HOUSTON - Tesoro Corp is replacing older railcars in its crude-by-rail fleet with ones that have the latest safety design, Chief Executive Officer Greg Goff told analysts on Thursday. He said 90 percent of Tesoro’s fleet consists of railcars that meet the latest design standards embraced by the rail industry for all tank cars manufactured after October 2011. By mid-2014, the company is replacing the remaining 10 percent with cars that meet the standards, he said. The upgrade comes after several explosive crashes that involved trains moving crude oil. Tesoro receives up to 50,000 barrels per day of North Dakota Bakken crude oil at its 120,000-barrel-per-day refinery in Anacortes, Washington.