My friend Patrick Welch and I were discussing some larger pipe fittings – in specific, 24 inch pipe. For NPS 14″ and up, the NPS and OD vaules are equal. In other words, an NPS 14″ dia pipe is actually 14 inches OD. The ID varries according to the material and Schedule. Not being concerned with that I am going to focus on a O scale 24″ pipe which will have a 1/2 inch OD. In addition I will be talking about a 21 inch OD pipe as that would be a multiple of 7/16 inch. In the “real world” this would be either 20 inch or 22 inch but for modeling purposes I will ignore that.
So. My preference is to use Evergreen tubing for this sort of thing, it being easily obtained. In the diagram, Evergreen #236 1/2″ and #234 7/16″ tubing center and right. To the left is a 1/2″ tubing that Patrick
Note that Welch’s tubing and the Evergreen 7/16″ both have a 9,7mm ID. This tells me that I should be able to make something to fit them all.