Abstract: Railroad tank cars are provided with spirally wound cylindrical tanks spanning and supported on wheeled trucks with a continuous weld extending the full length of the tank. A steel plate ribbon or strip is spirally wound in the form of a right circular cylinder with a continuous weld bonding the edges of the strip in abutted relation to provide the tank side wall. The open ends of the resulting cylinder tube are closed by welded-on end caps and suitable openings are provided in the tube for manways, vents, valves and the like. A heating coil may be provided on the inside or outside of the tank in intimate contact with the spirally wound ribbon and conventional insulation and jacketing may be provided around the tank. Drop center and center sump tank are provided by cutting the spirally wound tube along a diagonal plane, rotating adjoining sections 180.degree.