an acoustic signal, which is assessed by the system on a scale of zero to 10. Zero means the pipe is completely blocked, while 10 means completely open. It’s a quick and dirty way of determining whether a pipe needs to be cleaned or will need to be cleaned in the near future.

Then there are acoustic leak detection tools, or listening devices. While there are a variety of complex electronic versions out there, the simplest form of this concept is taking a stethoscope to the ground above a pipe and trying to hear the sound of a leak.

“It’s an art, not a science. You’ve got to sort of train your ear to do that,” Dunbar says. “You’re listening for the leak and hoping for the best.”

It’s a challenging method that requires knowledge of what to listen for, as well as knowing where the pipe is and where it’s going, which means they typically also have to be accompanied by locating systems. 

The benefit of acoustic over, say, smoke testing is that it’s possible to hear minor leaks — those that might not let enough smoke through to be noticed on the surface. The downside is it takes training, patience and practice.

Lastly under the acoustic assessment category is sonar profiling. This is more or less what it sounds like: A device emits a sonar signal and uses it to create a digital rendering of the pipe profile. It is often used in conjunction with laser profiling, as they are essentially the same concept with different applications.

Sonar and laser profiling

Similar to sonar, laser profiling constructs a profile of pipes using laser signals.

There’s one major difference between the two technologies: Laser is used to profile the empty space of a pipe, and sonar is used for water-filled pipe. This is why they are often used together. While one looks up, the other looks down, metaphorically speaking.

“They’re similar; I mean, they’re giving you the outline of the pipe — one is above water and one is below water. This allows you to get the profile of the pipe above and below. Sonar gives you the positional informational if there’s material in the invert of the pipe, and they both also give you the outline of the pipe,” Douglas says. “If your pipe is out of round (if the ovality is changed), that can be a structural issue, based on the material of pipe. For concrete pipe, if it has corroded, you’ll be able to understand where those areas of missing pipe wall are.”

These profiling systems can be attached to crawler systems but are typically applied via a floating pontoon-type device. Often one or both are used in conjunction with CCTV — this is typically called multisensor inspection.

Careful consideration

There are no pipe assessment methods that are definitively better or worse than any others. Of all the many methods that have come and gone over the decades, those that remain are all here for a reason. Deciding what tool to use comes down to what your utility's goals are.

“If someone is just looking for a general assessment of the pipe, the CCTV gives you a visual, obviously, and you’ll be able to see everything from structural defects to blockages,” Guillory says. “Then in some situations, you may be able to see leaks if they’re active, but a lot of times the CCTV will not identify leaks because leaks aren’t always visible to the naked eye. You could drive past a crack that leaks when it rains but if it’s not raining, it won’t be leaking when you’ve got a camera in there. And then you may not be able to tell if it’s severe or not. So it all works hand in hand.”

If you have a small crew and don’t have time to train an employee to become specialized in one method, smoke testing may work better than a listening device. Smaller utilities may not be able to afford a full accoutrement of profiling equipment so investing in a solid camera may be a smart move, or maybe you can get by with an SL-RAT.

“It depends on the scope of the job,” Guillory says. “Leaking pipes, that’s pretty much the basis of the trenchless industry. Everything we do — whether it’s assessing, fixing, lining, digging it up, whatever — has to do with a pipe leaking. There’s always new technology and the tried-and-true methods.”


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