Threaded Thermowell On Discharge of Centrifugal Compressor
Threaded Thermowell On Discharge of Centrifugal Compressor
(OP)
Hi everybody,
Is it allowable to install a threaded thermowell on the discharge of a centrifugal compressor, or it shall be connected to line via a RTJ flange. The discharge operating pressure will be 90 bars. FYI, thread is M30 and there will be an O-ring under crown(head) of the thermowell.
Thanks in advance.
Is it allowable to install a threaded thermowell on the discharge of a centrifugal compressor, or it shall be connected to line via a RTJ flange. The discharge operating pressure will be 90 bars. FYI, thread is M30 and there will be an O-ring under crown(head) of the thermowell.
Thanks in advance.





RE: Threaded Thermowell On Discharge of Centrifugal Compressor
RE: Threaded Thermowell On Discharge of Centrifugal Compressor
RE: Threaded Thermowell On Discharge of Centrifugal Compressor
Johnny Pellin
RE: Threaded Thermowell On Discharge of Centrifugal Compressor
Use a flanged connection, LWN nozzle connection not a built up flange, and use remote mounted connection heads. Use as short a thermowell was you can, and insulate the flange.
You also need to give consideration to the how close to the compressor you are located, and the wall thickness of the piping. Severe problems occur if you locate the sensor in an area where accoustic resonances associated with blade passing frequencies.
RE: Threaded Thermowell On Discharge of Centrifugal Compressor
To hacksaw: Using LWN makes tip of purchased instruments being more off-center and more out-off-flow. What about that?
RE: Threaded Thermowell On Discharge of Centrifugal Compressor
Accoustic resonances in the pipe with local pressure rises of 1-2 bar contribute to localized temperature variations(standing waves). These can be a more serious source of error.
You do have a longer well with flanged nozzles, but the LWN nozzles provide adequate support stiffness for your well calculations.
RE: Threaded Thermowell On Discharge of Centrifugal Compressor
RE: Threaded Thermowell On Discharge of Centrifugal Compressor
RE: Threaded Thermowell On Discharge of Centrifugal Compressor
sound advice is to use flanged thermowells for piping containing flammable gas or toxic gas. if you use a threaded thermowell, i would seal weld it once it is installed.
the flange type and gasket is also defined in API-614. for class 300# and below, a non-asbestos flange gasket is ok to use. for flange class above 300#, spiral wound gaskets are required (or an RTJ).
sometimes, a customer will require spriral wound on all flanges, regardless or pressure rating when containing flammable gases.
best practice, no threaded joints on flammable service piping. a root valve which is welded is required upstream of the gauges or pressure sensors. down stream of the welded root valve, threaded connections are allowed and are usually 1/2" NPT with 1/2" ss tubing.
RE: Threaded Thermowell On Discharge of Centrifugal Compressor
In practice, seal welds in the field do not have adequate controls and most will crack and leak depending on the temperature and the level of vibration involved.
Commonly the thermowell and the flange are different metals and seal welding creates problems as a result of differential thermal expansion as the temperature increased.
Even when the thermowell is factory welded, you can have difficulties in the heat affected zone even if the well is designed for welding.
Before you decide on how and where you are going to install your temperature sensor, you should check into the several published descriptions of thermowell failures at pipeline compressor stations.
RE: Threaded Thermowell On Discharge of Centrifugal Compressor
Thanks for your help.
RE: Threaded Thermowell On Discharge of Centrifugal Compressor
You won't find solutions, just a bit of insight into what has not worked and what failed.
RE: Threaded Thermowell On Discharge of Centrifugal Compressor