Defines the ratio of the normal operating external pressure to the design external pressure. The value of Fpe is used in Appendix R and Section 5.11 of the API 650 Code.
The minimum value of Fpe is 0.4. Values lower than 0.4 are automatically set to 0.4.
The maximum value of Fpe is 1.0. Values higher than 1 are automatically set to 1.
If your tank has zero external design pressure, enter 0.4 for Fpe.