By Andy Castagnola
A new, high-tech tool is helping PG&E ensure the integrity of its natural gas pipelines. And it’s all about lasers.
The utility has purchased a portable, handheld 3-D laser scanner, called the EXAscan from Canadian company Creaform. The EXAscan is able to replace time-consuming manual tasks and provide a much more detailed evaluation of a pipeline than was previously available. It can measure, for example, the extent of external corrosion or characterize any warping.
A trained engineer or technician simply holds the scanner a few inches above a section of pipeline. The device transmits data to a computer program, which creates a 3-D model of the object and displays it on a monitor. The software includes color coding to show where pipeline damage is most severe along with many other measurements. The data is accurate within 40 microns, or 0.0016 of an inch.
The applications for the device are just beginning to unfold, and they extend beyond gas engineering into PG&E’s electric operations and electric supply organizations. PG&E has been incorporating new tools and technologies into its projects as it upgrades the safety and reliability of its gas and electric systems.
Alex Gutierrez and his team at PG&E’s Applied Technology Services (ATS) laboratory in San Ramon are the keepers of the scanner. They’ve had it since last fall, and each person who uses it must go through a month of training, said Bronson Shelly, senior welding engineer.
Among the ways Gutierrez’s team has used the scanner for pipeline safety:
Ovality check: That’s engineer-speak for making sure the pipeline is at least 97 percent of being perfectly round, which is the standard margin of safety. The scanner can detect whether any outside forces have altered the pipeline’s shape since it was manufactured. One example: When the weight of a construction crane caused an underground water main to break recently in Emeryville, PG&E’s crews employed the scanner to make sure that the nearby gas line wasn’t damaged as well. The scanner found no concerns with its shape.
Corrosion assessment: Standard practice for measuring pipeline corrosion has been to dig down to a section of the pipe, draw an extensive grid of one-inch squares on the pipe, and then measure the “wall loss”—or effects of corrosion—square by square with a manual tool. A painstaking process, for sure. The laser scanner, on the other hand, captures the same information from the entire pipeline section within minutes and confirms whether that section is fit for service. “It’s night and day” compared with the manual process, Shelly said.
Dent analysis: Other projects, in Windsor and Bakersfield, involved scanning a dented piece of pipeline to gauge the damage. Crews used this information to determine the length of the repair sleeve, which is a metal band installed around a section of damaged pipe to allow continued safe operation. The laser scanner provided a much faster and more accurate assessment than the typical mechanical process would have, Gutierrez said.
Outside pipeline safety, hydroelectric engineers are beginning to see the advantages of the scanner, Gutierrez said. For PG&E’s Helms Pumped Storage Plant in the Sierra Nevada mountains above Fresno, the scanner helped perform a stress analysis on recently repaired rotors to ensure structural integrity of the power-generation equipment.
Because the stress test couldn’t be performed directly, the team needed to get creative. The process involved creating a negative mold of the repair cavity at Helms, shipping it to ATS, scanning the mold to create a 3-D model of the repaired area, and then converting the model into an electronic format for the stress analysis program. Sounds complicated, but the alternative manual process would have taken much longer and been less accurate.
The uneven contours of the rotors—much like the nooks and crannies of pipeline dents or external corrosion—is where the scanner is best suited, Gutierrez said. He emphasized that the EXAscan isn’t the right tool in every case, but where appropriate, it provides speed and detail far and above the mechanical way of doing things.
Email Andy Castagnola at firstname.lastname@example.org.