TEXAS CITY, TX --Several refineries and chemical plants in southeast Texas have restarted after power outages earlier this week shut them down. Officials with Dow Chemical and Valero say their facilities in Texas City on Friday had begun restarting some of their production units. BP's refinery began its restart process Thursday evening. The restart process was expected to take several days to complete. The facilities were knocked offline after experiencing power outages late Monday and early Tuesday. There were additional outages later Tuesday and Wednesday. The electricity provider believes the outages were caused by salt and other residue that has built up on transmission equipment at substations and other locations, leading to short circuits. The provider says it is working to clean affected equipment.