View a map of the PG&E pipelines in Palo Alto

The sight of PG&E workers testing mains and replacing pipes will become more commonplace on Palo Alto streets in the coming years as the company zooms in on three major gas lines stretching through the city.

Company trucks and field teams have become a visible presence over the past two months as PG&E crews conducted hydrostatic tests of Line 132, the line that was involved in a fatal San Bruno explosion in September 2010. The inspections -- which uncovered a small leak in a pipe segment near Page Mill Road and Hanover Street -- concluded this weekend when PG&E completed the final welding on the site and returned the pipeline to normal operations.

Such projects should become a norm in the next three years as the embattled utility company proceeds with an ambitious, state-mandated plan to test all pipelines similar to the one in San Bruno. The company also has to replace some of its oldest pipes and install automatic valves at various points in its gas-distributions system.

This will inevitably mean more road closures and construction work in Palo Alto, which has three PG&E pipelines passing under its streets.

PG&E officials gave a detailed report about the company's plans -- and its early results -- at last week's Palo Alto City Council meeting. Among its early projects is a plan to replace portions of Line 101 -- a pipeline that roughly parallels U.S. Highway 101 and that connects with Line 132.

Todd Hogenson, director of PG&E's Pipeline Safety Enhancement Plan, said Line 101 was installed in the 1920s and all of its segments have since been replaced. Though the stretch of Line 101 passing through the city is only 2.5 miles long, it includes no fewer than five different pipe types, ranging from 20 inches to 36 inches in diameter. This, he said, makes it difficult for the company to run inline tests through the pipe.

"There's no tool on the market today that can go from 36 inch to 24 inch," Hogenson told the council at the Nov. 14 meeting.

Hogenson said the company plans to modify the segment of Line 101 between Palo Alto and Milpitas over the next two years and to run inline-inspection tools -- generally known as "pigs" -- through the line in 2014.

"We want to upgrade this pipeline to accommodate inline-inspection tools," Hogenson said.

The company also plans to replace portions of the aged Line 109, which runs parallel to Line 101 along Middlefield Road. Hogenson said the line was installed in 1936 and has received little or no testing since then. The company plans to replace the 4.6-mile segment of Line 109 in Palo Alto in 2013, Hogenson said.

Meanwhile, all three PG&E lines in Palo Alto will operate under reduced pressure, he said. Shortly after the San Bruno explosion, PG&E reduced the pressure to 300 pounds per square inch, far below their capacity (Lines 101 and 132 both have the capacity of 400 pounds per square inch).

"PG&E has no intention of increasing operating pressure until all 1936 pipes have been replaced," Hogenson told the council.

Palo Alto officials voiced no objections to PG&E's plan to test and replace pipelines throughout the city, though Councilman Pat Burt said he was concerned about the company's decision not to hydro-test Line 109. The 1936 pipe -- unlike other local mains -- was put together through a "single submerged arc weld" method, in which the pipe cylinder is welded with one seam. Others, including Line 101, use a double-seam weld in which pipes are also secured from the inside. The company also has no records of tests conducted on Line 109.

According to the Utilities Department, Line 109 runs along Middlefield from Mountain View then turns up East Charleston/Arastradero Road and goes north along Foothill Expressway. About two-thirds of the line has been replaced in recent years.

Burt urged the company to consider testing the Palo Alto segment of the 1936 line rather than wait until 2013 to replace it. The line, he said, has all the characteristics of a "high-priority" segment.

"It's an old line; it's a single weld; it's in a school zone; and you have no testing record," Burt said.

Hogenson said PG&E plans to replace about 20 miles of the 1936 pipeline between Milpitas and San Francisco, including about 1.5 miles in Palo Alto. He said it costs PG&E more than $1.2 million per mile to hydro-test its mains and said the money would be better spent on replacing the aged pipes, including the Palo Alto segment of Line 109.

"We think replacement is really the best solution," Hogenson said.

In the meantime, PG&E is wrapping up its two-month long process of testing at Line 132. The Utilities Department announced that the company is now conducting general clean up and restoration of all areas of activity -- a process that is expected to stretch until the end of November.