Hello, I am an electrical engineer so these are uncharted waters to me. I need to know the approximate typical torsion coefficient of pipe in n.m/rad (or ft.lb/rad). Assuming the followings: steel pipe length: 10 meter inner radius:4" outer radius:4.5" I am just looking for typical, approximate, ballpark numbers. Nothing exact. Thanks,

The equation you need is (T/theta) = (G*J/L) (Nm/rad) G = 80 *10^9 N/m^2 for steel J=(PI/32)*(Do^4 -Di^4) polar moment of area of pipe L= 10 m length of pipe Substituting the values J= 106*10-6 m^4 G*J/L =805KNm/rad

I am a little confused... Do=4.5"=0.114m. Di=4"=0.102m. J=(3.14/32)*(0.114^4-0.102^4)=5.95E-6 m^4. How did you get 106E-6 m^4? thanks,

In your original posting you referred to an inner radius of 4" - which is 8" diameter. Also your outer radius was 4.5". Now you are saying the outer diameter is 4.5" - and the inner diameter is 4". Hope this explains the difference?