Hi,
Question for experienced designers of two-phase (steam/ water) piping systems?

How do you calculate the approxiamte slug loads at bends/ elbows - to be used as concentrated loads in the piping analysis?

thanks in advance,

Component Force = d.a.f. x density x flow area x velocity^2

Component Force is same for both orthogonal directions assuming it's a 90 deg bend.

thanks heaps

absoultely stupid question now - what's "d.a.f"?

cheers,

It means "Dynamic Amplification Factor" a value which is approximately 1.5 to 2, to convert static to impact load.


Cheers,

..and usually DAF=2

DLF - dynamik load factor
DLF = 2 is for a single impact load
Slug flow forces are not single impact load.
Slug flow forces are multiple forces over the time.

Although B31.1 Appendix II focuses on relief valve discharge, the dynamics discussion is appropriate here. I quote paragraph II-3.5.1.3 Dynamic Amplification of Reaction Forces. "In a piping system acted upon by time varying loads, the internal forces and moments are generally greater than those produced under static application of the load. This amplification is often expressed as the dynamic load factor DLF and is defined as the maximum ratio of the dynamic deflection at any time to the deflection which would have resulted from the static application of the load. For structures having essentially one degree-of-freedom and a single load application, the DLF value will range between one and two depending on
the time-history of the applied load and the natural frequency of the structure."
Note that a maximumm DLF (or that DAF) of 2 is true for a single application AND if only one mode of vibration is activated.