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Fatigue analysis with AutoPIPE Harmonic analysis command :
AutoPIPE does not have cyclic type of stress, therefore need to add a new code combination with H1 by itself for the RPM of the harmonic from a rotation compressor:
Combination Name = H1
Description = Harmonic Load case #1 for RPM = xxx .
Combination method = 1 Sum
Category = Occasional,
Case = H1.
Now, change the default "Allowable Stress" setting from "Automatic" (typical 1.33 *Sa) to 6500 psi. In this case, because a compressor is high cycle fatigue, API-618 mentions using a value of 26000 psi peak to peak. Therefore, use half of that which is 13000 psi peak to peak or to consider some SIF values typically would suggest using 13000/2 = 6500 psi for the Stress allowable.
Therefore, 26000/2 for peak to peak, /2 assuming a weld stress factor = 2, because the piping codes are typically based on SIF while fatigue values are typically based on stress concentration factors and there is a factor of 2 between SIF and stress concentration factors
AutoPIPE nuclear has a full fatigue analysis engine, however AutoPIPE Standard and Advance does not. This shortfall will be fixed in a future version of the application by enhancement CAE-CR-3268: Add fatigue analysis for ASME piping codes.
AutoPIPE Compressor Vibration Method
How can I include pulsation forces from piston type pump to piping?
Answer: (from Karim Rinawi)
The best way is to simulate the acoustic model using Bentley PULS. It will calculate the shaking forces and can export these using harmonic HMF file.
Otherwise you would need to assume some pipe harmonic forces at elbows. Sometimes you need to change the load frequency to match pipe resonance for worst scenario.
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