Sarnia Products Pipe Line, Waterdown, S Ont., a division of Imperial Oil Ltd., Toronto, recently located a pipeline leak in a 35-mile section between pumping stations by using a freezing tool to isolate sections of the line.
This approach saved the time and money usually required if a line is cut and hydrostatically tested to find a leak.
The segment isolated is part of a 170-mile, 12-in. pipeline between Sarnia and Toronto in southern Ontario carrying gasoline and distillates. A routine hydrotest had disclosed the leak.
The traditional method of cutting sections of the line and testing was rejected by Sarnia personnel as too time consuming and expensive.
Instead, they chose a system called Ice-o-lator offered by Sealtec Ltd., Burlington, Ont., (under license from Freeze Technology International Inc., Amarillo, Tex.).
This system temporarily closes down a line by forming an ice plug at any desired location without cutting or breaking into the line. Operators fit a special chamber over the pipe at a selected location and circulate liquid nitrogen between the chamber wall and the pipe (Fig. 1).
The temperature within the chamber drops to -320 F., and an ice plug starts to form inside the pipe. When the plug is fully formed, it can withstand full pressure differential from one side to the other. Normal operating pressure for the line is 1,000 psig.
Using batch pigging on the Sarnia line, operators replaced the product contained in the pipeline between the pumping stations with water for hydrostatic testing.
Initially the main line valves were used to shorten the line, and pressures were monitored on each side of the valves. The side that lost pressure identified the leak and eliminated any concern of leakage on the other side of the valve.
With the search area thus reduced, the Ice-o-lator system was then used further to reduce the search area between valves.
Shortly before the final location was reached, some of the pressure readings were stable on both sides of the ice plug. Operators realized that the leak had to be intermittent.
Line pressure was then oscillated between zero and maximum hydrotest pressure of 1,500 psig, causing the leak to open slightly and become consistent. The ice plug remained in place during the oscillations.
When the leak was pinpointed to within 200 yd, the pipeline was excavated and the exact location determined.
This entire process was noninvasive, and the pipeline suffered no damage, according to Sarnia.
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