High-Pressure Pipe Work

By Steve Hudson | September 28, 2010

In east central Florida, U.S. 192 provides a link between Melbourne to the southeast and the Orlando area to the northwest. Development in the area has brought steadily increasing traffic counts on that highway, prompting FDOT to undertake widening of the highway to four lanes.

Even though portions of the existing highway traverse relatively undeveloped areas, there are still some underground utilities that must be relocated before widening work can begin — and not the least of them is a major high-pressure Florida Gas Transmission Co. gas line that crosses the right-of-way.

The contractor handling the gas line relocation is Progressive Pipeline of Livingstone, Ala., which specializes in gas line construction throughout the eastern United States. In the course of this project, superintendent Korey Adams' crew has installed a total of 4,200 feet of new steel gas line — approximately 2,100 feet of 20-inch line and an additional 2,100 feet of 30-inch line.

Needless to say, relocating high-pressure gas lines is specialized work. The first part of the operation is to isolate the portion of line that is to be relocated. Working at each end, crews uncover a portion of the pipe, weld what's called a "saddle" onto the existing line, and secure a valve in place. Next, a 10-inch hole is drilled into the pipe, working through the saddle. The drill is then removed, and a device known as a "stopple" is then added to close off the pipe.

With the line isolated, a quarter-inch hole is drilled into the section of pipe to allow the construction team to check gas levels using an electronic gas sniffer.

"Once we determine that the gas levels are good," Adams says, "we use a torch to cut out a section of the pipe at each end."

Those pipe sections, once cut free, are removed.

Meanwhile, working on the surface nearby, crews welded together sections of the new steel pipe. The pipe arrived at the site in 40-foot joints, but prior to placement the welding crew joined those joints together into longer runs using a Lincoln Electric Classic II welding machine. Individual welds on the 20-inch pipe typically took 25 to 30 minutes to complete; welds on the larger 30-inch pipe typically required between 45 minutes and one hour to complete.

"The welds are 100-percent x-ray checked," Adams says, with additional pressure testing to confirm the integrity of the line.

Runs of new pipe were put together along the new pipe route. Several excavators, including a Deere 330, a Cat 330 and a Hitachi 330 — handled excavation of the cuts for the new pipe. The deepest cuts reached a depth of nine feet. Once the cuts were complete, the new pipe was set in the trenches using excavators assisted by a Cat 572 sideboom pipe-laying machine. Backfilling was handled by the excavators and by a Case 850 dozer. The new 20-inch line was placed first, followed by the 30-inch line.

In addition to the trenching work, the project involved a pair of bores — necessary to carry the new lines under Old Melbourne Highway. These bores, which parallel one another, were completed from the same pit by REM, based in Bolige, Ala.

Aside from the special considerations that go with working with high-pressure gas lines, a major factor complicating relocation of this line was a high water table at the tie-in point on the western end of the project. There, the water table was only 3.5 feet to 4 feet beneath the surface — a definite complicating factor, since the tie-in excavation at that location would have to be open for some time.

"Left to itself, water would quickly rush in to fill any excavation," notes Adams

To deal with the water and allow safe and dry completion of that tie-in, Progressive Pipeline worked with Greg Chevalier, Orlando branch manager for Holland Pump, to specify a wellpoint dewatering system for use on the project.

The plan that developed called for installation of 500 feet of wellpointing, with a Holland W8R rotary vacuum pump at the heart of the installation. A J4 jet pump was used to jet the 20-foot deep wellpoints into place.

Within minutes of the installation of the last of the points, the system began drawing down the water level within the work area. Water was discharged some distance from the excavation through a filtering system.

As Chevalier says, "You can't do much in Florida without pumps."

As the new line was installed and operational, most of the old line was removed for recycling. The portions passing under Old Melbourne Highway were filled with grout and will be left in place.

Overall, notes Progressive Pipeline's Adams, the project went smoothly.

"It's pretty straightforward work," Adams says, "but it can be dangerous if you're not careful." He adds, "We're big on safety, and everybody double-checks themselves and checks on each other, too."