Thermal Expansion in liquids
Thermal Expansion in liquids
(OP)
A recent Hazard study has highlighted the possibility of thermal expansion problems in exisitng acid and alkali pipework, all at ambient temperature.
Is there any information available regarding thermal expansion, due to ambient temperature differences, in liquids between 2 block valves.
I can't help but think there is minimal risk, but need to clarify the situation
Is there any information available regarding thermal expansion, due to ambient temperature differences, in liquids between 2 block valves.
I can't help but think there is minimal risk, but need to clarify the situation





RE: Thermal Expansion in liquids
taking this one step farther, calculate backwards... first think about how much additional pressure your valves/piping can stand. then calculate backwards to get the maximum temperature your pipework will stand. check if this temp. has been reached in plant's location the last 2 or 3 decades. if not - you're on the save side.
just my 2 cents.
chris
RE: Thermal Expansion in liquids
You can do a keyword search here but a rule of thumb is that blocked in liquids will increase 40 to 100 psi for every deg F temperature rise. What typically saves piping systems is that most valves are not truly bubble tight and it only takes a very small leakage rate to relieve the pressure. Some valves are however bubbletight and those are the ones where blocked in lines can leak, typically at flanges.
RE: Thermal Expansion in liquids
Pure water, 1000 kPag @ 20°C, has a molar density of 56.139 kgmol/m3 (according to HYSYS). Compressibility factor of water at this condition is 0.0073.
Raise the temperature to 30°C, molar density falls to 55.722 kgmol/m3. This means if the original system was had 1 m3 of water exactly, or 56.139 kgmol of water, the required volume to contain all of the water at the higher temperature is 1.0075 m3.
Now, assume water is in an infinitely rigid container of fixed volume 1.0000 m3, not subject to any thermal expansion. The pressure required to increase the molar density back to 56.139 kgmol/m3 at 30°C is 26350 kPag, assuming I'm using the molar density right.
Reality sets in, and you've got a little entrained gas, maybe one or two small pockets of vapour at instrument takeoffs and boltups, a little flexibility in piping, some bubbling across valves, it doesn't take much to eat up that extra 0.0075 m3 because of the higher compressibility of vapour.
RE: Thermal Expansion in liquids
RE: Thermal Expansion in liquids
RE: Thermal Expansion in liquids
Good posts by both of you and deserve a star each atleast.Though they are not matching numerically, after considering the compressibility factor I think they should.It is indeed a good technical explanation. Next time when I do hydrotesting of pipelines on a hot summer day, I will check this.
TD2K!
Is your sunsign Cancer?
RE: Thermal Expansion in liquids
RE: Thermal Expansion in liquids
RE: Thermal Expansion in liquids
TD2K!
I would like you to have a look at this Thread378-55233 and help me and the original poster out.
Regards,
RE: Thermal Expansion in liquids
If your HazOp is as serious and organized as the ones I have participated in, then any resultant action taken on this item MUST include a thermal relief valve that vents to a safe and controlled area (or volume).
You state this is acid and alkali fluids in existing pipework. These are, I presume, classified as HAZARDOUS fluids by OSHA. As such, you are obligated and mandated to provide safe and controlled relief of these fluids. This is not an option. You must provide relief for thermal expansion of these fluids. As a result, there can be no debating what the action item for this situation must be: it must have thermal relief - and designed in a safe and controlled manner.
I am telling you this from actual plant experience. This is a serious subject that must be handled in a serious manner. Do not rely on what others have mentioned about most valves not being truly bubble tight. This is worthless information where the HazOp is concerned because all it takes is for the valves to seal 100% one time and cause a pipe rupture with subsequent release of acid or alkali. You should be designing for the worst credible pressure scenario - and what I just described is both credible and possible. An analogous and similar fluid flow situation that often is addressed in HazOps is that of a check valve stopping the backward flow of a fluid. The fact that 100% of all check valves do not seal effectively is enough evidence to establish the universal HazOp rule that NO check valve will be assumed as halting backward flow. Similarly,I apply the bubble-tight feature of any block valve to your situation, but in a reverse logic: I will never assume that 100% of all block valves will leak sufficiently to relieve thermal expansion. I believe that most HazOp groups in the USA would agree with me on this point.
From a practical, engineering point of view why would anyone fail to incorporate a relatively cheap, 3/4" or 1" thermal relief valve (that doesn't require OSHA calculations nor documention!) to prevent what I just described? That isn't being very practical and much less safety-minded.
I believe you are wrong when you describe the situation as minimal risk. There is certainly a credible risk; and the consequences of someone getting doused with hazardous fluids is far too serious to classify as "minimal". I would implore you to install the required, cheap thermal relief valves and avoid such a scenario.
Art Montemayor
RE: Thermal Expansion in liquids
RE: Thermal Expansion in liquids