Toller wrote:
....

That made sense, since the pressure is so low in the narrow line. (yes, I
know the actual static psi is exactly the same, but the total pressure on
the walls is much less because the area is much less.)
....

No, pressure is force per unit area so 40 psi is the same no matter what
the diameter. Therefore the _FORCE_ exerted on the wall is
proportionally the same as to the larger diameter as area is directly
proportional.

Pipe and tubing wall thicknesses (for the same material) are scaled as
size increases (although in steps, not for every incremental size) so
the tensile stress is (very) roughly the same.

How much difference there is for plastic wall thicknesses versus size
I'm not sure, haven't looked specifically, but would expect them to be
similarly scaled as for tubing and pipe for economy in materials as
compared to required thickness for designed/rated pressure.

The only place the smaller diameter really makes a significant
difference is that the total _FORCE_ at the end cross-section may be
small owing to cross-sectional area...

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