The tank car was relatively uncommon until the 1870s, when the nascent petroleum industry ordered large quantities of metal tanks carried on wooden car bodies. By the early 1900s, a standard design had evolved that lasted throughout the steam and early diesel eras: an 8,000-11,000 gallon metal tank perched on a metal flatcar-like underframe.
The one big change during that time was the transition from riveted to welded construction, beginning in the late 1930s. Car builders introduced X-ray inspection of welds to ensure safety, as well as giant annealing ovens that could heat-treat assembled tanks to relieve joint stress. Welded tanks were stronger, less susceptible to rust and corrosion, and less likely to rupture in the event of a wreck.