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Thermal Expansion due to Relief System

asked Aug 31, 2016 in Process by Toby McYang (370 points)
When you have piping system that is completely filled with liquid and contains significant volumes, it should be studied for thermal expansion.

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answered Aug 31, 2016 by Toby McYang (370 points)
  • If the piping is less than 100 ft (30 m) in length and contains less than 240 gal (900 L) of liquid, then no thermal relief is required even if it is heated.
  • Short sections, such as pump manifolds, meter stations, and between isolating valves on control valve stations, do not typically need thermal relief. 
  • Unless specific sizing information is available, 3/4 in. x 1 in. NPT relief valves should be used.
  • Thermal relief valves should be provided on the cool side of all shell and tube heat exchangers if the cool side can be blocked in and if it is not already protected by a pressure relief valve.

Caution: The requirement of thermal relief on a given line should be evaluated and agreed with your client.