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Synopsis of Cured In Place Pipe Lining and Epoxy Pipe Restoration Methods In Use in 2016: Residential and Commercial, CIPP, PIP, UV, and Inversion

All throughout the United States there are literally hundreds of thousands of miles of various kinds of pipes ranging from ½” to 6’ in internal diameter that have overtime deteriorated and need replacement. These pipes may be rusted cast iron drains underneath homes or buildings, or they may be clay sewer pipes that have cracked, or concrete culverts that have deteriorated due to hydrogen sulfide corrosion, or corrugated metal culvert drains that have rusted allowing sand  infiltration which creates sinkholes in the surfaces above them. In addition, small diameter potable water pipes and large diameter water mains suffer from corrosion like any other pipes and have to be replaced after a number of years.

In all these cases to replace the pipes, excavation of concrete slabs, road surfaces, walls of high-rise buildings, factory floors, railway train tracks etc. has to occur at great expense to society and property owners. Factories have to stop production, homeowners have to move out of their homes for a few weeks, high rise building tenants have to go stay in hotels, and restaurants and shops have to quit selling their products and services. Once excavation has replaced the pipes, the decorative surfaces have to be restored which includes new tile, wood, asphalt, marble or landscaping. Also, furniture and equipment has to be taken out of storage and moved back into the property.

So it is no surprise that about 40 years ago alternatives to pipe excavation and replacement were developed, originally in Europe and Japan where the structures were older and the excavation of historic cobblestone streets for example was not an option. At first large diameter pipes were rehabilitated. The technology was easier to develop and install for larger pipes believe it or not. The small diameter pipes from 4” down to 2.5” were more complicated to rehabilitate and so be patented processes only became available about 15 years ago. Despite the fact that small diameter pipe lining has been around for more than a decade, most people don’t know that it exists.

Today various types of pipe rehabilitation are available under various names such as “cured in place pipe lining” or “CIPP”, “epoxy pipe lining”, “trenchless pipe lining” or simply “pipe lining”. They do vary somewhat in materials and installation and so we will discuss the differences at great length later in this article.

Benefits Of Pipe Lining

Benefits of pipe lining vary depending on the type of pipe lining being used. The material can be structurally so strong that it is designed to be a stand-alone, load-bearing pipe that can be underneath roads or railways or building footers and can support the weight above it even if the old host pipe has completely disintegrated. All types of pipe lining are designed to prevent excavation so they are much expedient than the old methods of pipe excavation and replacement, much more cost effective, and tenants and homeowners and property owners can stay during the installation instead of having to go live in a hotel and move all their furniture and pets into storage. In addition, depending upon the type of pipe relining, any pipe can be rehabilitated whether it is gravity fed, pressurized or even a vacuum type pipe.

General Stages Of Pipe Lining / Restoration

First there has to be a diagnosis of what is wrong with the pipe. Usually this involves a pipe video inspection. There are various kinds of small diameter video cameras ($10,000+) that are pushed along inside small diameter pipes, and for large diameter pipes the cameras are self propelled and operated from the back of a expensive video monitoring van or trailer ($100,000+). These sewer pipe video inspection services can be rented by the hour or day.

For small diameter pipes a smoke test might be performed to see where and to what extent corrosion has perforated the metal potable water lines. For large diameter pipes such as culverts, a pipe laser profiling inspection might be performed to determine whether the pipe has become malformed overtime. If it has become malformed place pipe lining can still be installed and it will conform to the shape of the pipe. In some cases if a pipe has become deformed, then that specific section of pipe might have to be excavated and replaced before cured in place pipe lining can be installed.

In all cases of pipe rehabilitation there has to be some kind of pipe preparation to prepare the surface to receive the new inner lining and to remove old corrosion and accumulated debris such as rocks and roots. For small diameter pipes (½”-3”), high pressure air flowing at high volume and containing an entrained silica or sand, is blown through the pipe that removes all the oxidation deposits. For larger diameter pipes a drain cleaning hydro jetting service or vacuum jetter will be used. They use high pressure water and vacuum system to clean out all the old sewage, rocks and other debris which is all stored inside of a mobile tank on the back of the truck. This is called “vac truck service”.

For residential pipes smaller hydro jetting machines are available and typically goes by the name “drain cleaning”. For city potable main lines a cable is pulled through the pipe and a pigging tool (which is a rough steel ball) is pulled through the pipe to remove all the old scale and rust. There are many other mechanical tools available that have been developed over time to remove stubborn adhering scale and corrosion deposits. But ultimately the inner pipe surface has been completely cleaned and the true extent of pipe deterioration is visible. Inside residential cast iron pipes for example we typically see long cracks along the bottom of the pipe or the crack has rusted so wide that the bottom of the pipe is completely missing or there are complete missing sections of pipe.

What Types of Pipe Lining Materials Are Used?

Epoxy Pipe Lining

In pipes that have experienced corrosion but still have structural integrity, a spray-on epoxy lining is applied from 1mm to say 6mm thick, depending upon the diameter of the pipe being rehabilitated. This type of pipe lining is called “epoxy pipe lining” and it is not designed to have structural strength by itself. So the associated warranties are typically 10 years or less. It is merely designed to seal off small holes that have developed due to corrosion.

There are very few companies that have patented their own epoxy and have gotten the required approvals from the FDA and NSF for use in potable applications. The 3 most well known in the US are: Nu Flow, Ace Duraflo and CuraFlo.

This epoxy pipe lining is designed to be sprayed on using centrifugal force from a rotating nozzle or it is blown through the pipe using high pressure and high volume air. For a 100’ length pipe of 4” internal diameter, you might use 8 x 180 CFM x 100 PSI tow-behind compressors attached to the pipe in parallel. 

If the holes are too large the epoxy would escape and so it would be better to use a structural liner called “cured in place pipe lining”.

Cured In Place Pipe (CIPP) Lining Materials

These materials are typically made of fiberglass, which has become less popular over time because it is not environmentally friendly. Newer liners are made of a polyester felt. But in either case the material is saturated using resin that is hardened using various methods discuss next. These “structural liners” are very strong and designed to support load-bearing environments where the old host pipe has completely disintegrated and they can have up to 50-year warranties.

The resins used vary widely in their composition. The most pertinent factor these days is to consider whether the resins contain a class of chemical compound called “styrenes”. These are known in the resin industry as “fillers”, which allows the manufacturers to effectively dilute the resin and increase the profitability of their sales.

The Problem With “Styrenes”

The problem with styrenes is that they kill fish and are otherwise environmentally unfriendly, in addition to that once the resin that has hardened the lining can shrink and remove itself from the host pipe thereby creating an interstitial space which allows for the infiltration of water or the exfiltration of sewage or the infiltration of sand, thereby negating the entire pipe lining process. In addition styrenes have a strong odor and can be offensive to building tenants or home owners.

The best alternative is 100% epoxy resin. This resin contains no styrenes, has no odor, and cannot shrink the liner. It is also 100% pure and contains no dilutants. Therefore it is much stronger (and more expensive) than other resins. For example the “Perma-Liner” brand we use is approved by the EPA, the FDA, the NSF and a slew of other various entities.

Materials Testing Required To Maintain Certifications

There are a number of pipe lining material manufacturers that have developed patented resins, liners, and custom installation equipment. But in order for these materials to maintain their approvals by the aforementioned entities, the materials have to meet certain physical strength and chemical / temperature resistance standards. There are almost 100 standards and specifications that have to be met, depending on the application and city requirements. So the manufacturers have to be tested by independent engineering companies randomly, say 3 times per year. Samples of liner and resin are pulled off a shelf by the engineering company and tested and these results have to be resubmitted to the various regulatory bodies.

Pipe Lining Installation Methods

Before a liner can be installed the resin has to be saturated into the fabric of the liner and the liner has to be installed before the resin can be hardened. For large diameter pipes, the liner is saturated at the manufacturer and transported in a refrigerated truck to the installation area. Refrigeration has to be used when the resin is exothermic (discussed below).

So how are these liners installed? Well it depends on the diameter of the pipe and whether only one or two access points are available.

Air and Water Inversion Installation

For large diameter pipes the liner is typically installed using hydrostatic water pressure. Imagine taking a sock and turning it partially inside out and holding it vertically and then filling the stock with water and allowing the water to turn the lock the right way out. This is called “water inversion”. Essentially large diameter pipes are lined by using water to turn the pipe lining material the correct way out in the pipe and then the far end of the liner is sealed and the whole liner is inflated with high pressure steam that hardens the resin within 20 or 30 minutes. Then the pipe can be put into use right away unless service connections have to be reinstated  (discussed next).

For smaller diameter pipes the same inversion type method is used to install the liner but instead of using water, air can be used to invert the lining inside of the pipe. Here is a video showing air inversion pipe lining.

Perma-Liner developed an incredible system (“Top-Gun Continuous Air Inverter”) however that uses air inversion to “shoot” an infinite length of liner. Air inversion is like water inversion but using pressurised air, and since air compresses more easily than water, it cannot be used on large diameter pipes, typically above 6” in I.D.

Pull-In-Place Installation

Another method which is commonly used today is “pull in place lining” (PIP) where a strong cable is strung through the pipe prior to pipe lining installation and the pipe lining material containing a temporary internal balloon, is pulled into the pipe into the correct position before inflation and subsequent curing. Two important factors about PIP lining is that small pieces of lining material that would normally cover up connecting branch lines inside the pipe, can be cut out ahead of time. This reduces pipe downtime since pipe connections do not have to be reinstated (cut open). Air or water inversion always covers up branch lines, which have to be “reinstated” when the liner is hard.

CIPP Lining Curing (Hardening) Methods

So in the pipe rehabilitation world there is a constant conflict between speed of installation (the faster the better) and “working time” before the resin hardens (the more time the better). Ideally we would like a resin that hardens really fast, but only when we are ready. It’s kind of how women feel about men.

Traditionally the resin was cured with steam or hot water. It’s dangerous however, people have died or been seriously injured from working with heated steam or water. So the industry developed exothermic or self-heating resin, which is really cool until it gets hot and hardens during installation before the liner is in position and excavation is required to remove it! That is every installer’s nightmare, literally every night before installation.

Another problem with exothermic resin is that cold environments may prevent the exothermic reaction from heating the resin to the point where it hardens, and the liner collapses when the inflated “calibration tube” is removed, and again excavation is required to remove it!

The reader has to understand that pipe lining is used when excavation for pipe replacement is absolutely, completely, not an option, like under the World Trade Center, or under a river (Perma-Liner lined 36” diameter and 400’ long pipes with multiple bends under a river somewhere). Imagine having to excavate that failed liner. How do you redirect a huge river?

So in addition to steam, hot water, exothermic resin, other methods have been developed to harden resin. Early tests with Viagra and Cialis resulted in early hardening, but dismal results in the long run.

This led to UV curing. Essentially a “chain of ultraviolet lights” is pulled through an inflated liner which has been saturated with a resin which hardens in 5 minutes when exposed to UV light. So installation can take as long as needed and pipe surface temperature is no issue. Right now it is used in Europe, Japan and China, and the US is catching up. Also, it’s very expensive and only available for large diameter pipes (6” and above).

Reinstatements – Dealing With Obstructed Pipe / Branch Lines After Lining

So as you can imagine if you install a new lining inside of an existing pipe that has branch pipes connecting to it, those branch connections would get covered up. This is most frequent issue that new residential customers want to have addressed. There are two ways to deal with the covering up of branch connections.

The first way is to use a pipe video inspection camera to measure the exact location of the incoming branch lines. Those distance measurements are used to cut out a small piece of the pipe lining material in a radial fashion from the longer length of pipe lining before the pipe lining is pulled into the pipe. The fact that a small piece of pipe lining material is radially cut out means that the liner being pulled into the pipe can rotate 360 degrees and the cut out section would never cover up the branch line. This method is used most often because it reduces the amount of pipe down time that building tenants or homeowners have to endure. The drawback is that a small section of pipe remains unlined. However that small section is typically inside of the “wye” connection which is a lot thicker and stronger than the pipe being rehabilitated.  In the future if the “wye” connection fails, it can be excavated and replaced if required.

The alternative way of lining the entire pipe and then coming back to cut out (“reinstate”) the service connections is more time consuming and therefore more expensive. Also there are limitations in terms of technology when it comes to reinstating pipes.

For large diameter pipes there are reinstatement cutters which travel inside of the relined pipe which typically consist of a combination of a video camera and a high-speed rotating grinding ball that can be controlled from outside of the pipe. The covered up pipe connection is then ground out to remove the obstructing pipe lining material. No water may flow down the pipe during this process because it would obstruct the video camera view.

It is also very time consuming. For example if you have a 400 foot liner going from manhole to manhole, it might require the reinstatement of 10 pipe connections which could take 2 or 3 days. That means every every house and building connected to that 400 foot section of pipe may not use the sewer systems for that period of time. In addition, the bypass pumping which was used during the pipe lining process has to be extended for another 3 days or 4 days while the pipe connections are reinstated.

But having said this when it comes to large diameter pipes that are lined which are typically a city bid or mandate, they are interested in complete water infiltration and exfiltration prevention, which is best achieved by inversion pipe lining followed by reinstatement cutting.

“Top Hat” Pipe Lining

Recently a solution to broken pipe connections between the main line and the branch line was perfected. There has always been an issue when both the branch line (“lateral”) have been lined, but the area where they connect is still un-lined.

So the “top-hat” liner was invented. It looks like a top hat in that there is a circular section (brim) that fits inside the main line, and it has a small extension that fits into the lateral, overlapping the lining inside the lateral. That way a complete seal is achieved.

Top hat seals main to lateral

Top hat seals main to lateral

Final Video Inspection and Testing

Depending on who commissioned the pipe restoration process, there may be some final testing to be done. They may want to perform some smoke testing to determine if all infiltration and exfiltration has being stopped. Usually there is a recorded video inspection that is performed as well. And finally a hydrostatic test might be performed which involves filling the relined pipe with water to see if the water level will drop, which determines if all the cracks and holes have been sealed.

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