AutoPIPE - Warning Code 589 - FLANGE (nozzle XX): the rating class is less than required rating class (XX)

Question:

When analysing a model in AutoPIPE Vessel the following warning number was reported.

589 FLANGE (nozzle XX): the rating class is less than required rating class (25).

Why and how to avoid it?

Answer:

This warning indicates the selected flange rating is inadequate for the computed design conditions per the applicable code and material limits. It commonly occurs when a flange rating is manually forced to a lower class than required, or when additional pressure sources (e.g., static head at the nozzle) raise the effective design pressure above the allowable for the selected PN/Class.

How to Verify or Avoid the Warning

1. Open Nozzle Properties
2. Navigate to Nozzle Neck
3. Select Edit Flange
4. Check whether the Rating has been forced
5. If forced, update it to a sufficient rating class

If the rating is not forced, AutoPIPE Vessel will automatically select an adequate flange class and no warning will be issued.

Example Explanation

Material: P355NH → Group 8E3 (Table G.1.1.1)
Code tables indicate PN16 is acceptable up to 250 °C (Table G.2.1‑4).

PN16 allowable pressure: 1.6 MPa (consistent with the standard flange tables).
Design pressure at vessel shell: 1.6 MPa
Additional static head at nozzle from liquid column: ~0.139 MPa
Effective pressure at nozzle: 1.6 + 0.139 = 1.739 Mpa

Since 1.739 MPa > 1.6 MPa, PN16 is insufficient → Warning 589 is triggered.

Conclusion

Warning 589 serves as an important check to ensure flange adequacy under actual operating pressures, including static head effects. To avoid the warning:

Do not force an undersized flange rating, or
Increase the flange class to meet the computed pressure requirements