The Guided Mole: The Next Generation of Piercing Tool
Piercing tool technology has been around since the early 1900s. The first patent for such technology dates back to WW I. The biggest limiting factor in the development of early piercing tools was a lack of good building materials. The idea of the piercing tool remained, but the first true operational models were not developed until the 1950s in Poland and the 1960s in Russia and Germany. The designs were simple, an air powered piston inside of a casing.
Accuracy and reliability were problems with early piercing tools. Improvements were made as the tools gained widespread use in the ‘70s and ‘80s. The ‘90s brought the next evolution in the piercing tool–steering. Today, 85 years after the first patent and design for a pneumatically powered piercing tool, the steerable piercing tool has become a reality.
Under the sponsorship of the Gas Research Institute (GRI), Foster Miller, Inc., Waltham, MA, developed the design for the steerable piercing tool in 1992. The design was simple. The tool would have a slanted head which, when rotated, would move the tool in different directions. With the cooperation of several entities, the steerable piercing tool is now available to the contracting public.
After development of the initial design and early prototypes, GRI enlisted the help of several large gas utilities to perform field tests including PSE&G, New Jersey, and KeySpan Energy and Delivery (formerly Brooklyn Union Gas), Brooklyn, NY. GRI had people to test the tool, now they needed someone to build it.
GRI Project Manager Renny said, “We have been trying to develop this technology since the early 1980s. Initial attempts failed. During the 1990s we took a step back and re-designed the tool. That’s when we developed the alliance with TT Technologies.”
According to TT Technologies President Chris Brahler, this project posed some difficult challenges. He said, “When we got involved with the project, there were already two prototypes under going testing. There was a lot of re-design and improvement that needed to be done with the tool. Steering was very difficult. We needed to improve tracking and locating as well as the body design itself. The initial design incorporated a hard-wired tracking system that didn’t function at an acceptable level. With the help of Digital Control [(DCI), Renton, WA], we were able to place a specially designed sonde in the tool head and track its movements with the locator. It was a tremendous improvement. “
After almost two years of testing and modifications, the Grundosteer is available to the contracting public.
Like conventional piercing tools, the Grundosteer® is pneumatically powered and driven by a piston in a casing. It features Teflon seals and tapes, as well as all modular construction for durability and long life. The tool can be surface launched or launched from a cradle in a pit.
The tool is 3 inches in diameter, weighs 85 pounds and is 87 inches long. In all respects it operates and functions like a regular piercing with the big exception of its steering capabilities. The Grundosteer can bore up to 200 feet. Sensors on the tool provide pitch and roll information to the operator and an above ground locator is used to track the tool’s position and movement.
Depending on soil conditions, the tool can be steered at a maximum 85-foot radius. The operator can make adjustments to the tool’s course by rotating the air hose with a hydraulic tensioning unit called a torquer. The wire reinforced air hose is placed in a specially developed torque frame where rotation takes place. The hydraulic torquer clamps down on the hose and allows the operator to turn it. A specially designed tapered steering head rotates accordingly then sets the tool’s course.
According to Brahler, reducing ground friction during steering was a major accomplishment. He said, “When we started working with the tool steering was difficult. By adding a friction sleeve we were able to reduce overall ground friction by up to 90%. As the operator turns the air hose, the tool actually rotates within the friction sleeve. This makes steering much easier and helps eliminate the need for special drilling fluid.”
Guiding the Mole
Steering is based on a simple clock configuration. Up is 12 o’clock; down is 6 o’clock, left is 9 o’clock and right is 3 o’clock. The tapered head can be positioned in one of these four directions and the tool will travel that way.
As the tool travels underground, the above ground locator displays the tool head’s position, along with grade, pitch and depth. When it is time to adjust the tool’s course, the operator stops the tool and puts it in reverse. After backing the tool up about a foot, the tool is stopped and the operator rotates the hose (and ultimately the tapered tool head) to accomplish the necessary change in direction. As the Grundosteer travels further into the bore, it is necessary to track the tool’s movements closely.
Brahler said, “This is where tracking the tool is extremely helpful. If after the course adjustment has been made, the locator does not detect the tool head in the proper position, further adjustments must be made. Keeping track of the path of the Grundosteer is also important. It is a good idea to mark the bore path with flags or spray paint every ten feet. These are just a few things we’ve learned through field testing.”
Feedback from the Field
A substantial amount of gas service line installation has been completed with the Grundosteer. Major gas utilities such as PSE&G and KeySpan Energy and Delivery, which both tested the tool during research and development, have now added it to their equipment arsenals.
Brahler said, “This tool is not designed to replace conventional piercing tools. Nor is it designed to replace directional drilling. It is meant to compliment existing equipment and add versatility. And that’s the kind of feedback we’re getting from the field. The tool is being used in situations that require some degree of tool navigation, but are not conducive to the use of a standard directional drill rig or conventional piercing tool.”
PSE&G has seen savings totaling over $50,000 on conversions and new installations completed with the Grundosteer over the last 2 years. KeySpan is also seeing the benefits of the tool on a number of difficult installations recently completed in their service area.
Norman said, “This is a new concept and people need to understand how this tool can be used. It’s great for those 100 to 150-ft long service connections were you have an incline or need to turn or need to operate within a very narrow environmental window. This tool is ideal for that. In addition, a generous amount of training and experience accompanies every tool, and I think that is also important.”
by Jim Schill
Trenchless Technology, July 2000