Crews with NW Natural recently removed two gas line inspection apparatuses temporarily installed above ground on both sides of Interstate 84, west of the NE 74th Avenue overpass. Federal regulations require natural gas suppliers to inspect their delivery pipes every seven years, promoting safety and efficient operation. The utility’s Pipeline Integrity Management Team inspected over eight miles of gas lines during this project, which completed work on Friday, May 9th.
Although regulations allow gas line inspections through several methods, NW Natural prefers the uses of an internal sensor device known as a Pipeline Inspection Gauge (pig) – the term pig may be a backronym as some sources atribute its name’s origin to a squealing noise produced by early versions of the tool while traveling through a pipe. A pig is a device that operators can insert into a gas line that is nearly the same diameter as the pipe. Once in the pressurized gas pipe, it travels with the fuel flow at around five miles per hour, measuring the thickness of the pipe wall along its path. “As the pig moves through the system, it’s generating a 3D picture from inside the pipeline that can show wall loss or corrosion, dents, contact with other objects underground, or other various anomalies,” explained NW Natural representative Dave Santen.
Operators insert the in-pipe sensor equipment into natural gas lines via access points called pig launchers. Crews installed two temporary access points above ground on either side of I-84 west of SE 74th Avenue to bypass the segment of gas pipe that runs under the I-84 overpass in this area. Current NW Natural engineering plans do not use pigs to scan the suspended line over the freeway. Instead, they use other approved inspection methods. Consequently, workers needed to excavate around the below-ground gas lines at NE Jonesmore Street and NE Broadway to attach the pig launcher and receiver so the sensor equipment could continue its path manually, bypassing the overpass attached line.
NW Natural representatives said the inspection went well, and crews have removed the above-ground equipment. Road workers will soon repair the pavement removed during this project. Future inspections of the gas line may be able to send the pig across the overpass. However, this once every seven-year process works well and does not disrupt the natural gas supply for customers who depend on it for heating and cooking.
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