For above ground piping FAC would be 0. Assuming you're running version 9, just let CAESAR II determine the restrained/unrestrained status of the buried elements. The reason for this is that if you have multiple load cases with multiple temperatures, an element could be restrained in one load case and unrestrained in another. Manually setting the restrained/unrestrained status of an element in the input permanently sets the status for all load cases.