Lou, the now closed Trinity plant is just down the street from my house. During the 80's they were making some 30,000 tankcars, but not like any other cars I've ever seen. If you do the math, only low density liquids could be hauled in a 30,000 gallon car and not go over 250 tons total weight with tank and contents. Most I saw were designed for medium pressure (less than 125 PSI as an educated guess) from the thickness of the ends and the plates rolled to be welded-up into the tank. I'd guess they were to haul methanol, acetone, methyl ethyl ketone or other light solvents, maybe ethers too. They never spent much time in any yard. They were loaded and put into trains usually the same day, if not the same shift. They came out of the old Sunoco refinery loading dock which is less than 1000' from the BNSF Cherokee Yard in Tulsa. A few made it to the SKO yard and went north into Kansas. (Coffeeville or further north or onto the UP, I can't say.) I have few good photos of them. I think most got GATX reporting marks. It's my impression that they were longish, at least 65', but I never measured one.
