When is it a good time to rehabilitate or repair a water pipe? Certainly, when the news crews are filming the break, the time for a proactive approach has passed.
However, there are several factors to consider when deciding whether to do a repair, retrofit, or replacement, industry experts note. They include the pipe’s condition, taking into account corrosion, wall thickness, and age. Another is its substrate: cast iron, asbestos cement, or ductile iron. Other factors are the project timeline, budget, cost to customers, and cost of delays to the traveling public during construction.
To be certain, pipe rehabilitation and replacement costs money. There are strategies to address that, notes Maury Douglas Gaston, manager of marketing services for the American Cast Iron Pipe Co., who recently completed a two-year tour of 60 major utility firms.
Gaston, a member of the American Water Works Association’s (AWWA) A21-Ductile Iron Pipe & Fittings Committee and chairman of Subcommittee 1, which governs ductile iron pipe design and manufacturing standards, says that from a financial standpoint, “the best utilities are the ones that have small, incremental rate increases every year regardless of whether they need it or not. Regardless of how much capital improvement money they’re spending the next year, a compounding 2 or 3% rate increase every year is going to be palatable to the ratepayers and you’re going to avoid the public outcry if you have a 9 or 12% increase every five years,” he says, adding that the incremental rate increases add cash to the balance sheet and improve the bond rating.
The American Cast Iron Pipe Co. manufactures ductile iron and spiral welded steel pipe from 4-inch to 12-foot diameters. The company also manufactures valves from 2 to 66 inches in diameter, fire hydrants, and bolted and unbolted joints that are available restrained to prevent joint separation or unrestrained if thrust is not an issue.
“Our Flex-Ring joint pipe is restrained, has five degrees joint deflection, and has proven to be very effective in horizontal directional drilling installations where a bore path is created, and then the pipe is either pre-assembled above ground and pulled through the bore path, or can be installed with the cartridge method where one 20-foot joint is assembled and pulled through,” points out Gaston.
The American Cast Iron Pipe Co. has done horizontal directional drilling installations in a variety of large diameters up to 42 inches, and in lengths as long as 1,000 feet or more for smaller diameters, says Gaston. Flex-Ring pipe also has proven to be very effective in pipe bursting applications, he adds.
The company has furnished a number of spiral-welded steel pipe projects where a larger diameter deteriorated pipe is slip-lined with a slightly smaller spiral-welded pipe, and the remaining space is sometimes grouted with sand or another material.
Cast iron pipe has been used for more than 200 years in the United States, points out Gaston, adding that old cast iron pipe was not lined. “If you see a photograph of a clogged-up, rusty-looking pipe, chances are that it was installed well before 1930, because in the period between 1923 and 1930, the cast iron pipe industry began to apply a thin lining of cement inside iron pipe which prevents tuberculation—a buildup of mineral deposits inside an unlined cast iron pipe.”
Being that pre-1920 cast iron lines were not cement lined, many of them tuberculated, restricting flow. “Typically, a utility would scour out that tuberculation, flush it out, and then cement line the pipe in situ,” he adds.
Gaston says Boston engaged in an in situ cement lining program in the early 1980s, cleaning and cement-lining all cast iron pipe. The initial intent was to first replace the oldest pipes, pinpointing priorities through conducting an assessment. But that assessment revealed that many of Boston’s oldest pipes were, in fact, in some of the best conditions. Using that as an example, Gaston says he believes assessments should be mandatory before taking actions on pipes.
Studying Boston’s Pipes
One of the oldest communities in the US, Boston indeed serves as a case study on how to properly assess a pipe’s condition for repair or replacement. Recently, Stephan Shea, director of engineering and design for Boston Water and Sewer Commission (BWSC), and James Pescatore, senior project manager for CDM Smith, presented to an AWWA conference the findings of the city’s pipe assessment and resulting actions.
Boston’s water pipe system dates to 1848. The 1,000 miles of water pipe includes cast iron and steel.
System improvements were conducted as the region expanded through annexation and reclaimed land. In the 1960s, the system showed signs of needing an upgrade due to leaks, deteriorated water mains, and low fire flows.
A 1967 study recommended all transmission mains be cleaned and cement lined as part of other enhancements. A 1986 study included new mapping, a hydraulic model, an expanded leak detection program, a hydrant replacement program, and a valve exercising program, as well as a requirement to replace or rehabilitate a minimum of 17 miles of water pipe each year for the subsequent 20 years. The improvements resulted in a hydraulically-strong distribution system with excellent water quality and relatively few main breaks.
American Cast Iron Pipe Co. technical director Gene Oliver
While examining the late 1990s trend of pipes installed in the 1950s through the 1970s breaking, it was noted that cast iron pipes from the 1950s and 1960s were cracking while some pipes from the early 1970s were breaking from corrosion.
An approach of replacing older water pipes was somewhat simplistic. Pipes that should have a life of 100 years or more were breaking long before that. It was noted that pipe walls for cast iron pipe had been getting thinner over the years and that ductile iron pipe walls were even thinner.
In 2007, Boston initiated a comprehensive study. It included a system description and history, a Massachusetts Water Resources Authority meter assessment, and examinations of non-revenue water, water use and population, hydraulic conditions, water quality, external corrosion, facilities information, facilities assessment, operational practices, design criteria, software and technology tools, and financial assessment.
Boston’s more than 1,000 miles of pipe, sized from 4–48 inches, and installed between 1848 and 2014, were examined.
A significant amount of the unlined cast iron pipe had been installed between 1890 and 1949; most of it was subsequently cleaned and cement mortar lined.
Between 1950 and 1970, lesser amounts of pipe were installed consisting mostly of cement-lined cast iron. From 1970 to the present, cement-lined ductile iron pipe was installed to improve hydraulic capacity and renew the system.
Samples of different-aged pipes across all neighborhoods were obtained from ongoing construction projects to provide a snapshot of the overall piping system condition and its chemical and physical characteristics. The sampling program was expected to yield information about corrosion, pipe failures, and longevity of pipes with and without cement linings.
Of particular interest were the corrosion results, as corrosion damage can be a major driving factor in pipe failure. Corrosion is measured by graphitization; the rates were compared to various contributing external factors such as soil types, high groundwater—particularly salt water intrusion—and the possible presence of stray direct current from Boston’s subway system.
The highest rates of pipe corrosion corresponded with fill areas in downtown Boston, the South End, south Boston, and east Boston where boundary changes involved filling in land claimed from tidal basins. The fill was not easily characterized because of the different sources ranging from landfill material to clean gravel from areas west of Boston.
While an initial supposition would be that older pipe—subjected to internal and external corrosion damage—would have a shorter service life than newer cement-lined pipe, it was found that the greater wall thickness of the older pre-1950 pipe provided more material to sacrifice to corrosion.
The city’s 12-inch diameter Class 52 ductile pipes—40% of BWSC’s system—have walls that are about 0.3 inches thinner than 1908 Standard 12-inch Class C pipe. For the 12-inch size, Class 56 ductile iron pipe has 0.12 inches more pipe wall thickness than Class 52 ductile iron pipe, which is believed to add about 90 years of life, based on the average external corrosion rate of 1.34 mils per year.
From the data collected, Class 52 ductile iron pipe was considered to have the shortest theoretical life of all of the pipe examined because its thin wall can corrode completely through sooner than other pipe materials.
The study points out that some weak points in pipe can be original manufacturing flaws. Failures often occur when mechanical forces such as internal pressure, excessive soil loads, bad backfilling, poor trenching practices, settlement, frost heaving, and direct impact by nearby excavation concentrate stresses at the weak points.
BWSC maintains a list of more than 38 years of water mains breaks from 1975 to the present day. Those breaks were examined using an advanced statistical model, Linear Extended Yule Process, that uses multiple regression functions to develop life expectancies of assets.
The findings of average service lives:
- Cement-lined ductile iron pipe installed prior to 1976: 65 years
- Cement-lined ductile iron pipe installed after 1976: 85 years
- Cast iron pipe with no cement lining installed between 1921 and 1949: 100 years
- Cast iron pipe with factory-applied cement lining installed between 1950 and 1968: 100 years
- Cast iron pipe installed between 1921 and 1949 without a cement lining but later lined in situ: 120 years
- Pit cast iron pipe with no cement lining installed between 1848 and 1920: 125 years
- Pit cast iron pipe installed without a cement lining between 1848 and 1920 and later lined in situ: 145 years
The service life data was input into a KANEW model that takes into account the install date for the all of the various pipes in the system and uses the service life curves to predict when particular classes of pipe will need to be retired from service. The model was utilized to predict aggregate long-term replacement and rehabilitation needs for the BWSC distribution system.
A night installation using HYMAX coupling
The KANEW model was used to develop a series of “what if” scenarios aimed at leveling out the year-to-year renewal volume. The final result was a recommendation of 11 miles of pipe renewal per year to sustain the system in the long run, a considerable reduction from BWSC’s prior goal of replacing or rehabilitating 17 miles of pipe per year.
It is noted that the KANEW model should be run at five-year intervals after the inclusion of new information for pipe breaks, pipe replacements, and pipe and soils sampling.
The evaluation enabled the application of a risk-based assessment methodology to determine the long-term replacement and rehabilitation needs for each pipe in the distribution system. The risk framework is derived from Asset Management principles, which consider “risk” to be the product of the probability of an event, such as a water main failure, and its consequences, such as a critical customer losing water service or a major hospital complex being flooded.
This computer based analysis reviewed the pipe break related data and used the statistical LEYP model to correlate breaks with spatial GIS information about corrosive soils, groundwater, fill areas, and proximity to rail lines that might influence the probability of pipe failure.
Additional information linked to specific mains was developed using the GIS and the hydraulic model. The GIS spatial analysis revealed the sensitive facilities and areas in the city where a pipe failure would have the greatest consequences. The hydraulic model assessed which mains were the most hydraulically critical regarding potential failure and service interruption.
The Annual Rehabilitation Planning (ARP) model weighs and ranks prior risk data to generate prioritized groupings of pipe segments that could be used to more strategically spend capital funds and make better informed infrastructure renewal decisions, augmented by engineering review, for pipe rehabilitation and replacement programs for the subsequent five years.
A second objective was to provide groups of pipe assets to select from over the subsequent 20 years. A 36-inch transmission main in an area of critical concern will carry a high ranking but a low probability of breaking. As such, that and similar pipes could be monitored for leakage or pipe wall corrosion as a precaution.
The process serves the long-term goals of reducing distribution system risk, maintaining existing low failure rates, and creating a sustainable, long-term rehabilitation and replacement strategy that minimizes the lifecycle cost of renewal of distribution system infrastructure.
As a result of the study, the BWSC created several action steps, including moving to the use of 56 ductile iron pipe to significantly increase the life of the pipe; poly-wrapping all new pipe in areas with poor soils or high groundwater; replacing or rehabilitating a minimum of 11 miles of pipe per year; using the ARP model as a guide to selection of pipes for replacement; collecting and analyzing pipe and soils samples each year; and rerunning the software using new main break and pipe analyses data.
Through renewal and replacement efforts, the BWSC system is now comprised of about 455 miles of cement-lined ductile iron pipe, 538 miles of cast iron pipe, and about 11 miles of steel mains; the remainder is comprised of miscellaneous materials.
An installation of HYMAX coupling in Haines City, FL
In determining whether to repair or replace a pipe, contractors focus on its structural integrity. “If the pipe wall is in good condition and there are simply joint or tuberculation problems because it was not cement-lined but the structural integrity of the pipe remains in place, that’s a perfect candidate for rehabilitation,” notes Gaston.
Because budgets are tight “there’s nothing like a preventative maintenance program,” says Gaston, adding a utility should aim for a condition assessment every 10–15 years.
Although a valve and a hydrant exercise maintenance program is not directly related to rehabilitation, when it’s being conducted in a particular area near a pipe network, there is an opportunity to do a condition assessment, points out Gaston.
The most cost-efficient approach is predicated on a number of factors, says Gaston: “Is it in an urban environment? Is it in a rural environment? Is it small diameter? Is it large diameter? What is the original pipe material made of?”
He points out that in a Houston project, a trenchless rehabilitation was desirable because of the economic impact of tearing up the streets in a particular commercial neighborhood. In another project in North Carolina, pipe-bursting was appropriate because the cast iron pipe could be broken, says Gaston.
“There are many aspects to cement pipe in the ground of which the public is unaware,” says Gaston. “There is some thought that asbestos is dangerous only if it is airborne and not waterborne, but nonetheless, there are millions of feet of asbestos pipes still delivering water to people. It can easily be broken with a pipe-bursting application.”
Gaston says he believes ductile iron pipe would be an “excellent” rehab/replace option for asbestos cement pipe.
“PVC pipe is known to suffer from fatigue in particular force mains where the pumps turn on and off,” he says. “If that becomes an issue, since PVC can be broken by pulling something through it, then pipe bursting would be good for that with ductile iron pipe.”
If there are corrosive soils, the ductile iron pipe needs to be wrapped in polyethylene encasement, adds Gaston. His company offers V-Bio, an enhancement and improvement polyethylene encasement. The product has a chemical infused on the inside of the polyethylene; the chemical kills germs and bacteria that can set up a period of brief initial corrosion for the first six months or so of the pipe’s installation, before the fresh supply of oxygen is depleted.
“This V-Bio product shuts all that down—the corrosion monitoring and graph is just a flat line from day one,” says Gaston. “We also offer zinc-coated iron pipe with an asphaltic top coat if areas have corrosive soils. Having said all that, if you have corrosive soils and you put zinc-coated iron pipe and encase it in polyethylene, you’re going to eliminate your external corrosion risk.”
Many utilities—particularly those with cast and ductile iron pipe—are planning for a 100-year life, “and that’s a reasonable expectation for cast and ductile iron pipe,” says Gaston.
“AWWA’s Buried No Longer report would substantiate a 100-year life for iron pipe,” he adds. “With that in mind, a lot of utilities target a 1% replacement of their system each year, which would mean they could replace the entire system every 100 years.”
Ductile iron pipe has been around for so long and pipe rehabilitation and condition assessment has come to the forefront so recently that many times, ductile iron pipe is not thought of as a rehabilitation or replacement option, says Gaston.
“Ductile iron pipe and cast iron has been around for more than 150 years. Its robustness with respect to [being] cleaned and in situ lined, and joints being replaced if they’re a problem, should not be overlooked as a replacement pipe,” he says.
“People tend to think that newer is better and that’s not always the case,” he adds. “Asbestos cement pipe came and went over a 20-year period of time, partly in response to the metal shortage in World War II. Pre-stressed concrete cylinder pipe was developed in the 1940s because it used less steel than the equivalent amount of iron in cast iron pipe. The pre-stressed concrete cylinder folks thought that it was going to be a temporary product that would be phased out when the war was over and metals were available again, but it held on.”
Gaston says many pre-stressed concrete cylinder pipelines have been slip-lined with slightly smaller spiral-welded steel pipe.
54-inch pipe at a Grand Island, NE, plant pipeyard
Coupling and Ground Movement
Krausz USA—which designs and manufactures coupling and repair clamp solutions for water and wastewater applications worldwide—recently launched its HYMAX VERSA coupling, an all-in-one product to stab-fit two separate pipes of same or differing materials and diameters, or wrap around the pipe’s damaged section.
It is designed to offer a range of options for installers to make repairs quickly and easily under different circumstances and conditions.
Case in point: in situations where cutting pipe involves adhering to stringent environmental precautions, HYMAX VERSA’s installation time is intended to be a fraction of that with standard repair techniques, since the pipe can be wrapped in one step without cutting away damaged pipe.
“With asbestos cement pipe, that it a key issue,” says Tom Gwynn, president of Krausz USA. “Once it has been cut, it creates a hazardous material site for any municipality that has to deal with it. Both the time and the repair costs start going up many times over.”
It also is useful in situations where pipes are not completely round and don’t easily fit into a standard coupling.
“We know it’s unconventional to think of a coupling that can be either stab-fitted or wrapped around pipe,” concedes Gwynn. “Regardless of how HYMAX VERSA is applied, however, it works similarly to our flagship HYMAX coupling, which has been used in more than one million installations across North America. This new product uses the same pressure-assisted gasket as in the HYMAX and allows for dynamic deflection. It also features heavy-duty construction to endure the most severe conditions.”
HYMAX VERSA’s parts are 100% stainless steel. Its weld-free construction is designed to resist corrosion since welded areas of couplings are often where corrosion starts. Additionally, the coupling’s bolts go through a molecular anti-galling process that embeds them with zinc to help minimize oxidization. These features make HYMAX VERSA an ideal coupling in corrosive ground conditions or “hot soil”.
HYMAX VERSA’s hydraulic pressure-assisted gasket inflates with increasing water pressure, allowing for dynamic deflection of up to three degrees on each side and reducing the risk of future pipe damage due to ground shifts and temperature changes.
HYMAX VERSA has an extra-wide tolerance of up to 1.3 inches and can take the place of multiple repair products. Additionally, HYMAX VERSA features top-facing bolts and lightweight construction.
“When it comes to repairing pipes, installers want a solution that stands the test of time and can be applied quickly,” says Gwynn. “HYMAX VERSA offers both. Its versatility means that it’s easier and faster to repair pipes and return operations to normal.”
Gwynn points out there are inherent dangers in working in a trench in the ground repairing a pipe. “Being down there the minimal amount of time possible is important, so speed and simplicity become very important,” he says.
Gwynn also mentions that the ground is in constant movement, such as between summer and winter. “It’s one of those things that puts stresses and forces on pipes that eventually cause them to fail, and it’s unavoidable,” he says. “Most pipe being rigid in nature, there’s areason why a pipe breaks where it does. It’s usually because the ground is moving in such a way that the point on the pipe is experiencing stresses higher than the rest of the pipe.”
Putting a flexible repair device on the break allows the pipe to continue to move as the ground moves, says Gwynn. “You now have a device that not only repairs the break, but can be a permanent repair, allowing the pipe to continue to move. And you’re not back digging it up to replace it or put another one on another 5 or 10 feet further down because now the point that’s been repaired is rigid and inflexible.”
For those whose objective is corrosion protection or tuberculation prevention, a pipe liner such as 3M Scotchkote Pipe Renewal Liner 2400 can quickly get the pipe back in service, notes Sunidh Jani, marketing development manager for 3M Infrastructure.
“If upon examination the pipe is also showing signs of wear and tear such as pin holes and cracks, Scotchkote Liner 2400 also extends the life of the pipe and provides some structural enhancement,” adds Jani. “However, if a pipe is showing signs of major degradation, it may be time to replace it.”
Scotchkote Liner 2400 from 3M is designed to allow water pipes to be cleaned and lined and returned to service much quicker and with less disruption than pipe replacement, says Jani. “Further, cleaning certain types of pipes and then lining them with Scotchkote Liner 2400 can help improve water quality and flow,” adds Jani. Scotchkote Liner 2400 has been applied in ferrous and cement pipes in the United States and other sites around the world.
The frequency with which a system should be evaluated for problems is site-specific, explains Jani. While everyone understands the need to maintain water infrastructure, no one likes to impose or receive a rate increase, points out Jani.
“Products like liners help solve an immediate need and allow funds to be used for other projects,” says Jani. “Liners can save a utility’s resources as they help reduce excavation and limit community disruption. By extending the life of the existing pipe, a utility stretches its resources so money can be spent on more areas to meet the greatest number of needs.”
Questions and Assessments
When New Jersey American Water managers look at the water pipe infrastructure to determine whether there is a need for rehabilitation or replacement, several factors are considered, says Mike Wolan, engineering manager at Project Delivery North.
“Some common factors that are considered include the age of the pipe, pipe material, leak history, flow characteristics, pipe integrity, potential disruption to customers, local conditions, and future needs,” he says.
Since no two projects are identical, ascertaining whether a pipe should be repaired or replaced depends on local conditions, says Wolan.
“The best approach is to ask some basic questions for every project,” he says, giving these examples: “Can the longevity of the existing pipe be extended? How difficult will it be to install new or rehabilitate the existing? Will there be any future maintenance concerns? What is the cost and value comparison between the different methodologies? Will water quality or hydraulic performance be improved? What environmental and social factors exist that are important or impact our customers?”
New Jersey American Water continuously monitors its system on a daily basis. Critical or emergency projects are accelerated based upon this gathering of information, says Wolan.
“Routine projects are prioritized using a pipeline prioritization model,” he says. “This model provides individual scoring and allows selection of projects with greatest need for construction first.”
Larry Schmidt, technical services engineer for Diamond Plastics Corp., says the company offers PVC pipe that is designed to not corrode or require maintenance of cathodic protection devices to prevent it from corroding.
In the arid Southwest, pipe assessment management is especially critical in saving water before it is lost.
Charles Scott, the engineering project manager of the asset management division of the Las Vegas Valley Water District, an end user of Diamond Plastics pipe, says the assessment task involves assessing a pipe’s condition, break history, the consequence of failure, and coordination of road improvement projects at the same time.
The system is relatively young—the average age of underground pipe is 21–22 years old—so the division doesn’t have a “sense of urgency” to replace a fixed number of miles of pipe per year, says Scott.
The Las Vegas Valley Water District system entails some 4,500 miles of pipe of six inches and larger, not including service laterals. The system is a combination of 60% PVC; 30% asbestos cement; and the remainder is steel, either cement mortar lined or concrete lined.
Scott says the Las Vegas Valley Water District started doing condition assessment eight years ago on small diameter asbestos concrete pipe. “The assessment technology works well,” he says. “The only problem is you can’t really assess the pipes that have been repaired numerous times because they have a number of clamps on them, so consequently, we’re only assessing pipe that hasn’t broken. We’re recommending areas to be replaced, sometimes in areas that hadn’t broken.
“You can’t get focused just on one part of the picture, which is only ‘assess and address’—you need to take a look at the bigger picture. You have to look at break history and a variety of other factors when selecting areas for rehabilitation.”
In doing pipe rehabilitation or replacement work, utilities such as the Las Vegas Valley Water District and New Jersey American Water typically use in-house resources. “We outsource some of the things we don’t have expertise in, such as statistical analysis,” says Scott. “We also do condition assessments in-house, but typically for the larger pipelines, we’ll outsource that.”
New Jersey American Water typically uses in-house resources to determine individual needs but will utilize outside consultants when appropriate.
Whether pipe work is done in-house or outsourced depends on the utility’s size and expertise.
“The options available have increased as the industry has matured,” notes Jani. “Now you can customize the solution to your situation. There are many good suppliers who offer ongoing, continual monitoring. So the final solution might include in-house staff, contractors, or an outsourced supplier or any combination of these.”
More sophisticated utilities might have in-house capability, says Gaston. “If I were a utility director, I would not invest my resources in condition assessment equipment and personnel; I’d outsource it to the experts,” he says. “Let them come in and do it and leave and not be burdened with that ongoing overhead. That seems to be the better business model today.”