Rehabilitating City Water Lines Using Trenchless Technology
Trenchless rehabilitation of city waterlines aids in the distribution of cleaner potable water using methods like CIPP and pipe bursting to fix corrosion, tuberculation and contamination.
Underneath roads and yards, homes and businesses alike are connected by a series of pipes. This network of plumbing pumps clean water to the public, and fresh water is a necessary resource in city infrastructure. However, in the United States, over 5,300 municipalities are still in noncompliance with the EPA lead standards. This contamination highlights the importance of waterline rehabilitation within the United States.
There are several different types of waterline issues that can cause contamination in a municipality’s drinking supply, one being corrosion. Corrosion occurs whenever galvanic field forms within the line. All it takes for a waterline to become home to a galvanic field is the connection of two dissimilar metals. These metals can be connected directly or indirectly and connect via an electrolyte such as water.
Corrosion in Metal Pipes
All types of metal pipes are subject to corrosion. However, different types of water can cause damage in different ways. Soft water allows corrosion to occur due to the lack of dissolved cations, while scale-forming water is less likely to aid in corrosion. Scale-forming water enables the precipitation of calcium or magnesium to form a coating to protect the pipe. Unfortunately, the scale developed from the precipitation builds up and ultimately clogs the pipe with lime and calcium. Over time, corrosion in pipes leads to corrosion fatigue.
Tuberculation in Metal Pipes
Another problem commonly found in waterlines are small mounds of corrosion known as tuberculation. These piles are often a reddish-brown color and may vary in size depending on the amount of damage.
Tuberculation begins a slime, which is an indicator of iron oxide precipitation. Iron bacteria attaches to the pipe and starts absorbing ferrous ions from the water; this causes the slime. This absorption creates an oxygen concentrated cell, which promotes the dissolution of the iron in the line. As the iron oxidizes, the product is a corrosion mixed with bio-deposits, ultimately forming tubercle. This damage is preventable using chemical treatments or concrete lines instead of metal.
Asbestos-Laced Water Pipes
Many municipalities still use asbestos permeated lines to transport water. The United States began using asbestos penetrated cement lines in 1931. The idea was that these lines would be durable and resistant to corrosion. At the time, these water pipes were expected to last around 70-years. Since then, more information has become available about the hazardous nature of asbestos, and the lines have begun to deteriorate.
The deteriorating pipes do pose a significant health risk. Fibers from broken lines clogged plumbing and can cling to laundered clothing and subsequently become airborne. Long-term exposure to water containing more than 7 million fibers per liter can cause benign polyps. Additionally, asbestos lines can be hazardous to workers replacing these lines, which is why trenchless operations are preferred when replacing asbestos-laced pipes, as these repairs require little to no air exposure to the underground pipes. (Learn more in "Asbestos Cement Pipe: Why It's a Problem and How Trenchless Can Fix It.")
Trenchless Rehabilitation Options
Rehabilitating waterlines is paramount to consumer health. Traditional methods require digging up and exposing the entire line to remove the pipe and replace it with a new piece; this process is known as conventional trenching, and this process is costly and time-consuming. Many cities are opting to use trenchless technology to save money and time. There are several options from which to choose.
Sliplining occurs when you insert a new pipe into the existing line. The newer line is much smaller in diameter which may be problematic for some areas. Due to the reduced size; workers must route the space in between the existing plumbing and the new pipe to prohibit infiltration.
While this is considered a trenchless technology, a lead-in trench and a lateral reconnect trench are required. These channels, however, are much smaller and less invasive than traditional trenching methods. (For more on sliplining, read "Sliplining or Pipe Bursting for Pipe Repair?")
Before inserting the new pipe, workers weld all lines above ground. While this method is cost-effective for lines close to the surface, deeper waterlines are more expensive to replace using sliplining.
Fold-and-form pipe is like sliplining in that new tube inserts into the existing line. However, with a fold-and-form pipe, the line is deformed or folded in on itself while running in place. Once in place, workers expand the tube back to its original shape.
While this process requires an entry trench, lateral reconnect is internal and does not need a particular channel. Workers may use a reconnect trench if they desire. Also, the fold-and-form pipe does not have as much space in between the existing and new lines. Therefore, no grouting is necessary. However, during rehabilitation, this method requires bypass pumping. (Read more about grouting in "Everything You Need to Know About Grouting in Trenchless Projects.")
Cure-in-place pipe, or CIPP, also uses a "pipe within in pipe" system to rehabilitate waterlines. However, CIPP is not a traditional pipe. Instead, it is a cloth liner permeated with resin. This cloth is flexible enough that during the insertion process, it can move around bends in the plumbing. Once it is in place, the resin hardens. (Learn more in "A Look at CIPP and Aging Drinking Water Infrastructure.")
As with the fold-and-form pipes, CIPP does not require annual space grouting as it fits close to the interior of the existing line. No lateral connection trenches are necessary, as they are all connected internally. Insertion of the liner occurs at the manhole, therefore; an entry trench is often unnecessary.
The final commonly used water rehabilitation option is pipe bursting. As the name implies, this method uses a pneumatic or hydraulic bursting mandrel to fragment the existing pipe. Behind the mandrel, a sleeve pipe is pulled into place and eliminates the current pipeline. Once in place, the sleeve pipe is lined with a new line. (Read on in "An Introduction to Pipe Bursting.")
Pipe bursting is best for brittle pipes. Cities often use this method for size-to-size or increased size installation. The former line is more often pushed into the surrounding soil.
For pipe bursting methods, a small entry and exit trenches are required to insert and retrieve the bursting mandrel.
What to Choose
Despite the similarities between the different types of trenchless waterline rehabilitation, determining which option to use relies on the state of the current plumbing, precisely what needs to happen to the original lines and the overall cost.
For overall cost efficiency, cured-in-place pipe is often the best choice. It is the least expensive and requires little to no digging of trenches. However, cities needing to increase pipe diameter should consider using a pipe bursting method to replace existing lines with larger ones.
Waterline rehabilitation is an essential topic for cities across the United States. Using trenchless technology to repair or replace these lines saves time and money while fulfilling the promise to provide clean, uncontaminated water to the populace.
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