On Jul 15, 10:16*pm, Gib Bogle wrote:

Pretty hard to cast a boiler, shirley?

Yes, they could only be cast by a few expert foundries (Coalbrookdale
being the obvious example), owing to their large size. Coalbrookdale
could cast these because of their past experience making try pots for
whaling. Even then, it was only the outer shell and cylinder being
cast - the inner flue was sheet iron work (being of smaller diameter,
it was inherently stronger).