Ductile Iron Used in HDD Construction

Large Diameter Ductile Iron Pipe
Used In HDD Construction Of Water
Transmission Line

by Rita Tubb -- Managing Editor

What is believed to be the longest directionally drilled installation of large diameter ductile iron pipe was recently made near San Antonio, TX, where 1,020 feet of 30-inch American Flex-Ring, flexible restrained joint ductile iron pipe, was placed across several bodies of water.

According to Roger Engelke, River City Engineering, New Braunfels, TX, who was responsible for engineering on the project, the record diameter HDD installation was made by TAUG HDD Ltd., Flower Mound, TX. The crossing was one of four carried out as part of a two-part construction program for the Canyon Regional Water Authority (CRWA) to bring water from Lake Dunlap on the Guadalupe River in McQueeney, TX to central Bexar County, about 30 miles away.

The three remaining crossings included a 806-foot section of 30-inch diameter iron pipe installed under Saltillo Creek, a 692-foot crossing under wetlands and one crossing under Saltillo Creek II where 24-inch pipe with 30-inch OD bells was installed.

Rodney Schwarzlose, area manager for Holloman Corporation of Converse, TX, the general contractor on the project, said that in addition to the 2,500 feet of HDD crossings the job involved the installation of some 18 miles of American 24- and 30-inch ductile iron pipe through open cut.

Continuing, Schwarzlose said, "The original specifications for this project called for high density polyethylene (HDPE) pipe to be used for the HDD crossings. To help cut costs and to obtain a quality, one-pipe material pipeline, the project owner, CRWA, wanted to use ductile iron pipe throughout."

Birmingham, AL-based American Ductile Iron Pipe Co.’s Marketing Specialist Ralph Carpenter is quick to point out that significant lengths of 4-inch through 12-inch diameter ductile iron pipe had been installed using horizontal directional drills. "The difference on this project was the pipe diameter," he said. "Prior to this project, the longest HDD of any significance -- using ductile iron pipe -- was done with 12-inch diameter pipe. Previous to that, the largest diameter ductile iron pipe of this type that had been installed through HDD was 36 inches in diameter. However, it only
involved an installation of about 300 feet.

The use of 30-inch diameter ductile iron pipe on this project put TAUG HDD in a completely different league.

"A key to the successful HDD installation of ductile iron pipe is the restrained joint pipe that was used. Developed by American Ductile Iron Pipe, the Flex-Ring joint provides liberal deflections, up to 4 degrees for 14- to 36-inch pipe, while maintaining full thrust capabilities.”

TAUG HDD’s President Keith Whitaker said the decision to use large diameter ductile iron pipe on the project posed some challenges. “Most drillers prefer to pull product they work with often, like HDPE pipe,” he said. “When the decision was made to change the pipe on this job from HDPE to ductile iron, I was asked if the larger diameter ductile iron pipe could be installed through HDD and if I still wanted to do the job. I felt certain that we could handle the installation and agreed to under take the project.” The project called for three HDD crossings using 30-inch ductile iron pipe with 36-inch OD bells, and a fourth crossing to install 24-inch ductile iron pipe with 30-inch OD bells.

While admitting to some uneasiness, Whitaker said that instead of starting with one of the shorter crossings, a decision was made to tackle the longest first – which was a 1,020-foot crossing on Lower Seguin Road at Woman Hollering Creek.

On this crossing, a 9 7/8-inch pilot bore was drilled that was enlarged by four back reaming passes to 54 inches.

A short distance into the first drill, it was plain that the ground was made up of cobbles, chunky rock and clays,” Whitaker noted. “We were able to use a jettable steering head to get through these ground conditions without any trouble.

“Our second crossing was a 30-inch diameter, 806-foot crossing at Saltillo Creek along SH-1604. Another 30-inch diameter, 692-foot crossing was completed across a wetland area where several small ponds were located.”

The last drill, also at Saltillo Creek along I-10, was 960 feet in length and 24 inches in diameter. Whitaker said the bore on this drill was enlarged by back-reaming to 44 inches.

Rig selection

To tackle the HDD on the project, TAUG HDD selected an American Augers DD140 drilling rig with 140,000 pounds of pullback and a Tulsa Rig Iron TT1000 mud mixing, recycling and pumping system with a maximum pumping volume of 450 gpm.

Preparation for the directional drills on the project was ongoing. “We were very concerned about this type of pipe installation because it had never before been used for an HDD installation of this length and pipe diameter,” Whitaker explained.

Although the project is basically in a rural setting, Whitaker said municipal jobs generally offer only minimal right-of-way and this one was no different. “We had about 30 feet of right-of-way to work in, which meant setting up a large rig within a very confined space.”

To reduce disturbance in the area, Holloman’s crew assembled the pipe in the trench using the box “cartridge method,” one joint at a time. This was a distinct advantage for ductile iron pipe over other pipe materials. American Ductile Iron also had personnel on site. Carpenter said that initially the start-up took about 20 minutes per cycle. “Within about 1½ hours of the initial pullback, Holloman’s crews had the cycle down to about 5 to 8 minutes.

“From this you can see that joint make-up is quick and that Holloman’s crews got the routine down very quickly. This was the first job that Holloman’s crews had been involved with using Flex-Ring pipe.”

Another challenge faced by Whitaker was a requirement calling for loose polyethylene (PE) wrap around the pipe to help reduce corrosion. The PE wrap had to remain attached to the pipe through-out the entire bore. “One of the tricks in keeping the plastic wrap on the pipe is good hole conditions,” Whitaker said. “Essential to this is a good slurry mix in the hole and having water in the pipe for buoyancy so that the pipe doesn’t drag on either the bottom or top of the hole.”

“For this reason,” he said, “we used between 100,000 and 150,000 gallons of drilling fluid on each respective bore.” Now that the HDD portion of the project is complete, Whitaker says he’s very impressed with the Flex-Ring pipe. “In fact,” he said, “I wouldn’t be afraid to pull it on the next job.”

According to Whitaker, the early concern regarding the pipe was primarily because this diameter and pull-length of ductile iron pipe had never before been carried out in an HDD installation. “We took extra time to swab and clean the bore so the bells on the pipe would not produce unnecessary drag. This proved not to be an issue. During the pulls con-ducted over the course of the project we never exceeded 80,000 pounds, even though Flex-Ring pipe is rated for 200,000 pounds of pulling load.”

TAUG HDD’s Drilling Superintendent Danny
Bennifield is shown at the rig’s controls during
one of the crossings on the project.

FOR MORE INFORMATION:
Flex-Ring ductile iron pipe: American Ductile Iron Pipe, (205) 325-1965
HDD rig: American Augers/Astec, (800) 527-6020