Thermocouple/dial thermometer

Thermocouples tend to be rehable, but dial thermometers may need to be puUed and verified for accuracy. 

Figure 7-85. For process piping 3-inch and larger, typical thermowell locations. Installation details thermobulb (g), thermocouple (f) (h) (i) and dial thermometers (j) (k) (I).

In Figure 7-86c, two 2-1/2-inch pipe elbows are installed together with a pipe spool piece at the lower end to increase its len h for the installation of a thermowell with a thermobulb. The other elbow adapter holds a dial thermometer in a 6-inch long thermowell. In Figure 7-86d, a single 2-1/2-inch pipe elbow is installed with suitable pipe reducers to fit the small size process line. The 1-inch elbow adapter holds a 6-inch-long well with a thermocouple (T/C). The T/C head is connected with an electrical conduit that carries the circuit to the temperature recorder on the control panel. 

Fig. no. of pipe detail followed by reference to the specific nominal pipe size Indicating dial thermometer with %" dia. bimetallic stem Thermowells for thermobulbs Immersion length starts with dimen-slon given below. Check with the scale shown on fig. Add the length required for the thermobulb. See scale for determining ordering length Thermocouple well... 

Ensure all flow and differential pressure indicators etre zeroed and calibrated. All control room pressure indicators need to be checked with a calibrated gage. All dial thermometers and outside pressure gages should be removed and checked for accuracy. The unsatisfactory ones should either be replaced or removed prior to the test and read with calibrated thermocouples, thermometers, or gages during the test. These calibrated devices should adequately fit in the existing fittings. 

Thermocouples/optical pyrometers/dial thermometers at appropriate places, e.g. on furnace shell, outgoing gas ducts, back surface of refractory bricks... 

I talked in the preceding section about unscrewing a thermocouple. This is perfectly safe. The same comment applies to extracting a screwed-in dial thermometer from a thermowell. However, sometimes less experienced people have made a deadly error in unscrewing a thermowell instead of a thermocouple. 

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