The ASME Code for Pressure Piping3 is the applicable code to follow in designing and installing piping. In addition to some specific requirements, the code lists some general precautions, such as the following:
• “Consideration must be given to expansion of liquid refrigerant trapped in or between closed valves and a means provided to prevent overpressure.”
• “Impact forces (including hydraulic shock and liquid slugging) caused by either external or internal conditions shall be considered in the design of piping components.”
• “Piping shall be arranged and supported with considerations to vibration.”
• “Piping systems shall be designed, arranged and supported so as to withstand reaction forces due to let down or discharge of fluids.”
These issues and several additional ones related to piping and valves will be addressed through an exploration of the following individual topics: (1) expansion of trapped liquid, (2) impact forces and shock caused by sudden deceleration of liquid, (3) liquid propelled by high-velocity vapor resulting from sudden reduction in pressure, (4) valving the oil drain line in an ammonia system, and (5) additional recommendations for safe piping practices.