The External Pressure module calculates materials properties and required thicknesses under external pressure. Because the software uses Young's modulus values in both the internal and external reinforcement calculation, this module is called even when the external design pressure is zero. However, in this case the required thickness and Maximum Allowable Working Pressure calculations for external pressure are skipped.
The required thickness under external pressure is calculated using the interactive method outlined in Paragraph UG-33 of the ASME Code. The effective length for toriconical sections is adjusted to include a fraction of the knuckle in the design length.