Good article.
I used to use 1" and 1-1/2" pipe to make 'cannons' when I was a teenager.
Fortunately I used my own CRUDE blackpowder.
But when one puts a pipe cap on both ends the obvious happens - it shatters so well (because it's hard and brittle) that I NEVER found any parts. Obviously I never hit that majic pressure level with just putting newspaper in one end.
Ya gotta be tough or lucky if you're stupid.
Iron pipe is CAST iron or welded seam pipe. Not designed nor intended for either such high pressure peaks.