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Doty Bros. tackles rehab project.

Ask anyone in the energy industry about attention to safety and they will tell you that the prudent operator pays close attention to pipeline performance. So, when Vintage Inc. of Tulsa, OK, suspected they had problems with a wet gas line at a plant in Santa Paula, CA, they called Dory Bros. Equipment Company, Norwalk, CA, to evaluate the problem and develop a solution.

The needed repair work was identified by CCTV inspections carried out by Doty's crews using video cameras provided by the Empire Pipe Cleaning Company. The inspections found that in addition to corrosion, some 10,000 feet of the eight inch diameter steel gas pipeline that had been in place since the 1930s had a number of small leaks. The CCTV inspection data also revealed that the inside of the pipe had obstructions hanging down at joint locations that ranged from 1/4- to 1/2-inch in length.

As explained by Doty Bros.' Superintendent/Estimator Gary McCredie, the cause for the problem found at the joint locations dated back to the time of construction. "In year's past," McCredie explained, "it was not uncommon to find weld spatter and the formation of slag or icicles at joint locations."

Selecting a rehab method

Although the cut and replace construction method offered a viable solution to repairing the 10,000-foot section of damaged line, the owners were looking for the most cost effective and efficient solution. After careful cost and site analysis by both Dory and Vintage officials, liner technology was selected to rehabilitate the gas pipeline. The method selected was SubTerra's SubLine system. As a SubTerra licensee, Doty Bros.' crews were familiar with the SubLine technique that involved a deformed and reformed polyethylene liner that can negotiate bends up to 22 degrees. The polyethylene pipe is deformed into a heart shape that is temporarily held by restraining bands. Once installed, the pipe is reverted back to its circular form by pressurizing it with water at an ambient temperature, which breaks the temporary restraining bands. This creates a close fit within the host pipe, sealing leakage and preventing corrosion.

Once the owners agreed on the use of the SubTerra lining method, the next order of business was addressing the obstructions inside the host pipe

According to McCredie, it took both time and engineering to come up with a tool that could be pulled through the line to remove the slag and icicles at joint locations inside the line.

"Ultimately, were able to develop a specially built scraper equipped with cutter blades to remove the steel debris," he said. "However, before any cleaning could commence, Doty Bros. needed a commitment from SubTerra that the cleaning method was sufficient and that they would be willing to warranty the liner once it was installed."

McCredie explained that once they were able to gain an assurance from SubTerra regarding the warranty, the host pipe was sufficiently cleaned and crews began assembling the equipment to install the liner.

He said the equipment spread mobilized to the site included a backhoe, dump trucks, a SubTerra SubLine machine, a hydraulic unit and generator to power the SubTerra machine, rollers to place the pipe on during stringing and a 10-ton Grundowinch supplied by TT Technologies that was equipped with 2,300 feet of cable to pull the pipe into place.

Four No. 412 McElroy fusion machines were provided by Rinker Hydro Conduit that supplied the 10,000 feet of polyethylene liner for the project.

Once the launch and exit pits were dug at 2,000-foot intervals along the pipeline route, the lining process proceeded rapidly. Dory Bros.' crew used the Grundowinch to pull the pipe into place.

McCredie said crews were able to pull an entire 2,000-foot liner section in a single 10-hour shift. Once pulled into the host pipe, water pressure was used to mold the liner to the host pipe.

In discussing some of the challenges involved in the liner installation, McCredie explains: "The SubLine method is a technology that was developed in the UK. As a result the company did not have time to provide the couplings required for the project."

McCredie noted that Viking Johnson had suitable couplings available. However, they would not recommend them for use on a line that was operating at the pressure of Vintage's wet gas line.

He said, "With time at a premium, it made no sense to try to have SubTerra furnish the needed couplings. Instead, after gaining approval from SubTerra, Doty designed a closure using a Friatec electro fusion coupling and a specially machined half closure device made by C&P Welding to encase the Friatec coupling.

"By doing this we were able to test and guarantee a 400 psi operating pressure. In fact, during the tests, operating pressures of 800 psi were reached."

Following the liner installation, the newly lined wet gas line underwent calibrated hydro tests for eight hours.

After the pipe passed the required tests, the launch and exit pits were refilled and the plant resumed full operation within a week.
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Title Annotation:Rehabilitation Technology
Author:Tubb, Rita
Publication:Underground Construction
Geographic Code:1USA
Date:Apr 1, 2004
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