When a 16” #150 Gate valve failed in the open position, the plant requested a re-stop of the pipeline through a 20+ year old linestop fitting from a defunct competitor. Further complicating the issue was that the internal corrosion of the completion plug locked in place making it impossible to remove. In order to use this fitting required drilling an 11.875” hole through the completion plug. This plug was 3.25” thick and made of a106 Carbon Steel. It was also necessary to recover both the cut coupon and the majority of the metal chips in order to avoid clogging intake strainers downstream. The Mill Water was at ambient temperature and operating at 110psi.
RJ Stacey technicians and management determined that a specialty tank cutter would be required to complete the tap for several reasons. Firstly the cutter allows cut material to clear once the cut depth is beyond 1” due to its extra Gullet depth. The tank cutter was designed to cut flat surfaces and requires less torque from the drive unit. Furthermore, this cutter allowed us to use a small machine that was portable to the confined position. Additionally, the tank cutter design produces ribbons of steel and evacuates them back into the cutter sub adaptor as it cuts. We calculated that the large volume of this material would require a sub adaptor for the collection of this material so that it wouldn’t interfere with the function of the tapping valve once the tap was complete.
The tap was a success. RJ Stacey produced the tap required for our technicians to perform a linestop in the 90dg fitting. The coupon was caught and only a tiny fraction of the “shavings” actually entered the pipeline, having no effect on downstream strainers. The entire project allowed the customer to regain control of the mill water system and replace a faulty valve without any effect on operations.