Hi ,
Quick question: when you size a two-phase line, do you check the turndown case?
Here's an example we ran in our two-phase flow calculator.
A 4-inch (DN100) reboiler return riser, 12 m (39 ft) tall, at 2.0 barg (29 psig):
Normal operation: liquid 43.2 m³/h (190 gpm) at 1.5 m/s (4.8 ft/s) - stable flow, all checks pass.
46% turndown: liquid velocity collapses to 0.68 m/s (2.2 ft/s) - the regime flips to slug flow.
The uncomfortable part? You can't resize your way out. A 2-3 inch line fixes the slugging but destroys the reboiler's circulation pressure balance due to high pressure drop. Avoiding slug at both cases needs a ~20-inch line, which won't be a practical solution.
The practical fix: keep the 4-inch line and design the supports for slug loads - rigid restraints at the elbow, tighter spans, dynamic load case in the stress model.
The engineers who catch this in design save their projects weeks of site rework. The ones who miss it meet it during commissioning or even operation, which shall lead to a lot of trouble.
Run your own two-phase scenario (free): [calcpad.boostrand.com]
Want the full line sizing methodology, including two-phase design?
[Check the Pipe Sizing course → boostrand.com/pipe-sizing]
Have a nice day!
Mohamad
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