Finished in 2009 at a cost of almost $7 billion, the REX natural gas pipeline - running from the gas fields of Colorado through Ohio to the edge of Pennsylvania - stands as one of the nation's most ambitious infrastructure projects in a quarter-century.

It was also a job plagued with problems, demonstrating that despite industry assurances that new lines are safer than ever, they may not be safe enough.

In 2009, just six weeks after passing a battery of final pressure tests, the line leaked natural gas - triggering an evacuation of nearby homes in southeastern Ohio. The leak occurred in a pipeline section that federal safety inspectors had previously flagged for poor construction techniques.

In a recent interview with The Inquirer, Cynthia L. Quarterman, the nation's top pipeline regulator, described the REX pipeline as "massive in size - and riddled with issues."

Quarterman said her agency, the Pipeline and Hazardous Materials Safety Administration, or PHMSA, is taking seriously the REX pattern of incidents and has an ongoing investigation into them.

She said she made REX her first field visit after taking over PHMSA two years ago.

"I wanted to go personally to send a message to the owners and operators of REX, that they needed to get their act together," Quarterman said.

Even so, the main owner of the pipeline - industry giant Kinder Morgan - has not been fined.

The leak in Ohio was the last in a string of problems with REX. One worker digging the line in Wyoming was incinerated when his bulldozer hit another buried line; another firm was fined for not marking it properly. In Kansas, independent inspectors said they received threats when they flagged bad work.

"It went off the rails in so many ways," one inspector said in an interview.

In a recent statement, Kinder Morgan did not address the problems in the REX line, but said it had one of the industry's best safety records.

"We are committed to operating our assets safely to protect the public, our employees, contractors and the environment," the statement said.

Short for Rockies Express, the REX line is big - 42 inches in diameter - and carries gas compressed up to 1,440 pounds per square inch. Every day, it carries 1.8 billion cubic feet of natural gas. That's enough to serve 18,000 American homes for a year.

At one point, Kinder Morgan explored extending the line from Ohio, through Pennsylvania, to Princeton, but that plan has been shelved.

As a frenzy of gas pipeline construction envelops Pennsylvania, the litany of problems that plagued the REX line tells a cautionary tale.

The line's main owner, Kinder Morgan, was founded in 1997 by Richard D. Kinder, a former president of Enron. This year, Kinder made Forbes magazine's list of the 50 wealthiest people in the United States, with a net worth of $6.4 billion.

In October, Kinder's company agreed to pay $21 billion to buy El Paso Corp. Once the deal closes next year, Kinder Morgan will become the biggest pipeline firm in the country, overseeing more than 67,000 miles of pipe.

After a spate of accidents earlier in the last decade, some critics wondered whether its pace of acquisitions was simply too fast.

In 2004, five workers were killed when a backhoe hit a Kinder Morgan gasoline line in Walnut Creek, near San Francisco.

A Kinder Morgan subsidiary was later convicted of six labor-code felonies and agreed to pay $15 million. Investigators said the company failed to mark the line properly before crews began digging.

PHMSA said later that the accident was part of a long list of problems on Kinder Morgan's West Coast pipelines. It blamed the firm for a "repeated failure" to use internal inspection tools to identify problems.

In one case, PHMSA officials said, the firm hadn't fixed a stretch of corrosion 14 feet long. The pipe ruptured in 2004, spilling 60,000 gallons of fuel into a wildlife marsh in San Francisco Bay. In the end, Kinder Morgan agreed to spend $90 million to improve the Pacific Operations system.

Most recently, federal regulators in May proposed to fine Kinder Morgan $425,000 for a 2009 accident in which 8,600 gallons of fuel oil spilled in Perth Amboy, N.J.

The regulators said the terminal there had no warning procedures to alert workers when a key valve was closed in error. In reply, Kinder Morgan said that the proposed fine was excessive and that it had improved its procedures.

As for the 1,679-mile REX line, at a PHMSA conference in 2009, a Kinder Morgan executive said the sheer scope of the project had made it hard to manage a series of personnel and quality-control shortcomings.