With numerous aging and deteriorating copper, PE, steel, and other types of plastic service lines and mains in need of replacement, the gas industry is always looking for new replacement techniques that limit disruption and speed installation times. Trenchless equipment manufacturer TT Technologies, Aurora, Ill., is working with several research groups and various gas utilities and contractors to develop new techniques and methods for effectively and efficiently replacing small diameter gas service lines, as well as 4- to 6-inch diameter gas mains.
According to TT Technologies product specialist, Collins Orton, there are two main reasons for the push to develop these trenchless systems. He said, “Basically it comes down to the need to upgrade aging distribution systems and trying to do it with minimal disruption. Minimal disruption helps keep customers happy, but with soaring restoration costs, specifically in pavement restoration, it means being fiscally responsible.”
Splitting Plastic Pipe
Plastic pipe got its first real usage for gas distribution systems in the late 1960s and early 1970s. But, according to published material from the American Gas Association, some limited usage of plastic pipe began all the back in the 1940s. Some of the pipe installed as recently as the 1980s, are proned to stress induced damage and needs repair or replacement. In other areas, growth and demand are driving the need to replace undersized plastic services.
According to Orton, splitting plastic pipe is not always the easiest task. He said, “The inherent nature of plastic pipe makes it very difficult to split. And it’s also what makes splitting the necessary process for effectively replacing it through a trenchless application. Plastic pipe lacks the rigidity needed in order for a pipe bursting application or a pipe extraction application to work.
So splitting becomes the preferred method, but that’s challenging as well. A bladed cutter configuration is needed to split the pipe. In the smaller diameters, your biggest challenge is getting the power necessary to split the pipe through a cable to the cutter and having a cable that’s strong enough to do the work and fit within the confines of very small, sometimes down to a ½-inch, diameter pipe.”
Large mains are also being replaced through this splitting technology. This type of splitting applications requires larger equipment and more closely resembles static pipe bursting. For this application a multi-bladed cutter is required in order to split what usually amounts to a fairly thick walled pipe. Retention of the existing pipe through a pipe retaining plate is also key in both applications.
Southern California Gas has been involved in several developmental projects utilizing the technology to split and replace aging Aldyl-A pipes.
With a service area that includes over 5 million customers, Southern California Gas Co., Calif., is the nation’s largest natural gas distribution utility. According to its corporate Web site, the company’s 20,000 square mile service area encompasses a large percentage of Central and Southern California, to the Mexican border.
Like many gas utilities around the country, much the same as water and wastewater entities, SoCal Gas is dealing with infrastructure integrity issues. Gilbert Ching is a senior engineer for Southern California Gas and runs the R&D program for the gas distribution portion of the company. According to Ching, Southern California Gas’s rehabilitation and replacement program, as well as determining whether to use the pipe splitting application, is driven by several factors. He said, “Just like any other company, you have to look at how your decision was made. Number one, you have to have a reason to replace it. Number two, it’s driven by costs. Are you going to perform another repair or replace the whole segment? And then prioritize your projects and select the least intrusive and cost-effective method.
“As part of SoCal, to learn more we had the opportunity to demonstrate the feasibility of pipe splitting on a 3,600-foot section of vintage 4-inch Aldyl pipe. It was a learning process for us and helped us understand the pros and cons of using pipe splitting which would serve as another option on future pipe replacement programs.”
The splitting project for SoCal Gas included splitting and replacing 3,600 feet of ailing 4-inch Adyl-A gas main with 4-inch Medium Density Polyethylene (MDPE) pipe. A Grundoburst 400G static pipe bursting machine was used as the hydraulic pulling system and a mutli-bladed cutting head was specially designed for the project.
According to Ching, jobsite layout is an important consideration for this project. He said, “You want to minimize interruptions to your customer. So the job was planned out to split 500 to 600 feet at a time and get that section re-energized before proceeding to the next segment or before the end of the day. The pipe splitting operation can be performed in both direction from a single excavation thereby reducing the number of launch and exit pits required and ultimately limit costs.”
Gas Main Splitting Process
This process is very similar to the static pipe bursting process. For splitting, a specially designed multi-bladed cutting head is pulled through the existing line by the hydraulic bursting unit. As the bladed cutting head is pulled through, it splits the host pipe. An expander behind the cutting blade enlarges the opening slightly to allow for easy sliding of the new PE pipe and tracer wire. The staging and layout area adjacent to the entry pit must be available to accommodate either coiled pipe trailer/carousel or butt-fusion equipment for straight pipes.
Ching said, “We’re trying to promote this technology of pipe splitting. For mains, this method is really more of a niche application where other underground facilities limit space for new pipe placement. But for replacing small diameter service, you need to find a family of pipe that needs to be replaced, based on its leakage history. Then you can plan out and pursue it as a capital project.”
Over the past several years small diameter pipe splitting techniques have been tested and developed with the help of various utility contractors and gas utilities.
Small Diameter Service Splitting Techniques
Throughout the Midwest, trenchless pipe splitting technology has been used to split and replace small diameter copper gas services. According to Orton, depending on the size and type of pipe being split, there are different tooling options. He said, “There are two different sizes of systems available for small diameter splitting situations. One offers 9,000 lbs of pullback and is typically used for host pipe diameters of 1/2- to 3/4-inch. The other 12,000 lbs of pullback and is used for host pipe diameters up to 1-inch. These units are much smaller than the static pipe bursting pullers used for splitting gas main lines.
“The trenchless application is ideal for this type of work. These services are typically running from main to meter, under lawns, landscaped areas, driveways, and sidewalks. By using the trenchless system, utility contractors or gas utility in-house crews are able to save a lot of time and money in terms of excavation and restoration. Plus, customers are back up and running the same day.”
After the existing copper or plastic service is designated for replacement, the service tees are located, both in the parkway, as well as under pavement (including sidewalks). Then keyholing can be performed by using a coring device for pavement or vacuum excavation equipment if the tee is located under a lawn. Depending on the existing pipe material, the specially designed splitting head and expander split the host pipe. Then the new pipe can be pulled directly behind the expander or, in some cases, the split service is retrieved first, then new service is pulled in place.
Keyhole Technology & Trenchless Benefits
Cost-saving opportunities are one of the most attractive benefits of the system, especially when it comes to excavation and restoration requirements. Orton said, “This tooling can be utilized through a keyhole in pavement applications, but also through a small hole excavation in the parkway, minimizing not only excavation requirements, but also, final restoration needs.
Pipeline & Gas Journal, September 2008