The March 11 move by Willbros Group, Houston, to buy Seattle-based InfrastruX Group for $480 million in cash and stock sets up a new energy-sector engineering giant.

Randy Harl, Willbros president and CEO, says InfrastruX will offer “a different but complementary focus” to Willbros on infrastructure for the oil-and-gas industry, including large pipelines. InfrastruX specializes in engineering and construction for gas and electric utilities, including small-diamater pipelines and transmission.

The company will become its own division in Willbors and retain its management team, 4,400 employees and location, according to a Willbros spokesman. InfrastruX CEO Michael Lennon will lead the parent firm’s new electric transmission and distribution segment.

Last year, InfrastruX owner Tenaska Power Fund LP announced plans to spin off InfrastruX into its own public company and filed for an initial public offering. Under the current acquisition, set to be completed by midyear, Tenaska will have a 20% stake in Willbros and two seats on the board.

Joseph Gibney, an equity analyst with New Orleans-based Capital One Southcoast who follows Willbros, says the deal has a construction-related benefit because of the potential of $1.3 billion in transmission work for one InfrastruX client,Texas utility Oncor, in the state’s competitive renewable-energy zone. But, he says, the purchase of InfrastruX is a “sizable bite in a predominately unrelated market.” Of InfrastruX’s 650 customers, its top 10, including Oncor, accounts for half its revenue.

The company says it has a backlog of $474 million, and, according to Willbros, InfrastruX would have accounted for 25% of Willbros revenues in 2009 on a pro forma basis.