UPDATE 2-US opens probe into steel pipe imports from 9 countries

* U.S. Steel among companies seeking import relief* U.S. energy boom has fueled demand for steel pipe* Next step is U.S. trade panel vote in mid-AugustBy Doug PalmerWASHINGTON, July 23 (Reuters) – The U.S. Commerce Department on Tuesday launched one of its biggest trade investigations in...UPDATE 2-US opens probe into steel pipe imports from 9 countries