ArcelorMittal invests to reopen Monessen Posted on 18/09/2012 by Uwe Niggemeier ArcelorMittal declared yesterday to invest 50 Mio. $ to restart the old Koppers coking plant in Monessen, PA. AM purchased the plant in 2008 and idled it in 2009 due to the economic crisis. Plans are to have the plant operational in mid 2014.