Vitrified clay pipes may feel old fashioned and out of date. However, despite being almost abandoned decades ago, they are making a comeback in cities looking for a durable material for their sewer systems. With trenchless technology, vitrified clay is slowly becoming the choice of municipalities.


A Brief History of Vitrified Clay Pipes

Vitrified clay pipes (VCP) date back to early civilizations. During the excavation of the Temple of Bel at Nippur, Babylonia, archeologists found t and knee joints made from baked clay. These joints dated back to around 4000 B.C., making them some of the oldest examples of clay plumbing.

The material continued to rise in popularity for sewage systems. Archeologists also discovered the use of clay water pipes in Ephesus's ruins, a city that once stood near the modern town of Selcuk in western Turkey. Experts believe that the city was built between 2000 B.C. and 1000 B.C. Wealthier parts of the town used clay pipes to run both hot and cold water to their homes.

By the 1800s, clay pipes were used across the globe. In the United States, clay pipes remained in use until the mid-1950s. At that point, clay pipes began to age, and cities began to move to other types of pipelines such as polyvinyl chloride (PVC) as a replacement. (Read also: Choosing Your Pipe: 8 Pipes to Consider for Your Trenchless Projects)


Advantages of Using Vitrified Clay Pipes

Using vitrified clay makes sense for a lot of cities. The material has properties that make it ideal for highly abrasive, highly demanding environments. It can handle waste with a high sulfur content without breaking down.

Unlike other pipe materials, vitrified clay can safely endure all standard sewer line cleaning methods. VCP can withstand aggressive cleaning from jet pressures of more than 5,000 psi and scraping using chain/cable type cutters. (Read also: Sewer Cleaning)

As vitrified clay pipes are a kiln-fired ceramic, it is inert. The pipeline properties do not change over time, giving newer pipes a life span of several hundred years when properly maintained. Older VCP lines may not have the same manufacturing quality as the new pipelines and may fail when stressed.


Disadvantages of Using Vitrified Clay Pipes

There are some disadvantages to using vitrified clay pipes as the city's sewage line of choice. Despite being able to withstand abrasion, they can become brittle. While they don't necessarily crumble under pressure, cracks can form, allowing for root intrusion into the waterline.

In some areas, it is better to go with a metal pipe instead of vitrified clay. While clay can withstand aggressive cleaning, the internal pipe pressure is lower than that of metal pipes. Areas with higher water pressure overall should not use this type of plumbing material. (Read also: The Lifespan of Steel, Clay, Plastic & Composite Pipes)

Of course, manufacturing of the clay pipes is limiting. Due to manufacturing constraints, the length of these pipes is limited. Areas that need longer than available pipelines should consider using a different option.


Using Trenchless Applications to Install Vitrified Clay Pipes

Despite other pipe materials growing in popularity since the 1950s, vitrified clay is making a comeback. More municipalities realize it is the better choice for them for their sewer needs. While it might not seem like the first choice in materials used for trenchless technology, there are few applications that workers can employ to replace current lines with new vitrified clay pipes.


Slurry Microtunneling

Slurry Microtunneling is a technique in which workers use tunneling equipment that matches the new pipeline's outside diameter. It is ideal for laying new sewer lines or other conduits throughout the city because it can move many solids, including sand, rock, and dirt, without workers opening a huge trench. It can keep towns from having to shut down parts of the city to lay new lines.

As the machine digs the tunnel for the new pipe, it grinds up the solids in the ground and pumps the waste out of the hole. There is a combination of water jets and slurry pumps to move the spoils up to the surface to remove the cuttings. The slurry pumps also help to counterbalance any groundwater the tunneling equipment may come into contact with.

As this environment can be very abrasive to the new pipeline, vitrified clay is ideal. The pipe also has a compressive strength of up to 18,000 psi, allowing workers to use jacking to force the tube into the line after the tunneling machine without the worry of breaking the line.


Pipe Bursting

Another trenchless technique that seems made for vitrified clay pipe is pipe bursting installation. This method allows workers to replace damaged lines without digging them up, which saves time and money. While this method is considered trenchless, workers do have to dig an entry pit and exit pit to use the tool.

Instead of using conventional trenching methods for rehabilitation, a machine that pulls a pipe bursting head through the existing line is used. The head splits apart the old line, pushing some fragments into the exit pit and smaller pieces into the soil above and below the new line. The new pipeline attaches to the back of the bursting head and is thus pulled into place.

Like with slurry microtunneling, vitrified clay is an excellent option for this technique due to its abrasive resistant outer coating. Additionally, unlike some pipelines, VCP does not require a carrier tube to pull it into place. Others need the additional piece of equipment that attaches to the back of the bursting head and carries the new line into place. (Read also: Sliplining or Pipe Bursting for Pipe Repair?)

Conclusion

Even after thousands of years, vitrified clay pipes are still a useful option for municipalities looking for a durable sewer line. Its abrasion resistance and high acid-resistant natural make it ideal for gravity sewers.