FARGO (AP) - Xcel Energy has started replacing a brand of natural gas pipe at hundreds of homes and businesses in North Dakota after it was blamed for a south Fargo house explosion about a year ago.

Xcel announced plans last October to replace the pipe manufactured by Century Utility Products Inc. by 2010.

The project affects 19.8 miles of Century main and about 1,300 gas services to homes and businesses in Fargo, West Fargo and Grand Forks and possibly Mapleton, Xcel spokeswoman Bonnie Lund said.

Xcel also is examining installation records and checking an additional 4.6 miles of main and 2,700 services to see if they need replacing, she said.

Customers have received notices from Xcel in recent weeks of work being done in their neighborhoods.

Maryanne Suhr said she got the letter on a Friday in July and work began the following Monday in front of her Fargo home.

The letter doesn't specifically mention Century pipe, but Suhr said she figured it pertained to the pipe because Xcel said last fall it was installed between 1971 and 1976. Her home was built in 1974.

The federal government warned in a 1999 bulletin that Century pipe installed from 1970 to 1973 "may fail in service due to its poor resistance to brittle-like cracking."

Suhr said she wasn't worried about the safety of her gas service. By Wednesday, the only signs of the pipe replacement at her home were two dirt indents in her lawn near her gas meter and sidewalk. Work continued across the street.

"They did a pretty good job of cleaning up," she said.

An explosion last Sept. 2 in Fargo injured five people, including one woman who was severely burned.

Xcel said it found a pinhole-sized leak in the service line, which allowed gas to migrate into the house. It is unknown what sparked the gas.

North Dakota's Public Service Commission hired a forensic engineering consultant to test the pipe.

The PSC received the test report from CRT Laboratories Inc. of Orange, Calif., in late May. Among the findings was a cavity in the pipe fusion that contained eight particles of apparent sand. Marks and patterns indicated a crack had started at the cavity's edge, the report stated.

"That's probably a point of some concern," said PSC Commissioner Kevin Cramer.

But Cramer said officials still don't know whether the fracture occurred pre- or post-explosion, or the exact source of the gas leak. The PSC expects to receive its inspectors' incident report within the next two weeks, he said.

Xcel hopes to finish the majority of the replacement project by year's end at a cost estimated at $4 million, Lund said.

Jodi Hanson, who lives next door to the house that exploded, was among those informed that no further work was needed. She and her husband have been waiting for the news so they can start resodding their lawn, which still has bits of glass in it from the explosion, she said.

"Now that I know they're done in our area and it's safe, we should be OK," she said.

Hanson said it was "a little scary" that Xcel hadn't replaced Century pipe in North Dakota earlier, even though it decided to do so in Minnesota after a similar natural gas explosion in October 2005 injured two people in Cottage Grove.

The Minnesota replacement project, which includes Moorhead, Dilworth and East Grand Forks, also is expected to wrap up this year at an estimated cost of $24 million, Lund said.