What is line stopping

Do you know what is a Line Stop ? OK, Let's introduce line stops to you as below : Line Stops (sometimes called Stopples) start with a hot tap, but are intended to stop the flow in the pipe. Line Stops are of necessity, somewhat more complicated than normal hot taps, but they start out in much the same way. A fitting is attached to the pipe, a hot tap is performed as previously detailed. Once the hot tap has been completed, the valve is closed, then another machine, known as a line stop actuator is installed on the pipe. The line stop actuator is used to insert a plugging head into the pipe, the most common type being a pivot head mechanism. Line stops are used to replace valves, fittings, and other equipment, once the job is done, pressure is equalized, and the line stop head is removed. The Line Stop Fitting has a specially modified flange, which includes a special plug, that allows for removal of the valve. There are several different designs for these flanges, but they all work pretty much the same, the plug is inserted into the flange through the valve, it is securely locked in place, with the result that the pressure can be bled off of the housing and valve, the valve can then be removed, and the flange blinded off. (See Figures 3 & 4, for more details) A. Line Stop Setup The Line Stop Setup includes the hot tap machine, plus an additional piece of equipment, a line stop actuator. The Line Stop Actuator can be either mechanical (screw type), or hydraulic, it is used, to place the line stop head into the line, therefore stopping the flow in the line. The Line Stop Actuator is bolted to a Line Stop Housing, which has to be long enough to include the line stop head (pivot head, or folding head), so that the Line Stop Actuator, and Housing, can be bolted to the line stop valve. Line stops often utilize special valves, called Sandwich Valves. Line Stops are normally performed through rental valves, owned by the service company who performs the work, once the work is completed, the fitting will remain on the pipe, but the valve and all other equipment is removed. FIGURE 2 - Valve, Pivot Head, Line Stop Housing and Line Stop Actuator “Stackup” B. Line Stop Operation A Line Stop starts out the same way as does a Hot Tap, but a larger cutter is used,. The larger hole in the pipe, allows the line stop head to fit into the pipe. Once the cut is made, the valve is closed the hot tap machine is removed from the line, and a line stop actuator is bolted into place. New gaskets are always to be used for every setup, but “used” studs and nuts are often used, because this operation is a temporary operation, the valve, machine, and actuator are removed at the end of the job. New studs, nuts, and gaskets should be used on the final completion, when a blind flange is installed outside of the completion plug. The line stop actuator is operated, to push the plugging head (line stop head), down, into the pipe, the common pivot head, will pivot in the direction of the flow, and form a stop, thus stopping the flow in the pipe. C. Completion Plug In order to remove the valve used for line stop operations, a completion plug is set into the line stop fitting flange (Completion Flange). There are several different types of completion flange/plug sets, but they all operate in basically the same manner, the completion plug and flange are manufactured, so as to allow the flange, to accept and lock into place, a completion plug. This completion plug is set below the valve, once set, pressure above the plug can be bled off, and the valve can then be removed. Figure 3 Completion Plug, attached to boring bar, with ball check valve, and plug holder Once the plug has been properly positioned, it is locked into place with the lock ring segments, this prevents plug movement, with the o-ring becoming the primary seal. Several different types of completion plugs have been developed with metal to metal seals, in addition to the o-ring seal. Figure 4, completion plug in place, boring bar is released and retracted, the tapping machine can now be removed, as can the valve and holder, leaving a plug ready to be blinded to complete the job. Key Points Line Stops: • Service Company supplied (rental) valve • Primarily to stop flow in the pipe • Higher pressure pivot head operations must be size on size, for lower pressure applications, a folding head may be used, subject to pressure and service limitations. • Should use new studs and nuts to bolt on blind flange, may want bleeder on blind flange. Thank you

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