Union Pacific has posted an April 18, 2016 article Steam Update: Preparing for Boiler Testing in the Community Ties section of its website.

The text is confusing. "The material we ordered was supposed to be in a specific diameter, but it arrived a little too big..."

An inch too big?

But, the video shows what I think is normal. A lot of superheater flues are large at the smokebox end and smaller at the firebox end. So the swaging is not a mistake, it is part of the plan.

So which is it, correcting a mistake, or just normal process for fabricating flues?

I would suggest that this is a poorly written article which wasn't proof read by someone who understood the process. Super-heater flues are swaged. There are a couple of ways of doing it. But the bottom line is that the small end is to the firebox tube sheet and the big end is in the front tube sheet. The photos show the standard configuration of a swaged flue so the text is the offending part of the story.

CCdW