I am after some clarification on the code requirements for flexibility as per B31.4. For restrained lines, Section 419.6.4(b) establishes a requirement for operating stress only. When analysing a buried section in Caesar the FAC value is set to 0.001. If the net axial force is compressive then Caesar will calculate a code stress for the operating case but also for the sustained and expansion stress. Although Caesar calculates the code stress for sustained and expansion, it is my understanding that for a restrained line, we only need to consider the operating stress as per 419.6.4 (b). Is my understanding correct?

Similarly if the pipe is above ground and the net axial force is compressive then Caesar will calculate a code stress for the operating case. The FAC value should then be set to 1 so that beam bending stresses are included in the longitudinal stresses. In this case Caesar will not calculate a sustained code stress, only operating and expansion although again the expansion case does not need to be considered.