Pipeline Safety: Hydrostatic Pressure Testing – Short Version

Southern California Gas Company is the nation’s
largest distributor of natural gas providing safe, reliable service to nearly 21 million
customers through more than 4,000 miles of transmission pipeline. Safety is our highest
priority, so we routinely conduct tests designed to measure that pipeline segments are sound,often
referred to as “pipeline integrity.” One of the common methods for assessing pipeline
integrity is the Hydrostatic Pressure Test. Hydrostatic Pressure Testing is a process
that uses water to exert pressure on a pipeline at levels greater than its usual operating
pressure. The segment of pipeline that is being tested
is temporarily removed from service by closing the nearest valves on both ends to stop the
flow of natural gas. Then the natural gas left inside the pipeline is safely vented. Excavations are dug at both ends of the segment
to expose the pipeline. Short sections of pipeline are removed from both ends of the
segment to be tested, and the ends are sealed with test head caps and end caps. Next, water
from nearby water tanks is pumped into the test head cap which also contains a foam
plug. The pumped water propels the plug through the test segment, pushing the air out and
filling it fully with water. The water pressure is then increased to a point higher than the
pipeline will normally operate to see if it has any leaks. After holding the increased
pressure for eight hours or more, the test is complete. If the hydrostatic pressure test
results in a leak or a rupture, the segment will be repaired or replaced. After a successful test, compressed air is
used to push the foam plug through the pipeline test segment and drain the water back into
the water tanks. The water is then disposed of in accordance with applicable regulations
and local requirements. The test head caps are removed, and multiple
foam plugs are pushed through the pipeline segment until it is thoroughly dried. Once
the pipeline segment is completely dry, the remaining end caps are removed and new pre-tested
replacement pipe is installed at both ends of the segment to reconnect it into the
system. Nitrogen gas is then injected into the restored pipeline segment and natural
gas from a partially opened valve pushes it to the other side to vent the remaining air.
Natural gas is safely reintroduced into the pipeline and it is brought back into service
by fully opening the valves. Finally, the excavated areas are graded and restored
as closely as possible to their pre-construction condition. Hydrostatic Pressure Testing is one of the
many tools Southern California Gas Company uses to help maintain the safety and integrity
of our natural gas pipeline system.

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