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[gokchooo]

hi,
I am asked to desing a flash drum in which vapor and liquid mixture of n-octane, 1-octene and hydrogen will be separated. I can not decide which construction material to design the flash drum. I learnt that carbon steel and stainless steel are some alternatives. Can you help me to make a decision?
Thanks

[Art Montemayor]

e133903:

You are assigned to design a flash drum and you don’t know how to select the materials of construction. First, what you are saying is that you are undertaking two designs: a process design and a mechanical design. I’ll assume you’ve completed the process design and are now at the mechanical design stage.

The key input data required for the mechanical design are:
1) the operating and design pressure;
2) the operating and design temperature;
3) any corrosiveness or erosive qualities associated with the fluid(s);
4) any solids or other contaminants included in the fluid;
5) extreme swings in pressure or temperature that may appear – especially pressure shocks such as steam or water hammer.
6) requirements for internal inspection or cleaning;
7) any special internal components required;
8) residence time required for liquid separated from vapor stream.

If you have a relatively clean fluid(s), free of corrosive or erosive components, then a carbon steel – such as A516 –Grade 70 – should be OK. If you have temperatures below -20 oF, it might be better to resort to the stainless steels – such as 316L. These are just examples of what you should be looking at. You should be making these judgments based on a logical and sensible approach. If you are expected to do a mechanical design, then I have to assume you have been trained to know the corrosive effects of some chemicals and the erosive action of solids. You should also be familiar with the temperature limits of the metals and the possibility of embrittlement. You should have completed at least one Strength of Materials course; if not, then all I’m stating to you is probably sounding like Greek and not making sense. If that’s the case, then you have no reasonable expectation of doing a credible mechanical design. Your decision should be based on what you know and what you have researched about the process and its characteristics that could present a hazardous condition for the vessel in question. If you don't have that knowledge nor have you done the research, then you won't be able to defend your choice of materials of construction - and that's what is ultimately required of the mechanical design.