4 replies to this topic

[Milutin]

Hi all,

On crude unit we have for pass fired heater with thermocouples on each pass exit.
We experienced thermowell fracture two time in last three years. When thermowell is broken crude oil start leaking. It is very unpleasant situation because of high crude oil temperature and possibility of fire.
Possible cause of fracture is pass vibrations on heater outlet.

I find in literature if there is possibility of thermocouple fracture it is necessary to install valve on thermovell end and in case of fracture it is possible to close valve, cut wires and stop leaking.

Does anybody know manufacturer or solution in this case?

Regards,

Milutin

[ashetty]

Hello Milutin

I Suggest you get a thermowell wake frequency test conducted (at your operating conditions) most vendors will do it for you, before you place your order.Thermowell failures often take place due to improper selection of thermowells. Install olny if the thermowell has passed the Wake frequency test.Another alternative is to install fequency collars.

Regards,

[Milutin]

Dear Mr. Ashetty,

Thank you for your answer. Can you suggest company who do wake frequency test. I find on internet, it is possible to calculate wake frequency, but on our four pass heater we have problem only on two heater passes. Reason is pass configuration. In case of calculating wake frequency we will have same results for all passes.

Pass configuration:
 shemaen.jpg   58.7KB   51 downloads

Regards,

Milutin

[davebartran]

Do you have particulars such as well size, materials of construction, flow rate or velocity?

Do you also have a coking problem in the heater tubes?

[indy]

Hi Milutin

From ENGº TIPS

If your thermo wells have no cabling for TDC signals, in that case you can install valves on thermo wells, any way when a leak happens, to handle the valve to stop the leak, will be a dangerous operation and operators can get burnt unless you install remote operated valves which is not very usual at those heater locations.

You have to check what causes vibrations on your thermo well stems
In my opinion these vibrations are due to coke particles impact against thermo well stems. In that case you have to decoke your heater and install extra strong stems to reduce the possibility of fracture due to vibration. You cam also consider the installation of internal pipe devices to jacket the end of stem of thermo well to fix it and impeach stem vibrations, this option should take into account the fluid dynamics.

Regards

Luis marques