TABLE OF CONTENTS In nuclear power plants, pressure transmitters are usually located away from the process in order to reduce the effect of ambient temperature on the transmitter's operability and qualified life. High ambient temperatures (70EC and above) can affect the transmitter's mechanical components and shorten the life of its solid-state electronics. Other reasons for locating a transmitter away from the process are to reduce the adverse effects of radiation and vibration and to make it easier for personnel to access the transmitter for replacement or maintenance purposes.
To transport a pneumatic or hydraulic signal from the process to a transmitter, sensing lines are used to connect the pressure transmitter to the process piping, reactor vessel, or primary flow elements. Depending on the application, there will be one or two sensing lines for each transmitter.
Sensing lines are also referred to as impulse lines or instrument lines. Both liquid-filled and gasfilled sensing lines can be found in nuclear power plants. Liquid-sensing lines are typically filled with either the process liquid or oil, depending on the sensing line's design and application. Gas-sensing lines are filled with steam, air, nitrogen, or other gases, and there is sometimes a point in these lines where they transition to another medium such as oil or water. To achieve this transition, a diaphragm, bellows, or condensate pot is installed in the sensing line.
The pressure sensing lines in the primary systems of nuclear power plants are usually made of stainless steel tubing...
