phil wrote:

    Would seamless pipe (4130) be a proper "tube type" material to use
for a shaft turning max 2000 RPM @ 200hp, 300 hp max?  The ends need to
be splined to slip onto a gear.

   If seemless pipe won't work, what might do the trick? It must be
hollow because I need to run a tube through it.

Dimensions are everything. Do you have a sketch?
What RPM is the engine generating 300 HP? Also what type of engine?
Four cylinder piston engines at 200 HP have much worse torque
pulses than 2 rotors or a six cylinder piston engine.
What is on the end of the shaft?

Paul Lamar

Since no one answered, I'll give my two cents:
1. I would suggest to use seamless mechanical tubing of near
90,000 - 110,000 psi tensile or higher, such as 1340, 3140, 4140, 4340, etc.
Even 1050 or 1060 might do. The higher steels are better against corrosion.
Do not use "pipe" per ASTM specs.

2. A quick calculation at 8000 psi stress and 300 hp shows that
you need about 19,400 mm3 polar section modulus Zp.

Suitable tubing is 2.5 in OD with 1/4 in wall (29,600 mm3),
or 3 in OD with 3/16 in wall (35,800 mm3)

Using a spline at the ends makes the 1/4 wall better suited.
A 3" OD Tube with 1/4" wall has 44,900 mm3 which might be overkill.

This is of course a rough calc for a reasonably short shaft, without
any consideration for vibrations and assuming a fairly even torque.

Instead of steel you may want to use seamless Alu-tubing that is lighter.
I am not sure what stress is used for Aluminium. Perhaps 4000 psi for 6061 T6

or of the 7 series Al. With Al the polar moment should be near 40,000 mm3.
A 4" tube with 1/4 wall has ~85,000 mm3. Quite safe.
A 4" tube with 3/16" wall is ~67,000 mm3.

No responsibility, of course, just a suggestion of the approximate size
required.

Rolf Pfeiffer

 
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