On Jul 15, 2:39*pm, Andy Breen wrote:

As did the Murray/Blenkinsop machines at Middleton (and elsewhere!)

There's a well-known period illustration of a Blenkinsop machine
showing a boiler that's clearly riveted from plates.

and, IIRC, the Gateshead "Trevithick" and its immediate descendent,
the Wylam 'Black Billy'.

Puffing Billy & Wylam Dilly survived a long time, along with their
wrought iron boilers. I don't know which you mean by the "Gateshead
Trevithick", but none of the Gateshead-built locos have any evidence
for using cast iron.


Presumably plates of a
suitable size got cheap enough somewhere between 1812-13 and 1814-15..

Price didn't change significantly - although everything, and
especially provender or iron goods, became cheaper after Napoleon,
hence the number of cast iron bridges dated 1816. What did happen is
that ironmasters could make _bigger_ plates, allowing the introduction
in the mid-1830s of the "long plate" boiler. This had plates long
enough that a whole boiler barrel could be made of four parallel
staves, without the need for either endwise joints or else very short
barrels (as Stephenson used with Rocket & later).