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When pipe is carrying a product, liquid or gas and requires maintenance or repair, the STOPPLE® Plugging System is designed to keep the system on stream. This system permits a section of line to be isolated and drained for necessary work while contents in the line are bypassed around the work area.
A Gulf Coast refinery had such a problem recently. A 48-inch relief header leading to a flare stack, 35 feet above ground level in a pipe rack, had to be isolated for installation of two expansion loops. An existing expansion joint packing gland could no longer control a leak and had to be replaced. It was decided to replace it with two expansion loops about 300 feet apart. Expansion and contraction of the pipe due to extreme temperature changes made installation of the loops necessary. This was a good time to do the work because some of the processing units connected to the header were down for maintenance. However, the refinery operator wanted to keep the remainder of the processing units in service. Shutting down that part of the operating system would mean significant loss in revenue.
The Baton Rouge Service Center of TDW Services, Inc., a subsidiary of T.D. Williamson, Inc., was selected to perform the STOPPLE operation and isolate the 48-inch line. Technicians Brady Butler, Brent Deaville, Ken Harold and Neal Harvey would do the work. Running parallel with this header was another relief header, this one 40 inches in diameter. If flare gases could be diverted from the larger line to the other by use of a "jump over," the larger line could be shut down to make the installation. Normal operating pressure of both lines was 5 psi at 150°F. Maximum pressure was 25 psi at 330°F.
Because of the low pressure, a folding STOPPLE Plugging Head could be inserted into the line to stop the flow. This would permit the use of a smaller tapping fitting and reduce the size of the necessary tap. This would significantly reduce the weight of the fitting and tapping equipment on the line, an important consideration because of the height above ground level. In this case, a 36 x 48-inch fitting was welded to the line. A 36-inch tap would be made and a 36 x 48-inch plugging head would be inserted into the line and opened to its 48-inch diameter to plug the line.
A 30-inch, "jump over" line would be connected to the 48-inch header at the connection point of one of the down-for-maintenance processing units. It would also be connected to a 30-inch fitting installed on the adjacent 40-inch header for that purpose. This provided rerouting of flare gases to the alternate line, permitting shutdown of the 48-inch line.
Six-inch taps were made through valved fittings on either side of the STOPPLE location, one for drainage and the other for the insertion of cleaning chemicals and steam into the header. A 2-inch purge fitting was also installed adjacent to the STOPPLE Fitting. Four additional 2-inch taps were required downstream for drainage of cleaning chemicals, steam and liquids.
The first phase of the work included welding the fittings to the line. TDW Services provided the fittings, and refinery personnel performed the welding. Before welding the 36-inch fitting, ultrasonic gauging was performed around the line to determine exact wall thickness. Caliper readings were taken at four points around the line to confirm pipe outside diameter.
After all fittings were welded in place, work started with making the 6-inch taps. Following this, four 2-inch taps were made downstream where the header split and joined a knock-out drum. These would be used for purging steam and cleaning chemicals.
Following this, a 30-inch tap was made on the 42-inch line and the "jump over" was connected between the flare lines. Next, using a TDW Model 1200 Tapping Machine, the 36-inch STOPPLE tap was made on the 48-inch line, and the STOPPLE Plugging Machine was installed. The folding plugging head was inserted into the line and opened, and the "jump over" was activated. At this time, steam and chemical cleaning agents were being released into the header before cutting it. The line was de-pressurized, and two sections were removed for installation of the two expansion loops. The plugging head remained in place two weeks while the expansion loops were being installed. All that time, flow was diverted through the "jump over" and the processing units remained in operation.
After the plugging machine was removed, a TDW Services cam plug was installed in the neck of the fitting and cam leaves extended into a fitting groove, securing it in place. An O-ring provided the seal, permitting removal of the SANDWICH® Valve. A blind flange was bolted to the fitting, completing the job. The fitting would remain on the header for future entry into the line, as required.
The STOPPLE Plugging System worked as advertised, avoiding the shutdown of major refinery processing units. Alternatives would have included a temporary fix of renewing the packing on the existing expansion joint to contain the leak, or shutting down all of the processing units connected to the header. Neither of these were desirable.
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