In AutoPIPE Vessel the value of pi is generally a calculated value in radians : PI=ACOS(-1).
From the past some formulae however were expressed with only 3.14 in the design code, hence in AutoPIPE Vessel the values of pi have been used in various cases - sometimes as either 3.14, sometimes using the formula above (most accurate value) or sometimes upto 7 significant digits.
The accurate result would be to use PI calculated as mentioned above, but it is not possible to say which values assume an accurate PI value and which values are considered 3.14 or upto 7 significant digits in the source code. Although there would be a discrepancy in the accuracy using the different values, the % difference would be very less and for example for large flange calculations with large loading this difference may become insignificant.
However, users are cautioned to use proper design judgment and if necessary validations with hand calculations and have appropriate margin in their final design dimension selection to accommodate accuracy discrepancies if they believe that the small difference due to the discrepancy is NOT acceptable in their design.