A Pig's Incredible and Historic Journey Over Mountains, Through Forests and Under Rivers 

By Melissa Subbotin 

There are a few ways to travel from Oregon to Antioch — vehicle, train, plane, bicycle or simply making the 300-mile journey on foot. 

There’s one other way, limited only to a specific technology known as a pipeline inspection gauge or “pig,” which made the 300-mile journey by navigating south within PG&E’s 36-inch diameter natural gas pipeline — Line 400, which extends over mountain ranges, through forests, under rivers and between farms and ranches.  

For the pig, it was traveling on official business, there to conduct an in-line inspection (ILI), one of the three types of inspections PG&E conducts on its transmission pipelines. The other two being hydrostatic pressure testing and direct assessment. Integrity assessments are conducted every seven years on PG&E transmission lines. 

A pig is a tool designed to navigate the inside of gas transmission lines, propelled by natural gas. PG&E utilizes different pig technologies. For this project, the pig was there to conduct integrity assessments — making sure every inch of the pipeline met PG&E’s rigorous safety and reliability standards as well as all federal and state compliance requirements.  It looks for issues likes dents, corrosion, cracks and changes to the metal that may warrant further examination. 

“One of the highlights from this project is that we were able to deploy new ILI technology, including an Electro Magnetic Acoustic Transducer, which provided extremely precise analysis of key parts of the pipeline,” said In-Line Inspection Manager Calvin Lui. 

Line 400 is one of four backbone pipelines that transport natural gas from out-of-state into PG&E’s extensive 50,000-plus mile natural gas distribution and transmission pipeline system, where it then supports over 5 million customers as well as power generation. It has a 1040 pound-force per square inch (PSI) maximum allowable operating pressure with portions averaging around 900 PSI. It’s among the highest pressures in PG&E’s pipeline gas transmission system. 

Over the past 10 years, teams of PG&E coworkers have been collaborating, planning, problem-solving and executing on a plan to conduct an ILI of the complete 300-mile span of this pipeline— a herculean undertaking that had some asking early on how it would even be possible. 

Because, when PG&E’s early engineers and gas crews first designed the locations and routes for gas transmission pipelines, they had to account for natural topography, geography, and other manmade obstacles. This made for right angles, turns and bends, and valves that a gas molecule can easily navigate, but are impassible for a pig. Pigs, the ones used to inspect pipelines anyway, did not exist 60 years ago when the routes for this pipeline were planned.   

“Everyone who worked on this project should feel extremely proud to have made this incredible undertaking such a huge success, and most importantly, helping deliver on our safety stand and ensuring that this critical pipeline continues to operate safely and reliably for our customers and hometowns. A big thank you to everyone who supported the line 400 ILI project,” Calvin added.   

Teams including Gas Pipeline Operations and Maintenance, Land and Environmental, Gas General Construction and Gas Transmission Engineering were challenged over the decade to not only design ports to launch and receive the pig, but also make sections of the line “piggable,” which often required modifications to the existing line.   

It’s easy to see how some may have questioned how a inspection of this entire line would even be possible given the diverse challenges it presented. But, this month, the pig completed its final leg of the very historic 300-mile journey, achieving the very first full in-line inspection of line 400.   

“I want to congratulate and thank every coworker who worked on this project for their commitment to safety — the safety of our hometowns and customers, their personal safety and that of their PG&E coworkers. This project was an incredible success for many reasons and I’m proud of everyone who supported it,” said Gas Operations Senior Vice President Joe Forline.