Prestressed Pipe Deterioration Prompts Large Utility to Seek Effective, Cost-efficient Approach

While North America faces the ?pay now or pay later? challenges of rehabilitating aging underground pipe infrastructure, another issue ? unrelated to age ? is lurking beneath the surface.

That concern centers on the quality of pipe materials. Several municipalities have faced or are now facing issues related to prestressed concrete cylinder pipe (PCCP) that was manufactured using Class IV prestressing wire.

PCCP ? when designed, manufactured and operated properly ? is a durable pipe material that should last many decades. Manufactured and installed since 1942, it has established a favorable performance record.
Yet more than 500 failures have been documented since the early 1970s, with the majority of these failures occurring in pipe manufactured by Interpace Corp. using Class IV reinforcing wire.

According to a 2008 report titled ?Failure of Prestressed Concrete Cylinder Pipe? published by the American Water Works Association Research Foundation (AWWARF) and the U.S. Environmental Protection Agency, in order to achieve high strength levels ?the wire was drawn through dies at a great rate of speed, creating temperatures in excess of 400 degrees F. That proved to be detrimental to the wire, both serving to induce longitudinal cracks and to make the wire particularly susceptible to hydrogen embrittlement.?

Pipes utilizing Class I, II and III wire have also experienced deterioration and sudden failures, but not at the rate of pipes utilizing Class IV wire. Once known as the Lock Joint Pipe Co., the company was at one time the largest producer of PCCP in the United States before it dissolved in 1984.

While the failure rate is not statistically significant against the backdrop of more than 180,000 miles of PCCP produced since 1942 (according to AWWARF) when the malfunctions occur, it is often sudden and has significant consequences.

Sudden Failure

Such was the case for the Miami-Dade Water and Sewer Department (MDWASD) in Florida. MDWASD serves the entire county, comprised of 2.2 million residents, plus visiting tourists. The department has 450,000 retail customer accounts and 12 wholesale accounts. Wholesale customer accounts are municipalities that choose to maintain their own local collection and transmission systems, but rely on MDWASD for regional transmission treatment and disposal.

In the middle of a June night in 2010 in Miami-Dade County, all flow from a 72-inch sewer force main came to an abrupt and unexpected stop.

?We knew something was wrong when our North District Wastewater Treatment Plant stopped receiving flows,? says Rod J. Lovett, the Chief of the Wastewater Collection and Transmission Line Division of MDWASD. ?When we received a call from our Emergency Communication Center reporting that a pipeline had ruptured adjacent to the Biscayne Canal and 17th Avenue, we went out and investigated.?

Sure enough, there had been a massive rupture. MDWASD quickly shut down the force main, rerouting it through other available force mains.

?It was difficult to do, but fortunately we were able to do that,? Lovett says. ?When we called in the emergency contractor to make the immediate repair, we hired a consultant to do a forensic analysis on the pipe that was damaged as well as the adjacent joint next to it that was removed because we just didn?t like the way it sounded.?

MDWASD had sounded the pipe on the inside and determined that there were hollow areas indicative of prestressed wire failure. A forensic analysis discovered that there had been hydrogen embrittlement of the prestressing wire. As a result, both joints of pipe were replaced.

Financial and Public Health Consequences

The problematic PCCP force main had been installed around 1979. Its failure had been a complete surprise to Lovett and his colleagues. Through subsequent research, Lovett?s department discovered that other municipalities had similar problems on the same vintage pipe but because Interpace had gone out of business, there had been no one to hold liable.

The consequences of the pipe failure ? which spilled more than 15 million gallons of untreated wastewater ? were significant and costly.

?The repair costs for the emergency contractor cost us $750,000. Along with internal costs, it was probably well over $1 million by the time we were done with it and getting it back in service,? says Lovett.

While the rupture did not affect any residential areas, its release of sewage into the Biscayne Canal initiated a public advisory against swimming and recreational activities in areas into which the canal feeds, including Biscayne Bay, coastal beaches and Oleta River State Park.

?The waters downstream were affected by coliform and fecal coliform,? says Lovett. ?There were ?no swimming? signs posted well downstream and even into the bay waters where this canal eventually connects.?

It is problematic any time a wire breaks on the inside of a PCCP, Lovett points out. PCCP is comprised of a layer of concrete as well as a thin, 10- to 16-gauge steel cylinder. This cylinder is wrapped with prestressing wire to give it its structural strength. Mortar or concrete is placed over the wire to provide corrosion protection.

That method replaced the older reinforced concrete cylinder pipe (RCCP), which had reinforcing wire embedded in the pipe. More concrete was required to manufacture that pipe.

?When the prestressing technology came along, it allowed the pipe to be made with prestressing wire, which gave the pipe its structural strength with a lot less concrete,? Lovett says.

Inspection Identifies Critical Areas

After the emergency repair was completed on the failed MDWASD sewer force main, the next step was to perform an underground inspection to ascertain the severity of the problem and determine if there were other areas of the pipe requiring rehabilitation to avoid another catastrophic failure.

Pure Technologies is the only company that possesses the technology to identify and report the extent of wire break damage in PCCP, Lovett notes.

Mike Garaci, Program Manager for Pure Technologies, works with utilities such as MDWASD to determine what technologies are needed for inspecting pipelines and assists them in the assessments, helping them to get rehabilitation programs in place in the most efficient manner.

?Right now, we?re the only company that has electromagnetic inspection techniques to identify wire break damage in prestressed concrete cylinder pipe,? says Garaci. ?This technology accurately and quantitatively identifies wire break damage so that a utility can manage these pipelines and decide where isolated repairs need to be implemented. This type of ?assess and address? program ensures the safety of a pipeline and offers a utility a significant capital savings over replacement of a pipeline.?

?A utility can deliver with almost surgical precision and fix what needs to be fixed and not fix things that don?t need fixing, which helps them save quite a bit of money, especially in these times when the funds for widespread repairs are not available,? he adds.

MDWASD took the damaged line out of service, rerouting the flows into parallel systems and dewatering the line in preparation for the inspection.

In a little more than a week, Pure Technologies conducted a manned entry of the pipe for a visual inspection and also performed a robotic inspection using electromagnetics to identify any pipe sections of potential concern. Approximately 3.7 miles of pipeline out of 4.5 were inspected; a couple of small reaches could not be inspected because of limited access, Lovett says.

Pure?s electromagnetic inspections ascertain a magnetic signature for each section of pipe to identify anomalies that are produced by zones of wire break damage. Various characteristics associated with an anomaly (length, magnitude, phase shift, etc.) are evaluated to provide an estimate of the number of broken wire wraps. This inspection method is able to quantify the amount of wire break damage and is the best method of determining a baseline condition of a pipeline.

Electromagnetic Inspection

As to the benefits of electromagnetics, ?there are a lot of technologies out there that assess pipelines, but because PCCP is a composite structure of concrete, steel and steel prestressing wires, and because of the failure mode (the steel prestressing wire that is wrapped around the pipeline under tension tends to break before a failure), the key is to find out where the wire is broken,? Garaci says. ?We can do that and provide the engineering analysis to indicate how many broken wire wraps a section of pipe can have before it should be replaced or if the risk of failure is still low enough shape to delay the repair.?

Lovett says while the inspection technology is not new, it is new to this type of pipe.

?This technology has been used since the 1960s in the oil fields,? he says. ?They?re mainly inspecting steel pipe. It emits and receives a signal and by the strength of that signal, it can determine whether you have any problems within the metallic forces of the pipe. It is the only technology that is available for this particular type of inspection.

?The only other method of inspection would be to destroy the pipe in order to inspect it,? Lovett adds. ?It would entail a destructive testing process in order to determine whether the wires were broken. The wires are covered with concrete, both inside and outside, and you can?t see them.?

Thus, the pipe would have to be excavated through the concrete layer to determine the location of the wire breaks.

?That would be completely unreasonable,? Lovett says. ?You would end up spending more money than it would cost to actually replace the pipe. This technology is very important to us.?

Lovett says the technology, as used for this particular pipe type, is not very old and evolving.

After getting a final report from Pure Technologies, MDWASD was able to pinpoint a 1.5-mile section of the force main pipe that had the most severe problem, with 25 percent of that section showing 50 or more wire breaks.

Some 10 percent more had a moderate problem with 25 to 50 wire breaks, and about 8 percent had some issues with fewer than 25 wire breaks.

?But even the pipe with the fewest wire breaks is a problem and will eventually result in a total failure,? Lovett points out. ?There were enough problems with the severe pipe that the management decided that the risk was too great to allow this pipe to continue to be in service through the rainy season.?

After Pure Technologies completed the inspection, the company informed MDWASD the system had significant damage and that the municipality should consider repairing a large portion of it, Garaci says.

Trenchless Solution Preferred

MDWASD officials sought a repair that could be done quickly. While sliplining with high-density polyethylene pipe (HDPE) was the preferred method, two primary concerns needed to be met: a capacity issue and lead time on the material.

The department ran a model of the smaller diameter HDPE pipe (59-inch internal diameter) and found that because of the hydraulic co-efficient, or the C-factor, on this HDPE pipe, the capacity was nearly the same as the existing larger diameter (72-inch) PCCP pipe.

?We were able to satisfy ourselves that this particular type of pipe with a reduction in diameter was not going to be an issue,? Lovett says. ?The other issue was lead time on the material. This is something we needed to do quickly.?

That?s because Florida?s rainy season begins in June.

The sliplining project contract was awarded by bid to Lanzo, a company with offices in Florida and Michigan that provides services in heavy construction, land development and trenchless technologies. The company is expected to reline approximately 1.5 miles of pipeline.

?They did quite an extensive repair on a mile-and-a-half of pipe ? they essentially relined this whole pipeline,? Garaci says.

The rehabilitation contract was bid at $4.6 million. Lovett notes that sliplining is the most cost-effective approach to fixing the problem. Pipe replacement would have cost more than $15 million, he adds.

Utility Credited for Swift Action

Garaci credits MDWASD for moving quickly on what was a significant problem.

?The turn-around time between our inspection and the relining of the pipe was a matter of months, which was amazingly fast,? he says.

Against the backdrop of dwindled resources resulting from the recession, Miami-Dade serves as a great example of a response to the ?pay now or pay later? dilemma, Garaci points out.

?This pipe?s failure cost a substantial sum to fix in direct costs alone,? he says. ?The indirect costs include the pollution of the bay. With the assessment technologies available today, Miami-Dade and other utilities can be proactive and prevent this sort of failure from happening. Yes, there are costs involved in being proactive, but they?re much lower than having another unexpected failure.?

With MDWASD being one of the largest utilities in the United States, ?people take notice of what they?re doing,? says Garaci. ?People have called us specifically because of the work we?re doing there; they?re certainly in the eye of other utilities.?

What happened in Miami-Dade County is a snapshot of what is happening elsewhere in North America, points out Mike Higgins, Vice President of Engineering Services at Pure Technologies.

?What we?ve seen in general across the United States and Canada is that there are many-large diameter major water transmission mains that clients are unable to replace due to capital constraints,? he says. ?It?s often best to manage those mains through inspection technology and addressing promptly what they find through inspection. We call it ?assess and address.?

?For large municipalities, these critical pieces of infrastructure convey water to millions of people. To properly understand the condition of the asset allows you to properly manage it.?

Just because a pipeline is underground doesn?t mean it should be forgotten about. The days of ?bury and forget? are over, Higgins points out.

?There?s an expression, ?What you cannot measure, you cannot manage,? ? he says. ?That?s true of pipelines. As stewards of our water infrastructure, it behooves pipeline managers to go in, find the problems and fix them.?

Looking Ahead

Going forward, Lovett says MDWASD will do with sewer lines what the county has already done with water lines and determine whether the particular vintage pipe exists in other force mains. Lovett says prestressed pipe is good pipe when it?s built according to industry standards.

?The problem is this particular company took shortcuts for those standards and that?s why we?re having failures. We?re not really concerned about prestressed pipe that was manufactured by other companies or manufactured during another time,? he says.

?We?re only concerned about prestressed pipe by Interpace during this specific period when they had been using substandard wire,? he adds. ?We?re going to look through our inventory to see if we have other pipes that fall into that category and we?ll probably do an inspection on those pipes as well.?

Overall, prestressed concrete pipe is a good type of pipe material, says Garaci, adding that in his company?s experience, only about 4 percent of it has problems. ?The issue with Miami-Dade was that it was PCCP made by a manufacturer who?s no longer in business,? he says. ?They were using a product that at the time they thought was good, but it was later shown to be defective and prone to failure.?

?Miami-Dade is being proactive with this type of pipe,? Garaci adds. ?They?re prioritizing their pipelines and infrastructure so that they?re looking at the most critical aspects of the system first using the inspection technologies available, and going through the system in a methodical way so they can determine what needs to be rehabilitated quickly and what needs to be budgeted for in the future.?

Garaci says every utility is facing challenges with respect to pipelines regardless of the materials of which they are constructed.

?Things deteriorate with time; it?s not unusual,? he says. ?It?s just a matter of how fast they deteriorate. The key for the utilities is to find out what has deteriorated to such an extent that it needs to be replaced.?

Carol Brzozowski is an environmental journalist based in Florida.

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