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TOPIC: Two phase flow piping support.

5 years 6 months ago #8411

  • Er.piping
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What care should be taken while supporting a two phase flow piping..?

Re: Two phase flow piping support. 5 years 6 months ago #3669

  • Jop
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You have not given any detail about the situation so I can only guess what it might be. Almost every project will have one or more situations where two phase flow piping will occur. Some are just the nature of the beast and some are the result of bad design and must be corrected before they leave the design office.

Examples of a two phase flow lines:
- the main transfer line from the heater to the inlet nozzle of the fractionation column
- the overhead vapor line from the top of a fractionation column to the overhead coolers
- a saturated steam line to a steam turbine

The risk with these two phase flow lines is slug flow. Slug flow is the result of pockets (low point pockets or high point pockets). Liquids in the two phase (or mixed phase) flow will tend to hang up in the low point until the pressure pushes it along. Conversely vapors will tent to build up in high point pockets until it is pushed along. The result is the slug flow that can tear the system apart.

The cure for this is constant awareness of the potential for two phase flow and the taking of the right precautions.
What are the right precautions?
- Learn and know the basics of the process. The Process Engineer should hold a P&ID review for the piping group before the start of the piping effort. Have the Process Engineer explain what is going on inside the equipment and the lines.
- Be aware, look for and eliminate pockets in lines.
- In the case of the Transfer line make sure it slopes up from the heater to the fractionation column.
- In the case of the line from the Fractionation column to the overhead coolers make sure it slops or drops down from the top of the column, to the cooler, to the Accumulator Vessel.
- Steam lines should always have a way to remove condensate before it builds up and damages some piece of equipment.

Now as for the support of a mixed flow line. The supports are very much the same as any other line BUT! if you know there will be slug flow then you and the Pipe Stress Engineer need to look at where Anchors, Guides and Snubbers may be required.
Do it once and Do it Right
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