| Applies To | |||
| Product(s): | AutoPIPE | ||
| Version(s): | ALL | ||
| Area: | Flange analysis | ||
| Original Author: | Bentley Technical Support Group |
Problem:
Does the flange analysis in AutoPIPE determine expected leakage rates or just leakage?
Solution:
No, AutoPIPE's Flange analysis calculations does not calculate a leakage rate, if the results are higher than the allowable, then flange is operating beyond its rated capacity thus increasing the likelihood that the flange will leak.
The Flange Analysis dialog can be used to analyze any flange in the model based on one of the following four analysis method options:
1. ASME Section VIII, Division 1, Mandatory Appendix 2, Rules for Bolted Flange Connections with Ring Type Gaskets
2. ASME Section VIII, Division 2, Section 4.16, Design Rules for Flanged Joints
3. ASME Section III, Appendix XI, Rules for Bolted Flange Connections for Class 2 and 3 Components and Class MC Vessels
4. ANSI Flange Loading Check
See the online help for Comparison of Flange Analysis Methods
A. "ANSI Flange Loading Calculations"
The flange loading check essentially involves determining the effective pressure in the flange due to operating pressure and external moment and force loads, and comparing it with the allowable pressure in the Table 2 of the ANSI B16.5 and 16.47. If the effective pressure is greater than the allowable pressure, then the flange is operating beyond its rated capacity. When the effective pressure is greater than the allowable pressure, the program will automatically increase the pressure rating to the next highest and perform the flange loading check again. This procedure is repeated until either the effective pressure is less than the allowable pressure, or the highest pressure rating is reached.
B. "ASME Section VIII, Rigidity Criterion"
The ASME Section VIII Division 1 and Division 2 flange analysis methods calculate several flange stresses, based on the loads and the flange, pipe, bolt and gasket geometry, and compares them to allowable stresses in Tables 1A, 1B, 3, 5A, and 5B of the ASME Section II, Part D. The main difference between the ASME Section VIII Division 1 and Division 2 flange analysis methods:
Division 1 refers to allowable stresses listed in Tables 1A and 1B, from ASME Section II, Part D.
Division 2 refers to allowable stresses listed in Tables 5A and 5B. The allowable stresses in Tables 1A and 1B are determined using the maximum principal stress. The allowable stresses in Tables 5A and 5B are determined using the distortion energy theory or Von Mises yield criterion.
Another difference is the consideration of an additional external moment due to the axial force and bending moment applied to the flange. This is only included in the Division 2 flange analysis method. However, in AutoPIPE we have made this an option for consideration in the division 1 flange analysis method as well.
Flanges that have been designed on allowable stress limits alone may not be sufficiently rigid to control leakage.