Piping flexibility analysis as per B31.3code requirements is dealing with two types of stress named as Sustained Stress and Displacement stress . Both types of stress must be considered separately because sustained stresses are associated with sustained forces while displacement stresses are associated with fixed displacements. SUSTAINED STRESSES: Sustained Stresses are stresses caused by loads that are not relieved as the piping system deflects. See the diagrammatic representation below to get an idea about this. The weight of the valve placed at the end of the cantilevered pipe induce Stress at the T-Joint. Regardless of the magnitude of the displacement (∆), the magnitude of the load (the weight of the valve) which causes the stress is unchanged. Therefore, to avoid catastrophic failure, the magnitude of any sustained stress must not exceed the yield strength of the material. Another example of a sustained stress is the hoop and longitudinal stres...
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