Two-phase flow

I'm laying out a plant and pipe rack and am faced with several lines indicated on PIDs as two-phase flow. The two-phase is shown to exist after going through a heat exchanger and continues on through three stages of separation where the vapours and liquids are piped to flare and storage respectively.
Are there certain piping considerations that I should be aware of for this type of system?

Its hard to visualize your situation.
It sounds like the heat exchanger is a line heater off a wellhead to a 3 phase separator (separating gas/oil/water). The water is metered and sent to a storage tank and the gas/oil is metered and put back together and sent down a pipeline to somewhere. The vapours are the PSV off the separator. Sorry dude.....but it sounds like your laying out a wellsite. Is that correct. I need more info.

How's life in Calgary? I just left there 6 months ago. Way to retarded for me. I would have road raged and killed someone sooner or later.

Jop and hc,
Sorry for lack of info. A little new to this concept of forums.
Yes, coming from a wellhead, the facility is to separate the oil from the muli-phase fluid, recover the vapours for re-injection and send the oil to storage.
The multi-phase comes from wellhead>inlet heater>inlet sep and is then pumped through another heater>hp sep>lp sep>vertical gas boot. All along the way (except at hp sep) the vapours are sent to compression for re-injection. The oil is sent to storage.
My question, more specifically I guess, is/was should the line carrying the multi-phase be sloped and/or not pocketed. Jop, you have basically answered that (even with the little info I gave). I will probably have to go back and forth across a central rack (up to rack>over and back down into equipment). As long as the line(s) are drainable back to major equipment would this be cause for great concern?

hc ... calgary is hoppin' (as you know).

Your emulsion from the wellhead is at a pretty high pressure. Prolly 2500#1500, 900# after the PCV. Based on my experience with wellsite design and what I'm visuallizing your project to look like high points are not an issue. I'd avoid pockets and keep your piping so that it drains into the equip and has no place to sit and freeze in those cold Alberta winters. Like Jop says step it up. I've never sloped my high line piping that I can remember. Alot of the time Separator inlet connections are pretty high compared to your wellhead piping and you never truely know the real life elevations of your wellhead conn's. We always used a standard. Your worrying to much about the gas vapours also on the upstream side of the separator. They're mixed in a slurry with gas and oil called emulsion. Not an issue until after the separator.