Las Vegas Completes Record Hot Taps

Oct. 1, 2000
TDW Services of Tulsa, Okla., set a record for hot tapping this past December, cutting two 96-inch holes in a 120-inch line supplying water from Lake Mead, Nevada, to a treatment plant in Las Vegas. The taps were needed to tie in two lines leading to a new 180-inch line that will supply water to a new ozone purification plant under construction.

By Gerald Grover

TDW Services of Tulsa, Okla., set a record for hot tapping this past December, cutting two 96-inch holes in a 120-inch line supplying water from Lake Mead, Nevada, to a treatment plant in Las Vegas. The taps were needed to tie in two lines leading to a new 180-inch line that will supply water to a new ozone purification plant under construction.

The Southern Nevada Water Authority (SNWA) has had this project in the planning stages for several years. Primary contractor is JR Jacks Construction of Las Vegas. Carollo, Black & Veatch Engineering designed and engineered the project. JCM Industries of Nash, Texas, contracted with TDW Services to build and install the two 102-inch fittings. The project was planned to the last detail, including training in the handling of the desert tortoise, an endangered species in the area.

Plans called for the taps to be made into the line 12 degrees above the horizontal, about 12 feet apart. Two taps were necessary because a single 102-inch hole, the largest possible through the 11-inch pipe wall, would not be big enough to supply the new plant. The taps would be made one at a time, with water flowing.

After the first tap was completed, the cutter was retracted and the tapping valve closed. At that time, the water was shut down for 20 hours while the pipe was drained, and the tapping machine and coupon removed, the internal pipe wall inspected and a blind flange installed on the fitting. Shutdown was limited to 20 hours to avoid any adverse effect to the Las Vegas water supply. At that point, water flow was restored, and the operation was repeated on the second fitting. The two 20-hour shutdown periods were planned in advance of the operation.

Once the contract was in hand, engineers of T.D. Williamson, parent company of TDW Services, began manufacturing a new Model 2400 tapping machine, along with the cutter. TDW had manufactured several of these machines, designed to tap 48-inch holes and larger, but none were in the continental United States. For the most part, they are located in major oil field areas such as the north slope of Alaska and the Middle East. Two 96-inch ID shell cutters with diamond tipped teeth were designed and manufactured. The 102-inch fittings, also requiring new design, were ordered from JCM Industries.

Well-laid plans sometimes go awry. They did in this case when the subcontractor providing the tapping valves could not make delivery on schedule. TDW Services representatives met with the contractor and engineering consultants. The job had to go forward, using the two preset 20-hour shutdown periods. TDW personnel assured the contractor of a 75 percent probability that the taps could be made without using a tapping valve by placing the tapping machine directly on the fitting. In this configuration, if anything went wrong, an unscheduled shutdown could be required. The contractor went to bat for TDW Services and the Southern Nevada Water Authority approved the modification.

During the manufacturing process, TDW Services personnel determined a test tap should be made. A 10 x 10 foot concrete slab, 11 inches thick and laced with rebar, was poured. It was mounted in a frame and made ready for tapping. Representatives from the SNWA, the two engineering firms and JR Jacks Construction were invited to observe. This was much tougher than the actual tap because it was done under flat-plate conditions. The test tap was successful and convinced the customer that the tap could proceed without a tapping valve.

Meanwhile, the JCM fittings were attached to the pipe. Templates of the pipe made earlier permitted manufacture of a scarfed neck that fit the pipe exactly. Two O-ring seals provided a seal around the neck area where the tap would be made. Twenty-four U-bolt bands attached and secured each fitting to the pipe. When the fittings were secured, the seals were tested by installing test ports on the fitting flange between the O-rings, and pressured to 35 psi.

After testing the fitting seals, the entire area, including the pipe and both fittings out to the neck, was encased in concrete. This stabilized the fittings on the pipe, providing support to the tapping machine, adapter, cutter and pilot drill, which weighed over 33,000 pounds, and compensated for the thrust forces of water flowing through the line.

On December 9, 1999, the tapping machine was installed on the first fitting. TDW Services Applications Engineer John Burke, assisted by Technician Bob Smith made the taps. Begun in mid afternoon, tapping through the 11-inch wall thickness took 17 hours over the next two days. It went without a hitch. When complete, the line was shut down and drained, beginning the 20 hour window. During this time, water in the line was pumped back into the lake, the tapping machine removed, the inside of the line inspected, and a blind flange installed.

The tapped coupon was recovered intact inside the cutter. It was removed and the 11 inch wall thickness confirmed.

The two technicians inspected and reworked the tapping machine as necessary, installed a new cutter and prepared for the second tap. This was begun the afternoon of December 18, and it too, required 17 hours to complete.

This was the second major size record set in recent years. A record line stopping operation was completed in 1995 when a 96-inch waste water line in Baltimore was plugged through a 60-inch tapped hole, while the line was cut and tied in to a new waste water treatment plant. A 60-inch temporary bypass kept the line in service.

About the author:

Gerald Grover is a graduate of Brigham Young University. He is a registered professional engineer and a certified water and wastewater treatment plant operator. Mr. Grover has worked as a design engineer, construction engineer, and on-site engineer in operating water and wastewater treatment plants. He is currently the construction manager for the Ozone Addition Project at the Alfred Merritt Smith water treatment plant near Las Vegas.

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