Thermal binding methodology and model description in wedge gate valves

Thermal binding is generally associated with a wedge gate valve that is closed while the system is hot and then is allowed to cool before attempting to open the valve. Mechanical interference occurs because of different expansion and contraction characteristics of the valve body and disk materials. Thus, reopening the valve might be prevented until the valve and disk are reheated. Solid-wedge gate valves are most susceptible to thermal binding. However, flexible-wedge gate valves experiencing significant temperature changes or operating with significant upstream and downstream temperature differences may thermally bind. Thermal binding occurs as a result of the valve design characteristics (wedge and valve body configuration, flexibility, and material thermal coefficients) when the valve is subjected to specific temperature during various modes of plant operation.
The main objectives are: -
• Study the occurrence of thermal binding in the sample valves, including the magnitude of temperature difference across the valve and the thrust needed to unseat a thermal bounded valve.
• Evaluate the operational configurations of safety-related power-operated (i.e., motor-operated, air-operated, and hydraulically operated) gate valves in its plant to identify valves that are susceptible to thermal binding.
• Perform further analyses as appropriate, and take needed corrective actions (or justify longer schedules), to ensure that the susceptible valves identified in 1 are capable of performing their intended safety function(s) under all modes of plant operation, including test configuration.