Even as the economy slumps and unemployment rises, strong demand for power plants, oil refineries and export goods has many manufacturers and construction contractors scrambling to find enough skilled workers to plug current and future holes. With the shortage of welders, pipe fitters and other high-demand workers likely to get worse as more of them reach retirement age, unions, construction contractors and other businesses are trying to figure out how to attract more young people to those fields. Their challenge: overcoming the perception that blue-collar trades offer less status, money and chance for advancement than white-collar jobs, and that college...