Hi there,
I have already gone through various topics discussed in the forum regarding the surge analysis. Those are indeed very helpful but there are a few unanswered queries regarding the fire water network that we are analysing for an offshore platform. Our network is Titanium with low allowable stress values and we are encountering multiple failures during the static analysis that we have performed before we move onto dynamic analysis.

1. The unbalanced dynamic forces from Pipenet have been forwarded by our Safety group on pipe segment basis with pressure wave speeds of the order of 900 m/s. Their model is very simplistic taking into account the pipe lengths and in-line valves/controls etc. We have input same value of the unbalanced static forces on all the elbow pairs defined for a particular pipe segment (with DLF=2).
2. The firewater network is very extensive with 3 fire water pumps and near the pumps the layout is very congested with scores of bypasses in a very limited space. There are many directional changes in each pipe segment and some elbow pair lengths are either fitting to fitting or around 2-3 meters only. The wave will take approximately 2.5-3.5 ms or shorter to pass through these pairs. Is this not a very short interval of time to be considered as a potential problem?
3. Is there any thumb rule or guideline for the minimum elapsed time interval above which the unbalanced forces should be considered as a problem? The reason I am asking is that by inputting unbalanced forces at all the elbow pairs we may land up in changing the layout or providing additional stoppers / guides etc. that could have been avoided otherwise.
4. Based on replies to point no. 2 above, Can we purge shorter elbow pairs and consider only a few elbow pairs in dynamic analysis also? Or do we need to input all the elbow pairs irrespective of the lengths?
5. Is it normal practice to take allowable stress values (for sus + surge) as 0.9 Sy?
(Reference paragraph 302.3.6 (a) of ASME B 31.3)

I look forward to replies.