pipe

Evergreen and Plastruct both have many sizes of styrene rod and tube that can be used for scratchbuilding.

Left overs

Left over sprues, they make great pipes.

Dowels painted to look like pipes.

how about

drinking straws. they are available in several diameters.

Thank you! I thought about

Thank you! I thought about sprues and straws. I guess I don’t know the scale diameter of the pipes, as I don’t know the 1:1 diameter. 

Pipe Diameter for Woodchip Conveying

The diameter can vary somewhat, based on the capacity of the pneumatic system and distance, but 8 to 12 inches would be common, 20 inches on the larger end, 6 inches in smaller systems with short lengths, for typical sawdust or wood chip pneumatic pipelines.

10-2 ,12-2,14-2 romex wire ,

10-2 ,12-2,14-2 romex wire , strip the outer pairing  jacket off . bend to the shape you want and then paint. Plumbing solder also works.

Long Radius Bends

To look prototypical, Remember to make your bends very gradual, use 30 or 45 degree bends where possible, keep 90 degree bends very long radius.  This is because of the friction or drag created when blowing the chips - the straighter the pipe, the less horsepower and air required.