Re: Friction Effects in Piping Systems

>I am using 0.3 as a friction coef. It is for the
>sliding friction.

How do you know that the friction force really is 30% of the normal force? Do you have measurements?

I'm really not just being a smart-ass. The real coefficient varies all over the place. For example, I've seen values for stainless on stainless taken from an exhaustive series of tests which range from 0.2 to 0.8. Marks Handbook lists 0.7 as the static coefficient for steel on steel, but it applies to laboratory clean and polished surfaces in vacuum. I've measured values on machined surfaces that's closer to 0.3 Harris and Crede show 0.15 for sliding friction for steel on steel. The values depend on surface condition, the presence of any liquid and speed for sliding friction. And contrary to the CW, the value does vary with surface pressure, although it's constant for ordinary pressures.

That's actually tangential to the original question of whether or not to ignore friction, but it is germane to how much faith you can have in the results of an assessment. Don't forget that both the high and the low values may produce non-conservative results. High values produce non-conservative displacments and conservative forces.

Christopher Wright P.E.    |"They couldn't hit an elephant at
chrisw@skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)