Shell and Tube heat exchanger design temperature
Shell and Tube heat exchanger design temperature
(OP)
thread124-390770: Tube side design temperature
Hi all,
As far as I have seen on this forum there are different opinions regarding design temperature for shell and tube HEx. Some say that it is ok to have same design temperature for shell and tube side, some say that it should be different. Main concern are the tubes whose op. temp. and consequently design temp. can be larger than the design temperature of other tube side elements, e.g. channels. This is valid under assumption that hot fluid is on the shell side.
I found in ASME VIII, Div. 1 UG-20 DESIGN TEMPERATURE following statement: "The design of zones with different metal temperatures may be based on their determined temperatures."
This means that I can specify one design temperature for tubes and other for other tube side elements of HEx. Is this correct or am I seeing something wrong?
Thanks in advance.
Hi all,
As far as I have seen on this forum there are different opinions regarding design temperature for shell and tube HEx. Some say that it is ok to have same design temperature for shell and tube side, some say that it should be different. Main concern are the tubes whose op. temp. and consequently design temp. can be larger than the design temperature of other tube side elements, e.g. channels. This is valid under assumption that hot fluid is on the shell side.
I found in ASME VIII, Div. 1 UG-20 DESIGN TEMPERATURE following statement: "The design of zones with different metal temperatures may be based on their determined temperatures."
This means that I can specify one design temperature for tubes and other for other tube side elements of HEx. Is this correct or am I seeing something wrong?
Thanks in advance.





RE: Shell and Tube heat exchanger design temperature
This principle will be the inevitable outcome on consideration of the operating range of flows down to min turndown, flow transients resulting in control loop upsets, and at least one operating and coincident trip loop failure scenarios.
RE: Shell and Tube heat exchanger design temperature
There is no sense to have e.g. design temperature for tube side 200C and for IN/OUT lines 100C.
RE: Shell and Tube heat exchanger design temperature
RE: Shell and Tube heat exchanger design temperature
I apologize if I went a little bit off-topic, but I think that this is also important during plant design.
RE: Shell and Tube heat exchanger design temperature
API RP 14J provides some guidance on pressure specification breaks. Analogy can be taken for temperature spec breaks.
Dejan IVANOVIC
Process Engineer, MSChE
RE: Shell and Tube heat exchanger design temperature
RE: Shell and Tube heat exchanger design temperature
RE: Shell and Tube heat exchanger design temperature
RE: Shell and Tube heat exchanger design temperature
This is a typical case where design temp for the shellside must be made equal to that for tubeside to account for the case when hot oil flows through the HX with little or no crude flow, which will happen when the hot oil SDV is nominally closed by action of the TSHH or by PSD or manually stopped, but is still leaking.
The TSHH setpoint can be used to derive the design temp for the crude side piping outside of the isolation block valves for the crude side.
A complication arises when in this case, hot crude inventory flows out of this HX at 190degC to the stage 2 sep during a restart after shutdown - the tubeside crude hot inventory flowing out should not raise the metal piping mean metal temp by much - take this into account when setting the design temp of the crude piping after the HX crude side downstream block valve. Heat transfer coeff from the flowing hot crude to the piping will also be low during this restart transient. Also check if the crude side LCV trim can handle this short term temp spike.
RE: Shell and Tube heat exchanger design temperature
- Failure of the hot oil temperature control loop (TIC) with TCV in fully open position (full flow of hot oil) results in crude oil flowing to equipment downstream at a higher-than-normal (uncontrolled) temperature. This can last for undefined period of time (no visible safeguards), hence it will define the design temperature for piping and instrumentation downstream of the heat exchanger.
SDV can also be moved closer to the exchanger, upstream of the level control valve and isolation valves.
Dejan IVANOVIC
Process Engineer, MSChE
RE: Shell and Tube heat exchanger design temperature
"This is a typical case where design temp for the shellside must be made equal to that for tubeside to account for the case when hot oil flows through the HX with little or no crude flow, which will happen when the hot oil SDV is nominally closed by action of the TSHH or by PSD or manually stopped, but is still leaking. "
When there is no crude oil flow PSD is beeing activated and Hot Oil Heater Unit burner and hot oil circulating pumps are stopped, therefore there is no flow in the hot oil system.
This other case with restart after shutdown is possible, but it can be difficult to predict (calculate) temperature spike downstream.
@EmmanuelTop
"Failure of the hot oil temperature control loop (TIC) with TCV in fully open position (full flow of hot oil) results in crude oil flowing to equipment downstream at a higher-than-normal (uncontrolled) temperature. This can last for undefined period of time (no visible safeguards), hence it will define the design temperature for piping and instrumentation downstream of the heat exchanger."
If TIC fails there is a shut down valve on hot oil inlet connected to TIT on crude outlet with HH switch. This HH switch should be something above TIC high value and should serve as a safeguard system if TIC fails.
Thank you all for replies and time invested, you have shed a new light (at least for me) on this topic.
RE: Shell and Tube heat exchanger design temperature
But you also have to account for the case of misoperation where the operator is flowing hot oil through the HX with no crude flow during startup. In most companies, this risk is significant.
Also, it is common practice to keep the hot oil pumps running for some time after a heater shutdown to cool down the radiant bank tubes in the furnace and dissipate the residual heat in the refractory bricks, and also to stop the trapped hot oil in the heating coils from coking up. So check again if this trip of the HO pumps is advisable. Stopping the HO pumps is only required for furnace exhaust stack TSHH, which may be an indication of a leak in the heating coils.
If the HO pumps are still kept running to protect the furnace coils and to prevent hot oil thermal degradation, leakage through this SDV is still possible since the hot oil will still be at 190degC for some time even though the furnace burners are stopped.
RE: Shell and Tube heat exchanger design temperature
There is also a question of SDVs closing sequence during ESD and PSD. If all SDVs on hot oil distribution lines close in the same time when fired heater burner is turned off there is no min flow for fired heater. Hot oil pumps would keep some flow through automatic recirculation valves but this action would keep the flow only for pumps, not for coil inside fired heater. Therefore some time gap between burner shut down and SDV closing should exist.
RE: Shell and Tube heat exchanger design temperature
RE: Shell and Tube heat exchanger design temperature
RE: Shell and Tube heat exchanger design temperature
RE: Shell and Tube heat exchanger design temperature
See also:
http://www.process-heating.com/articles/84799-tips...
http://igs.nigc.ir/STANDS/IPS/e-pr-410.PDF
https://www.icheme.org/~/media/Documents/Subject%2...
Dejan IVANOVIC
Process Engineer, MSChE
RE: Shell and Tube heat exchanger design temperature