Sleuthing Swimmer

An electromagnetic tool lets water utilities assess condition in prestressed concrete transmission mains without taking them out of service
Sleuthing Swimmer
An assessment using the PipeDiver tool helped Louisville Water Company get insights into the condition of its prestressed concrete cylinder pipe transmission mains that otherwise could not be inspected without being taken out of service.

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A break in a large water transmission main can be catastrophic, losing millions of gallons of water, requiring expensive repairs, and damaging property. A key question for water utilities is how to assess the condition of these mains as they age.

Traditionally, condition assessment on prestressed concrete cylinder pipe (PCCP) meant taking the main out of service for surveying with electromagnetic technology on robotic or manual platforms. But some mains can’t be depressurized and drained for such inspections without major service disruption.

Now Pure Technologies, with U.S. headquarters in Columbia, Md., offers the PipeDiver tool, designed for structural assessment of lines that because of operational constraints or lack of redundancy must remain in continuous operation.

The tool “swims” free in pressurized pipe, traveling from one end of a main to the other, recording information for later download and analysis. The water utility then can use the data to plan for cost-effective repair and rehabilitation as needed.

Michael Livermore, Midwest regional manager for business development with Pure Technologies, described the technology in an interview with Water System Operator. Taking part were Keith Coombs, manager of infrastructure planning, and Kelley Dearing Smith, manager of strategic communications, both of Louisville (Ky.) Water Company (LWC), which used the technology to assess 8.8 miles of 60-inch concrete transmission main in late 2011.

wso: Is the PipeDiver tool a brand new technology:

Livermore: This technology has been around for about four years. It is used to detect broken reinforcement wires within PCCP mains. It is propelled through the pipeline with the flow of the water. As it passes through the pipeline, it detects those wire breaks. By doing so it enables the utility to do some further analysis, calculate the condition of the pipeline with engineering methods, and determine whether to repair or continue to operate it.

wso: Can you provide a physical description of this tool?

Livermore: The tool is comprised of multiple modules about 15 inches in diameter and is a total of about 12 to 15 feet long, depending on the configuration needed for the pipe we’re assessing. It includes a battery module, an electromagnetic module that does the scanning, and a tracking module that enables a crew to follow the tool’s progress from the surface.

wso: How is the tool introduced to the pipeline?

Livermore: It can be inserted via a hot tap connection and insertion sleeve or an existing access or open chamber. Once inside the line, it travels with the flow of the water to an extraction point, which could be a hot tap connection and insertion sleeve, an existing access, an open chamber, or a reservoir.

wso: How does this technology assess pipe condition?

Livermore: The technology emits an electromagnetic field into the walls of the pipeline and then detects how that field passes through the wires that reinforce the pipe. What we’re looking for are breaks in the circuit of how that energy flows through those wires. Those indicate points where there are broken wires in the pipe reinforcement. The data is stored in the device until it reaches the extraction point, where it is taken out and connected to a computer that downloads the data.

wso: How is the data analyzed and used?

Livermore: Using the data, we’re able to go through and check for breaks. The information is used to provide a report telling the client which pipe sections have damage, if any, and quantifying it so they can go forward and repair the pipeline or take other action as warranted.

wso: How does the system record the location of the breaks?

Livermore: Each piece of pipe has a unique signature. The tool counts the number of sections from the insertion point to the extraction point by detecting certain anomalies in the magnetic field. Then, using background information from the utility, such as lay schedules and as-built drawings, we can determine where those anomalies are. That gives us a relatively accurate picture of the pipe and where the breaks are.

wso: How does this technology provide return on investment for the utility?

Livermore: Compared to the consequences of breaks that can occur in these mains, it is considerably less expensive to inspect a pipeline versus going forward, allowing a break to occur, and then repairing the pipeline and the related damage.

wso: In what sizes of pipes is this technology used?

Livermore: It is used primarily in lines 24 inches and larger. In the United States, we have assessed pipelines as large as 72 inches with the PipeDiver tool.

wso: If this is a free-swimming device, how is the speed of travel controlled?

Livermore: The utility controls the flow velocity based on parameters we agree upon in the planning process. The device is neutrally buoyant and has fins that come out of the cylinder sections where the electromagnetic tools are. The fins help keep the tool centered and provide resistance that allows the water to push it through the pipe. Typically, it moves at about 95 percent of the flow velocity, which is about one to five feet per second depending on the flow velocity within the system.

wso: What were the origins of the PipeDiver inspection in Louisville?

Coombs: We have more than 100 miles of PCCP mains in our system, and we had made plans over the years to start a condition assessment under a planned approach. In 2009, we had a catastrophic failure on a 60-inch main. A section of the pipe blew out on the side, and within less than an hour we lost about 15 million gallons of water. We estimated the cost at $1 million. If the pipe had been in a heavily developed area, the cost could have gone up exponentially.

wso: What immediate steps were taken after that event?

Coombs: We hired Pressure Pipe Inspection Co., which has since merged with Pure Technologies, to inspect as much of that main as we could while we had it shut down. They manually inspected about three miles of pipe using electromagnetic technology and found three other sections that had significant wire breaks. We dug up those sections and applied steel bands to the outside of the pipe.

At that point we decided we needed to accelerate our condition assessment program for PCCP. Shortly after that, we initiated a program to inspect all 100 miles of our PCCP mains ranging from 24 to 60 inches over a 10-year period. We are now in our third year of that program.

wso: Why did you use the PipeDiver technology for the assessment on the 8.8-mile main last year?

Coombs: There are parts of that pipe that don’t have redundancy.

wso: What were the logistics of performing that assessment?

Coombs: We had to coordinate with the operations people because the PipeDiver relies on the flow of water. You’ve got to push that water somewhere. We drew one of our tanks down to a low level, and when they were ready to launch the PipeDiver, we started pumping water to the tank. In the meantime it was pushing the PipeDiver through the pipe. It took a lot of coordination. You can imagine the amount of water you have to push through a pipe to maintain a speed of about 1 to 1.5 feet per second. That’s a big volume of water to push for six to eight hours.

wso: About what percentage of your PCCP mains will you be inspecting using the PipeDiver technology?

Coombs: Probably about one-third. On the remaining sections we will probably use robotic equipment. It also provides high-definition video capability, and so wherever we can we’re going to try to use that tool. The combination of video and wire breakage information is a good approach to use where possible.

wso: What have you learned so far from the PipeDiver investigation?

Coombs: Data collected over the past eight to 10 years shows that in a typical PCCP pipe system, anywhere from 3 to 4 percent of joints may be compromised due to wire breakage. On the main we just assessed, we had a wire breakage percentage of about 3.1, so we are toward the lower end of the range. That was somewhat reassuring to us.

Based on the draft report, we found three sections that were significantly compromised and had a great number of wire breaks — more than 100. Based on that information we excavated those and took remedial measures that included putting steel bands around the pipe. The bands replace the strength the wires would normally provide.

wso: Once you have the final report, what will be the next steps?

Coombs: With Pure Technologies and their subcontractor, Simpson, Gumpertz & Heger (SGH), we’re discussing a failure risk analysis. Are 20 wire breaks in a joint significant? I can’t tell you because I don’t know exactly where the pipe is, what pressure it’s under, how much cover it has, what type of embedment, what class of pipe it is. SGH takes all those factors into consideration and determines whether a given pipe has a risk of failing and how serious that risk is. That information will help us plan ahead.

wso: In the broadest sense, what do you see as the benefit of this technology?

Coombs: Our president told me it’s great that we are out fixing these pipes before they fail. From a public relations standpoint, from a cost standpoint, from a safety and risk standpoint, we really can’t tolerate transmission main breaks. This technology will help us identify pipes that are compromised and get them repaired or replaced in a timely fashion. Our goal is to not ever have another transmission main break.

Dearing Smith: When we have a main break or any type of distribution issue, that tends to get a lot of attention. What we are proud of now is the things we’re doing behind the scenes that are starting to get some attention that really have no customer impact. The great thing about using the PipeDiver technology is that customers were not without water, they were not inconvenienced, but at the same time we were doing them a huge service by helping to prevent large scale failures.


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