El Paso Natural Gas has received approval from the U.S. Department of Transportation’s Office of Pipeline Safety (OPS) to conduct more internal inspections on its rebuilt New Mexico pipeline, which ruptured August 19 killing 11 people (see NGI, Special Report). Since the explosion, flows through the line, which runs from West Texas to California, have been reduced to 85% capacity, to a rate of about 920 MMcf/d.
OPS said that the El Paso line has already been repaired and put through hydrostatic testing, which it passed. Hydrostatic testing checks for cracks by forcing high-pressure water through the line. Now El Paso has the green light to begin smart pig testing, which will examine the internal integrity of the line. The device, called a pig because of the sound it makes during inspections, has sensors and once placed inside the line, it can detect dents, deformities and changes in wall thickness.
Neither OPS nor El Paso released a timetable as to when the pigging would occur or how long it would take. However, once the testing is completed, the results will be evaluated by OPS, which then would determine if the line were safe for commercial use.
OPS has not issued actual regulations on smart pig use, but they have become increasingly sophisticated and more widely used. Even though hydrostatic testing can actually detect certain flaws that are invisible to smart pigs, the pigging process is considered a complement to the water testing and ensures more integrity in test results.
OPS requires all pipe to undergo at least one hydrostatic test after construction. Although not mandated, OPS also has proposed requiring pipelines that transport liquid petroleum products to use direct assessment methods such as pigging to evaluate the pipeline’s integrity. Other types of inspections include using magnetic particles or ultrasound to measure the pipe wall’s thickness.
Carolyn Davis, Houston
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