LTCS use for piping
LTCS use for piping
(OP)
I need the expert's advise on following design situation:
Hysys simulation indicates that while initial startup up temperature will drop to -30degF in the Gas piping system (due to JT effect). But after the process lines are pressurized and during normal operations, the temp will be above ambient. The pressurization will take about 30 minutes or so and the low temperature is expected to be limited to a small length of piping downstream of pressurization point. Source of pressurization is at 60 bar and normal operating pressure is about 20 bar.
Do we still need to design the piping for low temp and use LTCS like A333 or normal CS piping can be used.
Thanks
Hysys simulation indicates that while initial startup up temperature will drop to -30degF in the Gas piping system (due to JT effect). But after the process lines are pressurized and during normal operations, the temp will be above ambient. The pressurization will take about 30 minutes or so and the low temperature is expected to be limited to a small length of piping downstream of pressurization point. Source of pressurization is at 60 bar and normal operating pressure is about 20 bar.
Do we still need to design the piping for low temp and use LTCS like A333 or normal CS piping can be used.
Thanks





RE: LTCS use for piping
I know how I would do it.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: LTCS use for piping
As Dave says, what you need to do is actually work out what the metal temperature could be based on mass flow, size of pipe, heat transfer form the ambient ( you need to use the lowest ambient). Another issue is that sometime the safety guys get involved and then make you insulate it against cold contact, which just makes it worse!
In reality, the metal temperature of the pipe is often considerably higher than the calculated fluid temperatures and especially for gas, the specific heat capacity is often quite low. Especially for short duration events, you won't get icing to any degree, but long term at lower temperature than ambient air, it will attract a lot of condensation.
Depends on what it will cost to investigate it as opposed to just specifying the first 10m downstream to be A333 or Stl Stl. You could easily burn more costs from analysis than just specifying something that will cope with the min fluid temp.
I assume you've looked at potential hydrates, water drop out, HC liquid drop out?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: LTCS use for piping
However, it seems like the designer did not evaluate other possible scenarios that could result in temperatures below the design figure: depressurization from process conditions, evaporation of liquid inside the system (auto-refrigeration) - if any, depressurization from operating pressure and ambient temperature (cold blowdown for maintenance), etc. etc. If there are multiple scenarios in which low temperatures might occur, then it could be possible that more conservative material selection is needed.
Look at the Propane refrigeration units and Propane storage (bullets). Propane boiling point is around -40 degC at atmospheric pressure, and yet all Propane units I have seen so far are built of Carbon Steel.
Dejan IVANOVIC
Process Engineer, MSChE
RE: LTCS use for piping
RE: LTCS use for piping
RE: LTCS use for piping
RE: LTCS use for piping
The impact test is not envisaged as the worst case condition returns low temp. of -30 and the test may be required only below -45 deg or so.
It appears the modifying SOP ( Standard operating procedure ) to control the rate of cooling is the best solution as the phenomenon is only limited to start-up and that too for a relatively short duration.
Thanks