KBR, the engineering and construction unit of oil-services giant Halliburton (HAL) - Get Report, filed Friday for an initial public offering of up to $550 million of common stock.

The offering would amount to about a 20% stake in KBR, which has been the subject of probes into its work for the U.S. military in Iraq. Despite those inquiries, demand for KBR¿s work appears strong, driven by renewed global investment in oil and gas infrastructure.

The filing did not say how many shares KBR planned to sell or offer a price range.

KBR, which stands for Kellogg Brown & Root, would like to be listed on the

New York Stock Exchange

under the ticker "KBR." Halliburton, whose former CEO is Vice President Dick Cheney, in January disclosed that it planned to sell part of the unit in an IPO.

Halliburton shares ended Thursday up 43 cents, or 0.6%, at $77.12. Markets were closed Friday in observance of Good Friday.