What the Heck is Acoustic Pipe Inspection? — Part 3

Our series concludes by exploring the data collected by acoustic pipe inspection and how it is interpreted.
What the Heck is Acoustic Pipe Inspection? — Part 3
When successive data sets are compared, API can identify deteriorating condition trends or quantify a repair’s effectiveness.

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In the in the final part of our series on acoustic pipe inspection (or API) you’ll learn about the nature of the data that’s gathered. We’ll tell you what the data reveals, including how the information is interpreted and the long-term uses for the raw data and its derivative reports.

Quick review of API products

In Part 1 of our series on acoustic pipe inspection, or API, we explored three methods, featuring products from Pure Technologies and InfoSense. Both manufacture products designed to inspect pipes that are in use carrying liquids.

The Smart Ball and the Sahara, both manufactured by Pure Technologies, require that the pipes be full of flowing liquid. The SL-RAT from InfoSense requires a partially unobstructed pipe bore and is best suited to storm, sanitary or combined sewers. These pipes can be completely dry.

In Part 2 we learned how each device is deployed and retrieved. Deployment into fully charged lines is more complex and requires coordination with the pipe owner’s operations team to be sure there is product available to carry the SmartBall or Sahara through the pipes to be inspected. While SL-RAT could be deployed by a single individual, a two-person team is recommended.


Pure Technologies’ SmartBall and Sahara gather similar — but not identical — information as they are moved through the pipes by the flow of the surrounding water. Because the Sahara is tethered, both acoustic (sound) and visual images (CCTV) can be monitored in real time by the operator in a dedicated deployment vehicle. In both cases, the acoustical data is preserved in an audio file and may be visually presented as a graph showing frequency spikes on either side of a baseline.

Leaks, trapped gas pockets, lateral, junction, and service connections each have unique and identifiable sound signatures. Volume adds detail to the picture by giving an indication of the scale of the leak or size of the trapped gas pocket. A seasoned evaluator can interpret even subtle nuances.


When the operator hears or sees evidence of a fault, he can hover or reverse the Sahara’s sensor’s travel to get a better or prolonged “look” at the source of the sound. When he is satisfied that he has adequately documented the situation, the traverse can continue. Without an operator, the SmartBall has one fleeting opportunity to capture the moment and its data may be hours or days from analysis.

A crew member can be assigned to follow the Sahara’s progress by walking along the route. The operator, by cellphone or radio, may tell the walker to mark a problem spot for future reference and correlation with the remotely gathered data. Spot photos and field notes are independently collected by the walker and stored in a collateral file. The photos may enable more detailed excavation planning at complex sites. Simultaneous real time surface tracking with SmartBall gathered data is not possible.

The SL-RAT delivers segment condition assessments within about 90 seconds. The operator’s sole input task is an estimate of the distance between each manhole in a paired set. All of the computational tasks are done in the receiver which is communicating with the transmitter electronically as well as acoustically.  The receiver can store up to 199 segment condition ratings. Rated from zero to 10, each segment’s numerical score and the GPS identifiers for each manhole in the inspected pair constitute the entire data set for a manhole pair.

The segment rating is used to prioritize further inspections or in the case of complete obstruction, indicate immediate action. Because the SL-RAT’s conclusion relates to an entire segment and not a discrete spot, pinpointing an exact spot for excavation is reserved for another tool. The straight-line nature of the pipe segments and the general surface condition knowledge eliminate the need for crew walk over or site photos. Most crews plan their day’s inspection route using a GIS system map so that after two or more miles of inspections, they have circled back to an end point near their starting point – and their parked vehicle.

Data sets, storage and future reuse

The Sahara and SmartBall record acoustic information much like an audio cassette recorder. The sound’s characteristics can be seen as well as heard during playback. Unlike Sahara, SmartBall recordings are not available in real time.

The Sahara also captures CCTV images which can be viewed during the traverse and later as well. These are stored in “.avi” format video files contemporaneously with “.wav” format audio files. This integrated data set can be archived on a hard drive, flash drive or in a cloud and used as reference points when future traverses are completed.

The SL-RAT data, when downloaded to a computer or to the SL-RAT website, is depicted in an “.xls” spreadsheet. Once downloaded, the file size limitation (199 records) is no longer a concern. Data from the website (SL-DOG.com) storage can also be downloaded in a “.kmz” file format. The .kmz file opens with Google Earth and depicts the segments with their respective color-coded scores on the map.

One of the major benefits to all this is when successive data sets from the same inspection tool are reviewed and compared, all three tools’ data can identify deteriorating condition trends or quantify a repair’s effectiveness.

API recap

In the current marketplace there are two manufacturers producing API equipment for use in pipes that are in normal operation, whether they are full and under pressure, partially filled with gravity-transported material or completely dry gravity lines. Using two different technologies, the respective products do not cross compete for the same jobs and are somewhat complimentary.

SmartBall and Sahara devices are manufactured by Pure Technologies. Both are “go with the flow” devices. The former is untethered while the latter is released and later captured. Both are for use in pipes 6 inches in diameter or greater. The tether limits Sahara traverse distance to about 3,000 feet.  SmartBall traverses typically range up to 10,000 linear feet and are only limited by its battery life. 

The SL-RAT, manufactured by InfoSense, evaluates pipe segments that stretch between two adjacent manholes.  Typical pipe diameter ranges from 6 to 12 inches. Each receiver/transmitter pair can process up to 20,000 linear feet of pipe per day without confined space entry or product contact.

Pre-deployment planning and inspection day support activities vary; the Sahara requires a dedicated support vehicle while the others can be deployed from an unmodified pick up.

API is a proven and effective method for gathering information that compliments CCTV inspections and can enable more cost-effective inspection expenditures.


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