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National Grid Up-Rates Low-Pressure System With Internal Seals
• Map each section of pipe, identifying the number of seals needed, and take measurements to accurately identify locations of the joints to be sealed;
• Clean the pipe as required and prepare the joint location for seal placement;
• Apply lubricant to the sealing surface;
• Position the nitrile seal over the joint with the test valve located at the 3 o’clock or 9 o’clock position;
• Place carbon steel retaining bands in designated band channel locations and ready the appropriate hardware for the initial expansion;
• An expander tool is used to hydraulically load the retaining bands to predetermined pressures;
• Install a wedge to provide an interference fit with the retaining band design and remove the hydraulic tool;
• Perform a second expansion a minimum of 30 minutes after the initial expansion to ensure the retaining bands received the intended pressure after the rubber seal has been allowed to relax;
• Pressurize the seal to 10 psi. Using a soapy solution, check the perimeter edges for leakage. If there is any indication of leakage, seals are removed and the process is repeated until passing results are achieved; and
• Depressurize the seal and seal the test port with a countersunk, hex-head completion screw.
On projects with a significant quantity of seals, these processes are completed in an assembly-line fashion.
Bell said the crew spent up to 10 hours per day inside the pipe performing sealing activities that included removing debris, cleaning the joints, installing the seal and testing.
“As with any project of this nature, safety for the technicians inside the pipe and the pedestrian traffic was a high priority,” said Bell.
Miller used a six-man crew to complete approximately 110 seals in a seven-day period. A total of four excavations were required with all work taking place at night.
“This exciting project was a ‘win-win’ since the university was able to reduce its energy cost and carbon footprint while National Grid added a customer that is a vital asset to the community,” said Wencis. “In addition, through the assistance of Miller Pipeline, any inconvenience to the city of Boston and the university due to the construction process was mitigated as a result of the accelerated work schedule.”