Problem:

Support span suggestions to avoid piping vibration due to Harmonic load case in AutoPIPE ?

Solution:

The following are span suggestion to avoid resonance from compressor acoustic vibration. Typically for low speed motors e.g. 300rpm use multiplier 2.4 up to 4.0, i.e. 5hz x 2.4 = 12hz. High speed compressors e.g. 1800rpm use multiplier 1.4, i.e. 30hz x 1.4 = 42hz.

Then calculate pipe span based on this fundamental frequency (1st mode) for both fixed and simply supported ends. A typical pipe behaves somewhere between these two boundary conditions. Ref Roark Table 36 case 1b, 2b

fn = Kn/2/pi *SQRT (Eig/w/L^4)

hence Span (L) = E.I.Kn2/W/f12

where :

W = weight /unit length (kg/mm)

I = moment of inertia (mm4)

f1 = frequency (Hz)

E = Youngs Modulus (Mpa)

kn = 3.55 (Fixed Ends), 1.57 (simply supported)

See Also

Dynamic "Harmonic" Analysis

Bentley AutoPIPE