Here is a description of Cromor tubing from the Torelli website that clarifies how it is "seamed:"
3. 25CrMo4. This cro-moly is generally drawn to a tensile strength of 800 Newtons/square mm with 12% elongation, and makes tubes suitable for pro and semi-pro applications. Many people dismiss this tubeset as a "seamed" tubing. This is not true. The usual sense of a seamed tubing is of a plate of sheet metal wrapped around a round form and electro-welded. This is not the construction method for this steel. A billet is the thick, short piece of tubing that is drawn in the tubing factory into the thin, light bicycle tube, and it is this billet that is electro-welded in 25CrMo4. The act of drawing the thick steel tube into the thin tube gives the tubing much of its strength. Many high-tech mills use only electro-welded billets for their tubing fabrication. In any case, this is a high-quality, reasonably priced tubing that is used in some of the most elite of Columbus' tubsets. This tubing is found in Cromor, Gara, Thron, and the forks and rear triangle of Brain.
Todd Kuzma
Heron Bicycles
Tullio's Big Dog Cyclery
LaSalle, IL 815-223-1776
http://www.heronbicycles.com
http://www.tullios.com