Pigs, used to clean and inspect the inside of pipelines, line a shelf of the pig barn at the Prudhoe Bay oil field on the North Slope on Aug. 4.
AP Photo/Al Grillo
Chevron Corp., which merged with Unocal in 2005, maintains approximately 60 miles of offshore pipelines, and all get routine cleaning and periodic inspections using various technologies, said Chevron Operations Manager Dale Haines.
Two of those are “cleaning pigs” and “smart pigs,” devices that run through the pipes to perform their functions.
Cleaning pigs remove sludge and other deposits from the interior of the pipes. Runs are performed as frequently as once a week.
Their more exotic cousins, so-called smart pigs, contain sensing electronics that reveal a great deal about the condition of the pipes.
“Smart pigs can yield information such as internal or external corrosion anomalies, manufacturing defects, cracking defects or third-party damage and dents,” Haines said.
Data produced by a smart pig run is used to identify anomalies requiring immediate verification or repair. Once identified, the anomalies are located and measured directly, typically with Ultrasonic Thickness (UT) testing equipment, shear wave UT tools or radiography, Haines said.
“This assessment may then result in a pipeline repair or a conversion of service where the crude flow is permanently redirected through a different pipeline,” he said.
The time between smart pig runs varies and is governed by such things as the fluids transported in the pipe, information obtained from previous inspections and regulatory requirements, Haines said. Which smart pig is employed depends on what the pipe is made of and what information is sought.
Chevron is conducting smart pigging operations this summer, and once those are complete, all of the company’s offshore oil lines will have had a smart pig run through them, Haines said.
“Most of our Cook Inlet pipelines were installed long before smart pig technology was available, so utilizing this technology required that we modify pig launching and receiving facilities to accommodate the much longer smart pigs,” he said. “We continue to extend the capability of our launching and receiving facilities to allow us to utilize newer technology such as crack detection and high resolution smart pigs.”
There are other inspection tools, Haines said.
“Routine cathodic protection surveys are performed to ensure protection from external corrosion,” he said. “We perform annual side-scan sonar surveys to verify pipeline location, stability and any new external threats to our sub-sea pipelines.”
Pressure sensing equipment notifies operators if pipeline pressure decreases or increases, allowing them to isolate and inspect those sections of pipe.
Above-ground piping is routinely inspected for atmospheric corrosion and wall thickness evaluations are performed.
Pipeline valves are inspected twice a year and safety valves that provide overpressure protection are inspected and recalibrated annually, Haines said.
“We also conduct both fixed wing and helicopter overflights of our pipeline corridors looking for indications of leaks, construction activity, exposed pipeline, erosion or any other factors that may affect public safety or integrity of the pipelines,” he said.
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