It’s referred to as a 3-course tank, meaning there are 3 longitudinal seams. I’m unaware of any specific technical term for the seam. This 3-course riveted tank design was very common from the 1920s to the mid-1940s for tanks of 6,000 to 10,000 gallon capacities.

SHPX 20504 was one of 54 ACF Type 27 tank cars in series 20496-20549 built ca. mid-1937 in lot 1702. ICC-103, 8,000 gallons nominal, 40-tons. Shippers’ Car Line used this series of cars for general service with either short or long-term leases. 

InterMountain offered HO and O-scale models of these cars of this general type, the latter tooling later went to Atlas.

Regards,

Ed Hawkins