Back in the day, we pretty much had nothing but good ol' CCTV as our primary method of inspecting sewer pipes giving us data to assess their condition; IF the pipe didn't fog up for good video and/or the VHS tape got eaten in the player. Water pipes?
You either guessed on intuition or methodically took pipe wall samples ("coupons") to analyze corrosion and wall thickness loss. "Listening sticks" have been around forever, and they were for leak detection more than an actual condition assessment.
CCTV has come a long way with the NASSCO standard and vast improvements in camera optics, digital encoders, and transport vehicle technologies. Listening sticks turned into sophisticated acoustic systems. Quite frankly, the pipe inspection market has exploded with new technologies for evaluating sewer and drinking water systems.
Beyond acoustics and CCTV, specific methods have spilled over between Remote Field Eddy Current (RFEC) systems for finding broken wires in sewer, stormwater, and raw water pre-stressed reinforced concrete pipes. The latest crossover is Focused Electrode Leak Location (FELL) technology from our business partner Electro Scan Inc. FELL was initially developed for sewer. Yet, it is now available for potable drinking water systems too! Oh, and you can detect leaks from outer space using satellites, according to another partner Utilis. Artificial Intelligence (AI) is becoming almost commonplace for analyzing all the data streaming in.
A Google search on "utility pipe inspection technology" yields nearly 16 million hits. With all these technologies, how do you choose? Basic engineering and asset management principles give us at least three (3) primary factors to consider:
Access to the asset
Material of the asset
Whether your water/sewer utility is public or private, for-profit or non-profit/municipal, asset management is always about the business. Assets have an intent to serve, most commonly paying customers. That service is defined through Service Level Agreements and measured with Key Performance Indicators (KPIs). Most KPIs are looking for optimized performance and getting the "biggest bang for the buck," so business reasons come into play when evaluating inspection technologies for a condition assessment program. The ultimate question(s) we are answering with a condition assessment program is "What is the current state of my assets?", "How long will they last?", "Do I have enough funding to cover their replacement?"
Assuming you never have enough funding, resources, or time to inspect every asset, every foot of your pipe network, you need to prioritize. An asset criticality assessment immediately tells you which assets to inspect first. For typical pipe networks, this says transmission lines come before distribution lines. Unless you have excessive sewer stoppages and are under a Consent Decree and you have low flow in those fringe neighborhoods, so maybe you start there. Or an Inflow and Infiltration (I/I) analysis suggests that overflows occur in your lowest-lying segments, and you use elevation as a driver to prioritize those segments. This list can go on and on; the moral of the story is to let a business driver tied to a KPI help prioritize what should be inspected first instead of attempting to assess your entire system.
Access to the asset
Now that you have a prioritized list of assets to inspect based on a business reason, Engineering 101 is going to ask you, "How do I get to the asset?". Inspection methods are significantly different if you have Direct access (can physically see it, touch it) vs. indirect access that requires Remote methods for buried assets.
This conversation also diverges between vertical assets in facilities vs. linear assets out in a network. Most vertical assets have direct access as they are generally stored in some form of structure controlled by the utility. Pumps are typically accessible for maintenance and therefore accessible for direct inspection methods such as thermal and/or vibration readings that indicate structural and operational integrity. Yet even direct access may require high-tech devices such as drones flying up in the air to inspect a water tower 100 feet up.
Buried assets in a linear pipe network typically require remote methods. Yet even this diverges into inside-out vs. outside-in access. I immediately deviate from my logic with CCTV as it is inside-out.
CCTV video can "see" the inside pipe wall defects, but ultimately these defects are scored, creating a remote assessment of the condition. The promise of FELL is more direct as there is a measured "leak" from inside-out indicating a physical breach in the pipe wall integrity. Yet still not direct as there are algorithms that must interpret signals going through an unknown medium of soil outside the pipe wall. Ground Penetrating Radar (GPR) methods are outside-in, complicated by being on the surface and again going through complex soil profiles. Linear assets also lend themselves to longitudinal methods, i.e., an acoustic wavefront that doesn't travel inside-out or outside-in but along the pipe wall itself. The effectiveness of acoustics is directly related to my next factor: material.
Material of the asset
The type of material the asset is made of is probably the single most crucial factor for the underlying technology of the inspection method. The key differentiator is ferrous material (cast iron, ductile iron, steel) vs. non-ferrous (VCP, PVC, HDPE, Concrete).
Case in point, acoustics. Sound waves travel best through ferrous/metallic pipes. Condition is relative to the distance traveled by the sound wave; the farther the propagation of the wave, the better the condition of the metal pipe. It is important to know this does not work as well in plastic pipes because there's difference between the overall condition assessment of the asset vs. a singular breach of the structural integrity of the pipe wall. An acoustic signature due to the venturi effects of a leaking pressurized pipe is independent of material type but it seems there is always an exception to the rule.
Speaking of exceptions, pre-stressed, reinforced concrete pipes mentioned in the opening paragraph are a hybrid material; a non-ferrous pipe wall with ferrous bands inside. Traditional CCTV with an inside-out visual inspection of these pipes may show visible degradation with concrete spalling or not. A good RFEC inspection yields broken wire zones that will cause the imminent failure of the pipe wall integrity. Premature failures of vintage "Class IV" pipe are documented accordingly.
I have not even touched other technologies such as Radio Frequency (RF) or Light Detection and Ranging (LiDAR). A very informative inspection technology is Multi-Sensor that adds multiple sensors to CCTV, such as LiDAR, Sonar, and a form of GPR. Unfortunately, the length of this blog does not let me dive deep into the plethora of inspection technologies for assessing the condition of water and sewer systems. Still, I hope these three (3) factors of 1) Business, 2) Access, and 3) Material help you ask questions about what you want to achieve in the selection of an inspection technology for a condition assessment program.
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