Always referred to as Tubes rather than Pipes, the plumbing inside the boiler of a high pressure locomotive boiler ticks all the boxes for this subject.
This is the insides of the former Merchant Navy Class Loco Ellerman Lines
A rather grainy image as I couldn't get a good image with flash so had to go to high ISO
#114 Pipes for 118 pictures in 2018
Uploaded to Flickr by Clint__Budd on 4 July 2018