Q & A > Question Details
We have Shell and tube heat exchanger named E-201-11. This E-201-11 is exchanger just before pass heater of furnace of CDU. The service fluid is desalted crude (shell) and vacuum residue (tube) from bottom column.
Shell operating pressure is 19.7 kg/cm2 and tube operating pressere is 25.8 kg/cm2.
Pressure desain shell 30 kg/cm2 and pressure desain tube 36 kg/cm2.
Hydrotest pressure shell 43.5 and tube 37.5 kg/cm2.

What the main consideration of installing TSV at outlet of desalted crude?
Does it because of thermal expansion?

Now we are installing spare exchanger for E-201-11 but the type is plate and frame HE.
The operation mode will be one HE operated and one HE spare/standby.

My questions are :
Do we need to install relief valve at desalted crude outlet of new HE? Can we use 1 TSV for 2 HEs?
What may cause thermal expansion since reduced crude being pumped by bottom CDU?
 
Answers
28/08/2016 A: Eric Hennings, Technip Stone & Webster, EHennings@technip.com
With "spare" HX which can be isolated, best practice is drain and flush the HX when taken out of service. As added protection, thermal relief valves are added if procedures are not followed. Note that TSV are usually small capacity for inadvertent expansion of liquid full HX.
27/08/2016 A: Leonardo Leite Garcia de Souza, Petrobras SA / Duque de Caxias Refinery, llgs394041@yahoo.com.br
Two situations may arise: 1) if there are blocking valves isolating the HE's shells individually (I believe this is the case, since one of them is a spare), yes you are going to need a relief valve for thermal expansion - imagine that there is no flow at the shell side but there is hot VR flowing at the tube side. What happens? The crude isolated inside the shell is going to expand until failure of either the shell or the tubes. This is also the case when the shell is exposed to thermal radiation due to sun light or fire. 2) if there is a tube failure, the high pressure fluid (VR) can cause the shell to be pressurized beyond its design pressure, since the design pressure of the tube side is higher, and yes, again, you are going to need a relief valve; don't count on the pressure of the hydrostatic test, since at the end of your run the shell thickness may be thinner due to corrosion. The size of your relief valve is going to be defined by the highest relief flowrate between the cases. In some cases, if one flowrate is much higher than the others, the design engineer is going to use two relief valves, since the relief valve sized for the most severe case can show "chattering" for lower flowrates. Safety first and best regards!
13/08/2016 A: Apoorv Gupta, IOCL Haldia, apoorv.work19@gmail.com
It's quite surprising that Desalted crude (In shell side) and vacuum residue (In tube side) is considered in design stage. I think there will be high fouling effect in exchanger. Please relook into the heat exchanger design.
12/07/2016 A: Sudhakara Babu Marpudi, Dangote Oil Refinery Company, m_sudhakarababu@yahoo.com
Check the HAZOP study reports. Generally the justifications for relief valves are installed in lieu of HAZOP studies recommendations. This could be a fire case TSV.
01/07/2016 A: MUKTESH KULKARNI, TOYO ENGG INDIA LTD, kulkarni.muktesh@gmail.com
The shell side and tube side pressures mentioned by you indicate that there is a greater possibility of tube side fluid to get transferred to shell side on rupture of tube. However the shell side seems to be designed for a hydrotest pressure of 43.5 kg/cm2g which is significantly higher than the tube side design pressure. In such case relief valve may not be required.
Besides that you need to check the valve arrangement and the control/interlock system to check if there is any scenario wherein the shell side fluid would be blocked on the downstream with hot tube side fluid in line. Also in this case it would be interesting to know if the shell side pressure can rise to design pressure or not. An accurate analysis can be done with dynamic simulation. One common TSV for two exchangers should suffice if there is no intervening valve between the two.
01/07/2016 A: karthik ramesh, indian oil corporation, rameshkarthik810@gmail.com
Normally thermal relief valve is given due to thermal expansion to take care sudden by passing of hot fluid/cold fluid. in new designs the same has not been considered in our refineries.