PWHT thermocouple

[fazel1]

It is stated in ASME sec VIII that it is mandatory to attach thermocouple to the pressure part or vessels when PWHT, if they are more than one part or vessel. In secI nothing is found about this matter. we want to PWHT the drums base on secI and vessels base on secVIII, in a calibrated furnace. Is it realy mandatory to attach the thermocouple to these parts body, if we decide to PWHT them one by one?

 

[metengr]

If you PWHT each component separately in the calibrated furnace that you mentioned above, the answer would be no. You still need to have a PWHT process procedure for the AI to review, and some record of time and temperature to assure compliance with Code PWHT requirements.

 

[GenB]

You really need at lest 2 thermocouples attached to the boiler single or load.

 

[fazel1]

where is it stated that we have to attach two thermocouple to our parts if the furnace is calibrated?

 

[GenB]

note that all furnace controls must be calibrated,
the furnaces use thermocouples to control the heat and guess where is the best place to put the thermocouples,
There is nothing in the books (Code) only is common eng sense.

 

[stanweld]

Please refer to UW-40(8)(c)"...shall be the minimum temperature of the plate material of the shell or head of any vessel". As such at least one TC must be located on the vessel. You must also locate TCs at locations "of possible temperature variation..." Refer to UCS-56 (d);i.e., you must control the :...variation in temperature throughout the portion of the vessel being heated..."

 

[davefitz]

For large furnaces, there is normally found to be a significant temperature variation across the furnace. Likewise, for a vessel that has wide variations in thicknesses ( head vs shell) there can be a variation in metal temp vs time for the 2 different thicknesses.

For the advanced metals which have a narrow allowable band of PWHT temps ( eg P91), multiple thermocouples and recirc fans in the furnace ( to minimize temp stratification) may be required. Else, a hardness traverse of the vessel following PWHT may be needed to confirm proper PWHT.

When we obtain heat treated parts from overseas foundries, they normal provide the chart recorder output for the PWHT thermocuoples.

 

[stanweld]

Oops; another senior moment! Section I not VIII. I'm not sure how you will comply with PW-39.3 requirements regarding assurance of heating the "soak band" as defined therein without attaching CTs to the part. If you could demonstrate to the satisfaction of the AI that your procedure assures conformance, then you would not be required to do so as metengr stated.