Pipeline Condition Assessment Saves Dallas $15 Million

Mockingbird Lane is the premier “main drag” thoroughfare running through midtown Dallas, a busy boulevard that serves flourishing business districts, affluent neighborhoods, posh country clubs and heavy traffic generated by the Dallas Love Field airport. Stretching for more than three miles alongside Mockingbird Lane is a critical underground water transmission main serving the Highland Park and University Park city municipalities that are part of the Dallas County Park Cities Municipal Utility District (DCPCMUD).

Built in 1948 along with DCPCMUD’s water treatment facilities, the 36-in. diameter pre-stressed concrete cylinder pipeline had never suffered any failures during its entire service life. By 2009, DCPCMUD’s water treatment facilities were overdue for a major overhaul and upgrade, and the utility decided it would be wise to budget an additional $15 million for replacing the entire three miles of aging water pipeline.

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But did the pipeline truly need replacing? For the past 60 years, DCPCMUD had never performed a condition assessment inspection on the pipeline, because — well, it just couldn’t.

“We didn’t have a way to inspect it without de-watering the pipe,” says DCPCMUD general manager Larry McDaniel, explaining why the pipeline had never undergone an internal condition assessment during its entire service life. “That pipeline is the sole source of water for our 30,000 customers and can’t be taken out of service for an inspection. What we needed was a solution that keeps the transmission main in service while it’s being inspected — and that’s when we contacted PPIC about PipeDiver.”

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A high-tech pipe-condition diagnostic device, PipeDiver was developed by the Pressure Pipe Inspection Co. (PPIC), a firm specializing in developing large-diameter water and wastewater pipeline condition assessment solutions. The result of a dozen years of research and development, PipeDiver is designed for “free-swimming” through a full high-pressure pipeline while detecting and assessing damaged sections of pipe.

“Many utilities today cannot easily de-water their lines because of cost, complexity or regulatory issues,” says PPIC COO Cliff Jones.

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Since large-diameter pipelines often provide the bulk of a city’s vital water supply, the lack of supply redundancy runs the risk of having them out for service for days or weeks, causing entire industries and communities to run dry. “Unlike manned or robotic condition-inspection tools that require an empty or depressurized water pipeline,” says Jones, “PipeDiver removes this risk by guaranteeing an accurate inspection with no service shutdown, no dewatering and minimal site preparation and disruption.”

Like DCPCMUD, many municipalities and water utilities across North America are turning to pipeline specialists to conduct condition assessments of existing pre-stressed concrete cylinder (PCCP) transmission mains prior to repairing or replacing them. PPIC’s 14 years of inspection experience reveals a startling statistic: only 4 percent of inspected municipal PCCP pipes on average had moderate to high levels of distress — and the remaining 96 percent are still in good condition.

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Provided with conclusive PPIC field inspection data, utilities are often discovering that most aging water pipelines reaching the end of their rated operational life don’t necessarily need to be replaced. Accurate condition assessment information removes the guesswork when determining the remaining operation life of a utility’s underground assets. Prioritizing repair and replacement programs based on actual asset condition also enables utilities to dynamically “bridge the gap” between costly pipeline investment and effective risk reduction.

The Dallas Project

The Dallas PPIC field crew surveyed the scene where the three-mile pipeline ran parallel and sometimes underneath Mockingbird Lane and under other major roadways. The pipeline also deviated from a straight path in two locations, making 53- and 90-degree bends. However, PipeDiver features a flexible and articulated design that enables it to easily navigate through most butterfly valves and negotiate sharp bends and tight turns in any 24-in. diameter or larger pipe. As far as the crew was concerned, its real challenge was capturing accurate RFTC data about the condition of the pre-stressing wire wrapped around and embedded within the concrete pipe when it was manufactured six decades ago.

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PipeDiver uses patented Remote Field Transformer Coupling (RFTC) technology to reliably detect breaks in this pre-stressing wire that would normally go unseen and undiscovered. RFTC technology has become the standard for assessing the condition of large diameter PCCP pipe, and functions much in the same way as a radio transmitter and receiver. Producing an electromagnetic field (the transmitter), the pre-stressing wires within the pipe amplify the signal and are recorded by a data collection device (the receiver). RFTC detects, measures and quantifies the signal distortion caused by any broken pre-stressing wires, recording the precise location of all breaks along the pipeline, and enabling an accurate means to calculate overall pipe integrity.

“PPIC is the only one with this kind of RFTC technology,” says Gary Dreighton, CDM consulting engineer working with DCPCMUD. “PPIC is well established, and they have been doing this kind of electromagnetic pipeline testing for Dallas and other municipalities for quite a while. Since the District couldn’t afford to shut down and de-water the pipeline, their RFTC technology coupled with the in-service PipeDiver tool really lent itself to the situation.”

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The PipeDiver tool was assembled and fully tested before being sent to the site, along with the special launch and retrieval tubes needed to insert and recover the PipeDiver tool from the pipeline. Launched into the in-service pipeline through an installed upstream 12-in. “hot tap,” PipeDiver moves through the pipeline with the water flow while collecting data and is retrieved from an installed downstream tap.

The field crew uncovered the launch and retrieval pipe sections with an excavator along Mockingbird Lane, installed the hot taps and hoisted the launch and retrieval tubes into position while suspended from a 15-ft boom over the trench. After a pre-launch equipment test, the gate valve was opened and PipeDiver was launched into the pipeline. The PipeDiver tool location was tracked from above-ground checkpoints using in-place and man-operated monitoring devices that constantly update and record PipeDiver’s tool-movement and distance-travelled data. After three hours, the PipeDiver tool successfully finished its three-mile inspection journey through the pipeline. Captured and removed from the pipeline at the retrieval site, the PPIC field technician downloaded pipeline assessment data for analysis.

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Anxious DCPCMUD workers and contracting engineers waited for the preliminary results, worried about the extent of damage and distress discovered by PipeDiver’s RFTC technology. Though $15 million was budgeted for replacing the pipeline, it was likely that pipeline work along Mockingbird Lane would cost even more because of expenses associated with traffic control, permits and other issues. Further, a pipeline replacement project could generate complaints from nearby neighborhoods already tired of traffic construction and repair disruptions. Would PipeDiver’s inspection data reveal many distressed pipes needing immediate replacement or would they get lucky?

Surprise Results

It was not good news — it was great news. PipeDiver’s preliminary data was reporting only three pipes out of 1,100 pipe segments were showing any distress of concern.

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“That was pretty incredible,” says Dreighton. “I was thinking we would probably have to replace at least 5 percent of the pipe or more, at least 50 or 60 pipes along the entire pipeline. However, it appears that we don’t have to replace any pipes at this time. The analysis indicated that three pipe joints were shown to have moderate distress and only had five to 10 wire breaks per joint. It was almost too good to be true.”

“If the final numbers agree, PipeDiver saved us between $10 million to $15 million in funding we would have had to expend replacing that pipeline,” says McDaniel. “The bonds that built our plant and pipeline in 1950 were paid off in 1975, and we didn’t want to raise rates any further beyond that already projected with our plant improvements. In short, we didn’t want to have to raise rates again if we could avoid it.”

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Based on the assessment data, DCPCMUD decided against replacing the one moderately distressed pipe. The utility will monitor that pipe segment and recheck it in another two or three years to see the progress of the deterioration. If the wire distress progresses to a point where the pipe segment develops 30 or more wire breaks, DCPCMUD says it will likely replace it at that time.

“DCPCMUD avoided a really dirty and difficult reinstallation job,” says Dreighton. “They will have to pay to replace it sooner or later, but it’s nice to know their existing pipeline will last a few more years. These assets need to last 50 years or more to be economical because it’s really tough having to go for bonds every 20 years for pipe replacement. The trend now is to use pipe assessment tools like PipeDiver on a regular basis and replace only what needs replacing. If this pipeline lasts 100 years, they will really have gotten their money’s worth.”

David Stewart Jones is a freelance environmental technology writer and researcher.

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