Measuring temperature of a fluid in pipe and vessels is achieved by installing local temperature gauges or by temperature transmitter which send their output to process control room.
Temperature gauges consists of a metallic probe which is inserted into the pipe or vessel through a nozzle arrangement. Dial connected to probe shows temperature on a circular scale. Head of the guage is either fixed or swivel headed for various readout angles.
Then temperature must be read remotely, thermocouple type of temperature transmitters are used. They have a metallic probe same as gauge indicators, but instead of a dial attached to other end, they have a terminal head which houses electronics circuit which transmit temperature signal to process control room for process control and display on screen.
Both gauge indicators and thermocouples are generally flanged or screwed, and their pipe and vessel connetions sizes range from 1/2in to 2 in. Minimum pipe size usually required is 4″. If pipe is of smaller size, it is locally increased to 4″ NPD with the use of two reducers.
Temperature Instruments Piping Layout
- Temperature test wells shall be accessible from grade, permanent ladder or platform.
- Temperature Thermowell located in a pipeway shall be considered accessible with a portable ladder.
- Temperature indicators shall be visible from grade, ladder, or platform.
- Thermocouple and temperature indicators located less than 4500 mm above high point of finish surface and in a pipeway shall be accessible by portable ladder.
- Temperature Instruments above 4500 mm from high point of finish surface shall be accessible from platform or permanent ladder.
- On a distilation tower, temperature instrument must be located in liquid space.
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